02 ik iesys e introduction to industrial ethernet

SITRAIN training forAutomation and Industrial Solutions

IK-IESYSEthernet basics

SITRAINIK-IESYS / Ethernet basics Page 1

Automation and Drives

03/2007 © Siemens AG 2007 - Subject to change without prior notice

Introduction to Industrial Ethernet

Contents PageIndustrial automation levels, horizontal ................................................................................... 2Industrial automation levels, vertical ....................................................................................... 3Uniform bus system for all levels .............................................................................................. 4Industrial environment........................................................................................................................ 5Industrial Ethernet (IE) ................................................................................................................. 6ISO 7 layer model, part 1 ................................................................................................. 7ISO 7 layer model, part 2 ................................................................................................. 8Development timeline ...................................................................................................................... 9Industrial Ethernet – basic layout, previously ................................................................................. 10Example of Ethernet configuration, 2006 ................................................................................... 11Classification of different types of Ethernet ...................................................................................... 12Ethernet variants, Ethernet naming conventions............................................................................... 13Thick Ethernet 10Base5 ......................................................................................................... 14Thin Ethernet 10Base2 .......................................................................................................... 15Twisted-pair Ethernet 10BaseT ............................................................................................... 16Fiber-optic Ethernet 10BaseF ................................................................................................... 17Fast Ethernet 100BaseT ......................................................................................................... 18Gigabit Ethernet 1000BaseX .................................................................................................. 19Access methods are ....... ............................................................................................................. 20CSMA/CD access method, bus structure .................................................................................. 21CSMA/CD access method, process flow ................................................................................ 22CSMA/CD access method, collision domain .............................................................................. 23CSMA/CD access method, real-time response ............................................................................. 24The hub, multiport repeater .......................................................................................................... 25The switch ................................................................................................................... 26Hub compared to switch ........................................................................................................ 27Shared LAN compared to switched LAN ................................................................................ 28Switching technology, part 2 ......................................................................................................... 29Switching network: Spanning tree ................................................................................................. 30Network components in the OSI model: Repeater, hub/bridge, switch............................................... 31Network components in the OSI model: Router and gateway................................................................32






Industrial automation levels, horizontal

Data managementlevel

Control level

Fieldlevel

ManagingArchiving

Visualizing

Open-loopcontrol

Closed-loopcontrol

MeasuringPositioning

Switching

Industrial automation levelsIndustrial automation encompasses many segments. The tasks of these segments and the flow of information between them can be describedusing a simplified level model.

Components within one level communicate over bus systems that arecustomized and optimized for the functional requirements of that level.






Industrial automation levels, vertical


Fieldlevel

ManagingArchiving

Visualizing

Open-loopcontrol

Closed-loopcontrol

MeasuringPositioning

Switching

Control level

Vertical communicationThere also needs to be vertical communication between the levels. Productionspecifications are passed down to the lower levels. Conversely, process-related information from the lower levels is verifiedand archived at the management level.However, optimal flow of information is ensured only if the networks of theindividual levels work together in an optimal manner.






Uniform bus system for all levels


Fieldlevel

Control level

Internet

Uniform bus system across all levelsA largely uniform bus system is required to ensure optimal data flowacross levels.

The Ethernet version previously used in a commercial (office) environment with the CP/IP protocol forms the basis for this type of data integration.The automation network can be seamlessly linked to the company networkand the INTERNET.






Industrial environment

Electrical and magnetic interference (EMC)

Vibrations

Large temperatureranges

Corrosiveatmospheres

Industrial environmentEthernet-based networking technology was developed for communication in the commercial sector. However, for installations used in the industrial rather than the office environment, additional considerations must be taken into account.






