European Generic Cabling

Guide to application of standard EN standard (50173)

1 INTRODUCTION..................................................................................................................................................................5

1.1 NETWORKS IN CUSTOMER PREMISES.............................................................................................................................51.1.1 Local area networks.................................................................................................................................................61.1.2 Other communication systems in customer premises...............................................................................................7

1.2 STANDARDIZATION OF GENERIC CABLING.....................................................................................................................81.3 TERMINOLOGY..............................................................................................................................................................10

1.3.1 Terms and definitions.............................................................................................................................................101.3.2 Abbreviations..........................................................................................................................................................14

2 SCOPE AND GENERAL PRINCIPLES OF GENERIC CABLING.............................................................................16

2.1 SCOPE AND CONTENTS..................................................................................................................................................162.2 GENERAL PRINCIPLES OF THE STANDARD...................................................................................................................16

3 STRUCTURE AND FUNCTIONAL ELEMENTS OF GENERIC CABLING............................................................18

3.1 FUNCTIONAL ELEMENTS...............................................................................................................................................183.2 CABLING SUBSYSTEMS..................................................................................................................................................193.3 INTERCONNECTION OF SUBSYSTEMS............................................................................................................................203.4 INTERFACES, CHANNEL, LINK.......................................................................................................................................223.5 DIMENSIONING AND MINIMUM CONFIGURATION REQUIREMENTS.............................................................................24

3.5.1 Distributors.............................................................................................................................................................243.5.2 Cables and connecting hardware...........................................................................................................................253.5.3 Work area cords, equipment cords, patch cords and jumpers...............................................................................263.5.4 End user outlets......................................................................................................................................................263.5.5 Consolidation point................................................................................................................................................283.5.6 EMC, earthing and bonding...................................................................................................................................28

4 CHANNELS AND LINKS AND THEIR REQUIREMENTS.........................................................................................29

4.1 CLASSES OF CHANNELS AND LINKS..............................................................................................................................304.2 TWISTED PAIR CHANNELS AND LINKS AND THEIR REQUIREMENTS...........................................................................31

4.2.1 Transmission in twisted pair cable.........................................................................................................................314.2.2 Characteristic impedance and return loss.............................................................................................................344.2.3 Attenuation (insertion loss)....................................................................................................................................37When the signal propagates along a link or channel, its power is decreased. This phenomenon is called attenuation. Attenuation is caused by the resistive and dielectric losses of the link or channel and it can be seen as decreasing voltage and current when the distance increases. The unit of attenuation is decibel, dB (for cables the attenuation is expressed in dB/100 m). Attenuation sets limits for the length of a link and channel and the highest signal frequency to be transmitted. The concept of attenuation is shown in figure 4.6..................................................................................374.2.4 Pair to pair near end crosstalk loss, NEXT............................................................................................................384.2.5 Power sum near end crosstalk loss, PSNEXT........................................................................................................394.2.6 Pair to pair attenuation to crosstalk ratio, ACR....................................................................................................414.2.7 Power sum attenuation to crosstalk ratio, PSACR.................................................................................................424.2.8 Pair to pair equal level far end crosstalk loss, ELFEXT.......................................................................................434.2.9 Power sum equal level far end crosstalk loss, PSELFEXT....................................................................................444.2.10 Direct current loop resistance..............................................................................................................................454.2.11 Resistance unbalance...........................................................................................................................................454.2.12 Propagation delay................................................................................................................................................454.2.13 Propagation delay skew.......................................................................................................................................454.2.14 Unbalance attenuation.........................................................................................................................................454.2.15 Coupling attenuation............................................................................................................................................454.2.16 Alien crosstalk......................................................................................................................................................45

4.3 CHANNELS AND LINKS OF OPTICAL FIBRE CABLING AND THEIR REQUIREMENTS....................................................454.3.1 Attenuation.............................................................................................................................................................454.3.2 Propagation delay..................................................................................................................................................45

5 REFERENCE IMPLEMENTATIONS OF CABLING...................................................................................................45

5.1 REFERENCE IMPLEMENTATIONS FOR TWISTED PAIR CABLING..................................................................................455.1.1 Reference implementations for horizontal cabling.................................................................................................455.1.2 Reference implementations for backbone cabling..................................................................................................45

5.2 REFERENCE IMPLEMENTATIONS FOR OPTICAL FIBRE CABLING................................................................................45

6 REQUIREMENTS OF CABLES.......................................................................................................................................45

6.1 TWISTED PAIR CABLES..................................................................................................................................................45THE REQUIREMENTS OF TWISTED PAIR CABLES IN THE STANDARD EN 50173-1 ARE SPECIFIED BY USING THE REFERENCE TO THE STANDARD SERIES EN 50288. THE STANDARDS OF THIS SERIES ARE SHOWN IN TABLE 6.1........45

6.1.1 Constructional requirements..................................................................................................................................456.1.2 Electrical requirements..........................................................................................................................................45

6.3 OPTICAL FIBRE CABLES................................................................................................................................................456.3.1 Constructional requirements..................................................................................................................................456.3.2 Requirements of optical fibres................................................................................................................................45

7 REQUIREMENTS OF CONNECTING HARDWARE...................................................................................................45

7.1 REQUIREMENTS OF CONNECTING HARDWARE OF TWISTED PAIR CABLING..............................................................457.1.1 Mechanical requirements......................................................................................................................................457.1.2 Electrical requirements..........................................................................................................................................457.1.3 Pin and pair grouping assignments........................................................................................................................45

7.2 REQUIREMENTS OF CONNECTING HARDWARE OF OPTICAL FIBRE CABLING............................................................45

8 TESTING OF INSTALLED CABLING............................................................................................................................45

8.1 PURPOSE OF TESTING....................................................................................................................................................458.2 TESTING OF TWISTED PAIR CABLING...........................................................................................................................45

8.2.1 Test equipment........................................................................................................................................................458.2.2 Test interfaces and test configurations...................................................................................................................458.2.3 Testing of cabling, parameters to be measured and reasons for erroneous test results........................................458.2.4 Interpretation of test results...................................................................................................................................45

8.3 TESTING OF OPTICAL FIBRE CABLING.........................................................................................................................458.3.1 Test equipment........................................................................................................................................................458.3.2 Test procedures......................................................................................................................................................458.3.3 Parameters to be tested..........................................................................................................................................458.3.4 Interpretation of results..........................................................................................................................................45

9 APPLICATIONS SUPPORTED BY GENERIC CABLING..........................................................................................45

9.1 APPLICATIONS SUPPORTED BY TWISTED PAIR CABLING.............................................................................................459.1.1 Gigabit Ethernet in twisted pair cabling...............................................................................................................45

9.2 APPLICATIONS SUPPORTED BY OPTICAL FIBRE CABLING...........................................................................................459.2.1 Gigabit Ethernet in optical fibre cabling...............................................................................................................45

10 THE MOST IMPORTANT DIFFERENCES BETWEEN EN 50173-1 (2002) AND ITS OLDER EDITIONS (1995 AND 2000), ISO/IEC 11801 AND ANSI/TIA/EIA 568-B....................................................................................................45

10.1 DIFFERENCES BETWEEN EN 50173-1 (2002) AND ITS OLDER EDITIONS..................................................................4510.2 DIFFERENCES BETWEEN EN 50173-1 (2002), ISO/IEC 11801 AND ANSI/TIA/EIA 568-B...................................45

11 FREQUENTLY ASKED QUESTIONS AND ANSWERS............................................................................................45

12 Standards..............................................................................................................................................................................45

1 Introduction

1.1 Networks in customer premises

Communications networks are essential technical systems in modern customer premises. The variety of Communications networks in customer premises is large and the structure and extension of networks depend on the use and size of the premises. Telephone, local area networks (LAN) as well as control and automation systems are the basic communications networks in office and industrial environment. The importance of telecommunications is evident in all kind of work, but Communications are needed also in security systems and controlling the environmental conditions within the building. In addition to office and industrial environments the importance of communications has increases strongly also in residential environments. Internet has been the driving force for the increasing use of high-speed communications also at homes.

The plain old telephone service cannot satisfy the home users anymore and xDSL access is available economically all over the world. Traditionally a customer premises telephone network has been the most important telecommunications network in a building. The customer premises telephone network is an essential basic system in any building and it is installed at the same time as the building is built. In most countries governmental or other regulations set the requirements for customer premises telephone networks to ensure the compatibility and disturbance-free operation. In these regulations reference to international, regional or national standards can be used to give the more detailed requirements.

Traditionally the signals in the telephone network may be analogue or digital. The traditional analogue voice transmission uses the bandwidth of 300...3400 Hz. ISDN basic access (2B+D) operates at the speed of 144 kbit/s.

xDSL technologies developed during the last decade enable transmissions speeds from 512 kbit/s up to even 100 Mbit/s depending on the quality and performance of the cabling and the distance from operator’s node. The importance of the conventional telephone network has begun to decrease. One very significant reason for this is the enormous growth of mobile telecommunications. In a daily telephone conversation people increasingly more mobile telephones than old wired telephones. In many western countries the number of wired telephone subscribers has even been decreasing during last few years.

Ethernet and other network technologies enable also voice transmission (VoIP) over Internet Protocol (IP). The conclusion is, that in future the role of the conventional telephone network will change.

1.1.1 Local area networks

In modern commercial and office buildings a local are network (LAN) is a matter of course. Even in small offices the persons are working with workstations connected to LAN. Bigger companies use high speed LANs and also the LANs of each offices or agencies ate connected to each to form a company network. LANS are also coming to homes enabling the sharing of the Internet connection within the family. The transmission speeds of LANs have been growing rapidly during the whole short history of LANs. Table 1.1 shows the most important milestones of Ethernet development. During the last decade the speeds have increased multiplication factor 1000.

Table 1.1. Milestones in the standardization of Ethernet (IEEE and TIA/EIA).

Standard Name Transmission speed

Transmission medium Year of publication

IEEE 802.3 10Base5 10 Mbit/s Coaxial cable (thick) 1983 IEEE 802.3a

10Base2 10 Mbit/s Coaxial cable (thin) 1985

IEEE 802.3d

FOIRL 10 Mbit/s Multimode fibre 1987

IEEE 802.3i

10Base-T 10 Mbit/s Twisted pair cable (category 3)

1990

IEEE 802.3j

10Base-F 10 Mbit/s Multimode fibre 1993

IEEE 802.3u

100Base-T 100Base-FX

100 Mbit/s 100 Mbit/s

Twisted pair cable (category 5) Multimode fibre

1995

IEEE 802.3z

1000Base-SX 1000Base-LX

1000 Mbit/s 1000 Mbit/s

Multimode fibre Multimode or singlemode fibre

1998

IEEE 802.2ab

1000Base-T 1000 Mbit/s Twisted pair cable (category 5e)

1999

TIA/EIA-854

1000Base-TX 1000 Mbit/s Twisted pair cable (category 6)

2001

IEEE 802.2ae

10Gbase-SX 10Gbase-LX 10Gbase-EX 10Gbase-LX4

10 Gbit/s 10 Gbit/s 10 Gbit/s 10 Gbit/s

Multimode fibre (category OM3) Singlemode fibre Singlemode fibre Multimode fibre (WDM)

2002

The Ethernet technology is the main LAN technology all over the world. More than 90 % of all network adapters used in the world are Ethernet adapters. The most important other LAN technologies are: • Token Ring, 4 Mbit/s, 16 Mbit/s and 100 Mbit/s • FDDI and CDDI, 100 Mbit/s • ATM, 155 Mbit/s, 622 Mbit/s, 1,2 Gbit/s and 2,5 Gbit/s • Fibre Channel, 133 Mbit/s, 266 Mbit/s, 531 Mbit/s, 1062 Mbit/s, 2134 Mbit/s and 4268 Mbit/s

Modern local area networks are cabled by using the principles of generic cabling. Application dependent cablings began to belong to the history, when the first international standard of generic cabling was published in 1995. The new edition of international standard ISO/IEC 11801 supports LANS in twisted pair cabling up to 1000 Mbit/s and in optical fibre cabling up to 10 Gbit/s transmission speeds.

1.1.2 Other communication systems in customer premises Local area networks and telephone networks are the most common telecommunications networks in customer premises. These networks are also most visible to people working in the premises. Depending on the use and size of premises and on the needs of the organizations working in the premises there are also many other telecommunications systems in the customer premises. Operation of all these systems presumes some kind of telecommunication network including cabling. Examples of these systems are the following:

• Building automation systems • Fire alarm systems • Burglar alarm systems • Access control systems • Video surveillance systems • Master antenna system • Sound systems

Traditionally these systems have been cabled with separately by using dedicated cabling. One reason for this has been lack of generic cabling standard. But this is only one reason. These systems also have some special features, which set different technical or administrative requirements. For instance master antenna system commonly uses coaxial cabling, which is not supported by generic cabling and fire alarm systems may be regulated by local codes in such a way, which makes using generic cabling difficult or impossible. In many systems of the above list the cable types are basically similar to those used in standardized generic cabling. This means that there are possibilities to use the same cabling infrastructure for cabling of these systems.

1.2 Standardization of generic cabling

Generic cabling has established its situation as an appropriate, flexible, cost effective and long life cabling in customer premises. The generic cabling is used as a rule in office, commercial and industrial buildings and during last years it has been adopted also in residential buildings. The most common applications of using generic cabling are local are network (LAN) and telephone network. Interest in using generic cabling also for other applications is increasing continuously. Building automation is one example of these applications. Standardization activities of generic cabling have been intensive during the last 15 years and this has resulted in many international, regional and national standards. The history of standardization begins from the USA, where the first standard was published in 1991. This standard was EIA/TIA 568 Commercial Building Telecommunication Wiring Standard. Although this standard was national US standard, it soon reached a very high status all over the world. The term generic cabling was not used in this standard, but the principles of the cabling were already just those of generic cabling. The need of international standard was seen among the experts already in the end of 1980’s and after over five years working the working group 3 (WG 3) of the committee ISO/IEC JTC1/SC 25 finalized the first international standard of generic. This standard was published in 1995 with name ISO/IEC

11801 Generic Cabling for Customer Premises. In the same year, 1995, also the first European standard EN 50173 Information technology - Generic cabling systems and the second edition of the US standard ANSI/TIA/EIA 568-A were published.

The three standards published in 1995 were adapted very rapidly and the first generation of standardized generic cabling systems begun to grow all over the world. At the same time the transmission speeds of local area networks (LAN) were increasing first from 10 Mbit/s to 100 Mbit/s and soon from 100 Mbit/s to 1 Gbit/s and even 10 Gbit/s. Experts in the standardization bodies could very soon see that also the cabling had to be developed to respond to these new challenges. The need of a new standard became evident and new long lasting work begun again. As a first aid addendums and amendments to existing standards were published, but the final target was the totally new edition of each three standard. Finally in 2002 the second edition of ISO/IEC 11801 was approved in the final voting. In the same year also the second edition of the European standard was approved with a new number code EN 50173-1. The third edition of the US standard was published in several parts during 2000 – 2001. The main parts of this standard are ANSI/TIA/EIA-568-B.1 – B.3. The most important European generic cabling standards and draft standards are the following:

• EN 50173-1: Information technology – Generic cabling systems – Part 1: General requirements and office areas, 2002.

• prEN 50173-2: Information technology – Generic cabling systems – Part 2: Industrial premises. • prEN 50173-3: Information technology – Generic cabling systems – Part 3: Residential and Small

Office Home Office (SOHO) environments. • EN 50174-1: Information technology – Cabling installation – Part 1: Specification and quality

assurance, 2000. • EN 50174-2: Information technology – Cabling installation – Part 2: Installation planning and

practices inside buildings, 2000. • prEN 50174-3: Information technology – Cabling installation – Part 3¨: Installation planning and

practices external to buildings. • EN 50346: Information technology – Cabling installation – Testing of installed cabling, 2002. • EN 50310: Application of equipotential bonding and earthing in buildings with information

technology equipment, 2000.

Of the above listed standards prEN 50173-2, prEN 50173-3 and prEN 50174-3 are at draft stage, all the others have been published.

Standard EN 50173-1 is a system standard, which specifies the structure, functional elements, basic design and dimensioning, performance of links and channels as well as characteristics and performance of components (cables and connecting hardware) of the cabling. This standard thus specifies the basic structure and performance, but does not specify planning, installation, testing and documentation of the cabling. Standard EN 50173-1 is primarily intended for cabling in office environments, but it can easily be applied to any kinds of premises. Cabling standards for industrial premises (EN 50173-2) and residential premises (EN 50173-3) are expected to be published in 2005.

Standards EN 50174-1 and -2 were published in 2000 and EN 50174-3 is expected to be published in 2003. All the three standards are intended for those involved in the procurement, installation and operation of information technology cabling. Standard EN 50346 was published in 2002 and it specifies the testing requirements and methods of installed cabling. It shall be applied to balanced and optical fibre cabling. This standard is partly based on basic testing standard EN 61935-1. Standard EN 50310 specifies earthing and bonding of information technology equipment in buildings in relation to safety, functional and electromagnetic performance. The standard does not specify another earthing and bonding system, but selects out of the existing ones the best suitable system to information technology needs. The purpose of this guidebook is to dive guidance in application of the standard EN 50173-1 (2002), which is the basic standard in generic cabling. The standard EN 50173-1 (2002) includes many changes and new specifications compared with the previous edition EN 50173 (1995) and its Amendment 1 (2000). The most important new specifications are those of classes E and F twisted pair cabling and the new classes of optical fibre cabling. Also the respective new categories 6 and 7 for twisted pair cabling components and the new optical fibre categories OM1, OM2, OM 3 and OS1 are specified in this standard directly or by reference to the relevant component standard. The structure and interfaces have also been specified in a more precise way. The latest editions of the standards EN 50173-1, ISO/IEC 11801 and ANSI/TIA/EIA 568-B are practically harmonized. Some differences in details, however, still exist. These are related to the format of the standard, electrical safety and EMC. Also some terminological differences are to be found in the American standard. The three most important standards of generic cabling are international ISO/IEC 11801, European EN 50173-1 and American ANSI/TIA/EIA 568-B.

1.3 Terminology

The terminology of this book follows the European standard EN 50173-1. The most important terms with their definitions are presented in clause 1.3.1 and the most important abbreviations are explained in sub-clause 1.3.2.

1.3.1 Terms and definitions

Administration The methodology defining the documentation requirements of a cabling system and its containment, the labelling of functional elements and the process by which moves, additions and changes are recorded.

Application A system, with its associated transmission method, which is supported by telecommunications cabling.

Attenuation The decrease in magnitude of power of a signal in transmission between points. It expresses the total losses on cable consisting of the ratio of power

output to power input. Balanced cable A cable consisting of one or more metallic symmetrical cable elements

(twisted pairs or quads). Building backbone cable A cable that connects the building distributor to a floor distributor. Building

backbone cables may also connect floor distributors in the same building. Building distributor (BD) A distributor in which the building backbone cable(s) terminate(s) and at

which connections to the campus backbone cable(s) may be made. Building entrance facility A facility that provides all necessary mechanical and electrical services, that

complies with all relevant regulations, for the entry of telecommunications cables into a building.

Cable An assembly of one or more cable units of the same type and category in an overall sheath. It may include an overall screen.

Cable element The smallest construction unit (for example pair, quad, or single fibre) in a cable. A cable element may have a screen.

Cable unit A single assembly of one or more cable elements of the same type or category. The cable unit may have a screen.

Cabling A system of telecommunications cables, cords, and connecting hardware that can support the connection of information technology equipment.

Campus A premise containing one or more buildings. Campus backbone cable A cable that connects the campus distributor to the building distributor(s).

Campus backbone cables may also connect building distributors directly.

Campus distributor (CD) The distributor from which the campus backbone cabling emanates.

Channel The end-to-end transmission path connecting any two pieces of application specific equipment. Equipment and work area cords are included in the channel, but not the connecting hardware into the application specific equipment.

Centralised optical fibre cabling Centralised optical fibre cabling techniques create a combined backbone/horizontal channel. The channel is provided from the work areas to the centralised cross-connect or interconnect by allowing the use of pull-through cables or splices.

Connecting hardware Connecting hardware is considered to consist of a device or a combination of devices used to connect cables or cable elements.

Connection Mated device or combination of devices including terminations used to connect cables or cable elements to other cables, cable elements or application specific equipment.

Consolidation point (CP) A connection point in the horizontal cabling subsystem between a floor distributor and a telecommunications outlet.

Cord Cable, cable unit or cable element with a minimum of one termination.

Coupling attenuation Coupling attenuation is the relation between the transmitted power through the conductors and the maximum radiated peak power, conducted and generated by the excited common mode currents.

CP cable A cable connecting the consolidation point to the telecommunications outlet(s).

CP link The part of the permanent link between the floor distributor and the consolidation point, including the connecting hardware at each end.

Cross-connect An apparatus enabling the termination of cable elements and their cross-connection, primarily by means of patch cords or jumpers. Incoming and outgoing cables are terminated at fixed points.

Distributor The term used for a collection of components (such as patch panels, patch cords) used to connect cables.

Equipment cord A cord connecting equipment to a distributor. Equipment room A room dedicated to housing distributors and application specific

equipment. External network interface

A point of demarcation between public and private network. In many cases the external network interface is the point of connection between the network provider's facilities and the customer premises cabling.

Fixed horizontal cable The cable connecting the floor distributor to the consolidation point, when a CP is present, or to the TO when a CP is not present.

Floor distributor (FD) The distributor used to connect between the horizontal cable and other cabling subsystems or equipment. (See telecommunications room).

Generic cabling A structured telecommunications cabling system, capable of supporting a wide range of applications. Generic cabling can be installed without prior knowledge of the required applications. Application specific hardware is not a part of generic cabling.

