COMP 421 /CMPET 401COMP 421 /CMPET 401

COMMUNICATIONS and NETWORKING

CLASS 2

OSI Reference ModelOSI Reference ModelDeveloped by the International Standards Organization Developed by the International Standards Organization (ISO) to facilitate the international standardization of (ISO) to facilitate the international standardization of communications protocolscommunications protocols

For U.S.: ANSI (American National Standard Institute) - For U.S.: ANSI (American National Standard Institute) - www.ansi.orgwww.ansi.org

OSI is ISO's Basic Reference Model for Open Systems OSI is ISO's Basic Reference Model for Open Systems Interconnect (hence: ISO/OSI)Interconnect (hence: ISO/OSI)

The Reference Model itself is The Reference Model itself is notnot a Network Architecture a Network Architecture (does not specify any protocols or services)(does not specify any protocols or services)

The ISO/OSI Reference ModelThe ISO/OSI Reference ModelThe model describes computer communications protocols in a The model describes computer communications protocols in a general sense to facilitate discussiongeneral sense to facilitate discussion

No assumptions are made regarding:No assumptions are made regarding:Programming language bindingsProgramming language bindings

Operating system bindingsOperating system bindings

Applications programming interfacesApplications programming interfaces

Development of the model started in the mid-1970’sDevelopment of the model started in the mid-1970’s

Biggest ProblemsBiggest ProblemsVery long time to complete the model and protocol standardsVery long time to complete the model and protocol standards

Very hard to understand the detailed standardsVery hard to understand the detailed standards

Difficult (expensive) to get the standards documentsDifficult (expensive) to get the standards documents

OSI MODELOSI MODEL

Open Systems Interconnection Reference Model (OSI Model) Is a layered abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnect initiative. The model divides the functions of a protocol into a series of layers. Each layer has the property that it only uses the functions of the layer below, and only exports functionality to the layer above. A system that implements protocol behavior consisting of a series of these layers is known as a 'protocol stack' or 'stack'. Protocol stacks can be implemented either in hardware or software, or a mixture of both. Typically, only the lower layers are implemented in hardware, with the higher layers being implemented in software

OSI MODELOSI MODEL

The seven layers divided into two important subnets: 1. Communications Subnet – This is comprised of the lower 3 layers

2. Host Process – This is comprised of the upper three layer

The network layer is middle layer and the first end to end layer. It acts as buffer between the two subsets.

ISO/OSI Reference Model - Why 7 LayersISO/OSI Reference Model - Why 7 Layers

One layer for each level of abstractionOne layer for each level of abstraction

Each layer performs (ideally) a limited, well defined Each layer performs (ideally) a limited, well defined functionfunction

Functions for each layer are selected with Functions for each layer are selected with International International StandardizationStandardization as a goal as a goal

Layer boundaries are chosen to minimize information Layer boundaries are chosen to minimize information crossing the interfacecrossing the interface

Want to keep the model manageable (5 would have been Want to keep the model manageable (5 would have been nice) but not have to jumble together distinct functionsnice) but not have to jumble together distinct functions

Data Unit

OSI ModelOSI Model

Application

Session

Transport

Network

Physical

Presentation

Data Link

Application

Session

Transport

Network

Physical

Presentation

Data Link

App Process X App Process Y

Physical Transmission MediumCommunication Path

BITS

Data Unit

Data Unit

Data Unit

Data Unit

Application Data

Application Data

AH

PH

SH

TH

NH

F A C FCS F

OSI Layer 1OSI Layer 1Layer 1 is the Physical Layer. It handles bit transmission betweenone node and the next. The functions of this layer include interfacing with the transmission media, encoding the data signal, defining the range of the voltage or current magnitudes, defining the connector sizes,shape, and anything generally associated with the physical transmission of a bit stream.