Industrial Ethernet (IE)

High temperature compatibility of

network components

Rugged mechanics and industry-standard

cables and connections

EMC immunity through special

shielding and the use of fiber-optic

conductors

Increased availability through redundant network

structures

Compliance with real-time requirements through appropriate network

segmentation and the use of switching technology

Industrial Ethernet

Industrial EthernetThrough the use of special network components, Industrial Ethernet takes the strict requirements of production/the process environment into account. However, interaction with conventional Ethernet components is also ensured.






ISO 7 layer model, part 1

7: Application layerThis layer encompasses the application-specific services of the various communication applications. These include basic services and protocols such as FTP file transfer, e-mail, virtual terminals, etc.

6: Presentation layerThis layer ensures the independence of the different data formats used.

5: Session layerThis layer organizes the dialogbetween the communicating partners.

ISO 7 layer modelThe tasks and functions performed by communication systems are varied and complex.This is why ISO developed the OSI reference model. This 7-layer architecture specifies which protocols and services can beimplemented in the individual layers.

7: Application layerThis layer encompasses the application-specific services of the various communication pplications. These include basic services and protocols such asFTP file transfer, e-mail, virtual terminals, etc.

6: Presentation layerThis layer ensures the independence of the different data formats used.During sending, the data to be transferred is converted to a uniformintermediate format so that it can be interpreted correctly by the connected computers. When the data is received, the intermediate format is converted to the format required by the individual computers.

5: Session layerThis layer organizes dialog between the communicating partners.It establishes, maintains and clears the connection andsynchronizes the flow of data between the application processes.






ISO 7 layer model, part 24: Transport layer

This layer is primarily concerned with ensuring thatdata actually arrives at its destination.

3: Network layerThis layer is responsible for transferringdata packets between the source and destination. This includes routing, addressing of other networks and data flow control.

2: Data link layerThis layer transfers bits between two systems. This includes controlling access to the transmission medium (access method), as well as detection and elimination/signaling of transmission errors.

1: Physical layerThis layer is responsible for the correct transmission of individual bits over the physical channel. The main activities involved here are the encoding of signals and specification of the transmission medium and transmission devices.

4: Transport layerThis layer is primarily concerned with ensuring that data actually arrivesat its destination. It is able to trigger data retransmission if data were lost.

3: Network layerThis layer is responsible for transferring data packets between the sourceand destination. This includes routing, addressing of other networks and data flowcontrol.

2: Data link layerThis layer transfers bits between two systems.This includes controlling access to the transmission medium (access method), as well as detection and elimination/signaling of transmission errors.

1: Physical layerThis layer is responsible for correct transmission of individual bits over the physical channel. The main activities involved here arethe encoding of signals and specification of the transmission medium andtransmission devices.






Development timeline

IndustrialEthernet bus system SINEC H1

OpticalIndustrial Ethernet SINEC H1FO

OLM/ELM Twisted-pair cabling/FOCWeb server

GIGABITModular switchesIndustrial securityReal-time Ethernet fieldbus/PROFINETIWLANRapidroaming

Fast Ethernet switchesFC cablingMOBICWLAN

1985 1989 1996 2000 2005

History

1985 Ethernet in industrial applications for SIMATIC and PC/PG1991 PROFIBUS products for SIMATIC S5 and PC/PG1993 Fiber-optic cables for PROFIBUS1994 AS-Interface for SIMATIC and PC/PG1994 Flexible fiber-optic-cable networks for PROFIBUS by means of OLM1995 Industrial twisted pair cables for Ethernet1996 Flexible FOC/ITP networks for Ethernet via optical/electrical link module1998 FastConnect cable system for PROFIBUS 1998 Internet technology used in automation: Market launch of the first IT CPs for SIMATIC

S71999: Switching technology and high-speed redundancy for Industrial Ethernet via

OSM/ORM1999 Fast Ethernet for SIMATIC and PC/PG2000 FastConnect cable system for Industrial Ethernet 2001 First industrial WebPad on the market: MOBIC T8 Mobile Industrial Communicator2001 PROFINET: Distributed and open automation solutions based on Industrial Ethernet2003 Industrial wireless LAN in the industrial environment