Horizontal cable A cable connecting the floor distributor to the telecommunications outlet(s). Hybrid cable An assembly of two or more cable units and/or cables of different types or

categories in an overall sheath. It may include an overall screen. Individual work area The minimum building space that would be reserved for an occupant. Insertion loss Resulting from the insertion of a device into a transmission system, the ratio

of the power delivered to that part of the system following the device, before insertion of the device, to the power delivered to that same part after insertion of the device. The insertion loss is expressed in decibels.

Insertion loss deviation The difference between the measured insertion loss of cascaded components and the insertion loss as determined by simply adding their individual component losses.

Interconnect A technique enabling equipment cords (or cabling subsystems) to be terminated and connected to the cabling subsystems without using a patch cord or jumper. Incoming or outgoing cables are terminated at a fixed point.

Interface A point at which connections are made to the generic cabling.

Jumper Cable, cable unit or cable element without connectors used to make a connection on a cross-connect.

Keying A mechanical feature of a connector system, which guarantees polarisation or prevents the connection to an incompatible socket or optical fibre adapter.

Link Either a CP link or permanent link, see CP link and permanent link. Longitudinal conversion loss

The logarithmic ratio expressed in dB of the common mode injected signal at the near end to the resultant differential signal at the near end of a balanced pair.

Longitudinal conversion transfer loss The logarithmic ratio expressed in dB of the common mode injected signal at the near end to the resultant differential signal at the far end of a balanced pair.

Multi-user telecommunications outlet assembly (MUTOA) A grouping in one location of several telecommunications outlets.

Optical fibre cable A cable comprising one or more optical fibre cable elements.

Optical fibre duplex adapter A mechanical device designed to align and join two duplex connectors.

Optical fibre duplex connector A mechanical termination device designed to transfer optical power between two pairs of optical fibres.

Overfilled launch A controlled launch where the test fibre is overfilled with respect to both angle and position to simulate LED launches.

Pair The two conductors of a balanced transmission line. It generally refers to a twisted-pair or one side circuit of a quad.

Patch cord Cable, cable unit or cable element with connector(s) used to establish connections on a patch panel.

Patch panel An assembly of multiple connectors designed to accommodate the use of patch cords. It facilitates administration for moves and changes.

Permanent link Transmission path between the telecommunications outlet and the floor distributor. It excludes work area cords, equipment cords, patch cords and jumpers but includes the connection at each end. It can include a CP link.

Quad A cable element that comprises four insulated conductors twisted together. Two diametrically facing conductors form a transmission pair.

Screened balanced cable A balanced cable with an overall screen and / or screens for the individual elements.

Side circuit Two diametrically facing conductors in a quad that form a pair. Small form factor connector

An optical fibre connector designed to accommodate two or more optical fibres with at least the same mounting density as the connector used for

balanced cabling. Splice A joining of conductors or optical fibres, generally from separate heaths. Telecommunications A branch of technology concerned with the transmission, emission and

reception of signs, signals, writing, images and sounds; that is, information of any nature by cable, radio, optical or other electromagnetic systems.

Telecommunications room An enclosed space for housing telecommunications equipment, cable terminations, interconnect and cross-connect.

Telecommunications outlet (TO) A fixed connecting device where the horizontal cable terminates. The telecommunications outlet provides the interface to the work area cabling.

Transverse conversion loss The ratio between the common mode signal power and the injected differential mode signal power.

Twisted pair A cable element that consists of two insulated conductors twisted together in a determined fashion to form a balanced transmission line.

Unscreened balanced cable A balanced cable without any screens.

Work area A building space where the occupants interact with telecommunications terminal equipment.

Work area cord A cord connecting the telecommunications outlet to the terminal equipment.

1.3.2 Abbreviations

ACR Attenuation to crosstalk ratio ANSI American National Standards Institute ATM Asynchronous transfer mode BD Building distributor BFOC Bayonet fibre optic connector (so called ST connector) B-ISDN Broadband ISDN BRA Basic rate access (ISDN) c Speed of light in vacuum (∼300 m/μs) CENELEC Comite Europeen de Normalisation Electrotechnique CD Campus distributor CP Consolidation point CSMA/CD Carrier sense multiple access with collision detection (Ethernet) EIA Electronic Industries Association ELFEXT Equal level far end crosstalk loss

EMC Electromagnetic compatibility EMI Electromagnetic interference EN Norme Europeenne FC Optical fibre connector type FC FD Floor distributor FDDI Fibre distributed data interface FEXT Far end crosstalk loss FOIRL Fibre optic inter-repeater link FWHM Full with half maximum GI Graded index IEC International Electrotechnical Commission IEEE The Institute of Electrical and Electronics Engineers IDC Insulation displacement connection ISDN Integrated services digital network ISO International Organization for Standardization IT Information technology ITU International Telecommunication Union LAN Local area network LCL Longitudinal conversion loss NEXT Near end crosstalk loss MM Multimode NA Numerical aperture NT Network termination ODF Optical distribution frame OTDR Optical time domain reflectometer OSI Open systems interconnection PBX Private branch exchange PC Physical contact PMD Physical layer medium dependent PRA Primary rate access (ISDN) PSACR Power sum attenuation to crosstalk ratio PSELFEXT Power sum equal level far end crosstalk loss PSFEXT Power sum far end crosstalk loss PSNEXT Power sum near end crosstalk loss SC Optical fibre connector type SC SC-D SC duplex connector SDH Synchronous digital hierarchy SM Singlemode ST Optical fibre connector type ST (BFOC/2,5) STI Surface transfer impedance TIA Telecommunication Industries Association TC Telecommunication closet TE Terminal equipment TO Telecommunication outlet

TP-PMD Twisted pair physical medium dependent WAN Wide area network

2 Scope and general principles of generic cabling

2.1 Scope and contents

The generic cabling specified in generic cabling (EN 50173-1) is a structured telecommunications cabling system, capable of supporting a wide range of applications. Generic cabling can be installed without prior knowledge of the required applications. The cable types used in the cabling are balanced cables and optical fibre cables. Generic cabling does not support coaxial cabling. The cabling may cover one or more buildings within a campus. The standard is optimised for premises, where the maximum distance over which telecommunications services are distributed, is 2000 metres. However, the principles of the standard may be applied to larger installations. Although the original basis of generic cabling has been office environment, the principles of the generic cabling can be well applied to all kinds of buildings, where telecommunications cabling is needed. Different kinds of commercial buildings, schools and universities, laboratories, industrial buildings and factories and storehouses are examples of these. During last years the principles of generic cabling have been adopted also in residential cabling. Standardization work is going on in CENELEC in order to produce specific standards for generic cabling in industrial and residential environments. Generic cabling is a multi-vendor cabling, which may be implemented with material from single and multiple sources. It supports a wide range of services including voice, data, text, image and video.

The standard specifies the following:

• Structure and configuration for generic cabling • Implementation requirements and options • Performance requirements for channels, links, cables, connecting hardware and cords

The standard also dives information about the applications supported by the cabling. Electrical safety and protection, fire safety and electromagnetic compatibility (EMC) requirements are covered by other standards and by regulations, which shall be followed. The standard gives information about these standards and regulations.

2.2 General principles of the standard

In order to conform to the European standard EN 50173-1 the installed generic cabling shall fulfil the following requirements:

• The configuration and structure conform to the requirements of the standard. • The interfaces to the cabling conform to the requirements of the standard. • The performance of balanced channels meets the requirements of the standard. • Local regulations on safety and EMC are met.

Planning

Structure of cabling meets requirements of standard:

•Campus backbone, building backbone and horizontal cabling•Interfaces•Configuration and dimensioning

Equipment interfaces meet requirements of standard:

•Twisted pair cabling:RJ45 in TOs and distributors•Optical fibre cabling:SC in TOs, SC or other (e.g.MT-RJ, LC orVF-45) in distributors

Testing

Performance of channels meet requirements of standard:

•Dimensioning rules of standard are followed•Components specified in standard are used•Installation according to EN50174-1, -2 and-3

Electrical safety regulations are followed

Cabling conforms to standard EN 50173-1

Figure 2.1 Principles of conformance.

The standard has been written and its requirement have been set in such way that the performance requirements of channels and links will be met, if:

• The configurations and lengths specified in reference implementations are applied. • Cables and connecting hardware meet the requirements of the standard. • Cabling is installed with good skill and proper workmanship in accordance with the standards series

of EN 50174.

If all the requirements listed above are met, no conformance testing is required by the standard. However in practical situations it is strongly recommended to test each link or channel after installation. This is the only way to ensure the conformance. The required tests and inspections shall be defined in the cabling installation specification and quality plan according to EN 50174-1. The principles of the standard also mean that the channel will meet the prescribed performance requirements, if it is created by adding of appropriate components to a permanent link or CP link meeting the prescribed performance. Appropriate component means equipment cord, patch cord, CP cable or work area cord meeting the relevant performance and length requirements. Hence it is not necessary to test the channel, if the permanent link has been tested and found to meet the performance requirements. However, the channel performance shall be assured, when a channel is created by adding more than one cord to either end of link meeting the performance requirements. This is the case, when a cabling installation contractor installs the CP link first, and at a later time extends this to a permanent link or channel. The channel performance shall then be assured at least by using appropriate equipment cord, CP-cable and work area cord, but also testing is recommended. It is recommended to use system specific components, such as cables and cords, connecting hardware and panels, which clearly meet the specified mechanical an transmission requirements. This is the best way to ensure already beforehand the compatibility of components and the performance of the links and channels.

3 Structure and functional elements of generic cabling

The standard EN 50173-1 defines the functional elements of the cabling and describes, how they are interconnected to form subsystems. The standard also defines the interfaces, at which the application specific equipment is connected to the cabling. These interfaces are at distributors and telecommunications outlets.

3.1 Functional elements

The functional elements of generic cabling are as follows:

• Campus distributor, CD • Campus backbone cable • Building distributor, BD • Building backbone cable • Floor distributor, FD • Horizontal cable • Consolidation point, CP • Consolidation point cable, CP cable • Telecommunications outlet, TO

Groups of these functional elements are connected together to form cabling subsystems. There are three subsystems. These are as follows:

• Campus backbone cabling • Building backbone cabling • Horizontal cabling

3.2 Cabling subsystems

The cabling subsystems are connected together to create a generic cabling system as shown in figure 3.1.

Terminal equipment

CD BD FD CP TO

Campus backbone Building backbone Horizontal cabling Work area cabling

Generic cabling system

Figure 3.1. Structure of generic cabling.

The campus backbone cabling extends from the campus distributor to the building distributor(s) usually located in separate buildings. The campus backbone cabling includes campus backbone cables and mechanical termination of the campus backbone cables at both the campus and building distributors together with associated patch cords and/or jumpers at the campus distributor. The equipment cords in the campus distributor are application-specific and are not included in the campus backbone cabling, although they are a part of the channel. Building distributors may be also directly connected with campus backbone cables to each other to improve the failure tolerance. Where the building distributor does not exist, the campus backbone cabling subsystem extends from the campus distributor to the floor distributor.

The building backbone cabling extends from building distributor(s) to the floor distributor(s). The building backbone cabling includes building backbone cables and mechanical termination of the building backbone cables including the connections at both the building and floor distributors together with associated patch cords and/or jumpers at the building distributor. The equipment cords in the building distributor are application-specific and are not included in the building backbone cabling, although they are a part of the channel. Floor distributors may be also directly connected with building backbone cables to each other to improve the failure tolerance. The building backbone cabling shall be continuous and without any splices in twisted pair cables.

The horizontal cabling extends from a floor distributor to the telecommunications outlet(s) connected to it. The horizontal cabling includes horizontal cables, mechanical termination of the horizontal cables at the telecommunications outlet and the floor distributor together with associated patch cords and/or jumpers at the floor distributor, and telecommunications outlets. Horizontal cabling may include one consolidation point (CP). Horizontal cables shall be continuous from the floor distributor to the telecommunications outlets unless a consolidation point is installed. The equipment cords in the floor distributor and the work area cords are application-specific and are not included in the horizontal cabling, although they are a part of the channel.

3.3 Interconnection of subsystems

In generic cabling the functional elements of subsystems are interconnected to form a basic hierarchical topology as shown in figure 3.2. According to figure 3.2 the cabling from each distributor follows star topology. In addition to this basic star topology direct connections between distributors may be built for backup purposes. Horizontal cabling may include one consolidation point.

According to the standard it is also possible to combine building backbone cabling and horizontal cabling to form a centralized cabling. In the example of figure 3.3 the principle of centralized cabling has been applied in a part of the cabling. In centralized optical fibre cabling the combined building backbone and horizontal cabling may be implemented with direct cabling, with splice in floor distributor or with patching in floor distributor. In the case of direct cabling there is no need of floor

distributor at all. The principles and requirements of centralized cabling are described more in detail in clause 5.2 of this guidebook.

BD BD

CD

BD

FD FD FD FD

TO TO TO

TO TO

CP

optionalbackupconnection

optional

Figure 3.2. Basic structure of generic cabling.

Distributors are located in spaces reserved for this purpose. These spaces are telecommunications rooms and equipment rooms. The requirements of location of distributors are specified in the standard EN 50174-1. Indoor cables are installed in pathways, which may consist of shelves, trays, trunking, ducting or conduit systems. Outdoor cables are installed in ducts or directly in ground. Between buildings also tunnels can be used. Building entrance facility is required to provide all necessary mechanical and electrical services for the entry of telecommunications cables into a building. These includes e.g. pathways from entrance point to the nearest distributor and possible cable joint from outdoor to indoor cable.

Telecommunications outlets are located in work areas and they are installed in trunking system, trays, service poles or on wall depending on the way of installation of horizontal cabling. Figure 3.4 shows an example of generic cabling in 4-floor building. In this example three distributors are located in telecommunications room of the first floor. Campus distributor is needed for terminating the campus backbone cable going to the other building and the access cable to public network. Building distributor is needed for terminating the building backbone cabling of the building and to connect this cabling to campus backbone cabling. Floor distributor serves the horizontal cabling of the first floor.

Figure 3.4. Example of generic cabling.

3.4 Interfaces, channel, link

The standard EN 50173-1 defines three types of interfaces for the cabling. These are:

• Equipment interfaces • Test interfaces • Public network interface

Equipment interfaces are located at the ends of each subsystem. Each distributor includes equipment interfaces, which may be interconnects or cross-connects. Figure 3.5 illustrates these two types of interfaces.

Equipment Equipment cord Horizontal cabling

BDCD

FD

ODF

FD

TO

CP

Equipment Equipment cord Patch cord Horizontal cabling

Figure 3.5. Equipment interface in distributor may be a) interconnect or b) cross-connect.

In a horizontal cabling there is also an equipment interface at the telecommunications outlet. A consolidation point in horizontal cabling is not an equipment interface.

Test interfaces are located at the ends of each subsystem. In a horizontal cabling there is also a test interface at the consolidation point, when this exists. Figure 3.6 illustrates the possible equipment interfaces and test interfaces in horizontal cabling in the case of interconnect in the floor distributor.

EquipmentTerminalequipment

EI EI

FD CP TO

EI = Eqiupment interface

TI

TITI

TI

TI = Test interface

TI

CP link

Permanent link

Channel

Figure 3.6. Equipment and test interfaces in the horizontal cabling. The definitions of channel, permanent link and CP link are also shown.

The performance of the cabling is defined between and at the test interfaces and the cabling is also tested at these interfaces. The sections between the test interfaces are as shown in figure 3.6 and they are the following:

• Channel • Permanent link • CP link

Channel in horizontal cabling is the transmission path between information technology equipment (e.g. LAN switch) and terminal equipment. A typical horizontal cabling channel consists of: • Horizontal cable from the patch panel of the floor distributor to the telecommunications outlet and the

connecting hardware at both ends. • Horizontal cabling channel may include also one consolidation point (CP), as in figure 3.6. • Equipment cord in the floor distributor. • Work area cord in the work area.

For the purposes of testing, the channel excludes the connections at the application-specific equipment. This means that the plug connectors of equipment cord and work area cord at equipment ends are not included in the channel. For the applications that are to be run it is important that the generic cabling channel is designed to meet the required class of performance. Channels are classified into different classes based on their performance. These classes are described in detail in clause 4.1 of this guidebook.

Permanent link in horizontal cabling is the transmission path between the patch panel of floor distributor and the telecommunications outlet. A typical horizontal cabling permanent link consists of: • Horizontal cable from the patch panel of the floor distributor to the telecommunications outlet and the

connecting hardware at both ends.

• Horizontal cabling permanent link may include also one consolidation point (CP), as in figure 3.6.

The permanent link also includes the connections at the patch panel and at the telecommunications outlet. This means that the plug connectors of equipment cord and work area cord at cabling ends are included in the permanent link. Permanent links are classified into different classes based on their performance. These classes are described in detail in clause 4.1 of this guidebook.

CP link horizontal cabling is the transmission path between the patch panel of floor distributor and the consolidation point. A typical horizontal cabling CP link consists of:

• Horizontal cable from the patch panel of the floor distributor to the consolidation point and the connecting hardware at both ends.

The CP link also includes the connections at the patch panel and at the consolidation point. This means that the plug connectors of equipment cord and CP cable at cabling ends are included in the CP link. CP links are classified into different classes based on their performance. These classes are described in detail in clause 4.1 of this guidebook.

Public network interface generally is located in the campus or building distributor. The standard does not specify its requirements. Only reference to national and local regulations is made. These regulations shall be taken into account in the planning stage of the cabling. It is probable that CENELEC will star standardization work on this topic and the standard will be published as a part of the EN 50174-series.

3.5 Dimensioning and minimum configuration requirements

The number of subsystems in the generic cabling system depends much on the size of the premises, number and distribution of buildings within premises area, purpose of use of the premises and the information technology strategy of the premises owner and/or user. The simplest basic case is such that there is one campus distributor in the campus, one building distributor in each building and one floor distributor in each floor. If, however, there is only one building, no campus distributor and campus backbone cabling are needed. On the other hand, in a large building more than one building distributor may be needed. In this case also campus backbone cabling within the building is needed to connect the building distributors together. A small generic cabling may only consist of one floor distributor and its horizontal cabling.

3.5.1 Distributors Distributors should be located such that the resulting cable lengths are consistent with the channel performance requirements of the standard and that the maximum allowed cabling lengths are not exceeded. The standard EN 50173-1 gives reference implementation models with dimensioning rules, which can be used to ensure the above-mentioned conditions. These models are explained in detail in chapter 5 of this guidebook. In any case the following maximum channel lengths should always be followed:

• Maximum channel length in horizontal cabling is 100 m. • Total maximum channel length of horizontal, building backbone and campus backbone cabling is

2000 m.

The design of the distributors shall also ensure that the lengths of patch cords, jumpers and equipment cords are minimized and administration should ensure that the design lengths are maintained during operation. According to the standard there should be a minimum of one floor distributor for every 1 000 m2 of floor space reserved for offices. A minimum of one floor distributor should be provided for every floor. If a floor is sparsely populated (e.g. a lobby), it is permissible to serve this floor from the floor distributor located on an adjacent floor. The floor distributor density recommended by the standard is, however, in many cases too high and may lead to uneconomical solution. Therefore the optimal floor distributor density should be considered case by case. As a rule of thumb the density of one floor distributor/3000 m2 has shown to be more appropriate than that recommended by the standard. The functions of multiple distributors may be combined, when needed. For example in figure 4.4 the functions of campus, building and floor distributor (first floor) have been combined.

3.5.2 Cables and connecting hardware In the generic cabling the cables are twisted pair cables and optical fibre cables. Twisted pair cables may unscreened, overall screened or pair screened. The performance of a twisted pair cable is expressed with its category. There are three categories and the category is defined based on the upper limit frequency of the cable. Also the connecting hardware of twisted pair cables are categorized in the same way. The categories and their upper limit frequencies are those shown in table 3.1.

Table 3.1. Categories of twisted pair cables and associated connecting hardware.

Category Upper limit frequency5 100 MHz 6 250 MHz 7 600 MHz

The optical fibres used in optical fibre cables are multimode fibres or singlemode fibres. Multimode fibres are categorized in three categories according to the bandwidth of the fibre. These categories are OM1, OM2 and OM3. There is only one category for the singlemode fibre:OS1. In optical fibre cabling the connector type used in telecommunications outlets is type SC. In distributors type SC or other standardized types are used. Twisted pair cables and optical fibre cables are discussed in detail in chapter 6 and connecting hardware in chapter 7 of this guidebook.

3.5.3 Work area cords, equipment cords, patch cords and jumpers

The work area cord is used to connect terminal equipment to the telecommunications outlet and the equipment cord is used to connect information technology equipment (e.g. LAN switch) to the cabling in the distributor. These cords are non-permanent and often application dependent. Therefore they are not parts of the generic cabling. The standard EN 50173-1, however, specifies the performance of these cords. When cords meeting these specifications are used to create a channel, the requirements of the channel will be met provided that the permanent link meets the relevant requirements. The maximum length of equipment cords to be used in campus and building distributor is 30 m. In the horizontal cabling the dimensioning rules of reference implementations shall be used. These rules are presented in chapter 5 of this guidebook.

The patch cord and jumpers within the distributors are included to the generic cabling. These cords shall meet the same specifications as work area cords and equipment cords. The maximum length of patch cord and jumpers to be used in campus and building distributor is 20 m. In the horizontal cabling the dimensioning rules of reference implementations shall be used.