The Physical layer performs services requested by the Data link layer. The major functions and services performed by the physical layer are:

(a) establishment and termination of a connection to a communications medium;

(b) participation in the process whereby the communication resources are effectively shared among multiple users, e.g., contention resolution and flow control; and,

(c) In user equipment and the corresponding signals transmitted over a communications channel.

OSI Layer 1 - Physical layerOSI Layer 1 - Physical layer

Primary function is transmitting raw bits over a physical Primary function is transmitting raw bits over a physical communications channelcommunications channel

Primary design issues include: mechanical, electrical, Primary design issues include: mechanical, electrical, functional, procedural characteristicsfunctional, procedural characteristics

what voltage represents a “1” versus a “0”what voltage represents a “1” versus a “0”

How many pins in and the shell shape the connector.How many pins in and the shell shape the connector.

Defines functions between the system and transmission mediumDefines functions between the system and transmission medium

Specifies sequence of events by which bits streams are Specifies sequence of events by which bits streams are exchanged across the physical mediumexchanged across the physical medium

By “raw bits” we mean there is no interpretation of the By “raw bits” we mean there is no interpretation of the bits - stream of bits in and bits outbits - stream of bits in and bits out

OSI Layer 2 - Data Link layerOSI Layer 2 - Data Link layer

Primary function is to make Layer 1 into what appears to Primary function is to make Layer 1 into what appears to be a channel be a channel free of undetected errorsfree of undetected errors

Deals with data in chunks (typically 100s-1000s of Deals with data in chunks (typically 100s-1000s of bytes) generally called bytes) generally called FramesFrames

This layer must create/recognize frame boundariesThis layer must create/recognize frame boundaries

remember - Physical layer does not careremember - Physical layer does not care

often requires special bit patterns to signal boundariesoften requires special bit patterns to signal boundaries

may have to deal with possibility of pattern appearing may have to deal with possibility of pattern appearing in datain data

OSI Layer 2OSI Layer 2Data link layer Layer 2 responds to service requests from the Network layer and issues service requests to the Physical layer. The Data link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical layer. Note: Examples of data link protocols are HDLC and ADCCP for point-to-point or packet-switched networks and LLC for local area networks.

In other words it maintains the reliable communications link betweenadjacent nodes. The DLL inserts addresses in the data frame and provides error control for the data.

OSI Layer 2 - Data Link layerOSI Layer 2 - Data Link layer

Among the key issues dealt with are:Among the key issues dealt with are:

Error handling (e.g. corrupted frame)Error handling (e.g. corrupted frame)

Flow controlFlow control

Providing various qualities of serviceProviding various qualities of service

For For BroadcastBroadcast networks, a key issue is controlling networks, a key issue is controlling access to the channel:access to the channel:

Use a sub-layer called the Use a sub-layer called the Media Access ControlMedia Access Control (MAC) sub-layer(MAC) sub-layer

OSI Layer 3 - Network layerOSI Layer 3 - Network layer

Primary function is to control the operation of the layers belowPrimary function is to control the operation of the layers below

Among the key issues dealt with are:Among the key issues dealt with are:

Routing packets from source to destination through the network Routing packets from source to destination through the network (or multiple networks) using static or dynamic routing algorithms(or multiple networks) using static or dynamic routing algorithms

Controlling congestion in the networkControlling congestion in the network

Accounting functions (for billing)Accounting functions (for billing)

Translating between protocols across heterogeneous networksTranslating between protocols across heterogeneous networks

Concerned with AddressingConcerned with Addressing

OSI Layer 3OSI Layer 3Network layer Layer responds to service requests from the Transport layer and issues service requests to the Data link layer. The Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport layer. The Network layer performs network routing, flow control, segmentation/desegmentation, and error control

This layer establishes the path for the traveling data packet

OSI Layer 4 - Transport layerOSI Layer 4 - Transport layer

First First end-to-endend-to-end layer layer

Uses the network to (most often) provide higher layers with a Uses the network to (most often) provide higher layers with a connection oriented, reliable, error free channel that delivers connection oriented, reliable, error free channel that delivers messages (or byte stream) in ordermessages (or byte stream) in order

Layer 4 of the OSI Model coordinates communications between systems.