Industrial Ethernet – basic layout, previously

Fiber-optic cable

Starcoupler

Fan-outunit

KYDE

Triaxial cable

Technical dataStandard Ethernet to IEEE 802.3/ISO 8802.3 or Ethernet Blue Book

Access method CSMA/CD (Carrier Sense Multiple Access/Collision Detection)

Transmission rate 10/100 Mbit/s

Transmission Electrical: Double-shielded coaxial cable, industrial twisted pairmedium Optical: Fiber-optic cable (glass)

Max. no. of nodes Over 1,000

Approx. network rangeElectrical: 1.5 kmOptical: 4.5 km, 150 km, or 1300 km if switches are used

Topology Line, tree, star, redundant ring

Automation Management and cell levelslevel






Example of Ethernet configuration, 2006

MES level

Office network

MES level

Automation network

Data server

ProductionmastercomputerComputer

ServerWorkstation

computer

HMI Automation cells

Service computer

Service computer

Firewall






Classification of different types of Ethernet

20 m200 m2,000 mLength of collision domain

After 4,096 bits;After 512 bits;After 512 bits;Slot time (cable action period)

Multimode: 3,000 mSingle mode: 26 km

100 m

OSM, ESM

Twisted pair: 10 BaseTFiber optic: 10 Base-FL

Star, tree, line

48 bits

64 bytes

1,518 bytes

CSMA/CD

0.01 microsecond

100 Mbit/s

802.3u

Fast Ethernet

Multimode: 3,000 mSingle mode: 26 km

Multimode: 300 mMax. length of a fiber-optic-cable path

100 m100 mMax. length of a TP path

SCALANCE Bus coupler (transceiver)Optical link module, electrical link module, active star coupler, mini UYDE, MINI OTDE

Network components

Twisted pair: 10 BaseTFiber optic: 10 Base-FL

Coaxial: 10 Base5Twisted pair:10 BaseTFiber optic: 10 Base-FL

Supported media

Star, tree, lineStar, tree, lineTopology

48 bits48 bitsLength of address field

64 bytes64 bytesSmallest data packet

1,518 bytes1,518 bytesLargest data packet

CSMA/CDCSMA/CDAccess methods

0.001 microsecond0.1 microsecondDuration of one bit

1,000 Mbit/s10 Mbit/sData rate

802.3z802.3IEEE standard

Gigabit EthernetEthernet

IEEE standard 802.3The international Institute of Electrical and Electronic Engineers (IEEE)defined the first Ethernet standard, 10BASE5, in 1985. This standard,which was based on a coaxial cable transmission medium, laid thefoundations for the first Industrial Ethernet. This network, which went under the name SINEC H1 and was improvedby the introduction of a triaxial cable for the industrial environment, hasbeen used successfully in process and production automation for many years.Since the very beginning, both the IEEE standard and the SIMATICNET product range have constantly been updated with the latest technologies, which further improve the flexibility and performance capability of Ethernet networks. This includes the introduction of transmission via fiber-optic and twisted-pair cables and the tenfold increase of the transmission rateby means of Fast Ethernet. All versions are based onbaseband transmission and the CSMA/CD access method.

Baseband transmission technologyEthernet to IEEE 802.3 uses baseband transmission technology.This means that data is transferred to the transmission medium(e.g., connecting cable) unmodulated, in a pulse shape. The transmission medium forms a single transmission channel, which mustshare its capacity with the connected data terminals.All connected data terminals receive the data transmitted via themedium at the same time. Only one data terminal may send data atany one time. If several data terminals send data at thesame time, this will lead to data collision on the transmission medium.

The data signals of the senders concerned will destroy one another. Transmission rights need to be assigned in order to regulate access to the shared transmission medium by the data terminals. The IEEE 802.3 standard regulates access in accordance with the CSMA/CD method.