3.5.4 End user outlets

The generic cabling should be designed in such way that end user outlets are to be installed throughout the usable floor space. A high density of outlets will enhance the ability of the cabling to accommodate changes. Outlets may be presented singly, or in groups. A common way is to use double outlets. In a double outlet there are two outlet interfaces in the same physical enclosure. The minimum requirements of telecommunication outlets according to the standard EN 50173-1 are the following: • Each individual work area shall be served by a minimum of two outlets. • The first outlet shall be provided with category 5 or higher category twisted pair connecting hardware

and shall be terminated to a 4-pair cable of the same category. • The second outlet may be provided with optical fibre connecting hardware or with category 5 or

higher category twisted pair connecting hardware and shall be terminated respectively to two optical fibres or to a 4-pair cable of the same category.

• Each outlet shall have a permanent means of identification that is visible to the user. • Devices such as baluns and impedance matching adapters, if used, shall be external to the outlet.

Figure 3.7 illustrates the minimum configuration of end user outlets.

FD

TO TO TO TO

Figure 3.7. Minimum configuration of outlets in work areas.

In the basic implementation of the generic cabling each telecommunications outlets serves only one individual work area. According to the standard this kind of telecommunications outlet is called single user telecommunications assembly. The following additional requirements apply to the single user telecommunications outlet assembly:

• A single user telecommunications outlets assembly shall be located in user-accessible locations. • The performance contribution of work area cords, patch cords, jumpers and equipment cords shall be

taken into account to ensure that the channel requirements of the standard are met.

In open offices a group of telecommunications outlets may serve more than one individual work area. According to the standard this kind of group of telecommunications outlets is called multi-user telecommunications assembly. The following additional requirements apply to the multi-user telecommunications outlet assembly:

• A multi-user telecommunications outlet assembly shall be located in an open office work area so that each furniture cluster is served by at least one multi-user telecommunications outlet assembly.

• A multi-user telecommunications outlet assembly shall serve a maximum of twelve work areas. • A multi-user telecommunications outlet assembly shall be located in user accessible, permanent

locations. • A multi-user telecommunications outlet assembly shall not be installed in ceiling spaces or any

obstructed areas. • The performance contribution of work area cords, patch cords, jumpers and equipment cords shall be

taken into account to ensure that the channel requirements of the standard are met. • The length of the work area cord should be limited to ensure cable management in the work area.

3.5.5 Consolidation point In an open office environment it may be useful to install a consolidation point in the horizontal cabling between the floor distributor and the telecommunications outlet. This enables the flexibility of relocating telecommunications outlets in the work area, when required. One consolidation point is permitted between a floor distributor and any telecommunications outlet. The consolidation point shall only contain passive connections.

In addition the following requirements apply to a consolidation point:

• A consolidation point shall be located so that each work area group is served by at least one consolidation point.

• A consolidation point shall serve a maximum of twelve work areas. • A consolidation point should be located in accessible permanent locations such as ceiling voids and

under floors. • For twisted pair cabling, the effect of multiple connections in close proximity on transmission

performance should be taken into consideration when planning the cable lengths between the floor distributor and the consolidation point. The minimum length of 15 m is recommended.

• A consolidation point shall meet the documentation and labelling requirements.

The concepts of a multi-user telecommunications outlet assembly and a consolidation are different. Thee principal difference is in the way, how terminal equipment are connected to the cabling. In the case of a multi-user telecommunications outlet assembly the terminal equipment are connected directly with work area cords to the multi-user outlets in the same way as in the case of single-user telecommunications outlet. A consolidation point is the other end of the CP link, which is expanded to

a permanent link by using a CP cable. At the other end oh this CP cable there is a telecommunications outlet, to which the terminal equipment is connected with work area cord. A typical application of a consolidation point is in the horizontal cabling in an open office environment, where the horizontal cables are installed on cable trays. The simplest consolidation point in this case is so called ceiling outlet. CP cable is installed within the service pole and the telecommunications outlet is in the lower end of this pole.

3.5.6 EMC, earthing and bonding

The generic cabling is a passive system and cannot be tested for EMC compliance individually. The equipment to be connected to the cabling shall, however, meet the requirements of relevant EMC standards. This applies to both immunity and emission. These requirements shall be met also, when the equipment have been connected to the cabling system to form a telecommunication system, e.g. local area network.

To minimize the electromagnetic interferences the cabling shall be installed according to the requirements of the standard series EN 50174. The requirements for earthing and bonding are also specified in the standard series EN 50174 and in standard EN 50310.

4 Channels and links and their requirements

The performance of the generic cabling is specified for channels and links. The definitions of channel, permanent link and CP link are presented in clause 3.4 of this guidebook. The standard specifies many transmission requirements for both channels and links. The performance of the channel determines the applications, which are supported by the cabling. Therefore it is essential to ensure the channel performance in planning and implementation of the cabling. The generic cabling, however, is application independent and therefore it is important to specify also the performance of the application independent section of the cabling, i.e. permanent link. This specification is used as an acceptance criterion for the installed cabling. When permanent link meeting the relevant specification is expanded to channel by connecting cords (e.g. work area cord and equipment cord in horizontal cabling) to both ends, the channel will meet the channel specification. This will happen, if the lengths and performance of these cords meet the requirements of the standard. In many cases the horizontal cabling at first stage is implemented only as a CP link. In this the performance of the CP link is the acceptance criterion. When CP link is expanded to a permanent link, the performance shall be verified again. The meaning and use of requirements of channel, permanent link and CP link are shown as a summary in table 4.1.

Table 4.1. The meaning and use of requirements of channel, permanent link and CP link.

Aspect Channel Permanent link CP link Meaning of performance

Determines the applications, which are supported.

Ensures the performance of the installed cabling and is basis for the performance of the channel.

Ensures the performance of the installed CP link and is basis for the performance of the permanent link and the channel.

Need to test Only when the performance testing of the channel is required for special reasons.

Shall be tested always after installation.

Shall be tested always after installation, unless the CP link is extended immediately to a permanent link.

Other aspects Test results are valid only for the configuration, which was tested. If equipment cord or work area cord is changed, test results are no more valid for new configuration. The performance of the link cannot be concluded based on channel performance.

If the lengths and performance of equipment and work area cords meet the requirements of the standard, the channel will meet the channel specification.

When CP link is expanded to a permanent link, this should be tested.

4.1 Classes of channels and links

Twisted pair and optical fibre channels and links are classified into different classes based on their characteristics. Based on this classification it is easy to know, which applications are supported by the cabling. Information about applications supported by the generic cabling is given in chapter 9 of this guidebook. The classes defined to twisted pair cabling are shown in table 4.2. The classes are based on the upper limit frequency.

Table 4.2. Classes of twisted pair cabling.

Class Upper limit frequency A 100 kHz B 1 MHz C 16 MHz D 100 MHz E 250 MHz F 600 MHz

The channel or link of a certain class always meets also the requirements of the lower classes. For horizontal cabling the requirements of classes D, E and F have been defined so that they will be met by

using cables and connecting hardware of categories 5, 6, and 7. But this will happen only, when installation has been carried out according to standard series 50174 and with professional skill. According to the standard EN 50173-1 the performance of horizontal cabling shall be at least that of class D. The classes defined to optical fibre cabling are shown in table 4.3. The classes are based on the channel length, over which applications are supported.

Table 4.3. Classes of optical fibre cabling.

Class Channel length OF-300 300 m OF-500 500 m OF-2000 2000 m

The classes of the optical fibre cabling are based only on channel lengths, over which applications are supported. This length, however, depends on the fibre category and the application to be supported. Optical fibre categories are explained in detail in clause 6.3 of this guidebook.

4.2 Twisted pair channels and links and their requirements

4.2.1 Transmission in twisted pair cable Signal transmission in a twisted pair cable is based on balance. Therefore in the standard these cables are called balanced cables. In balanced transmission the both conductors of the signal circuit are at the same electrical position related to environment – usually to the earth potential. Theoretically balanced transmission represents conditions, where no electromagnetic interferences exist. This means that the signal transmitted on a channel or link is not subject to any interference and does not cause any interference to its environment. On the contrary, in unbalanced transmission the conductors are in different electrical positions related to the earth potential and the system is subject to interferences. In balanced conditions the following are in force: • The voltages of the two conductors have the same absolute values, but opposite polarities.

Therefore the electric fields caused by the conductors cancel each other (figure 4.1). • The currents flowing on the two conductors have the same absolute values, but opposite directions.

Therefore the magnetic fields caused by the conductors cancel each other (figure 4.1). • Interference voltages from the environment do not affect the transmission, because the voltage

between the conductors of the pair remains unchanged due to balance (figure 4.2). • When magnetic field flows through the loop made by the pair, the currents induced by the magnetic

field cancel each other due to the pair twist (figure 4.3).

If also the equipment connected to the balanced channel are balanced (symmetrical), the whole system is free of interferences. Perfect balance of channels and links as well as of equipment, however, cannot be achieved. The unbalance of channels and links is caused by the unbalance of cables, connecting hardware and terminations.

Tx Rx

Transmitter Receiver+E

-E

+H -H

+U/2

-U/2

+I

-I

Figure 4.1. In perfect balance no interference is emitted to the environment.

Balanced transmission Interface cannot affect

Tx Rx

Transmitter Receiver

+H+U/2

-U/2

Interference

+H

+U/2+H

-U/2+H

Unbalanced transmission Interface affects

Tx Rx

Transmitter Receiver

+H+U

Interference

+U+H

Connected to earth potential

Figure 4.2. Interference from environment does not affect the balanced transmission.

To make the principle of balance easier to understand the situations in figure 4.2 are presented as extreme ideal situations: perfect balance and perfect unbalance.

Magnetic field flows through the loop made by the pair

Tx Rx

Figure 4.3. The currents induced by the magnetic field cancel each other due to the pair twist.

The standard EN 50173-1 specifies many transmission characteristics, which are used to describe the performance of the twisted pair cabling. These characteristics are discussed in the following. For each characteristic also the requirements of EN 50173-1 for classes D, E and F channels and permanent links are presented. In the standard the requirements of permanent links are specified so that they depend on the length of the link and on the number of connections in the link. The requirements presented in the following are based on the maximum configuration. This means 90 m length and three connections. This configuration includes a consolidation point.

The characteristic describing the performance of the twisted pair cabling are the following:

• Return loss, RL

• Attenuation (insertion loss) • Pair to pair near end crosstalk loss, NEXT • Power sum near end crosstalk loss, PSNEXT • Pair to pair attenuation to crosstalk ratio, ACR • Power sum attenuation to crosstalk ratio, PSACR • Pair to pair equal level far end crosstalk loss, ELFEXT • Power sum equal level far end crosstalk loss, PSELFEXT • DC loop resistance • DC resistance unbalance • Propagation delay • Propagation delay skew • Unbalance attenuation • Coupling attenuation

4.2.2 Characteristic impedance and return loss

Impedance is the ratio of voltage to current. In twisted pair cabling the characteristic impedance is the ratio of the voltage between the conductors of the pair to the current flowing on these conductors. The unit of characteristic impedance is ohm (Ω). In a homogeneous twisted pair the characteristic impedance is constant along the whole length of the pair. The voltage and current are decreased in the direction of propagation, but the ratio of the voltage to the current remains constant. At low frequencies and with short lengths the characteristic impedance is not meaningful, because the wavelength of the signal is long compared with the length of the transmission line. The characteristic impedance becomes important, when the frequency is so high that the quarter of the wavelength is of same magnitude or smaller than the length of the line. In practice this means usually a frequency higher than 100 kHz. In the traditional analogue voice transmission the characteristic impedance does not have a meaning, but at ISDN frequencies it begins to be an important characteristic. According to the standard EN 50173-1 the nominal characteristic impedance of twisted pair cabling is 100 Ω. The characteristic impedance of a link or channel is affected by all the components of the link or channel: cables, cords and connecting hardware. Thee input and output impedance of the equipment to be connected to the channel shall have the same characteristic impedance as the channel within certain tolerances.

In real links and channels the characteristic impedance never is perfectly constant, because there are impedance inhomogenities in cables. Also connecting hardware and terminations represent impedance inhomogenities. Each local change of characteristic impedance causes a reflection, which depend of the magnitude of the change in impedance. The greater the impedance change is, the greater voltage is reflected in backward direction. If there is a break (open circuit) in the transmission line, the signal voltage is totally reflected back. In this case the coefficient of reflection = 1. Another extreme case is a short circuit, which also causes the total reflection. In this case, however, the polarity of the voltage is changed to opposite and the coefficient of reflection = -1. If the characteristic impedance is changed to

any other value between 0...∞, the coefficient of reflection depends on the magnitude of the change. The relationship between the characteristic impedance and reflections is illustrated in figure 4.4.

Characteristic impedances: Z1 and Z2 , Return loss: Ah = 20 lg (1/ρ)Reflection coefficient: ρ = (Z1 - Z2 ) / ( Z1 - Z2)

Figure 4.4. Change of impedance causes reflection.

There are always innumerable number of greater or smaller changes of characteristic impedance in a link and channel. At each point of change a reflection is born and the sum of these small reflections can be measured at the near end of the link or channel. The return loss is the measure of this total sum of reflections coming from the whole length of the link or channel. This situation is presented in figure 4.5.

ZUi

rU

Changes in characteristic impedance

Structural return loss SRL= 20 lg(Ui /Ur) (dB)

ρ = 1

Z 2 =

ρ = - 1

Z 2 = 08

Z 1

Z 1

Z 1

Z 1 Z 2

Z 2 = Z 1

ρ = 0

Figure 4.5. Reflections in the link or channel and their combined effect.

The return loss is a measure of the total reflected signal power from the cable pair due to the impedance inhomogenities within the pair. Return loss is expressed in decibels (dB). For example return loss of 20 dB means that 1 % of the signal power and 10 % of signal voltage fed to a link or channel is reflected back to the near end. Reflections are caused by the internal impedance inhomogenities in the link or channel.

Table 4.4. Return loss requirements of class D, E and F channels and permanent links (maximum configuration).

Frequency, MHz

Minimum value of return loss, dB

Class D Class E Class F Channel Link Channel Link Channel Link

1 17,0 19,0 19,0 21,0 19,0 21,0 16 17,0 19,0 18,0 20,0 18,0 20,0 100 10,0 12,0 12,0 14,0 12,0 14,0250 8,0 10,0 8,0 10,0600 8,0 10,0

Values of return loss at frequencies for which the measured channel or permanent link attenuation is below 3,0 dB are for information only.

4.2.3 Attenuation (insertion loss)

When the signal propagates along a link or channel, its power is decreased. This phenomenon is called attenuation. Attenuation is caused by the resistive and dielectric losses of the link or channel and it can be seen as decreasing voltage and current when the distance increases. The unit of attenuation is decibel, dB (for cables the attenuation is expressed in dB/100 m). Attenuation sets limits for the length of a link and channel and the highest signal frequency to be transmitted. The concept of attenuation is shown in figure 4.6.

U0 U1

Tx Rx

Attenuation a = 20 lg(U0/U1) (dB)

U0

U1

Voltage

Figure 4.6. Attenuation of link or channel.

Attenuation increases proportionally to the square root of frequency, when the frequency is increased.

Table 4.5. Attenuation (insertion loss) requirements of class D, E and F channels and permanent links (maximum configuration).

Frequency, MHz

Maximum value of attenuation, dB

Class D Class E Class F Channel Link Channel Link Channel Link

1 4,0 4,0 4,0 4,0 4,0 4,0 16 9,1 7,7 8,3 7,1 8,1 6,9 100 24,0 20,4 21,7 18,5 20,8 17,7 250 39,5 30,7 33,8 28,8

600 54,6 46,6

4.2.4 Pair to pair near end crosstalk loss, NEXT

In the case of perfectly balanced link or channel there exists no electromagnetic coupling from the pair to the environment. In practice there is, however, always more or less electromagnetic coupling caused by imperfect balance. Unwanted electromagnetic coupling from one pair to another pair is called crosstalk. In addition to imperfect balance, also impedance mismatches and ways of termination affect the crosstalk phenomenon. The unwanted crosstalk signal can be measured at near end and at far end. Near end means the same end as where the (disturbing) signal is transmitted to the cable and far end means the other end. Pair to pair near end crosstalk (NEXT) loss is the measure of near end crosstalk from one pair to another pair. The unit of NEXT is dB (decibel). The definition of NEXT is shown in figure 4.7

Near end crosstalk loss NEXT = 20 lg(U0/U2) (dB)

Figure 4.7. Pair to pair near end crosstalk loss, NEXT.

It is important for transmission that crosstalk is controlled and kept within specified limits. Especially in applications, where the differences of signal levels in pairs are high, crosstalk characteristics are critical. For the same reason in two pair duplex transmission (e.g. 100Base-T) the near end crosstalk is more critical than the far end crosstalk.

Table 4.6. NEXT requirements of class D, E and F channels and permanent links (maximum configuration)

Tx Rx

Rx Tx

U2

U0 U1

Frequency, MHz

Maximum value of Next, dB

Class D Class E Class F Channel Link Channel Link Channel Link

1 60,0 60,0 65,0 65,0 65,0 65,016 43,6 45,2 53,2 54,6 65,0 65,0100 30,1 32,2 39,9 41,8 62,9 65,0 250 33,1 35,3 56,9 60,4600 51,2 54,7

Values of NEXT at frequencies for which the measured channel or permanent link attenuation is below 4,0 dB are for information only.

4.2.5 Power sum near end crosstalk loss, PSNEXT

While pair to pair NEXT means crosstalk between two pairs, power sum NEXT (PSNEXT) takes into account the crosstalk from all other pairs to one pair. In a four-pair cable each pair is subject to crosstalk from three other pairs. This means that in a four-pair cable the power sum NEXT (PSNEXT) is the sum result of three crosstalk signals. PSNEXT is expressed in dB (decibelFigure 4.4 illustrates the concept of PSNEXT.

NEXT21

NEXT31

NEXT41

Pair 1

Pair 2

Pair 3

Pair 4

NEXTXY= PairtopairNEXTbetween pairsX and Y, dB

PSNEXT= Sum resultof thecrosstalk from all three other pairs to one pair, dB

Figure 4.8. Power sum near end crosstalk loss, PSNEXT.

PSNEXT is critical, when all four pairs of the cable are used simultaneously in duplex transmission (e.g. 1000Base-T).

Table 4.7. PSNEXT requirements of class D, E and F channels and permanent links (maximum configuration)

Frequency, MHz

Maximum value of PSNext, dB

Class D Class E Class F Channel Link Channel Link Channel Link

1 57,0 57,0 62,0 62,0 62,0 62,016 40,6 42,2 50,6 52,2 62,0 62,0100 27,1 29,3 37,1 39,3 59,9 62,0250 30,2 32,7 53,9 57,4600 48,2 51,7

Values of PSNEXT at frequencies for which the measured channel or permanent link attenuation is below 4,0 dB are for information only.

4.2.6 Pair to pair attenuation to crosstalk ratio, ACR

In the presence of the near end crosstalk there is a risk that a higher-level signal on one pairdisturbs an attenuated lower-level signal at the near end. This situation is shown in figure 4.9,where the signal propagating to direction A causes crosstalk to the other pair carrying a signal direction B. The unwanted crosstalk signal is as many decibels lower than the signal transmitted tdirection A as the NEXT value expresses. This unwanted signal is presented by dashed line. The received signal propagating to direction B is as many decibels lower than transmitted signal in the other end as attenuation (a) expresses. Attenuation to crosstalk ratio (ACR) is the difference between NEXT and attenuation in decibels (dB). It can be expressed by the following formula:

ACR = NEXT - Attenuation (dB)

Near end crosstalk NEXT = 20 lg(U0/U2) (dB)

Attenuation a = 20 lg(U0/U1) (dB)

Attenuation to crosstalk ratio ACR = 20 lg( U1/U2) = NEXT -a (dB)

Figure 4.9. Combined effect of attenuation and NEXT.

The signal propagating to direction A should not disturb the signal propagating in the other pair to direction B. Therefore ACR should be sufficiently high. In this sense the nature of ACR is very much same kind as signal to noise ratio.

Table 4.8. ACR requirements of class D, E and F channels and permanent links (maximum configuration)

Frequency, MHz

Minimum value of ACR, dB

Class D Class E Class F Channel Link Channel Link Channel Link

1 56,0 56,0 61,0 61,0 61,0 61,016 34,5 37,5 44,9 47,5 56,9 58,1

Tx Rx

U0 U1

U2

Rx Tx

U0

Direction A

Direction B

100 6,1 11,9 18,2 23,3 42,1 47,3250 -2,8 4,7 23,1 31,6600 -3,4 8,1

4.2.7 Power sum attenuation to crosstalk ratio, PSACR

Power sum attenuation to crosstalk ratio (PSACR) is defined as the difference between PSNEXT and attenuation:

PSACR = PSNEXT - Attenuation (dB)

Table 4.9. PSACR requirements of class D, E and F channels and permanent links (maximum configuration).

Frequency, MHz

Minimum value of PSACR, dB

Class D Class E Class F Channel Link Channel Link Channel Link

1 53,0 53,0 58,0 58,0 58,0 58,0 16 31,5 34,5 42,3 45,1 53,9 55,1 100 3,1 8,9 15,4 20,8 39,1 44,3 250 -5,8 2,0 20,1 28,6600 -6,4 5,1

4.2.8 Pair to pair equal level far end crosstalk loss, ELFEXT

Equal level far end crosstalk loss between two pairs (ELFEXT) expresses, how much lower the unwanted crosstalk signal in the far end of the disturbed pair is than the wanted signal at the far end of the disturbing pair. If the unwanted crosstalk signal is too high compared with the wanted signal, it may cause errors in transmission. ELFEXT is expressed in decibels, dB. Figure 4.10 illustrates the concept of ELFEXT.

Tx Rx

U0 U1

Tx Rx

U0 U1 U3

Attenuation a = 20 lg(U0/U1) (dB)

Far end crosstalk loss ELFEXT = 20 lg(U0/U3) (dB)

Equal level far end crosstalk loss ELFEXT = 20 lg(U1/U3) = FEXT -a (dB)

Figure 4.10. Pair to pair equal level far end crosstalk loss, ELFEXT.