Ethernet variants, Ethernet naming conventions

10Base5 Coaxial cable (3/8 inch)

Standard Transmission medium

10Base2 Coaxial cable (3/16 inch)

10BaseT Fiber-optic cable

100BaseT Fiber-optic/Twisted pair

1000BaseX Fiber-optic/Twisted pair

10 Mbit/s systems

100 Mbit/s systems

1,000 Mbit/s systems

Ethernet naming conventionsStandard IEEE 802.3 defines several Ethernet versions,whose main differences lie in their transmission rates and the cabling technology they use. The naming conventions shown were laid down in order to distinguish between the different versions.

Data rate in Mbit/sThis field indicates the applicable data rate in Mbit/s. It can range from10 Mbit/s to 10,000 Mbit/s. The original data rate of 3 Mbit/s and the 1 Mbit/s version are no longer used.

Transmission methodBase (baseband)In a baseband, digital signals are fed directly into the cable as pulses, i.e., thesignals are transported unmodulated (10Base5).

Broad (broadband)In a broadband system, multiple carrier frequencies are used and the signalto be transmitted is modulated up to these carrier frequencies. This enables multiple messages to be transmitted simultaneously and independently (10Broad36).

Max. length/Cable typeThe data in this field can have different meanings.It can be used to specify the maximum cable length per segment, in 100 m (10Base5 = 500 m).It can also indicate the cable type. The name 10BaseTis used for twisted pair cables and 10BaseF is used for fiber-optic cables.






Thick Ethernet 10Base5

Thick Ethernet 10Base5The figure above shows the original cabling of an Ethernet networksegment. In this bus structure, the Ethernet coaxial cableis routed via every station and every station is connected via a short connecting cable.

Coaxial cable (yellow cable)Ethernet 10Base5 uses a 3/8-inch, 50-ohm coaxial cable.Due to emission and attenuation, the maximum length for a cable segment is 500 m. This type of cable is more uncommon today as it is not particularly easy to use.

TerminatorA coaxial segment must be terminated at each end with 50-ohm terminators.This prevents reflections and associated signalcorruption.

ControllerThe Ethernet controller executes the functions of the MAC layer. These includedata compilation, the calculation of checksums for sent frames,and the checking of checksums for received frames.The controller is connected to the transceiver by means of the transceiver cable.

TransceiverData terminals are connected to the coaxial cable by means of transceivers,which are also known as MAUs (Medium Attachment Units). Thereare two different designs, which use a different type of connector.Coaxial cable connector and vampire terminal connection.






Thin Ethernet 10Base2

Coaxial cable

BNC connector

50-ohm terminatingresistor

BNC T fitting

GroundShielding

Central conductor

Shielding

DielectricExteriorinsulation

Dielectric

Ethernet controller

Thin Ethernet 10Base2This version uses a thin coaxial cable. Although this type of cable doeslead to decreased attenuation and is less immune to interference,it is more than adequate for smaller networks.

As this version does not cost as much as that using the yellow cable, it isknown as Cheapernet.






Twisted-pair Ethernet 10BaseT

Twisted-pair Ethernet 10BaseT10BaseT refers to Ethernet networks based on twisted pair cabling. The bus topology is a star topology. A hub (multiport repeater) forms the central point from which twisted cable pairs lead to the individual stations.These networks are very common and cost-effective.

Twisted pair: A twisted pair usually consists of a four-core copper cable twisted in pairs. A distinction is made between shielded (STP) and unshielded (UTP) cables.The maximum transmission length depends on theshielding; however, it must not exceed 100 m.

Cable category: UTP and STP describe the cable's design, but UTP cables are further broken down into categories defining the requirements of the cable and plug-in connector. Cables used for 10BaseT must meetthe specifications for category UTP-3 as a minimum.

Plug-in connector: Conventional twisted pair Ethernet cabling uses 8-pin (Western)connectors. There is a wide range of different types ofthese connectors, such as the new RJ45 plug connector.