ELFEXT is critical, when more than one pair in the cable are used to transmission in the same direction (e.g. 1000Base-T).

Table 4.10. ELFEXT requirements of class D, E and F channels and permanent links (maximum configuration).

Frequency, MHz

Minimum value of ELFEXT, dB

Class D Class E Class F Channel Link Channel Link Channel Link

1 57,4 58,6 63,3 64,2 65,0 65,0 16 33,3 34,5 39,2 40,1 57,5 59,3 100 17,4 18,6 23,3 24,2 44,4 46,0

250 15,3 16,2 37,8 39,2600 31,3 32,6

4.2.9 Power sum equal level far end crosstalk loss, PSELFEXT

While pair to pair ELFEXT takes into account crosstalk between only two pairs, power sum ELFEXT takes into account the crosstalk from all other pairs to one pair. In a four-pair cable each pair is subject to crosstalk from three other pairs. This means that in a four-pair pair cable the power sum ELFEXT is the sum result of three crosstalk signals. PSELFEXT is expressed in decibels, dB. Figure 4.11 illustrates the concept of PSELFEXT.

FEXT31

FEXT41

Pair 1

Pair 2

Pair 3

Pair 4

FEXT21

FEXTXY = Pairtopair far end cross talk loss between pairs X and Y, dB

ELFEXTXY = FEXTXY-attenuation(dB)

PSELFEXT = Sum result of the crosstalk from all three other pairs to one pair, dB

Figure 4.11. Power sum equal level far end crosstalk loss, PSELFEXT.

PSELFEXT is critical, when all four pairs of the cable are used simultaneously in the same transmission direction. Such situation is e.g. in the case of Gigabit Ethernet 1000Base-T.

Table 4.11. PSELFEXT requirements of class D, E and F channels and permanent links (maximum configuration)

. Frequency,

MHz Minimum value of PSELFEXT, dB

Class D Class E Class F

Channel Link Channel Link Channel Link 1 54,4 55,6 60,3 61,2 62,0 62,0 16 30,3 31,5 36,2 37,1 54,5 56,3 100 14,4 15,6 20,3 21,2 41,4 43,0 250 12,3 13,2 34,8 36,2600 28,3 29,6

4.2.10 Direct current loop resistance

Direct current loop resistance (DC loop resistance) is the resistance of the loop formed by the conductors of the pair, when ends of the pairs are connected together in the far end. Due to pair twist the DC loop resistance is 1...5 % greater than twice the resistance of one straight conductor. Figure 4.12 shows the definition of the DC loop resistance. The DC loop resistance is important in applications, in which the power to the terminal equipment is fed through the twisted pair cabling. An example of such application is the power feeding of an access point of wireless local area network (WLAN). Therefore the DC loop resistance is specified and is important to know. The unit of DC loop resistance is ohm (Ω).

Table 4.12. DC loop resistance requirements of class D, E and F channels and permanent links (maximum configuration).

Maximum value of DC loop resistance, Ω Class D Class E Class F

Channel Link Channel Link Channel Link 25 21 25 21 25 21

4.2.11 Resistance unbalance

The resistance unbalance expresses, how much the DC resistances of the conductors of the pair differ from each other. It is defined a shown in figure 4.12. The resistance unbalance has its own effect on the total balance of the pair and in this way on the immunity and emission. It may also be critical in remote power feeding systems.

a

b

Resistance unbalance: ΔRab

ΔRab = (Ra – Rb) : (Ra + Rb ) x 100 (%)

DC loop resistance= Ra + Rb

Figure 4.12. DC loop resistance and resistance unbalance.

Table 4.13. Resistance unbalance requirements of class D, E and F channels and permanent links (maximum configuration).

Maximum value of resistance unbalance, % Class D Class E Class F

Channel Link Channel Link Channel Link 3 3 3 3 3 3

4.2.12 Propagation delay

The propagation delay is the time, during which the signal propagates from one end of a kink or channel to the other end. The propagation delay may be critical, when the application is delay-critical. The standard specifies the maximum values in microseconds (μs).

Tx Rx

U0 U1

L

Voltage wave propagates the length L in time tt = propagation delayVelocity of propagation v = L/tVelocity factor = v/c, where c = 300 m/μs (speed of light in vacuum)Typically velocity factor is 0,6...0,7 (60…70 %)

Figure 4.13. Definition of propagation delay and other concepts related to it.

Table 4.14. Propagation delay requirements of class D, E and F channels and permanent links (maximum configuration).

Frequency,

MHz Maximum value of propagation delay, μs

Class D Class E Class F Channel Link Channel Link Channel Link

1 0,580 0,521 0,580 0,521 0,580 0,521 16 0,553 0,496 0,553 0,496 0,553 0,496 100 0,548 0,491 0,548 0,491 0,548 0,491 250 0,546 0,490 0,546 0,490600 0,545 0,489

4.2.13 Propagation delay skew

In a twisted pair cable each pair has a different propagation delay due to different lay lengths in their pair twist. This is necessary for controlled crosstalk conditions. Difference between the greatest

(shortest lay length) and the smallest propagation delay (longest lay length) is called propagation delay skew. The skew shall be less than a certain limiting value. The skew is expressed in microseconds (μs).

Each pair has a different propagation delay due to different lay lengths in their pair twist.Difference between the greatest and the smallest propagation delay shall be less than a certain limiting value.

t

Figure 4.14. Propagation delay skew.

Table 4.15. Propagation delay skew requirements of class D, E and F channels and permanent links (maximum configuration).

Frequency, MHz

Maximum value of propagation delay skew, μs

Class D Class E Class F Channel Link Channel Link Channel Link

1 0,050 0,044 0,050 0,044 0,030 0,026 16 0,050 0,044 0,050 0,044 0,030 0,026 100 0,050 0,044 0,050 0,044 0,030 0,026 250 0,050 0,044 0,030 0,026600 0,030 0,026

4.2.14 Unbalance attenuation

The measure of the total balance of a link or channel is unbalance attenuation, which is expressed in decibels, dB. The greater the unbalance attenuation is the better the balance is. The standard defines

unbalance attenuation as longitudinal conversion loss (LCL) at near end according to figure 4.15. LCL is measured at the near end of a link or channel.

Pair

Z Z

UL

UT

UL is longitudinal voltage (common mode)UT differential voltageatnear end

Unbalance attenuation at near end (LCL) = 20 lg (UL/ UT) dB

Figure 4.15. Definition of unbalance attenuation.

Testing of unbalance attenuation of an installed cabling is complicated and unpractical. Therefore no limit values are specified for classes D, E and F. Minimum requirement for class C is 30 dB at 1 MHz and 24 dB at 16 MHz.

4.2.15 Coupling attenuation

As a result of the imperfect balance of the twisted pair cabling an electromagnetic field is emitted to the environment of the cabling. Also for the same reason an external electromagnetic induces interference voltages and currents into the cabling. The interferences emitted by the cabling and the interferences induced into the cabling shall be within the specified limits. The coupling attenuation is a measure of both emission and immunity of the twisted pair cabling. It is defined as the ratio of the power transmitted to the pair to the power coupled into its environment expressed in logarithmic way. Thus the unit of coupling attenuation is decibel, dB. The test method of coupling attenuation has been standardized and the principle is shown in figure 4.16.

Z

P 1

Z

Z

Z

G

Z

Z

Z

PP

P 2

Movableabsorbingclamp

Power meter

Teminator

Screen (if any)

Signalgenerator

Coupling attenuation Ac= 10 lg(P1/P2) dB

Figure 4.16. Coupling attenuation.

The coupling loss in unscreened (UTP) cabling is determined only by the balance. In screened cabling (FTP, S-FTP or STP) the coupling attenuation depends also on the screening effectiveness of the screen(s). This means that the coupling attenuation of screened cabling is usually greater than that of UTP cabling.

Testing of the coupling attenuation of an installed cabling is complicated and unpractical. Therefore the requirements of the standard are still under consideration. The sufficient coupling attenuation can, however, be ensured by the proper component choice and skilful installation. The coupling attenuation requirements of twisted pair cables and connecting hardware are well specified. Also testing of these components is less complicated and possible to carry out as type tests.

4.2.16 Alien crosstalk

When frequencies used for transmission are increased, there is a risk of crosstalk between cables. This is called alien crosstalk and the risk becomes evident at frequencies above 100 MHz. The risk is highest with Siamese category 6 UTP cables. The risk can be avoided with 6 dB additional marginal in PSNEXT. As shown in figure 4.17 the power sum crosstalk from the adjacent cable shall be 6 dB greater than the PSNEXT requirement of the single cable.

PSNEXT PSNEXTAlien

PSNEXTAlien ≥ PSNEXT + 6 dB

Figure 4.17. The risk of alien crosstalk can be avoided with 6 dB additional margin.

Alien crosstalk cannot be detected in normal acceptance testing. The best way to avoid alien crosstalk is to use cables, which fulfil the additional 6 dB margin requirement.

4.3 Channels and links of optical fibre cabling and their requirements

The standard EN 50173-1 specifies three classes for optical fibre cabling. These classes are:

• Class OF-300 supports applications over the channel length of minimum 300 m. • Class OF-500 supports applications over the channel length of minimum 500 m. • Class OF-2000 supports applications over the channel length of minimum 2000 m.

The class of optical fibre cabling includes no information of the fibre type. The classification is based only to the achievable channel length. The applications supported over this length, however, depend on the optical fibre category. The categories are: OM1, OM2 and OM3 for multimode fibres and OS1 for the singlemode fibre. The fibre categories are discussed in detail in clause 6.3 and supported applications in clause 9.2 of this guidebook.

The performance of the optical fibre cabling is described with the following characteristics:

• Attenuation • Propagation delay The standard EN 50173-1 specifies requirements of these characteristics for each class.

4.3.1 Attenuation

When the optical signal propagates along the optical fibre, the optical power is decreased. Optical power is lost also in fibre splices and in optical connections. The unit of optical fibre channel attenuation is decibel (dB). (For optical fibre cables the attenuation is expressed in dB/km). The attenuation is specified within certain wavelength windows, which represent the used wavelengths. These wavelength windows are the following:

Multimode fibre: 850 nm (790...910 nm) 1300 nm (1285...1330 nm)

Singlemode fibre: 1310 nm (1288...1339 nm) 1550 nm (1525...1575 nm)

The attenuation of the fibre is mainly caused by two factors: absorption and scattering. The absorption in the optical fibre is both intrinsic and extrinsic. The intrinsic absorption consists of infrared (IR) and ultraviolet (UV) absorption and the extrinsic absorption is mainly caused by impurities in the fibre. Among the most significant impurities to cause attenuation are OH-ions. In the scattering the small (microscopic) density perturbations in the glass material make the propagating light to be distributed in many directions including the reverse direction.

Attenuation of multimode fibres is greater than that of the singlemode fibre. The reason for this is that in the core of the multimode fibre there are more doping materials, which in fact are impurities. In multimode fibre the propagating optical power is distributed into many modes and each mode has a different attenuation. The total attenuation depends of the mode distribution within the core area of the multimode fibre. In the singlemode fibre only one mode is propagating and the theoretical limit for the attenuation is set by the Rayleigh scattering. This theoretical lower limit of attenuation is 0,16 dB/km at the wavelength of 1550 nm.

In addition to the fibre attenuation the total channel attenuation also depends on additional attenuation of optical fibre splices and connections in the channel. The requirements of channel attenuation in the standard are based on an allocation of 1,5 dB attenuation for connections. These requirements are shown in table 4.16.

Table 4.16. Attenuation requirements for optical fibre channels.

Maximum value of channel attenuation, dB Channel class Multimode Singlemode

850 nm 1300 nm 1310 nm 1550nmOF-300 2,55 1,95 1,80 1,80 OF-500 3,25 2,25 2,00 2,00 OF-2000 8,50 4,50 3,50 3,50

4.3.2 Propagation delay

The propagation delay may be important and critical in some applications and in complex networks consisting of multiple cascaded channels. Therefore it may be important to know it sometimes. The standard EN 50173-1 does, however, not specify the propagation delay. Naturally, the propagation delay of a channel depends on the channel length. When the propagation velocity of the light in the fibre (depends on refractive index) is known, it is possible to find out also the propagation delay. With the channel lengths of classes OF-300, OF-500 and OF-2000 the propagation delay will not cause any problems for the supported applications.

5 Reference implementations of cabling

The standard EN 50173-1 contains reference implementations for twisted pair and optical fibre cabling. These reference implementations can be used as an aid for planning and to ensure that the channels meet the specified requirements. The reference implementations have been designed so that the performance requirements of channels will be met, when: • Cables and connecting hardware meeting the requirements of the standard are used in accordance

with the reference implementations. • The rules of cabling lengths of the reference implementations are followed. • Installation is carried out in accordance with the specifications of the standard series EN 50174 and

with professional skill.

5.1 Reference implementations for twisted pair cabling

Reference implementations have been presented for both horizontal and backbone cabling.

5.1.1 Reference implementations for horizontal cabling

The basic principle is that:

• Category 5 cables and connecting hardware shall be used to create class D cabling • Category 6 cables and connecting hardware shall be used to create class E cabling • Category 7 cables and connecting hardware shall be used to create class F cabling

The standard describes four models of reference implementation for horizontal cabling. In this guidebook only two models are described. These models are those, where the equipment interface in the floor distributor is an interconnect. The models are shown in figure 5.1. For clarity the same letters of designation are used as in the standard EN 50173-1. This means models a and c.

EquipmentTerminalequipment

FD TO

Eqiupmentcord

Channel

Work areacord

EquipmentTerminalequipment

FD CP TO

Eqiupmentcord

Channel

Work areacord

Fixed horzontal cable

Fixed horzontal cable

CP cable

Model a

Model c

Figure 5.1. Cabling models a and c for horizontal cabling.

In the model a of figure 5.1 the fixed horizontal cabling is continuous from the patch panel of the floor distributor to the telecommunications outlet. In model c the consolidation point (CP) is included and the fixed horizontal cabling extends only to the consolidation point. From consolidation point the cabling runs as the CP cable to the telecommunications outlet. In the both models the channel also includes the equipment cord in the floor distributor and the work area cord in the work area.

The equations shown in table 5.1 can be used to determine the lengths of different cabling sections for models a and c, when the performance of the cables, cords and connecting hardware is known. The equations are based on the following assumptions:

• The cables used in equipment and work area cords are flexible cables, which have maximum 50 % greater attenuation than the fixed horizontal cable.

• The cables used in equipment and work area cords have the same attenuation per length unit. • The cable used in the CP cable may of the same type as the fixed horizontal cable or it may be a

flexible cable. The attenuation of CP cable may differ from that of both the fixed horizontal cable and the flexible cables.

Table 5.1. Length equations of models a and c for classes D, E and F.

Model Length equation for the channel Class D Class E Class F

a H = 109 – FX H = 107 – 3 – FX H = 107 – 2 – FX c H = 107 – FX – CY H = 106 – 3 – FX – CY H = 106 – 3 – FX – CY

H = maximum length of fixed horizontal cable, m F = combined length of equipment cord and work area cord, m C = length of CP cable, m X = ratio of flexible cable attenuation (dB/m) to fixed horizontal cable attenuation (dB/m) Y = ratio of CP cable attenuation (dB/m) to fixed horizontal cable attenuation (dB/m)

In addition to table 5.1 the following restrictions apply:

• The physical length of the channel shall not exceed 100 m. • The physical length of the fixed horizontal cable shall not exceed 90 m. • When a multi-user telecommunications outlet assembly is used, the length of the work area cord

should not exceed 20 m. • When a consolidation point is used, it should be located at least 15 m from the floor distributor.

Example of using table 5.1:

Basic data: Channel class E

Combined length of equipment cord and work area cord F = 10 m Attenuation of equipment cord and work area cord is 50 % greater than that of fixed horizontal cable, X = 1,5 Length of CP cable C = 4 m

Attenuation of CP cable is same as that of fixed horizontal cable, Y = 1 Question: What is maximum length of fixed horizontal cable (FD-CP)? Solution: Maximum length of fixed horizontal cable:

H = 106 – 3 – FX – CY = 106 – 3 – 15 – 4 = 84 m

5.1.2 Reference implementations for backbone cabling

For backbone cabling only one reference implementation model is described in the standard EN 50173-1. The channel of this model includes a patch cord (or jumper) and an equipment cord at both ends. The model can be used for building backbone and campus backbone cabling and it s shown in figure 5.2.

EquipmentTerminalequipment

BD or FD

Eqiupmentcord

Channel

Equipmentcord

Fixed horzontal cable

Patchcord

CD or BD

Figure 5.2. Backbone cabling model.

The equations shown in table 5.2 can be used to determine the lengths of different cabling sections, when the performance of the cables, cords and connecting hardware is known. The equations are based on the following assumptions:

• The cables used in equipment and patch cords are flexible cables, which have maximum 50 % greater attenuation than the fixed backbone cable.

• The cables used in equipment and patch cords have the same attenuation per length unit.

Table 5.2. Length equations of backbone cabling for classes C, D, E and F.

Category Length equation for the channel Class C Class D Class E Class F

5 B = 170 – FX B = 105 – FX 6 B = 185 – FX B = 111 – FX B = 105 – 3 – FX

7 B = 190 – FX B = 115 – FX B = 107 – 3 – FX B = 105 – 3 – FX B = maximum length of fixed backbone cable, m F = combined length of equipment cords and patch cords, m X = ratio of flexible cable attenuation (dB/m) to fixed backbone cable attenuation (dB/m)

Question: What is the maximum combined length of equipment cords and patch cords F? Solution: 90 = 105 – 3 – FX

F is solved: F = (105 – 3 – 90)/X = (105 – 3 – 90)/1,5 = 12/1,5 = 8 m

5.2 Reference implementations for optical fibre cabling

According to the standard the optical fibre cabling can be implemented with two alternative main strategies:

• Conventional hierarchical cabling • Centralized cabling

The conventional hierarchical cabling means that the cabling has separate subsystems of campus backbone, building backbone and horizontal cabling according to the basic principle of generic cabling. These cablings are terminated in distributors and the horizontal cabling is also terminated to telecommunication outlets. The application dependent optical information technology equipment (e.g. LAN switch) are located in distributors, where they are connected to the cabling. Optical fibre horizontal cabling may also include one consolidation point. The connector type used in optical fibre horizontal cabling is SC-D (SC-Duplex). In the centralized optical fibre cabling the building backbone and horizontal cabling are combined so that there are no active equipment between the building distributor and the telecommunications outlet. The optical fibre channel extends from the building distributor to the telecommunications outlet. The standard describes three models for implementation of centralized optical fibre cabling. These are the following:

• Patched cabling • Spliced cabling • Direct cabling

Figure 5.3 shows the three simplest models of all models described in the standard EN 50173-1. The standard also defines models, which include a consolidation point between the floor distributor and the telecommunications outlet and models, which include cross connect in the building distributor.

BD

SC T0

S SS SC T0

S S

FD

FD

C T0FD

S SS SS C C S

BD

BD

b) Spliced cabling

c) Direct cabling

a) Patched cabling

BD = Building distributorFD = Floor distributorTO = Telecommunications outletC = ConnectionS = Splice

Figure 5.3. Three models for centralized optical fibre cabling.

The achievable channel length in optical fibre cabling depends on the cabling class: 300 for OF-300, 500 m for OF-500 and 2000 m for OF-2000. The same rules apply to the conventional hierarchical cabling and to the centralized cabling. In conventional cabling, however, the maximum length of the horizontal channel is 100 m. If the total attenuation of splices and connections in the channel exceeds 1,5 dB, the achievable channel lengths are smaller than those specified to each class. The standard EN 50173-1 contains a table, which gives the equations for calculating the channel lengths in this case.

6 Requirements of cables

The requirements of to be cables used in campus backbone, building backbone and horizontal cabling are specified in the standard so that the channel and permanent link performance requirements will be met. Requirements have been specified for the following cables:

• Twisted pair cables • Flexible twisted pair cables used in cords • Optical fibre cables The requirements are mainly specified by using reference to separate cable standards and part of the requirements have also been written in the standard itself.

6.1 Twisted pair cables

The requirements of twisted pair cables in the standard EN 50173-1 are specified by using the reference to the standard series EN 50288. The standards of this series are shown in table 6.1.

Table 6.1. Twisted pair cable standards of series EN 50288.

Designation of standard Scope of standard Upper limit frequency, MHz

EN 50288-1 General requirements and test methods 100 – 600 EN 50288-2-1 Category 5 screened cable 100 EN 50288-2-2 Category 5 screened flexible cable 100 EN 50288-3-1 Category 5 unscreened cable 100 EN 50288-3-2 Category 5 unscreened flexible cable 100 EN 50288-4-1 Category 7 cable 600 EN 50288-4-2 Category 7 flexible cable 600 EN 50288-5-1 Category 6 screened cable 250 EN 50288-5-2 Category 6 screened flexible cable 250 EN 50288-6-1 Category 6 unscreened cable 250 EN 50288-6-2 Category 6 unscreened flexible cable 250

As can bee seen from table 6.1 the cables are divided to different categories according to the upper limit frequency. Cables for fixed installation (solid conductors) and flexible cables (stranded conductors) have their own standards. Flexible cables are used in equipment, work area and patch cords. CP cable may have solid or stranded conductors. Category 5 and 6 cables may be screened or unscreened. Category 7 cable is always pair screened. Cables usually are 4-pair cables and colour system of conductors is as shown in table 6.2. The basic constructions of 4-pair cables are shown in figure 6.1. These constructions ate unscreened, overall screened and pair screened cable. Two 4-pair cables may also be attached to each other in the manufacturing stage to form a Siamese cable.

Table 6.2. Colour system of 4-pair cable.

Pair a-conductor colour b-conductor colour

1 white-blue blue 2 white-orange orange 3 white-green green 4 white-brown brown

a) Unscreened (UTP) Overall screened (FTP, S-FTP) c) Pair screened (STP)

Figure 6.1. Basic constructions of twisted pair cables.

In an unscreened cable the electromagnetic interference characteristics are determined only by the balance and there is no metallic screen. This cable type is generally called UTP cable. Overall screened cable has an common overall metallic screen around the cable core. This screen is usually made of plastic reinforced aluminium foil. The foil is longitudinal and is overlapped to ensure the coverage. The metallic side of the foil is inwards and in contact with a tinned copper conductor, which is called a drain wire. This kind of cable is generally called FTP cable. This construction may reinforced with a tinned copper braid over the foil. The braid improves the mechanical strength and it also improves the screening effectiveness at low frequencies. This cable type is generally called S-FTP. In a pair screened cable each pair has been individually screened with metallic foil. The screens usually have a common drain wire. This cable type is generally called STP cable. In addition to pair screens the cable may also have a common overall screen, which usually is made of braid.

6.1.1 Constructional requirements

Constructional requirements have been specified to ensure the reliable operation of the cable during its use. Also the installation and connectivity aspects are very important. However, the cable standards do

not specify the constructions in detail. Only those characteristics are specified, which are important in order to ensure the reliable use as well as installation and connectivity. Some constructional requirements of category 6 cables are shown in table 6.3. The relevant cable standards are EN 50288-5-1 and EN 50288-6-1.

Table 6.3. Constructional requirements of category 6 cables.

Characteristics Requirement Category 6, screened Category 6, unscreened

Standard EN 50288-5-1 EN 50288-6-1 Conductor diameter 0,5 mm ≤ d ≤ 0,8 mm 0,5 mm ≤ d ≤ 0,8 mm Screening of pairs Optional. Metallic foil, metallic braid or

combination of these. No screening

Common screening Metallic foil, metallic braid or combination of these.

No screening

Crush strength 1000 N/1 minute/100mm Near end crosstalk, return loss and characteristic impedance shall remain within the specified limits.

Minimum bending radius

Single bend 4xdia/4 cycles Near end crosstalk, return loss and characteristic impedance shall remain within the specified limits.

Pulling force Load shall be 25 N per pair (i.e.100N 4 Pair). Near end crosstalk, return loss and characteristic impedance shall remain within the specified limits.

Temperature range Installation 0...+ 50 °C Operation -40...+ 60 °C

Fire safety has become more and more important aspect in cabling. Cabling installation shall not degrade the fire safety of the building. Both cable choice and way of installation affect the fire safety. The fire safety aspects related to cable constructions and materials are:

• Flame spread in cable, IEC 60332-1 and IEC 60332-3 • Acidity (and corrosivity) of the smoke gases produced by the burning cable, IEC 60754-1 and IEC

60754-2 • Smoke production of the burning cable, IEC 61034-1 and IEC 61034-2

Fire safe cables are flame retardant or fire retardant (FR), halogen free (HF) and low smoke (LS) cables. Table 6.4 summarises the most important aspects in the fire performance of cables according to IEC standards.

Table 6.4. Fire performance characteristics of cables.

Characteristics Test standard (IEC) Flame retardant (FR) IEC 60332-1 Fire retardant (FR) IEC 60332-3 Fire resistant IEC 60331 Halogen free (HF), zero halogen (0H)

IEC 60754-1 and IEC 60754-2 (Halogen content <5 mg/g)

Low smoke (LS) IEC 61034-1 and IEC 61034-2 60 % transmission of light

According to the new classification the cables are divided into six classes AC, BC, CC, DC, EC and FC

depending on their fire performance. Same kind of classification will be applied also to other construction products. A cable meeting the class AC requirements is practically fire resistant and a cable of the class FC is a cable, the fire performance of which is unknown or which does not meet the requirements of the class EC . For classes BC, CC and DC also additional classification is used. This additional classification is based on smoke production, production of flaming droplets/particles and acidity of smoke gases. Additional attributes s1, s2 and s3 (smoke production), d0, d1 and d2 (droplets/particles) and a1, a2 and a3 (acidity) are used in this additional classification.

Test methods of the fire performance in accordance with the new classification system are specified in European standard series EN 50266, EN 50267 and EN 50268.

6.1.2 Electrical requirements

In the cable standards the electrical characteristics of the twisted pair cables have been specified so that the cabling will meet the requirements of the standard EN 50173-1, if it has been planned and installed in a proper way. The transmission requirements have been specified up to the upper limit frequency of each category. In addition, some other electrical requirements have been specified. These requirements are related to reliability. The following electrical characteristics are specified in the standards of twisted pair cables:

DC and low frequency characteristics

• DC-loop resistance

• Resistance unbalance (DC) • Capacitance unbalance to earth • Dielectric strength • Insulation resistance

High frequency characteristics

• Characteristic impedance • Return loss, RL • Attenuation • Pair to pair near end crosstalk loss, NEXT • Power sum near end crosstalk loss, PSNEXT • Pair to pair equal level far end crosstalk loss, NEXT • Power sum equal level far end crosstalk loss, PSNEXT • Propagation delay • Propagation delay skew • Unbalance attenuation • Coupling attenuation • Transfer impedance (screened cables) • Screening attenuation (screened cables)

The characteristics listed above are mostly the same as those specified for channels and links. The meaning and importance of these characteristics are discussed in clause 4.2 and in its sub-clauses. These characteristics for the cables have been specified for 100 m cable length an at temperature of 20 °C. Dielectric strength and insulation resistance, which are included in DC characteristics, are related to the reliability of a twisted pair cable. The dielectric strength is specified between conductors and in screened cables also between conductors and the screen. The unit is kV. Insulation resistance is expressed in MΩxkm and is tested with voltage of 100 – 500 V.

The list of high frequency characteristics also includes two screening characteristics for screened cables. These express the screening effectiveness of the screen. Transfer impedance is used in the frequency range of 1 – 30 MHz and screening attenuation is used from 30 MHz to the upper limit frequency of the category.

In the cable standard IEC 61156-5 twisted pair cables have been divided into three types based on their coupling attenuation. This classification is some kind of additional classification for category 5, 6 and 7 cables and it is shown in table 6.5.

Table 6.5. Classification of twisted pair cables based on the coupling attenuation (IEC 61156-5)

Type Frecuency range MHz Coupling attenuation dB

I 30-100 ≥ 85,0 100 – upper limit frequency ≥ 85,0 − 20 · lg (f/100)

II 30-100 ≥ 55,0 100 – upper limit frequency ≥ 55,0 − 20 · lg (f/100)

III 30-100 ≥ 40,0 100 – upper limit frequency ≥ 40,0 − 20 · lg (f/100)

The upper limit frequency mentioned in the table is 100 MHz for category 5, 250 MHz for category 6 and 600 MHz for category 7.

UTP cables usually represent type III, FTP and S-FTP cables type II and STP cables type I.

6.2 Cords used in twisted pair cabling

Cord is a common name for the following cables: • Work area cord • Equipment cord • CP cable • Patch cord

Cords are usually factory made connectorized cables. According to the standard EN 50173-1 the cables used in cords shall meet the same requirements as the cables used for fixed installation and are of the same category. Two exceptions, however, are allowed: attenuation and DC loop resistance may be maximum 50 % higher. The standard specifies the electrical requirements of category 5, 6 and 7 cords in detail. The requirements of cables used in cords are specified in cable standards, which are shown in table 6.1 of this guidebook.

6.3 Optical fibre cables

6.3.1 Constructional requirements The constructional, mechanical and environmental requirements of optical fibre cables are specified with reference to the standard series EN 60794, which includes the standards shown in table 6.6.

Table 6.6. Standards of optical fibre cables included in series EN 60794.

Designation of standard Scope of standard

EN 60794-1-1 General requirements and test principles EN 60794-1-2 Test methods EN 60794-2 Indoor cables EN 60794-3 Outdoor cables

The constructions of optical fibre cables are usually divided into three types. These types are:

• Stranded construction • Slotted core construction • Single tube construction

These constructions are illustrated in figure 6.2.

Stranded construction Slotted core construction Single tube construction

Figure 6.2. Basic constructions of optical fibre cables.

The colour system for fibre identification according to the Finnish standard 5648 is shown in table 6.7. This colour system is used only in cables manufactured in Finland.

Table 6.7. Finnish colour system for fibre identification.

Fibre Colour of fibre coating First fibre Blue 2., 6., 10., etc. fibre White 3., 7., 11., etc. fibre Yellow 4., 8., 12., etc. fibre Green 5., 9., 13., etc. fibre Grey last fibre Red

The most generally used colour system in the world is the colour system specified in US standard ANSI/TIA/EIA 598. This colour system is shown in table 6.8.

Table 6.8. Colour system of optical fibres according to ANSI/TIA/EIA 598.

Fibre number Colour Fibre number Colour 1 Blue 13 Blue with Black tracer 2 Orange 14 Orange with Black tracer 3 Green 15 Green with Black tracer 4 Brown 16 Brown with Black tracer 5 Slate (=Grey) 17 Slate with Black tracer 6 White 18 White with Black tracer 7 Red 19 Red with Black tracer 8 Black 20 Black with Yellow tracer 9 Yellow 21 Yellow with Black tracer 10 Violet 22 Violet with Black tracer 11 Rose (=Pink) 23 Rose with Black tracer 12 Aqua (=Tourqoise) 24 Aqua with Black tracer

The most important installation characteristics (table 6.9) of optical fibre cables are:

• Maximum pulling force • Crush strength • Minimum bending radius • Minimum installation temperature

Table 6.9. Typical installation characteristics of optical fibre cables.

Characteristics Indoor cables Outdoor cables Maximum pulling force 1-fibre cable: 100 N

2-fibre cable: 200 N Other cables: 500...750 N

Direct burial and duct cables: 1200...3000 N Armoured direct burial cables: 5000...8000 N Aerial cable: 6000...10000 N

Crush strength -plate 100 mm -mandrel 25 mm

2000 N 1000 N

4000...8000 N 1000...2000 N

Minimum bending radius -During pulling -Final bending

1- and 2-fibre cables: 40 mm Other cables: 20...30 × D 1- and 2-fibre cables: 30 mm Other cables: 15 × D

20...30 × D 15 × D

Minimum installation temperature

-5 …0° C -15 °C

6.3.2 Requirements of optical fibres

In generic cabling both multimode and singlemode fibres are used. Multimode fibres to be used are of type 50/125 μm and 62,5/125 μm. In these designations the first number means the core diameter and the second number means cladding diameter. The core and cladding dimensions shall meet the requirements of type A1a (50/125 μm) and A1b (62,5/125 μm) of the standard EN 60793-2-10Multimode fibres are divided into three categories based on the bandwidth. The categories are: OM1, OM2 and OM3. The standard EN 50173-1 specifies maximum attenuation and minimum bandwidth for the multimode fibres. The requirements for different categories are shown in table 6.10.

Table 6.10. Optical requirements of multimode fibres.

Category, fibre type Maximum attenuation dB/km

Minimum bandwidth MHz x km

LED source Laser source850 nm 1300 nm 850 nm 1300 nm 850 nm

OM1, 50/125 μm and 62,5/125 μm 3,5 1,5 200 500 Not specified OM2, 50/125 μm and 62,5/125 μm 3,5 1,5 500 500 Not specified OM3, 50/125 μm 3,5 1,5 1500 500 2000

The widely used multimode fibre 62,5/125 μm is typically a category OM1 fibre. The other traditional multimode fibre type is 50/125 μm fibre, which was already early specified in ITU-T G.651. This fibre is typically a category OM2 fibre. Category OM3 fibre represents a new generation of multimode fibres.

The category of the singlemode fibre is OS1. The singlemode fibre shall meet the requirements of the type B1 of the standard EN 60793-2-50. Maximum attenuation at wavelengths of 1310 nm and 1550 nm is 1,0 dB/km and the cut-off wavelength of the cabled fibre shall be below 1260 nm.

Figure 6.3 illustrates the light propagation in a multimode fibre and a singlemode fibre.

a) Multimode fibre

Transmitted pulses Pulses become wider and are attenuated,when Received pulsesthey propagate along the multimode fibre.

T = Interval between two succesive pulses If pulses become too wide they cannot be distinguished

b) Singlemode fibre

Transmitted pulses In the singlemode fibre pulses become not so Received wide and ere also attenuated less than in the pulsesmultimode fibre

Figure 6.3. Light propagation in a) multimode fibre and b) singlemode fibre.

In a multimode fibre the light propagates along numerous paths i.e. in several modes. The light rays propagated along different paths uses different times to propagate from end to end. This cause spread of the light pulses propagating in the fibre. This phenomenon restricts the bandwidth of the signal to be transmitted in the fibre. In figure 6.3a the time between two successive light pulses shall not be too short, in order to avoid the errors caused by the pulse spread. This means that the repetition rate (f = 1/T) of the light pulses shall not be too high. Bandwidth is a measure of this highest allowed repetition rate. The bandwidth of a multimode fibre is expressed in MHzxkm. This unit takes into account the fibre length. In addition to the fibre itself, also the type of light source affects the fibre bandwidth. As can be seen in figure 6.4, the LED source fills the whole core area with optical power. The core is overfilled and a great number of modes are present. This condition is called overfilled launch (OFL). In the case of laser or VCSEL source the optical power is concentrated only in a small area around the central axis of

T T

T

the number of modes is much smaller than in the case of LED source. This condition is called restricted mode launch (RML). For these reasons the LED bandwidth is smaller than the laser bandwidth. Both source types (LED and laser/VCSEL) are used in LAN applications and therefore also the bandwidth has been partly specified for both source types. LED source is used e.g. in 100 Mbit/s Ethernet. Laser and VCSEL sources are used e.g. in Gigabit Ethernet.

Figure 6.4. LED source and laser source with multimode fibre.

The propagating light pulses also lose optical power in the fibre. This is called attenuation. The unit of fibre attenuation is dB/km. Attenuation of a singlemode fibre is smaller than that of a multimode fibre.

7 Requirements of connecting hardware

Connecting hardware is a device or a combination of devices used to connect cables or cable elements, such as twisted pairs or optical fibres. In practice connecting hardware are RJ45 plugs and jacks used in twisted pair cabling and SC connectors or other optical fibre connectors and adapters used in optical fibre cabling. In the generic cabling connecting hardware are used for the following purposes:

• Termination of cables, connecting of equipment and cross connecting in distributors. • Optional consolidation point in horizontal cabling. • Telecommunications outlet.

Tx LEDTx LED

Tx VCSEL orlaser

TxTx VCSEL orlaser

Connecting hardware shall be compatible with the cables to be used. This means both mechanical and electrical or optical compatibility. A good quality connecting hardware also has the following characteristics:

• Marking, which to identify the type and performance of cabling. • Construction, which enable easy handling and management of cabling. • Possibility to test and monitor cabling and active equipment. • Structural protection against physical damage and ingress of contaminants that may affect

performance. • A size and shape, which enable a space efficient termination density in distributors and other

termination points. • Electromagnetic screening, continuity of screening and termination of screens in the case of screening

cabling.

The standard EN 50173-1 specifies the most important mechanical and electrical or optical requirements for connecting hardware of twisted pair and optical fibre cabling. The requirements are partly specified by using reference to separate connector standards and partly as requirements written in the standard itself.

7.1 Requirements of connecting hardware of twisted pair cabling

The standard EN 50173-1 specifies the mechanical and electrical requirements for connecting hardware of twisted pair cabling. A part of the separate connector standards is still at draft stage, but the standard already includes references to them. The connector standards are listed in table 7.1.

Table 7.1. Connector standards of twisted pair cabling.

Standard Scope of standard EN 60603-7-2 Category 5, unscreened EN 60603-7-3 Category 5, screened EN 60603-7-4 Category 6, unscreened EN 60603-7-5 Category 6, screened EN 60603-7-7 Category 7 IEC/PAS 61076-3-104 Category 7, alternative, non-RJ45 compliant

The standard EN 50173-1 points out, that assurance should be sought from suppliers that the combinations of components within connecting hardware are able to meet the electrical and mechanical requirements of the standard.

The essential requirements of connecting hardware are the following:

• Mating dimensions and tolerances to ensure the mechanical compatibility of plugs and jacks. • Requirements of cable termination. • Requirements of mechanical endurance. • Electrical requirements of mated connectors.

Examples of RJ45 jacks used in twisted pair cabling are shown in figure 7.1

Figure 7.1. RJ45 jacks.

7.1.1 Mechanical requirements

The most important mechanical requirements of connecting hardware of twisted pair cabling are shown in table 7.2.

Table 7.2. Mechanical requirements of connecting hardware (RJ45) of twisted pair cabling.

Characteristics Requirement Cable termination compatibility Nominal conductor diameter 0,5 mm – 0,65 mm Conductor type Solid or stranded Nominal diameter of insulated conductor - category 5 and category 6 - category 7

0,7 mm – 1,4 mm 0,7 mm – 1,6 mm

Number of conductors 8 Cable outer diameter - jack (female) - plug (male)

≤ 20 mm ≤ 9 mm

Termination of screen According to EN 50174-2 Mechanical durability Number of terminations - non-reusable IDC - reusable IDC

1 ≥ 20

Number of connections - telecommunications outlet - other interface

≥ 750 ≥ 200

7.1.2 Electrical requirements

In the standard EN 50173-1 and in the standards of the series EN 60603-7 the electrical characteristics of the connecting hardware have been specified so that the cabling will meet the requirements of the standard EN 50173-1, if it has been planned and installed in a proper way. The transmission requirements have been specified up to the upper limit frequency of each category. In addition, some other electrical requirements have been specified. These requirements are related to reliability. Plugs and jacks that are intermateable shall be backward compatible with those of different performance categories. Backward compatibility means that mated connections with plugs and jacks from different categories shall meet all requirements for the lower category component. It shall, however, be noticed that the performance of the connection created by a plug and a jack of different categories is determined by the lower category. This principle is illustrated in table 7.3.

Table 7.3. Backwards compatibility principle.

Plug Jack

Category 5 Category 6 Category 7 Category 5 Category 5 Category 5 Category 5 Category 6 Category 5 Category 6 Category 6 Category 7 Category 5 Category 6 Category 7

The following electrical characteristics are specified for connecting hardware of twisted pair cabling:

• Return loss, RL • Attenuation (insertion loss) • Pair to pair near end crosstalk loss, NEXT • Power sum near end crosstalk loss, PSNEXT • Pair to pair far end crosstalk loss, NEXT • Power sum far end crosstalk loss, PSNEXT • Propagation delay • Propagation delay skew • Input to output resistance • Input to output resistance unbalance • Current carrying capacity • Transfer impedance (screened connectors) • Unbalance attenuation

7.1.3 Pin and pair grouping assignments

Jack connectors (RJ45 female) are used in telecommunications outlets and in patch panels of distributors and plug connectors (RJ45 male) are used at ends of cords. The standard EN 50173-1 specifies the pin and pair grouping assignments for RJ45 jacks. This standard, however, defines only the basic principle of the pin and pair grouping assignments to be used. The relation between pins and pairs is in detail specified in another standard EN 50174-1. Two alternatives for 4-pair cables have been specified in this standard. These alternatives use designations A and B. The alternatives A and B are equivalent with the alternatives T568A and T568B of the US standard. Pin and pair grouping assignments A and B specified in the standard EN 50174-1 are shown in table 7.4 and figure 7.2. In table 7.4 the designations A and B of the standard EN 50174-1 are used and in figure 7.2 the designations T568A and T568B of the US standard are used. Figure 7.2 is a front view of jack connector.

Table 7.4. Pin and pair grouping assignments for RJ45 jack, alternatives A and B.

Pairs and conductors Pins of RJ45 jack Alternative A Alternative B

Pair 1, a-conductor (blue-white) 5 5 Pair 1, b-conductor (blue) 4 4 Pair 2, a-conductor (orange-white) 3 1 Pair 2, b-conductor (orange) 6 2 Pair 3, a-conductor (green-white) 1 3 Pair 3, b-conductor (green) 2 6 Pair 4, a-conductor (brown-white) 7 7 Pair 4, b-conductor (brown) 8 8

T568A

PAIR 1

PAIR 2

PAIR 3 PAIR 4

1 2 3 4 5 6 7 8

T568B

PAIR 1

PAIR 3

PAIR 2 PAIR 4

1 2 3 4 5 6 7 8

T568A

PAIR 1

PAIR 2

PAIR 3 PAIR 4

1 2 3 4 5 6 7 8

PAIR 1

PAIR 2

PAIR 3 PAIR 4

1 2 3 4 5 6 7 8

T568B

PAIR 1

PAIR 3

PAIR 2 PAIR 4

1 2 3 4 5 6 7 8

T568B

PAIR 1

PAIR 3

PAIR 2 PAIR 4

1 2 3 4 5 6 7 8

Figure 7.2. Pin and pair grouping assignments for RJ45 jack, alternatives T568A and T568B A. Front view of RJ45 jack.

The pin and pair grouping assignments of table 7.4 and figure 7.2 apply to category 5 and 6 cables and connectors. There are two standards for category 7 connecting hardware. The RJ45 compatible category 7 connecting hardware is specified in the standard EN 60603-7-7. The other category 7 connecting hardware type is specified in the standard IEC/PAS 61076-3-104 and it is not compatible with RJ45

type. Both types of category 7 connecting hardware are to be used with pair screened cables. Therefore these connecting hardware shall provide means to terminate the pair screens. The pin and pair grouping assignment of category 7 jack according to EN 60603-7-7 is shown in figure 7.3.