Hub: Hubs are characteristic of networks with star or tree topologies. A hub has numerous ports for connecting stations and other devices.If signals are sent, the hub copies these signals and passes themon to ALL the connected stations.






Fiber-optic Ethernet 10BaseF

Fiber-optic cable

Fiber-optic Ethernet 10BaseF10BaseF refers to a series of standards that use fiber-optic cables as atransmission medium. Due to the long-range transmission paths,these systems are often used to connect distant network segments.

Fiber-optic cables In fiber-optic cables, information is transmitted over thin glassfibers using extremely short light pulses. The cable contains twoglass fibers, enabling simultaneous sending and receiving(FD = full duplex).






Fast Ethernet 100BaseT

100BaseTX 2 pairs, category 5 UTP

Standard Transmission medium Max. distance

100 m

100BaseFX Multi-mode fiber 400 m

100BaseT4 4 pairs, min. category 3 UTP 100 m

100BaseT2 2 pairs, min. category 3 UTP 100 m

Fast Ethernet Fast Ethernet is an LAN standard for a transmission rate of 100 Mbit/s. It is anatural expansion of 10BaseT and the two are compatible.New capabilities, such as full duplex, have also been added.There are several versions of 100BaseT, which have different physical layers and, as a result, differenttransmission media.






Gigabit Ethernet 1000BaseX

1000BaseTX 4 pairs, category 5 UTP

Standard Transmission medium Max. distance

100 m

1000BaseCX 2 pairs, STP 25 m

1000BaseSX Multi-mode fiber (short wave) 275 m

1000BaseLX Mono-mode/Multi-mode fiber (long wave) 5,000/550 m

Gigabit EthernetGigabit Ethernet technology provides a data transfer rate of 1,000 Mbit/s. This LAN system is also based on the CSMA/CD method, but is uses optimized physical transmission and logical signal encoding. Gigabit Ethernet is compatible with the 802.3 standard and provides seamlessintegration into existing networks.






Access methods are .......

CentralCentral

Deterministic(can be predicted)

Deterministic(can be predicted)

DistributedDistributed

Stochastic(random)Stochastic(random)

Stochastic access (random)The station wishing to transmit data transfers it to a free channel without first seeking permission to do so.

Resolving issues arising from collisions, e.g., if a transmission is repeated following a random delay time- Simple- Fast if there is not much traffic- Delay time fluctuates randomly with no upper limit- CSMA/CD for local networks (Carrier Sense Multiple Access with

Collision Detection)

Deterministic access (can be predicted)An explicit order is defined, in accordance with which stations transmit data to free channels.

Stations are permitted to transmit data in a specific order (e.g., cyclically)- The need to seek permission minimizes the delay time- An upper limit can be specified for the delay time, priorities if necessary

Important examples: Token method for LAN polling method






CSMA/CD access method, bus structure

Carrier Sensing (CS): All stations continuously listen to the transmission medium.

Multiple Access (MA): Equal competing access of all stations wishing to send data.

Collision Detection (CD): Listening to the medium during the transmission process, detection of any collisions.

Ethernet bus structureIn conventional Ethernet technology, all stations are attached to the samecable line (linear bus, linear structure). The Ethernet stations arecompletely independent, they are not synchronized by a higher-level networkmaster (as with PROFIBUS DP ) or by a token that is passedaround (as with PROFIBUS).So, the stations compete to access the bus, meaning that access controlis needed.

Access controlAccess control is the responsibility of the data link layer (layer 2). This layerhas to detect when two or more stations are attempting to send data at thesame time. To this end, Ethernet uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method.

Carrier Sensing (CS)All stations continuously listen to the transmission medium.

Multiple Access ( MA)Equal competing access of all stations wishing to send data.

Collision Detection (CD)Listening to the medium during the transmission process, detection of anycollisions.