PAIR 3

PAIR 2 PAIR 4

1 2 3 4 5 6 7 8

PAIR 1

3’ 6’ 4’ 5’

PAIR 3

PAIR 2 PAIR 4

1 2 3 4 5 6 7 8

PAIR 1

3’ 6’ 4’ 5’

Figure 7.3. Pin and pair grouping assignment of category 7 jack according to EN 60603-7-7. Front view of category 7 jack

The construction of category 7 jack according to EN 60603-7-7 is such that it is mechanically compatible with category 5 and 6 plugs. In the upper part of the connector mating interface there are eight pins as in the normal RJ45 jack. In addition, there are two pairs of pins (3’-6’ and 4’-5’) in the lower part of the interface. The jack also includes a switch, which is used to recognize the type of the plug mated to the jack and to switch the relevant pins based on the type (category) of the plug. When the plug according to standard EN 60603-7-7 is mated to the jack, the pin pairs 1-2, 3’-6’, 4’-5’ and 7-8 are switched to be operative.

7.2 Requirements of connecting hardware of optical fibre cabling

The optical fibre connector type used in a telecommunications outlet according to the standard EN 50173-1 is type SC-D, i.e. SC duplex connector. The characteristics and requirements of this connector type are specified in the standard IEC 60874-19-1. In addition, part of the requirements has been written directly in the standard EN 50173-1. For identification of the fibre type the following colours of the connectors shall be used:

• Multimode fibre: beige • Singlemode fibre, physical contact (PC): blue • Singlemode fibre, angled physical contact (APC): green

These markings are in addition to, and do not replace, other markings specified in EN 50174_1 or those required by local codes or regulations. IN telecommunication outlets and in distributors also single SC connectors may be used on the cabling side as shown in figure 7.5.

Figure 7.5. Use of SC connectors (Stran Technologies).

In other points than in telecommunications outlets also other connecter types than SC connectors may be used. Such points are distributors and consolidation points. Also these connectors shall meet the mechanical and optical requirements specified in the standard. Examples of these alternative connector types are listed below:

• IEC 61754-18: MT-RJ; 2 fibres/ferrule • IEC 61754-19: SG; 2 fibre without a ferrule (this connector is commercially known better as type VF-

45) • IEC/PAS 61754-20: LC; 1 fibre/ferrule or 2 fibres/2 ferrules

All the three connectors listed above represent small size and higher mount density. They are also commonly called SFF connectors (Small Form Factor).

Ruggedized ST LC Connector FC codnnector

Figure 7.6. Examples of optical fibre connectors.

The polarity of fibres is ensured by the mechanical structure of the duplex connector. The structure is such that the wrong polarity is prevented. With single connectors the polarity is ensured by using relevant marking.

The most important requirements of optical fibre connectors specified in EN 50173-1are shown in table 7.5.

Table 7.5. Requirements of optical fibre connectors

Characteristics Requirements Optical characteristics Insertion loss, maximum 0,5 dB, 95 % of matings

0,75 dB, 100 % matings Attenuation of fibre splice, maximum 0,3 dB Return loss, minimum -Multimode -Singlemode

20 dB 35 dB

Mechanical characteristics Mechanical endurance ≥ 500 mating cycles Strength of coupling mechanism 40 N, 1 min Cable pulling 50 N, 1 min

8 Testing of installed cabling

The test methods of installed cabling are specified in the standard EN 50346 and treatment of test results are specified also in the standard EN 50173-1. The standard EN 50173-1 refers to these two standards. The standard EN 50346 does not define which tests should be applied or the quantity or percentage of installed cabling to be tested. The test parameters to be measured and the sampling levels to be applied for a particular installation should be defined in the installation specification and quality plans for that installation prepared in accordance with EN 50174-1. According to the standard EN 50174-1 the quality plan the following shall be specified before testing:

• Treatment of fail results • Treatment of marginal results

8.1 Purpose of testing

As mentioned in clause 2.2 the standard EN 50173-1 does not require testing, if the requirements of the standards have been followed in planning and implementation of the cabling. However, the installed cabling shall be always tested after installation. This is the only way in practice to verify that the cabling meets the specified requirements. Test results shall be documented and saved with care so that they are available to serve for use, maintenance and troubleshooting. According to the standard EN 50346 testing of installed cabling may be used for:

• Performance acceptance of installed cabling • Ensuring that the cabling supports a certain application • Troubleshooting

The test methods specified in EN 50346 are not applicable to testing of connecting hardware and patch cords. Performance acceptance of installed cabling Acceptance testing is used for performance testing and acceptance of installed cabling after installation. Testing is used to verify that the cabling meets the performance requirements specified in EN 50173-1. The test configuration for acceptance test of twisted pair cabling is the permanent link defined in EN 50173-1. Ensuring that the cabling supports a certain application Applications supported by the generic cabling ate listed in table 9.1 of this guidebook. When the existing cabling is intended to be used for a new application, it can be tested. Such situation appears for example, when a horizontal cabling of the old class D (1995) is wanted to be used for the Gigabit Ethernet (1000Base-T). To ensure that the existing cabling supports this application, it may be tested as permanent link according to the new class D specified in EN 50173-1 (2002). If the cabling passes the test, it will support the Gigabit Ethernet.

Troubleshooting The cabling can be tested also in the case of an evident fault in the cabling. Troubleshooting of twisted pair cabling can be carried out by channel testing or link testing and using the relevant

Teletekno Oy 27.7.2003 67 performance specifications. In the case of optical fibre cabling optical time domain reflectometer (OTDR) is also often used.

Cabling under test The cabling should be tested in conditions, in which the temperature and levels of electromagnetic interference (EMI) are the same as during operation. Temperature affects attenuation, attenuation related parameters (e.g. ACR) and d.c. loop resistance. The test parameters in test equipment are based on the temperature of 20 °C. Measurements shall either be made in conditions, which represent the intended operational environment, or have correction factors applied to the measured results in accordance with manufacturers specifications in order to reflect the intended operating environment, or be clearly documented as being undertaken in unrepresentative conditions.

8.2 Testing of twisted pair cabling

8.2.1 Test equipment

This clause describes the characteristics of field testers for twisted pair cabling and gives information about testers on the market.

8.2.1.1 Accuracy classification of testers

Field testers are classified into different levels according to the accuracy of the tester. The classification is specified in the standard EN 61935-1. The level to be used for testing class E is Level III, which is specified up to 250 MHz. The Level III accuracy of length, propagation delay and delay skew is shown in table 8.1.

Table 8.1. Level III accuracy of length, propagation delay and delay skew.

Parameter Length Propagation delay Delay skew Range 0 – 305 m 0 – 1 μs @ 10 MHz 0 – 100 ns @ 10 MHz Accuracy 0,1 m 1 ns 1 ns Tolerance ± 1 m ± 4 % ± 5 ns ± 4 % ± 10 ns

The accuracy of other parameters depends much on the frequency. For example the tolerance of return loss for permanent link testing is typically from 1,5 dB to more than 2,0 dB with commercial testers. Calibration of test set with proper interfaces adaptors improves the tolerance significantly. Therefore calibration is strongly recommended.

8.2.1.2 Field testers on the market

There are many kinds of field testers on the market and their characteristics differ from each other. The most common field testers used for testing of class D and E cabling are listed in table 8.2. These all are Level III testers. Examples of field testers are shown in figure 8.1.

Table 8.2. Most common field testers.

Manufacturer Model Accuracy level Fluke Networks DSP-4X00 Level III Fluke Networks OmniScanner 2 Level III Agilent WireScope 350 Level III

Figure 8.1. Examples of field testers.

8.2.1.3 Cabling interface adaptor

Different cabling interface adaptors are available for field testers. The two main types are:

• Permanent link interface adaptor • Channel interface adaptor

Permanent link interface adaptor

A permanent link interface adaptor is used for testing the permanent link or CP link. The characteristics of interface adaptors vary with manufacturers, but the basic characteristics are the same. An interface adapter is provided with a fixed 1 m long test cord. A module with RJ 45 plug can be attached to the free end of the test cord. The proper module to be used shall be ensured before testing from the manufacturer of the cabling system to be tested. As described in sub-clause 8.2.2 the module is included in the test configuration, but the test cord is not included to it. Different types of modules are on the market included system specific and universal modules.

Examples of a permanent link interface adaptors are shown in figure 8.2.

Figure 8.2. Permanent link interface adaptors.

The maximum operational lifetime of the interface adaptor specified by the manufacturer shall be taken into account. The typical lifetime is 2500 connector mating cycles. However, also other factors, such as handling, affect the lifetime.

Channel interface adaptor A channel interface adaptor is used when for some reasons it is needed to test the channel performance (from equipment to equipment). This interface adaptor is provided with RJ 45 jack. Examples of a channel interface adaptor are shown in figure 8.3.

Figure 8.3. Channel interface adaptors.

8.2.1.4 Calibration and maintenance

Test equipment need maintenance and updating from time to time. Manufacturers of test equipment release updates of test software at least always, when new interface adaptor types are coming into market and when changes in standards are taking place. New software versions can be downloaded from manufacturers´ web sites and they can be installed to testers by using the PC software supplied with the tester.

Calibration

Test equipment should be calibrated at intervals recommended by the manufacturer, typically once in a year at minimum. Calibration certificate shall be used to verify the calibration and a copy of this certificate should be delivered to the customer together with the test results. If required the calibration report shall also be presented to the customer. The local and remote equipment shall be calibrated with each other at least once in a month. It is even recommended to calibrate the equipment each time before the new testing sequence. This is to ensure the correct operation of the test equipment with each other and to avoid fail results due to wrong operation of the equipment.

8.2.2 Test interfaces and test configurations Channel and links are described in clause 4.2 of this guidebook. This sub-clause explains the test interfaces of channels and links. According to the standard EN 50173-1 the permanent link testing shall be used for the acceptance testing of installed cabling. If the cabling includes a consolidation point (CP), CP link testing is used for acceptance of CP link. Channel testing is used to ensure the performance of the whole transmission path from equipment to equipment.

8.2.2.1 Permanent link testing

Permanent link testing is used for testing of the installed cabling. It includes a horizontal cable, a telecommunications outlet, connecting hardware of patch panel in the floor distributor and an optional consolidation point (CP). Also the test connector modules of interface adaptors are included to the permanent link. A permanent link may include maximum three connections and the maximum length is 90 m. From the test specification menu of the field tester Permanent Link (PL) shall be selected. Permanent link testing includes three optional configurations: maximum configuration, three connections and two connections. The two-connection option can be used also for CP link testing. The attenuation margin in this case is expressed related to channel requirements. Figure 8.4 illustrates the test configuration.

FD CP TO

Permanent link Permanent link

Figure 8.4. Permanent link test configuration.

8.2.2.2 CP link testing

CP link testing shall be performed, if the horizontal cabling includes a consolidation point (CP) and the contractor is responsible only for the CP link installation and testing. A typical consolidation point is a so-called ceiling outlet in the horizontal cabling in an open office environment, where the horizontal cables are installed on cable trays. CP link testing is performed by using permanent link interface adaptors and Permanent Link (PL) specification with two-connection option. The CP link includes two connections and maximum 90 m length of cable. The limiting values are different from those of Permanent Link with maximum configuration. If the CP link passes the test, the permanent link performance, however, cannot be ensured, because e.g. the NEXT and RL limits are the same for both configurations. Figure 8.5 illustrates the CP link test configuration.

FD CP

CP link CP link

Figure 8.5. CP link test configuration

8.2.2.3 Channel testing

Channel testing is used to ensure the performance from equipment to equipment. The main application of channel testing is troubleshooting. Channel testing is not used for acceptance of installed cabling, because the channel configuration includes application specific and non-permanent components (work area cord and equipment cord). The channel includes the same components as the permanent link and also a work area cord, an equipment cord and an optional cross connect in the floor distributor. The plug connectors at the equipment ends of the cords are not included in the channel. A channel may include maximum four connections and the maximum length is 100 m (see reference implementations in 5.1.1). Figure 8.6 illustrates the channel test configuration with three connections.

FD CP TO

Channel Channel

Figure 8.6. Channel test configuration with three connections.

8.2.3 Testing of cabling, parameters to be measured and reasons for erroneous test results Testing of cabling

Testing is performed by using a field tester, which automatically measures all the parameters required by the standard. Before testing the following shall be ensured:

• Calibration of the tester • Condition of interface adaptors • Charge condition of battery • Appropriate performance specification selected for testing, e.g. EN 50173-1 Permanent Link Class E • Appropriate cable type selection or correct NVP

Parameters to be measured

The electrical parameters to be measured are described in detail in clause 4.2 of this guidebook. This sub-clause describes testing of other parameters in addition to those and gives information about the most common reasons for fail results of certain parameters.

Wire map

The first test performed by the field tester is the wire map test. The tester transmits a test pulse to the cabling and based on reflected and transmitted pulses the tester interprets, whether or not the conductors have been connected in a proper way. Splitted pairs are detected by an AC signal transmitted to the cabling. The tester shows graphically the test result of the wire map test and any error can be easily found. The most common errors in the wire map are the following:

• Open o The conductor is not in contact with connector pin. Termination may have been failed or

the conductor may be broken. • Crossed pair

o The twisted pair has been terminated in a crossed way at the other end connector. • Splitted pairs

o The conductor or the twisted pair has been terminated at the both connectors in the same way, but to wrong pins.

• Short circuit o Conductors are in direct contact (short circuit) with each other.

Figure 8.7 shows examples of erroneous wire maps: a) crossed pair, b) open, c) short circuit and d) splitted pairs.

12364578S

12364578S

Continuetest

FAIL

Continuetest

Continuetest

Split pairs detected1,2-7,8

Pin 8 Open 1.0 m

Pair 1,2 Shorted: 24.3 m

12364578S

12364578S

12364578S

12364578S

12364578S

12364578S

Figure 8.7. Examples of erroneous wire maps as shown in tester’s display.

Length

Length is not a pass/fail criterion in acceptance testing. If the specified maximum length of the cabling is exceeded, the tester gives a warning, which is informative. The length of each pair is different due to different lay lengths of the pair twist. According to the standard EN 61935-1 the nominal velocity of propagation (NVP) shall be calibrated for the pair with the longest lay length (shortest pair). If the correct NVP has been set to the tester, the test result will be shown as the cable sheath length (within the accuracy of the tester). Length is not measured directly, but it is calculated based on the measured (round trip) propagation delay and NVP for each pair. The calculation is made by the tester software. The formula used for calculation is the following:

Length = (propagation delay x NVP x speed of light)/2

It is very important that the correct NVP has been set to the tester. Typical NVP is 0,69 for an UTP cable and 0,74 for FTP cable. Each cable type, however, has its individual NVP and therefore NVP should be checked and ensured from the cable data sheet before testing. The real NVP may also differ from its nominal value in some degree and therefore the measuring tolerance is remarkable. The accuracy aspects of the tester itself are explained in sub-clause 8.2.1.1 of this guidebook. The maximum length in permanent link testing is 90 m and in channel testing it is 100 m.

Near end crosstalk loss (NEXT)

Fail in NEXT test is one of the most common reasons for the failed cabling testing. Usually the reason for NEXT fail is one of the following:

• Untwisted length of the pair is too long • Cable has been damaged during installation • Defective connector • Defective cable

The reason for fail and the location of fault can be detected by using the time domain crosstalk (TDX) function, which is available in most testers. This function and the procedure are described in sub-clause 8.2.4.2 of this guidebook. Testing of NEXT with short cabling lengths causes often problems. Therefore the NEXT requirements specified in EN 50173-1 have been eased for short lengths, typically shorter than 15 m. In fact the same rule is applied also to longer lengths at low frequencies. The principle of the rule is that values of

NEXT at frequencies for which the measured attenuation is below 4,0 dB are for information only. The same easement rule is applied also to PSNEXT. Return loss (RL) Fail in return loss (RL) test is also a common reason for the failed cabling testing. Reflections in the cabling are caused by the impedance inhomogenities along the cabling. Usually the reason for RL fail is one of the following:

• Untwisted length of the pair is too long • Cable has been damaged during installation • Too sharp cable bending or too much pressed cable, e.g. too tight binding • Defective connector • Defective cable

The reason for fail and the location of fault can be detected by using the time domain reflectometer (TDR) function, which is available in most testers. This function and the procedure are described in sub-clause 8.2.4.2 of this guidebook. Testing of RL with short cabling lengths causes often problems. Therefore the RL requirements specified in EN 50173-1 has been eased for short lengths, typically shorter than 10 m. In fact the same rule is applied also to longer lengths at low frequencies. The principle of the rule is that values of RL at frequencies for which the measured attenuation is below 3,0 dB are for information only.

8.2.4 Interpretation of test results Marginal result The asterisk (*) associated with the test result (Pass or Fail) means that the difference of the measured value and the specified requirement is smaller than the accuracy of the tester. This means that Pass* may in fact be Fail or Fail* may be Pass. The situation is illustrated in figure 8.8. The accuracy aspects of testers are explained in sub-clause 8.2.1.1 of this guidebook.

Amplitudi = Amplitude Taajuus = Frequency

Hyväksymisalue = Pass region Hylkäysalue = Fail region

Raja-arvo = Limiting value Fail*-alue = Fail* region Pass*-alue = Pass* region

Tarkkuus = Accuracy

Figure 8.8. Marginal results.

The treatment of marginal results shall be specified in the quality plan of the cabling installation. Marginal results may be treated in a number of ways including: • Verification of the normalisation of the test system • Acceptance of all marginal results • Rejection of all marginal results • Acceptance of marginal pass results (Pass*) and rejection of marginal fail results (Fail*) • Repetition of the measurement using a test system with improved measurement accuracy

The common practice is that the marginal fail results (Fail*) are rejected and the marginal pass results (Pass*) are accepted. Repetition of testing should be performed with improved measurement accuracy; this requires calibrated interface adaptors.

8.2.4.1 Test report

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Each tested cabling section shall be reported. The test reports can be downloaded from the tester to PC using the software supplied with the tester. This should be done every day. The software is also used to save the test reports on the hard disk of PC and to print the reports. The reports shall be delivered to the customer in electronic format, e.g. on CD or in printed format. Usually only the summary of the test results is printed. According to the standard EN 50346 the test report shall include the following documentation of each parameter:

• Details of the parameter • Details of the test system • Test equipment type and manufacturer, serial number and calibration status, • Details of the cabling interface adaptors (type, reference numbers, manufacturer and relevant

performance) • Measurement accuracy • Details of the cabling under test • Reference numbers • Date of the test (the time of the test may also be recorded) • Relevant environmental conditions • Test operator • Measured result • Required result

The test report shall state, whether the test result is Pass or Fail and it shall also include the following results of performance testing:

• Wire Map showing the connection of each conductor, including the screen continuity, when relevant • Attenuation (Insertion Loss), worst value • Near end crosstalk loss (NEXT), worst margin and worst value in both directions • Power sum near end crosstalk loss (PSNEXT), worst margin and worst value in both directions • Equal level far end crosstalk loss (ELFEXT), worst margin and worst value in both directions • Power sum equal level far end crosstalk loss (PSELFEXT), worst margin and worst value in both

directions • Return loss (RL), worst margin and worst value in both directions • Propagation delay, worst value • Delay skew, worst value • DC loop resistance, Worst value

Figure 8.9 shows an example of a test report. (TO BE ADDED)

Figure 8.9. Example of a test report

Worst value is the worst value of the parameter. This is the greatest or smallest value depending on the parameter. For example for NEXT it is the smallest value and for attenuation it is the greatest value. In addition to the worst value also the related frequency is given.

Worst margin is the smallest difference of the measured value and the specified requirement. In addition to the worst margin also the related measured value and frequency are given. The worst margin may positive or negative. Negative margin means Fail. The concepts of worst value and worst margin are illustrated in figure 8.10.

taajuus = frequency huonoin NEXT-marginaali = worst NEXT margin

huonoin NEXT-arvo = worst NEXT value

Figure 8.10. Worst value and worst margin.

8.2.4.2 Troubleshooting

The testers on the market include diagnostics tools, which can be used to detect and locate crosstalk and reflections in the cabling. The tester transmits a pulse to the pair and observes the crosstalk signal and the reflected signal simultaneously in the time domain. The location of crosstalk and reflection is shown in the tester display in length axis. This helps to locate the points of crosstalk and reflections and

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saves time in troubleshooting. Figure 8.11 shows an example of NEXT fault detected by HDTDX function of the tester.

Figure 8.11. TDX display showing the location of NEXT fault.

It can be seen from the figure that remarkable crosstalk appears at the near end connector (length of 1 m) and at far end connector (length of 64 m). There are also smaller NEXT points within the cabling. In this case the rejection of the test result (Fail result) is caused by too long untwisted length at the connectors. The fault is repaired by re-terminating the pairs at both ends and maintaining the pair twist as far as possible.

Figure 8.12 shows an example of RL fault detected by HDTDR function of the tester.

NextPairs

Adjust scale Moves cursorAdjust scale Moves cursor

Cursor at 64,3 m

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50

12060

HDTDX Analyzer Pairs 1,2 -3,6

0 m

Figure 8.12. TDR display showing the location of RL fault.

It can be seen from the figure that there are many points within the cabling, where characteristic impedance is changing. At the near end connector (length of 1,1 m) the impedance differs is –2 % from its nominal value. Connector is always a point of reflection and this is not the most common reason for the Fail result of RL test. Return loss (RL), however represents the cumulative effect of all reflections within the cabling and therefore many small reflections (caused by change of impedance) can together cause the Fail result. In this case the rejection of the test result (Fail result) is caused by compressions of too tight binding of the cable. The fault is repaired by loosening the binding or in worst case by installing a new cable. The great reflection at the far end is caused by the mismatch of the equipment.