CSMA/CD access method, process flow

1

2

3

Carrier Sensing (CS) Before sending, a station first listens to the line to determine whetherdata exchange is already taking place between stations.

Points 1 and 2: If the transmission medium is available, the station begins its transmission.However, because other stations can also transmit at the same time (MA), the senderlistens to the transmission in order to detect any possible collisions. Iftransmission takes places with no collisions, station 3 recognizes from thereceiver address inside the data packet that it is the intended recipient andaccepts the data. All other stations ignore the packet.

Point 3: A certain execution time must be taken into account for all lines. For example, station 2 may erroneously consider the bus to be available because it has not yetreceived the signal sent by station 1. If station 2now starts sending, a collision occurs.

If a sending station detects a collision, it immediately stops transmission and sends a collision signal (4 to 6 bytes with a special bit pattern).All sending stations then stop transmission, and the line is quiet.

After receiving a collision signal, the stations wishing to sendwait a random delay time and then attempt to resend the data.

If this new attempt also fails, the delay time becomes longer. After 16collisions in succession, the access algorithm is aborted and thehigher-level software must decide how to proceed.

This flowchart again provides an overview of how the CSMA/CD accessmethod works.






CSMA/CD access method, collision domain

Collision domainA collision domain is a network area in which collisions may occur betweensending stations as a result of the CSMA/CD method.It also includes all Ethernet segments connected to the collision domainover a repeater (signal amplifier).






CSMA/CD access method, real-time response

Network loading

Average delay

Real-time responseThis graph shows that, if CSMA/CD is used and the load on the bus increases,transmission times increase sharply too, as there is a greater risk of collisions.A real-time response can, therefore, not be guaranteed. This means that the network must be appropriately segmented in order to reduce the likelihood of a collision.






The hub, multiport repeater

The hubFunctionally, the hub is the counterpart of the repeater in a twisted-paircabled network with a star topology.As it features multiple ports, it is also known as a multiport repeater.Like repeaters, hubs are used as a simple way of increasing the expansion of a network.

• Hubs work on the physical layer (layer 1) of the OSI model.

• Their sole function is to work as a distributor. All stations connected to a hubshare the entire bandwidth made available via the hub(e.g., 10 Mbit/s or 100 Mbit/s).

• The connection between the computer and the hub only has access to thisbandwidth temporarily.

• A hub accepts a data packet and sends it to all other ports.This procedure results in all ports being occupied. This technology is not particularly

effective, but it does have the advantage that hubs of this type are easy and cheap to manufacture.

• Two hubs are connected via an uplink port on a device or by means of acrossover cable (the transmission and reception cables are crossed).

• Special stackable hubs are also available, which, depending on the make,can be cascaded with connecting cables.

• The number of possible stations can be increased by connecting severalhubs. However, there is a limit to the number of stations whichcan be connected (repeater rule on previous slide).






The switchCollisiondomain 1

Collisiondomain 2

Collisiondomain 3

The switchThe switch is a high-speed packet-switching system used to divide local networksinto segments. Like the bridge, theswitch operates on layer 2 of the ISO/OSI reference model. Every port of aswitch forms a separate network segment with its own collision domain.This enables a switch to not only increase the performance capability of thenetwork as a whole, but also that of each individual segment.

Function Within the switch, a particular port is assigned to each MAC address in arouting table. An incoming data packet is transmitteddirectly to the port of the receiver, based on its destination address. A switch can establish multiple connections simultaneously between pairs of ports,thus considerably decreasing collision overhead.






Hub compared to switch

The switch transfers a frame to a certain port, based on its destination address. It also enables multiple connections to be established between ports simultaneously. Every port can access the full Ethernet bandwidth and work in, among others, full-duplex mode.

If A transmits data to B, this data is also forwarded to all the other users connected to the hub.

The 10 Mbit/s Ethernet bandwidth is equally available to all nodes, which must share it.

Hub Switch

A B A D E B C FG H

General The individual ports on a switch can send and receive data independently of one another. The ports are interconnected via an internal high-speed bus (backplane). As far as possible, data buffers ensure that data frames are not lost.Packets/frames can be forwarded in a switch in the operating modes below, which differ in terms of their delay times and error compensation:

Cut through This is a very fast method, which is primarily used by better switches. The switch only looks at the MAC destination address of the received frame, makes a decision as regards forwarding and forwards the frame accordingly. The frame is not checked for errors, in order to save time. Therefore, the switch also forwards damaged frames, which must then be picked up by other layer-2 devices or higher network levels.

Store and forward This is the most basic, but also the slowest switching method, which can be performed by every switch. The switch makes a forwarding decision based on the MAC destination address as usual, then uses the frame to calculate a checksum, which it compares to the CRC value stored at the end of the packet. If there is any discrepancy, the frame is rejected. This ensures that no faulty frames are distributed in the LAN. Store and forward is the only switching method which can be used if the sender and receiver are working at different transmission rates or with duplex modes, or if they are using different transmission media.

Spanning tree Bridges and switches communicate via the (rapid) spanning tree algorithm(IEEE 802.3d,w) to prevent data packets looping endlessly within a network. In a meshed system, various connections are temporarilyswitched to standby mode in order to create a tree topology.






Shared LAN compared to switched LAN

Switched LAN• Each individual collision domain

has access to the entire bandwidth• Local data traffic remains local, so

the load is separated• Maximum range for each collision

domain

Shared LAN• All network nodes share the available

bandwidth, e.g., 10 Mbit/s• Liable to collisions• All frames pass through all segments• Repeaters, hubs, optical link modules,

etc., require compliance with configuration rules and restrict the maximum range

Data traffic

Fragment free This is faster than Store and Forward, but slower than Cut Through. It is more commonly found on better switches. It checks whether a frame reaches the minimum length of 64 bytes required by the Ethernet standard and then transmits it to the destination port immediately, without carrying out a cyclic redundancy check. Fragments below 64 bytes are usually "debris" created by a collision, which no longer represent a meaningful packet.

Advantages of switches• If two network nodes receive data simultaneously there are no collisions (see CSMA/CD), as the switch can internally transfer both transmissions simultaneously via the backplane. If data arrives at an output port faster than it can be forwarded over the network, it is buffered. If possible, flow control is used to prompt the sender(s) to send the data more slowly.

• If eight computers are connected via an 8-port switch and two computers are both sending data to one another at full speed, so that four full-duplex connections are established, in theory you have eight times the speed you would achieve with a corresponding hub where all the devices would share the maximum bandwidth - 4 * 200 Mbit/s as opposed to 100 Mbit/s. However, two aspects contradict this theoretical calculation: For one thing, the internal processors are not designed to run all ports at full speed and a hub with multiple computers will never reach 100 Mbits either, as the more collisions that occur, the more load the network is subjected to, which in turn restricts the bandwidth.

• The switch records in a table which station can be reached via which port. During continuous operation, the MAC sender addresses of the forwarded frames are saved. Data is then only forwarded to the port where the receiver is actually located. Packets

with unknown MAC destination addresses are treated as broadcasts and forwarded to all ports, with the exception of the source port.






Switching technology, part 2Cut throughThe switch only looks at the MAC destination address of the received frame, makes a decision as regards forwarding and forwards the frame accordingly. The frame is not checked for errors in order to save time. Therefore, the switch also forwards damaged frames, which must then be picked up by other layer-2 devices.

Store and forwardThis is the most basic, but also the slowest switching method, which can be performed by every switch. The switch makes a forwarding decision based on the MAC destination address as usual, then uses the frame to calculate a checksum, which it compares to the CRC value stored at the end of the packet. If there is any discrepancy, the frame is rejected. This ensures that no faulty frames are distributed in the LAN. Store and Forward is the only switching method which can be used if the sender and receiver are working at different transmission rates or with duplex modes, or if they are using different transmission media.