8.3 Testing of optical fibre cabling

8.3.1 Test equipment Testing of optical fibre channels and links in generic cabling is performed by using the same equipment as for twisted pair cabling and by using light source and optical power meter. Optical time domain reflectometer (OTDR) is used usually only in longer distances and in troubleshooting, unless other specified in the quality plan.

8.3.1.1 Test equipment on the market

There are a lot of optical fibre test equipment on the market. These equipment differ from each other in characteristics and in prices. Light source and optical power meter are used is used to measure the optical power at the near end and far end of the optical fibre cabling. Figure 8.13 shows and example of light source and optical power meter.

Adjust scale Moves cursorAdjust scale Moves cursor

Reflections= - 2% at 1.1 m

+25

0

60300 m-25

NextPairs

1X NextPairs

1X

HDTDR Pair 1,2

Field testers used for testing of twisted pair cabling can be also be used for testing of optical fibre cabling, if optical fibre interface adaptors are used. Most tester manufacturers have this option. Optical fibre interface adaptors are available for multimode fibres and singlemode fibres with different light sources. The principle of using these adaptors is the same as in using light source and optical power meter. Adaptors are provided with optical fibre connectors, to which the optical fibre test cords can be connected. The connector type at the other of the test cord can be chosen to be compatible with that used in the cabling. When optical fibre interface adaptors are used with the relevant software, the attenuation test can be performed easily. With some equipment it is even possible to perform the attenuation test at two wavelengths and in two directions at the same time. Figure 8.14 shows examples of optical fibre interface adaptors.

Figure 8.13. Light source/optical power meter.

Figure 8.14. Example of an optical fibre interface adaptor.

There are also many types and models of OTDR on the market. The differences in these equipment are mainly in easiness of use and in PC software to be used with them. When an OTDR is intended to be purchased, the fibre types to be used, lengths to be tested and required light sources shall be known. OTDR equipment are quite expensive and they usually cannot be utilized effectively in generic cabling testing. Therefore OTDR tests should be required in generic cabling only in special cases. Because of the dead zone caused by the pulse width it is no use to test a cabling with the length of some tens of meters. By using a special long test cord, however, this can be made. OTDR is mainly used for testing of long backbone and trunk lines, when detailed information is needed from the line. Figure 8.15 shows an example of an OTDR.

Figure 8.15. Example of an OTDR (Aligant).

Figure 8.16 illustrates the display of an OTDR and the information given by it.

Pow

erleve

l(dB

m)

Distance

fusion splice connectionbend breakmecanicalsplice

Figure 8.16. Interpretation of an OTDR display.

8.3.1.2 Calibration and maintenance

Test equipment, such as light sources, optical power meters and OTDRs need regular maintenance. Test equipment should be calibrated at intervals recommended by the manufacturer, typically 1 – 2 years. Calibration is important for ensuring that the function and the reference levels of the test equipment are correct.

8.3.2 Test procedures It is vitally important to clean all connectors and adaptors each time before connecting. Any dirt in connectors and adaptors degrades significantly the performance and no reliable result of the real performance of the cabling can be obtained. Cleaning cassettes or cotton swabs can be used for cleaning. Examples of these are shown in figure 8.17. Teletekno Oy 27.7.2003 77

Figure 8.17. Cleaning cassette and cotton swabs.

Cleanness can be ensured only by using a microscope designed for this purpose or a video microscope. The ends of optical fibre connectors shall be protected with dust caps, always when not in use. Light sources (laser, VCSEL and LED) operate at wavelengths, which are not visible for human eye. Direct watching to the end of optical fibre or connector is absolutely forbidden, because the optical power is dangerous for the eye and may damage the retina of the eye. The microscope used for connector inspection shall be provided with laser/LED filters. Warning stickers should be used in each mechanical structure containing optical fibre equipment, devices or components. Visible light laser source (figure 8.18) can be used for identifying the optical fibres. This method, however, gives no information of the cabling performance. The principle is that visible light is sent to the fibre end and bending of the fibre causes light leakage from the fibre.

Figure 8.18. Visible light laser source (Photom).

Fibre continuity test can be used to ensure that no breaks exist within the optical fibre channel or link. This test can be used to check the condition of connections and splices, but it does not always reveal the weak points, which increase attenuation. Fibre continuity test is performed by sending visible light with laser source or lamp to the fibre end.

Multimode fibre cabling is tested at two wavelengths: 850 nm and 1300 nm. When a twisted pair field tester is used with optical fibre interface adaptors, two fibres can be tested at both wavelengths at the same time. This saves much time. When a separate set of light source and optical power meter is used, only multimode fibres can be tested, because the light sources usually are LED sources. The same equipment can, however, be used for both 50/125 μm and 62,5/125 μm fibres. Singlemode fibres are tested at wavelengths of 1310 nm and 1550 nm. The light source type is laser or VCSEL.

Measurement of attenuation with insertion loss method

In the insertion loss method the optical power level P1 (dBm) is first measured at the end of a short fibre (reference test cord). Reference power measurements shall be repeated periodically as necessary. Situations requiring the re-establishment of reference conditions include optical power changes, temperature fluctuations, a move to a different location, and jumper/adapter replacement due to degradation. Then the fibre to be measured is connected between the reference fibre and the power meter and the power level P2 (dBm) at the end of the fibre is measured. The principle is illustrated in figure 8.19.

Figure 8.19. Measurement of attenuation with insertion loss method.

The attenuation of the fibre is the difference between the two power levels.

A = P1 - P2 (dB)

The test equipment can usually be calibrated to show directly the attenuation in dB and calculations are not needed. Special reference test cords should be used for the measurement of the reference power level. The test cords shall be 1 m to 5 m long, and shall have core diameter and numerical aperture nominally equal to those of the cabling under test.

8.3.3 Parameters to be tested The parameters to be tested in the case of optical fibre cabling are attenuation (insertion loss), length (optional), propagation delay (optional) and return loss (optional). The standard EN 50173-1 specifies these parameters for each optical fibre cabling class. The parameters are described in clause 5.4 of this guidebook.

WW

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AttenuationA = P - P (dB)1 2

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Light source Power meterFiberto be measured

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Attenuation

For cabling that only contains connecting hardware at the local and remote ends, it is only necessary for the measurement to be made in one direction. When the cabling contains intermediate connecting hardware, bi-directional testing is required.

Testing of multimode fibre

The launch condition category to be used should be defined in the relevant cabling or application standard. Unless specified otherwise in a reference document, light sources of category 1 shall be used. Category 1 light sources result in the highest measured attenuation.

Light sources are used in the following way:

• In practice category 1 means a LED source • Category 2 means usually VCSEL source • LED source is used, when testing is performed in accordance with the requirements of EN 50173-1

• VCSEL source is used, when testing is performed in accordance with the requirements of IEEE 802.3z

Unless otherwise specified by the relevant cabling or application standard, the optical fibres within the test cords shall have core diameter and numerical aperture nominally equal to those of the cabling under test.

The test cords shall be 1 m to 5 m long, and shall contain optical fibres with coatings, or contain appropriate mechanisms that remove cladding modes of the light.

According to the standard EN 50346 multimode optical fibre test cords connected to light sources shall incorporate a mandrel wrap in order to maximise measurement repeatability. The wrap shall consist of five, close wound, non-overlapping turns of the cord around smooth cylindrical mandrels having the following diameters:

• 50/125 mm optical fibre o 15 mm for cables of 900 μm diameter o 18 mm for cables of 3 mm diameter

• 62,5/125 mm optical fibre o 17 mm for cables of 900 μm diameter o 20 mm for cables of 3 mm diameter

All optical power measurements shall be recorded to one significant digit in the decimal place.

The standard EN 50346 specifies two methods for testing the attenuation of multimode optical fibre cabling. Method 2 is preferred. In method 1 test cord 1 is connected between the light source and the optical power meter as shown in figure 8.20. The displayed optical power P1, which is the reference power, is recorded.

Figure 8.20. Reference power measurement for method 1.

The test cord is disconnected from the optical power meter without disturbing the connection to the light source, and it is attached to the cabling under test at the test interface. Test cord 2 is connected between the test interface at the remote end of the cabling under test and optical power meter as shown in figure 8.22. The displayed optical power P2, which is the test power, is recorded. It is important to note, that the loss of test cord 2 affects the test power measurement. In method 2 three test cords are connected between the light source and the optical power meter as shown in figure 8.21.The displayed optical power P1, which is the reference power, is recorded.

Figure 8.21. Reference power measurement for method 2.

Test cord 3 is disconnected from adaptors without removing the adaptors from test cords 1 and 2 at their point of connection. The test cords at their connection point to the test equipment shall not be

Light source

Optical Powermeter

Test cord 1

P1P1

Light source

Optical Powermeter

Test cord 1 Test cord 2Test cord 3

P1P1

disturbed. Test cord 1 is connected to the local end and test cord 2 is connected to the remote end of the cabling under test as shown in 8.22. Test cord 3 is not used in the test power measurement. The displayed optical power P2, which is the test power, is recorded.

v

Figure 8.22. Cabling test measurement for methods 1 and 2.

Propagation delay

The optical fibres shall be tested using equipment capable of measuring optical signal propagation in the time domain. Optical time domain reflectometers and certain types of light source/optical power meter equipment provide this facility.

Length

The optically measured length of an optical fibre may differ from the physical length of the cable. Within a given length of cable containing multiple optical fibres each individual optical fibre may have a different length. Typically the fibre is 2 – 4 % longer than the cable. The test equipment software calculates the length by using the propagation velocity or the group refractive index given by the cable manufacturer.

8.3.4 Interpretation of results

Light source

Optical Powermeter

Test cord 1 Test cord 2

P2P2

cabling undertest

8.3.4.1 Test report

When twisted pair filed tester with optical fibre interface adaptors are used, same kind of the reports can be obtained as in twisted pair cabling testing. This makes the management of test results easy, because the results can be saved in the same file. If light source/optical power meter equipment without memory is used, the results shall first be recorded manually, i.e. in writing, and later they can be written in a spreadsheet file. The test report shall include the information of the measured value, measurement accuracy and wavelength. If there is a specified acceptance criterion for the test, the report shall also include the information of Pass result, Fail result or marginal result.

9 Applications supported by generic cabling

Generic cabling supports telecommunications applications, which are based on transmission in twisted pair or optical fibre cabling. Applications based on unbalanced (e.g. coaxial) transmission are not supported. When the performance of the cabling channel is known, also the supported applications are known. The most common telecommunications applications supported by the generic cabling specified in the standard EN 50173-1 are listed in the tables of the following sub-clauses. Most of these are LAN applications. Some more information has also been given about Gigabit Ethernet and 10 Gbit/s Ethernet.

9.1 Applications supported by twisted pair cabling Applications supported by twisted pair cabling are listed in table 9.1. A certain class also supports all applications supported by all the lower classes.

Table 9.1. Applications supported by twisted pair cabling.

Application Standard or specification Additional name of application Class A (100 kHz) Customer premises telephone network

X.21 ITU-T Rec. X.21 V.11 ITU-T Rec. V.11 Class B (1 MHz) So – extended bus ITU-T Rec. I.430 ISDN basic access So – point to point configuration ITU-T Rec. I.430 ISDN basic access

S1/S2 ITU-T Rec. I.431 ISDN primary access CSMA/CD 1Base5 ISO/IEC 8802-3 Star Lan Class C (16 MHz) CSMA/CD 10Base-T ISO/IEC 8802-3 Ethernet CSMA/CD 100Base-T4 ISO/IEC 8802-3 Fast Ethernet CSMA/CD 100Base-T2 ISO/IEC 8802-3 Fast Ethernet Token Ring 4 Mbit/s ISO/IEC 8802-5 ISLAN ISO/IEC 8802-9 Integrated Services LAN ISLAN16-T ISO/IEC 8802-9 DAM 1 Isochronous Ethernet Demand Priority ISO/IEC 8802-12 VGAnyLAN ATM LAN 25,60 Mbit/s ATM Forum af-phy-

0040.000 ATM-25/Category 3

ATM LAN 51,84 Mbit/s ATM Forum af-phy-0018.000

ATM-52/Category 3

ATM LAN 155,52 Mbit/s ATM Forum af-phy-0047.000

ATM-155/Category 3

Class D (100 MHz) CSMA/CD 100Base-TX ISO/IEC 8802-3 Fast Ethernet Token Ring 100 Mbit/s ISO/IEC 8802-5t High Speed Token Ring CSMA/CD 1000Base-T ISO/IEC 8802-3 Gigabit Ethernet Token Ring 16 Mbit/s ISO/IEC 8802-5 TP-PMD ISO/IEC FCD 9314-10 Twisted Pair Physical Medium Dependent

ATM LAN 155,52 Mbit/s ATM Forum af-phy-0015.000

ATM-155/Category 5

Class E (250 MHz) CSMA/CD 1000Base-TX TIA/EIA-854 Gigabit Ethernet ATM LAN 1,2 Gbit/s ATM Forum af-phy-

0162.000 ATM-1200/Category 6

Class F (600 MHz) FC-100-TP ISO/IEC 14165-114 Fibre Channel: 100 MByte/s Twisted Pair Phy Interf

9.1.1 Gigabit Ethernet in twisted pair cabling

Gigabit Ethernet in twisted pair cabling has been specified in two different standards. These standards are: • IEEE 802.3ab (1999). This version is designated with 1000Base-T and the minimum requirement for

cabling is class D channel. • ANSI/TIA/EIA-854 (2001). This version is designated with 1000Base-TX and the minimum

requirement for cabling is class E channel.

Gigabit Ethernet 1000Base-T specified in the standard IEEE 802.3ab uses transmission technique, in which the transmitted 1000 Mbit/s data signal is splitted into four sub-signals. The data transmission rate of each sub-signal is 250 Mbit/s. These four 250 Mbit/s signals are transmitted over the four pairs of the cable and at the receiver end they are combined again to form 1000 Mbit/ signal. Transmission mode is full duplex, which means that bi-directional and simultaneous 250 Mbit/s transmission is used on each pair. The system is illustrated in figure 9.1. The figure also shows the disturbing phenomena of one pair and one transmission direction.

Figure 9.1. In 1000Base-T the1000 Mbit/s data signal is splitted into four 250 Mbit/s signals, which are transmitted over the four pairs of the cable. Bi-directional and simultaneous 250 Mbit/s transmission is used on each pair (full duplex).

Transceivers used in 1000Base-T includes complicated signal processing electronics to cancel the effects of disturbances. Equalizers are used for compensating the attenuation, echo cancellers for

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cancelling the reflections and NEXT cancellers for cancelling NEXT. Far end crosstalk is not cancelled and even the cancelling of echoes and NEXT is not perfect, too. Therefore there always exist disturbances, which degrade the quality of transmission. These disturbing phenomena shall be within specified limits.

Original target of the standard of 1000Base-T was that it would be supported by the old class D channel, which was specified in 1995. Nowadays, however, the general opinion is that the minimum cabling requirement for 1000Base-T is the new class D channel, which was specified in 2000. This new class D channel is practically the same as the category 5e channel specified in the US standard. The new class D was really specified already in 2000, two years before the totally new edition of EN 50173-1 (2002). If the old (1995) class D cabling is intended to be used for 1000Base-T, the cabling channel shall be tested according to the new channel D specification.

In new cabling it always recommended to use class E horizontal cabling. This gives much better operating margin than the class D channel, which is just the minimum requirement. Better operating margin also guarantees higher effective data transmission rate, because the number of errors decreases and less resending of data frames is needed. This can been directly seen as the real data transmission rate of the user.

The transmission technique used in 1000Base-T requires quite complicated electronics. This means 4 transmitters, 4 receivers, 4 echo cancellers and 12 NEXT cancellers at each end of the channel. The power consumption and heat production of this kind of electronics is significant. To avoid this problem an alternative transmission system was developed. In this system the 1000 Mbit/s data signal is splitted only into two sub-signals, both having the data transmission rate of 500 Mbit/s.

These 500 Mbit/s signals are transmitted over four pairs so that two 500 Mbit/s signals are transmitted on two pairs to one direction and two 500 Mbit/s are transmitted on two pairs to the other direction. The system is specified in the US standard ANSI/TIA/EIA 854 and it is designated with 1000Base-TX. The transmission rate on each pair is 500 Mbit/s and therefore class D cabling performance is insufficient. The minimum requirement for this system is class E channel. The transmission system of 1000Base-TX is illustrated in figure 9.2.

Figure 9.2. In 1000Base-TX the1000 Mbit/s data signal is splitted into two 500 Mbit/s signals, which are transmitted over the four pairs of the cable. Two 500 Mbit/s signals are transmitted on two pairs to one direction and two 500 Mbit/s are transmitted on two pairs to the other direction (full duplex).

Equipment and network adapters for both 1000Base-T and 1000Base-TX are on the market. Until now the market share of 1000Base-T has been very much greater than that of 1000Base-TX. The transmission technique of 1000Base-TX is used also in 1,2 Gbit/s ATM LAN.

9.2 Applications supported by optical fibre cabling Applications supported by different classes are shown in table 9.2 for each fibre category. The proper fibre category can be chosen, when the required channel length and the application to be supported are known.

Table 9.2. Applications supported by optical fibre cabling.

Application Category OM1 Category OM2 Category OM3 Category OM4850 nm 1300 nm 850 nm 1300 nm 850 nm 1300 nm 1310 nm 1550 nm

10Base-FL & FB OF-2000 OF-2000 OF-2000100Base-FX OF-2000 OF-2000 OF-2000ATM 155 OF-500 OF-2000 OF-500 OF-2000 OF-500 OF-2000 OF-2000ATM 622 OF-300 OF-500 OF-300 OF-500 OF-300 OF-500 OF-20001000Base-SX OF-300 OF-500 OF-5001000Base-LX OF-500 OF-500 OF-500 OF-200010GBase-SR/SW 10GBase-LR/LW OF-200010GBase-ER/EW OF-200010GBase-X4/LW4 OF-300 OF-300 OF-300 OF-2000

Attenuation

NEXT

RT

500 Mbit/s 500 Mbit/s

RT

500 Mbit/s 500 Mbit/s

500 Mbit/s 500 Mbit/s

R T

500 Mbit/s 500 Mbit/s

R T

FEXT

Attenuation

NEXT

RT

500 Mbit/s 500 Mbit/s

RT

500 Mbit/s 500 Mbit/s

RT

500 Mbit/s 500 Mbit/s

RT

500 Mbit/s 500 Mbit/s

500 Mbit/s 500 Mbit/s

R T

500 Mbit/s 500 Mbit/s

R T

500 Mbit/s 500 Mbit/s

R T

500 Mbit/s 500 Mbit/s

R T

FEXT

As can be seen from table 9.2, the optical fibre channel length (class) achieved with different fibre categories depends on the application. This shall be taken into account when choosing the fibre type and category. For example the channel length of 2000 m (class OF-2000) can be achieved with all categories, if the application to be supported is 100Base-FX. But if the channel length of 2000 m (class OF-2000) is required also for Gigabit Ethernet, singlemode fibre (OS1) shall be used.

9.2.1 Gigabit Ethernet in optical fibre cabling

Gigabit Ethernet in optical fibre cabling is specified in the standard IEEE 802.3z (1998). The standard specifies two basic cabling alternatives depending on the wavelength to be used. These alternatives are the following: • 1000Base-SX. This is used with a multimode fibre at the wavelength of 850 nm. • 1000Base-LX. This is used with a multimode fibre at the wavelength of 1300 nm or with a

singlemode fibre at the wavelength of 1310 nm.

Transmitters to be used in optical fibre Gigabit Ethernet applications are laser or VCSEL transmitters. LED transmitter is too slow for Gigabit applications. The transmission requirements of optical fibre channels to be used for Gigabit Ethernet are specified in the standard IEEE 802.3z. Most important requirements for different wavelengths and fibre types are shown in table 9.3.

Table 9.3. Most important transmission requirements of optical fibre channels to be used for Gigabit Ethernet specified in IEEE 802.3z.

Wavelength Fibre type Fibre bandwidth MHz⋅km

Maximum channel length m

Maximum attenuation of channel dB

850 nm 62,5/125 μm 160 220 2,33 850 nm 62,5/125 μm (OM1) 200 275 2,53 850 nm 50/125 μm 400 500 3,25 850 nm 50/125 μm (OM2) 500 550 3,43 1300 nm 62,5/125 μm (OM2) 500 550 2,32 1300 nm 50/125 μm 400 550 2,32 1300 nm 50/125 μm (OM2) 500 550 2,32 1310 nm 10/125 μm (OS1) Large 5000 4,50

Table 9.3 includes also optical fibres do not meet the requirements of the standard EN 50173-1. The use of these fibres is to be avoided in new cabling. The requirements of table 9.3 are met, if the fibre types and channel lengths specified in the standard EN 50173-1 are used. Table 9.3, however, provides useful information, when an existing optical fibre cabling is intended to be used for Gigabit Ethernet. The applicability of the existing optical fibre cabling can be tested based on requirements of table 9.3.

9.2.2 10 Gbit/s Ethernet in optical fibre cabling The standard IEEE 802.3ae of 10 Gbit/s Ethernet was published in 2002. 10 Gbit/s Ethernet is specified for both LAN and WAN applications and it supports the level STM-64 (10 Gbit/s) of SDH system, which is used in public telecommunications networks. 10 Gbit/s Ethernet is specified only for optical fibre. The twisted pair system is under consideration. The standard specifies transmission techniques for multimode and singlemode fibres and for three wavelength windows. Also wavelength division multiplexing (WDM) is included in the standard. The summary of different transmission systems is shown in table 9.4.

Table 9.4. Transmission techniques used in 10 Gbit/s Ethernet.