Spanning treeBridges and switches communicate via the (rapid) spanning tree algorithm (IEEE 802.3d,w) to prevent data packets looping endlessly within a network. In a meshed system, various connections are temporarily switched to standby mode in order to create a tree topology.

General The individual ports on a switch can send and receive data independently of one another. The ports are interconnected via an internal high-speed bus (backplane). As far as possible, data buffers ensure that data frames are not lost.Packets/frames can be forwarded in a switch in the operating modes below, which differ in terms of their delay times and error compensation:

Cut through This is a very fast method, which is primarily used by better switches. The switch only looks at the MAC destination address of the received frame, makes a decision as regards forwarding and forwards the frame accordingly. The frame is not checked for errors, in order to save time. Therefore, the switch also forwards damaged frames, which must then be picked up by other layer-2 devices or higher network levels.

Store and forward This is the most basic, but also the slowest switching method, which can be performed by every switch. The switch makes a forwarding decision based on the MAC destination address as usual, then uses the frame to calculate a checksum, which it compares to the CRC value stored at the end of the packet. If there is any discrepancy, the frame is rejected. This ensures that no faulty frames are distributed in the LAN. Store and Forward is the only switching method which can be used if the sender and receiver are working at different transmission rates or with duplex modes, or if they are using different transmission media.

Spanning tree Bridges and switches communicate via the (rapid) spanning tree algorithm(IEEE 802.3d,w) to prevent data packets looping endlessly within a network. In a meshed system, various connections are temporarilyswitched to standby mode in order to create a tree topology.






Switching network: Spanning tree

Fiber-optic cable

Spanning tree

In order to prevent data packets from looping in the network, variousconnections are switched to standby with closed machines so that a tree topologyis created.

Bridges and switches communicate over the spanning treeprotocol (IEEE 802.1d) or the rapid spanning tree protocol(IEEE 802.1w). Their message frames are represented in yellow. Switches of theSCALANCE X400 product range offer the time-optimized variant. In the eventof an error, they only require a few seconds to reconfigure new trees.






Network components in the OSI model: Repeater, hub/bridge, switch

Repeater/hub (star hub)- "Refreshes" and forwards the incoming signals - Immediately forwards the information to all

partners connected to the repeater/hub.- No filtering, load separation or intervention in

communication- The use of repeaters/hubs is restricted to a

single collision domain.

Application

Presentation

Session

Transport

Network

Data Link

Physical

Repeater / Hub

Physical Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Bridge / Switch

Data Link Data Link

Physical Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Bridge/switch- Connects collision domains. The maximum

extension is only limited by the delay of the data packets between two nodes.

- Load separation: Data traffic can be spread overdifferent subsegments.

- Data traffic is not interrupted if individual stations fail.

- Parallel communication






Network components in the OSI model: Router and gateway

Application

Presentation

Session

Transport

Network

Data Link

Physical

Router

Network Network

Data Link Data Link

Physical Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Router- Decouples networks on the basis of layer 3

addresses (IP addresses)- Controls traffic between networks (routing)- Protocol-independent, offers routing

functions and flow control

Application

Presentation

Session

Transport

Network

Data Link

Physical

Gateway

Application Application

Presentation Presentation

Session Session

Transport Transport

Network Network

Data Link Data Link

Physical Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Gateway- A gateway converts services.- Security mechanisms are possible

(firewall, proxy).- A gateway comprises hardware and software

for connecting different networks, whereby all protocols can be converted (all 7 OSI layers).

02 ik iesys e introduction to industrial ethernet

Documents

ethernet variants

gigabit ethernet

fast ethernet

ethernet 10base2

ethernet naming conventions

fiberoptic ethernet

twistedpair ethernet

thick ethernet 10base5