Name Encoding of data Transmission speed in channel

Transmission mode

Wavelength

10GBase-SR

64B/66B

10,3125 Gbit/s Serial transmission

850 nm10GBase-LR 1310 nm10GBase-ER 1550 nm10GBase-SW

9,95 Gbit/s (SDH)

850 nm10GBase-LW 1310 nm10GBase-EW 1550 nm10GBase-LX4 8B/10B 12,5 Gbit/s WDM ~1300 nm

S = short wavelenght L = long wavelenght E = extra long wavelenght R = 64B/66B encoding LAN W = 64B/66B encoding WAN X = 8B/10B encoding

10GBase-SR/SW is optimal in building backbone and short campus backbone cabling. The achievable channel lengths are 26 – 300 m depending on the optical fibre type. The optical fibre to be used is multimode fibre of type 50/125 μm or 62,5/125 μm. As can be seen from table 9.5 the achievable channel length with the traditional 62,5/125 μm fibre is only 32 m, but the OM3 fibre supports the application up to 300 m. The optical fibre meeting the requirements of EN 50173-1 and the channel lengths with these fibres are printed with bold font type in the table. The transmitter type in 10GBase-SR/SW is VCSEL.

Table 9.5. Channel lengths of 10GBASE-SR/SW with different fibre types.

Fibre type Fibre bandwidth, 850 nm, MHz⋅km Channel length, m

62,5/125 μm 160 26 62,5/125 μm

(OM1) 200 32

50/125 μm 400 66 50/125 μm (OM2) 500 82 50/125 μm (OM3) 2000 300

10GBase-LR/LW is optimal in building and campus backbone cabling exceeding 300 m. It can also be is used WAN applications. The fibre type to be used is the normal singlemode fibre (OS1) and the wavelength is 1310 nm. The transmitter type in 10GBase-LR/LW is laser and the achievable channel length is 10 km. 10GBase-ER/EW can be used in long distance WAN applications. The fibre type to be used is the normal singlemode fibre (OS1) and the wavelength is 1550 nm. The transmitter type in 10GBase-ER/EW is laser and the achievable channel length is 40 km. 10GBase-LX4 has been developed for the existing optical fibre cablings and it is based on WDM technology. The fibre type is a multimode or a singlemode fibre. In this system the signal is splitted into four sub-signals, which are transmitted in the same optical fibre, but at different wavelengths. This is the principle of WDM. The wavelength window to be used is the 1300 nm window. The system requires four laser transmitters and four receivers for both transmission directions. The principle of this system is illustrated in figure 9.3. The error detection requires additional bits and therefore the total transmission rate in the channel is 12,5 Gbit/s and not 10 Gbit/s.

Wavelengths:λ1 = 1275,7 nm, λ2 = 1300,2 nm, λ3 = 1324,7 nm and λ4 = 1349,2 nm ±5,7

Figure 9.3. WDM system used in 10GBase-LX4.

The achievable channel lengths for 10GBase-LX4 are shown in table 9.6. The system can be used in building backbone cabling and short campus cabling, which consist of multimode fibres of lower category than OM3.

Table 9.6. Channel lengths of 10GBase-LX4 with different fibre types.

Fibre type Fibre bandwidth, 1300 nm, MHz⋅km

Channel length, m

62,5/125 μm (OM1 and OM2) 500 300 50/125 μm 400 240

50/125 μm (OM1 and OM2) 500 300 10/125 μm (OS1) - 10 000

Tx1

Tx2

Tx2

Tx2

Rx1

Rx2

Rx2

Rx2

Timing

Timing

WDM

WDM

λ1

λ2

λ4

λ1

λ2

λ3λ3

λ4

Optical fibre

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

λ1 + λ2 + λ4 λ3 +

12,5 Gbit/s

Tx1

Tx2

Tx2

Tx2

Rx1

Rx2

Rx2

Rx2

Timing

Timing

WDM

WDM

λ1

λ2

λ4

λ1

λ2

λ3λ3

λ4

Optical fibre

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

3.125Gbit/s

λ1 + λ2 + λ4 λ3 + λ1 + λ2 + λ4 λ3 +

12,5 Gbit/s

10 The most important differences between EN 50173-1 (2002) and its older editions (1995 and 2000), ISO/IEC 11801 and ANSI/TIA/EIA 568-B

10.1 Differences between EN 50173-1 (2002) and its older editions

The first edition of the standard EN 50173 was ratified and published in 1995. It was this standard, in which the structure and requirements of the generic was specified first time. This first edition defines and specifies the following: • Structure and functional elements of generic cabling • Interfaces and dimensioning of cabling • Classes A, B, C and D of twisted pair cabling • On class of optical fibre cabling • Performance of twisted pair and optical fibre links • Categories 3 and 5 of twisted pair cables and connecting hardware • Optical fibre cables and connecting hardware

Amendment 1 of EN 50173 (1995) was published in 2000. This amendment is designated with EN 50173/A1 (2000). The most important meaning of this amendment was the new specifications of class D to support Gigabit Ethernet (1000Base-T). The category 5 cable specifications, however, were not updated at this stage. The interfaces of cabling were also specified more precisely as before and the concept of permanent link was defined. The performance of classes A, B, C and D was specified first time to both channels and permanent links. The standard EN 50173-1 was published in 2002. This standard replaces the standards EN 50173 (1995) and EN 50173/A1 (2000). The most important differences of EN 50173-1 (2002) as compared with its older editions are the following: • New classes E (250 MHz) and F (600 MHz) of twisted pair cabling and the corresponding categories

6 and 7 of twisted pair cables and connecting hardware. • New specifications of class D (100 MHz) links and channels and new specifications of category 5

cables. (The new category 5 is practically equivalent with category 5e specified in the US standard).

• New classes OF-300, OF-500 and OF-2000 of optical fibre cabling and new fibre categories OM1, OM2, OM3 and OS1.

• New revised definitions of link and channel: − Permanent link: Installed cable with connectors at both ends. No cross-connect. − CP link: Link between floor distributor and consolidation point. − Channel: Transmission path from one equipment to another. Includes installed cabling,

connectors, equipment cord, work area cord and optional cross-connect. • Performance specified for channels, permanent links and CP links. • New specifications for twisted pair cabling: Return loss (RL), PSNEXT, PSACR, ELFEXT,

PSELFEXT, delay skew.

• Reference implementations with dimensioning rules. • Centralized optical fibre cabling as a new cabling alternative. • Detailed cable specifications are not included in the standard. Reference to cable standards is used. • Category 3 has been left out. Also 150 Ω cabling has been left out. • The latest editions of international ISO/IEC 11801, European EN 50173-1 and American (US)

ANSI/TIA/EIA 568-B have been approximately within the same time schedule and they practically harmonized.

10.2 Differences beween EN 50173-1 (2002), ISO/IEC 11801 and ANSI/TIA/EIA 568-B

The factual contents of international standard ISO/IEC 11801 (2002) is practically equivalent with the European standard EN 50173-1 (2002). The main differences are in the format of the standards. Also the references in ISO/IEC 11801 are made to international standards (IEC and ITU-T), while EN 50173-1 uses mainly European references (EN and ETSI standards). This difference has, however, practically no effect on the factual contents of the standard, because most of the reference standards are identical and have even the same numerical designation (e.g. IC 60603-7 and EN 60603-7). The standard ISO/IEC 11801 includes more appendices, which are informative (not normative). The American (US) standard ANSI/TIA 568-B consists of the following parts:

• ANSI/TIA/EIA-568-B.1: Commercial Building Telecommunications Standard Part 1: General Requirements, 2001

• ANSI/TIA/EIA-568-B.2: Commercial Building Telecommunications Standard Part 2: Balanced Twisted-pair Cabling Components, 2001

− ANSI/TIA/EIA-568-B.2-1: Addendum 1 -Transmission Performance Specifications for 4-pair 100 Ω Category 6 Cabling, 2002

− ANSI/TIA/EIA-568-B.2-2: Addendum 2, 2001 − ANSI/TIA/EIA-568-B.2-3: Addendum 3 - Additional Considerations for Insertion Loss

and Return Loss Pass/Fail Determination, 2002

• ANSI/TIA/EIA-568-B.3: Commercial Building Telecommunications Standard Part 3: Optical Fiber Cabling Components, 2000

− ANSI/TIA/EIA-568-B.3-1: Addendum 1 - Additional Transmission Performance Specifications for 50/125μm Optical Fiber Cables, 2002

Also the standard ANSI/TIA 568-B has practically the same factual contents as the European standard EN 50173-1. The most important differences between EN 50173-1 and ANSI/TIA/EIA 568-B are listed in table10.1.

Table 10.1. Differences between EN 50173-1 and ANSI/TIA/EIA 568-B.

Topic EN 50173-1 ANSI/TIA/EIA 568-B Terminology Campus distributor

Building distributor Floor distributor

Main cross-connect Intermediate cross-connect Horizontal cross-connect

Twisted pair cabling

Cable and connector categories 5, 6 and 7. No 150 Ω cabling. Cabling classes A, B, C, D, E and F.

Cable and connector categories 5e and 6. Also 150 Ω cabling. Categories are used also for cabling. No classes. Requirements of category 5e and 6 links and channels are substantially the same as requirements of class D and E links and channels in EN standard.

Optical fibre cabling

Fibre categories OM1, OM2, OM3 and OS1. Cabling classes OF-300, OF-500 and OF-2000.

No fibre categories, but mainly the same fibre specifications. No cabling classes.

Supported applications

→ 10 Gbit/s Ethernet → 10 Gbit/s Ethernet

References EN standards, ETSI standards.

US standards (ANSI, IEEE, UL).

EMC European standards. US standards.

11 Frequently asked questions and answers

Does the standard allow using of so-called Siamese cable?

Yes, the standard allows it. The standard EN 50173-1 specifies additional requirements for hybrid and multi-unit cables, and cables connected to more than one telecommunications outlet. The so-called Siamese cable is included to this group. First, of course, these cables are required to meet the transmission requirements for the corresponding cable category. Additionally, the PSNEXT between all non-fibre recognised cable units or elements shall be 3 dB better than the specified pair-to-pair NEXT required at all specified frequencies for the same category. In practice this means that the PSNEXT between cables shall be 6 dB better than the PSNEXT of the cable itself. Improving the crosstalk characteristics of the cable itself does not improve the crosstalk characteristics between two cables (alien crosstalk). Therefore structural means have to be used. In the case of the Siamese UTP cable the additional crosstalk margin can be achieved by making the neck between two

cables sufficiently wide. This increases the distance between the two cables. In the Siamese FTP cable the screens of the cables always ensure a sufficient margin and there is no risk of alien crosstalk.

What is the difference between category 5 and 5e?

Originally category 5 was specified for twisted pair cables and connectors to be used up to 100 MHz. In the US standard the word category is applied also to channels and links. Category 5 requirements of cables and connectors were specified in EN 50173 (1995). When the transmission rates very soon increased (Gigabit Ethernet), it was necessary to specify new requirements for category 5. The requirements included e.g. PSNEXT, ELFEEXT and PS ELFEXT. In the United States the cable meeting the new requirements was called enhanced category 5, abbreviated 5e. 5e. In the international and European standardization bodies first only requirements of class D were revised and then later also the new category 5 cable was specified. The name, however, still remained the same, category 5 without the letter e. The category 5e cable specified by the American (US) standard ANSI/TIA/EIA 568-B is practically the same as the category 5 cable specified in the 2002 editions of the standards ISO/IEC 11801 and EN 50173-1. The upper limit frequency is still 100 MHz, but the performance is higher than that of category 5 of the year 1995. The new (2002) category 5 and the category 5e support Gigabit Ethernet (1000Base-T). The old (1995) category 5 does not support Gigabit Ethernet.

What is the four connections model in horizontal cabling?

The channel performance requirements specified in EN 50173-1 for class D, E and horizontal cabling are based on the channel length of 100 m and four connections. This model includes a consolidation point (CP) and it also includes a cross connect in the floor distributor. The model is shown in figure 11.1.

Figure 11.1. Requirements of horizontal cabling channel are based on 100 m channel length and four connections.

Equipment

Terminalequipment

3

FD CP TO

Eqiupmentcord

Patchcord

Workareacord

CPcable

1 2 4

Channel 100 m

Equipment

Terminalequipment

3

FD CP TO

Eqiupmentcord

Patchcord

Workareacord

CPcable

1 2 4

Channel 100 m

The implementation shown in figure 11.1 is not very commonly used in the Nordic Countries, because usually interconnect (no cross connect) is used in the floor distributor. The most common implementations are shown in figure 5.1 of this guidebook.

Does the cabling length mean the length of the cable or the length of the pairs within the cable?

The cabling lengths defined and specified in the standard always mean physical lengths of the cables, i.e. lengths measured along the cable sheath. Due to the pair twisting the lengths of the twisted pairs are always greater than the cable length. The shorter the lay length of pair twisting is the greater is the difference compared with the cable length. The lay lengths of pair twisting of the pairs also differ from each other. This is necessary in order to control the crosstalk. When the length of the twisted pair cabling is tested, in fact the propagation delay is measured. The test equipment software calculates the length based on this propagation delay and the nominal velocity of propagation (NVP) of the cable. There fore the correct NVP shall be set in the test equipment. NVP takes into account also the effect of pair twisting. According to the testing standard EN 61935-1 NVP shall be calibrated for the pair, which has the longest lay length. The test result of this pair equals to the physical length of the cable. The inaccuracy of the test equipment, however, causes a difference from the actual value. According to the standard EN 50173-1 the length is not a pass/fail criterion for the cabling. The test result of length is only informative. If the horizontal cabling is really too long for the application, this will be indicated by some other test, for example exceeding of attenuation. However, the length rules of the standards shall be followed, because the performance requirements are based on these requirements.

Who needs class F and category 7?

The upper limit frequency of the class F cabling is 600 MHz and this cabling can be implemented by using category 7 cables and connecting hardware. The 600 MHz frequency range of class F/category 7 always requires pair screened cabling. The development of the category 7 started in Germany, where screened cabling has traditionally been used more than unscreened cabling. The first proposal of the class E/category 7 standard was of German origin. Standardization process in ISO/IEC started almost immediately after 1995, when the first editions of generic cabling standards had been published. At that time the 600 MHz performance was still called class E/category 6. Very soon after that USA made a proposal of 250 MHz cabling and in it was decided in ISO/IEC that two new classes/categories will be specified. These were class E/category 6 (250 MHz) and class F/category 7 (600 MHz). The only known application, which requires the class F, is FC-100-TP specified in the standard ISO/IEC 14165-114. This is the Fibre Channel 100 MB/s in twisted pair cabling. (Note: MB/s means megabytes/second). This application is used only in computer rooms. It is not used like local area networks (LAN). Also in computer rooms the real optical fibre version of the Fibre Channel is more common than this twisted pair version. Class F (category 7), however, makes the range of standardized cabling alternatives to be chosen more complete. It also provides a solution to applications, where 600 MHz bandwidth and/or excellent

screening are needed. On the other hand the multimode fibre is becoming competitive alternative for class F cabling, which uses heavy construction cables and connectors and is not very easy to install.

Unscreened or screened cabling?

This question is popular and it has been asked since the first days of the generic cabling. Sometimes the discussion on this topic has also been very intense. One reason for this is surely the strong image, which is created by words “unscreened” and “screened”. The black-and-white way of thinking may lead to such interpretation that one cable is without any protection against interferences and the other has been perfectly protected fro interferences. The situation is not so simple. The interference protection of a twisted pair cable is always primarily based on sufficient balance. The sufficient balance requires uniform and regular pair twisting with a short lay length. The category 6 UTP cables shall have very good pair twisting in order to meet the crosstalk requirements. These kinds of cables also have good protection against interferences and they also emit very little interferences. Good or bad crosstalk characteristics and good or bad EMC characteristics are both based on god or bad balance. EMC characteristics can be still improved by using common screening (FTP or S-FTP), pair screening (STP) or both. Category 7 cables are always pair screened. At frequencies extending to 600 MHz the crosstalk can be controlled only by using pair screens. As a basic rule it can be recommended that UTP is an optimal solution for category 5 and 6. Screened cables are recommended to be used only for special reasons. As an example of such reason are conditions, where more strict limits of immunity and emission are required than specified European EMC standards. If screened cabling is used, the continuity of screening and earthing of screens are important. Otherwise the benefits of the screening may be lost. The continuity means that the screening shall be continuous from end to end of the channel. The screening shall also totally surround the cables and connectors. The screening shall be continuous from end to end also in the case, where only one end is earthed, which is the minimum requirement. Usually the screening is earthed only in distributors. Earthing at the other end depends on the equipotential bonding of the building. If there are potential differences more than 1 V between any two earthing points, the risk of earth loops is evident. Standard EN 50174-2 gives more guidance and information about earthing and equipotential bonding.

12 Standards

Planning, installation and testing • EN 50174–1, Information technology – Cabling installation – Part 1: Specification and quality

assurance. • EN 50174–2, Information technology – Cabling installation – Part 2: Installation planning and

practices inside buildings. • prEN 50174–3, Information technology – Cabling system installation – Part 3: Installation

planning and practices external to buildings. To be published in 2003. • EN 50310, Application of equipotential bonding and earthing in buildings with information

technology equipment. • EN 50346, Information technology – Cabling installation – Testing of installed cabling

Twisted pair cables

• EN 50288–1, Multi-element metallic cables used in analogue and digital communication and control – Part 1: Generic specification.

• EN 50288–2–1, Multi-element metallic cables used in analogue and digital communication and control – Part 2-1: Sectional specification for screened cables characterized up to 100 MHz – Horizontal and building backbone cables.

• EN 50288–2–2, Multi-element metallic cables used in analogue and digital communication and control – Part 2-2: Sectional specification for screened cables characterized up to 100 MHz – Work area and patch cord cables.

• EN 50288–3–1, Multi-element metallic cables used in analogue and digital communication and control – Part 3-1: Sectional specification for unscreened cables characterized up to 100 MHz – Horizontal and building backbone cables.

• EN 50288–3–2, Multi-element metallic cables used in analogue and digital communication and control – Part 3-2: Sectional specification for unscreened cables characterized up to 100 MHz – Work area and patch cord cables.

• EN 50288–4–1, Multi-element metallic cables used in analogue and digital communication and control – Part 4-1: Sectional specification for screened cables characterized up to 600 MHz – Horizontal and building backbone cables.

• EN 50288–4–2, Multi-element metallic cables used in analogue and digital communication and control – Part 4-2: Sectional specification for screened cables characterized up to 600 MHz – Work area and patch cord cables.

• EN 50288–5–1, Multi-element metallic cables used in analogue and digital communication and control – Part 5-1: Sectional specification for screened cables characterized up to 250 MHz – Horizontal and building backbone cables.

• EN 50288–5–2, Multi-element metallic cables used in analogue and digital communication and control – Part 5-2: Sectional specification for screened cables characterized up to 250 MHz – Work area and patch cord cables.

• EN 50288–6–1, Multi-element metallic cables used in analogue and digital communication and control – Part 6-1: Sectional specification for unscreened cables characterized up to 250 MHz – Horizontal and building backbone cables.

• EN 50288–6–2, Multi-element metallic cables used in analogue and digital communication and control – Part 6-2: Sectional specification for unscreened cables characterized up to 250 MHz – Work area and patch cord cables.

Connecting hardware for twisted pair cabling

• EN 60603-7, Connectors for frequencies below 3 MHz for use with printed boards – Part 7: Detail specification for connectors, 8 way, including fixed and free connectors with common mating features

• prEN 60603-7-2, Connectors for use in d.c., low frequency analogue and in digital high speed data applications – Part 7-2: Detail specification for 8-way, unscreened free and fixed connectors, for data transmissions with frequencies up to 100 MHz

• prEN 60603-7-3, Connectors for use in d.c., low frequency analogue and in digital high speed data applications - Part 7-3: Detail specification for 8-way, screened, free and fixed connectors, for data transmissions with frequencies up to 100 MHz

• prEN 60603-7-4, Connectors for use in d.c., low frequency analogue and in digital high speed data applications – Part 7-4: Detail specification for 8-way, unscreened, free and fixed connectors, for data transmissions with frequencies up to 250 MHz

• prEN 60603-7-5, Part 7-5: Detail specification for 8-way, screened, free and fixed connectors, for data transmissions with frequencies up to 250 MHz

• EN 60603-7-7, Connectors for use in d.c., low frequency analogue and in digital high speed data applications – Part 7-7: 8 way connectors for frequencies up to 600 MHz

• IEC/PAS 61076-3-104, Connectors for electronic equipment - Part 3-104: Detail specification for 8 way, shielded free and fixed connectors, for data transmission with frequencies up to 600 MHz

Optical fibres and optical fibre cables

• EN 60793–2–10, Optical fibres – Part 2–10: Product specifications – Sectional specification for category A1 multimode fibres

• EN 60793–2–50, Optical fibres – Part 2–50: Product specifications – Sectional specification for class B single-mode fibres

• EN 60794–1–1, Optical fibre cables – Part 1–1: Generic specification – General • EN 60794–1–2, Optical fibre cables – Part 1–2: Generic specification – Basic optical cable test

procedures • EN 60794–3, Optical fibre cables – Part 3: Telecommunication cables – Sectional specification

Optical fibre connectors • IEC 60874-19-1, Connectors for optical fibres and cables – Part 19-1: Fibre optic patch cord

connector type SC-PC (floating duplex) standard terminated on multimode fibre type A1a, A1b – Detail specification.

• IEC 61754-18, Fibre optic connector interfaces - Part 18: Type MT-RJ connector family • IEC 61754-19, Fibre optic connector interfaces - Part 19: Type SG connector family • IEC/PAS 61754-20, Fibre optic connector interfaces - Part 20: Type LC connector family

EMC of LAN equipment

• EN 55022, Limits and methods of measurement of radio interference characteristics of information technology equipment

• EN 55024, Information technology equipment - Immunity characteristics -Limits and methods of measurement

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