May also perform flow controlMay also perform flow control

Often performs multiplexing of multiple transport connections Often performs multiplexing of multiple transport connections over one or more network connectionsover one or more network connections

Generally requires Address (or naming)Generally requires Address (or naming)

OSI Layer 4OSI Layer 4Transport layer Layer 4 responds to service requests from the Session layer and issues service requests to the Network layer. The purpose of the Transport layer is to provide transparent transfer of data between end users, thus relieving the upper layers from any concern with providing reliable and cost-effective data transfer.

This layer provides reliable delivery of host messages originating at layer 7 the same way as the DLL assures reliable delivery of frames between adjacent nodes. This is the layer responsible forSegmenting long messages in smaller units (packets) and thenReassembling them at the other end.

OSI Layer 5 - Session layerOSI Layer 5 - Session layer

Manages dialog control (e.g. may manage who’s turn it is Manages dialog control (e.g. may manage who’s turn it is to talk in a high-level half-duplex protocol)to talk in a high-level half-duplex protocol)

Manages synchronization of transactions which may need Manages synchronization of transactions which may need to be able to to be able to roll backroll back in case of a crash in case of a crash

Sort of an Sort of an unwanted layer,unwanted layer, this layer is usually very this layer is usually very thinthin and little more than a pass through for most protocolsand little more than a pass through for most protocols

Key services provided includeKey services provided include::Dialogue disciplineDialogue discipline

Grouping - data mark as belonging to a special groupGrouping - data mark as belonging to a special group

Recovery – checkpoint mechanismRecovery – checkpoint mechanism

OSI Layer 5OSI Layer 5

Session layer Layer 5 responds to service requests from the Presentation layer and issues service requests to the Transport layer. The Session layer provides the mechanism for managing the dialogue between end-user application processes. It provides for either duplex or half-duplex operation and establishes checkpointing, adjournment, termination, and restart procedures

In other words it establishes and terminates process to process communications Sessions between hosts.

OSI Layer 6 - Presentation layerOSI Layer 6 - Presentation layer

Rather than being concerned with Rather than being concerned with movingmoving information, information, the Presentation layer is concerned with the the Presentation layer is concerned with the interpretation of information representationinterpretation of information representation

Ensures that the Ensures that the syntaxsyntax and meaning is the same for and meaning is the same for each participant in a communicationeach participant in a communication

Provides for standard representation and may provide Provides for standard representation and may provide capabilities for conversion of datacapabilities for conversion of data

OSI Layer 6OSI Layer 6

Presentation layer Layer 6 responds to service requests from the Application layer and issues service requests to the Session layer. The Presentation layer relieves the Application layer of concern regarding syntactical differences in data representation within the end-user systems. Note: An example of a presentation service would be the conversion of an EBCDIC-coded text file to an ASCII-coded file.

Simply put this layer establishes the syntax in which data isexchanged between the two hosts. It provides a data manipulation function rather than a communication function (data compressionand data encryption are examples of this layers activities)

OSI Layer 7 - Application layerOSI Layer 7 - Application layer

The layer where end-user applications liveThe layer where end-user applications live

This is the highest level of abstraction and the level This is the highest level of abstraction and the level which is of primary importance (for most users)which is of primary importance (for most users)

All the rest of the layers exist to support these All the rest of the layers exist to support these applicationsapplications

Layering exists so we can move these around to Layering exists so we can move these around to different machines, and so they can communicate different machines, and so they can communicate across any platforms - across any platforms - Open Systems InterconnectOpen Systems Interconnect

OSI Layer 7OSI Layer 7

Application layer The highest layer, layer 7 interfaces directly to and performs common application services for the application processes; it also issues requests to the Presentation layer. The common application services provide semantic conversion between associated application processes.

OSI ExamplesOSI Examples

Layer Examples

7 - Application HTTP, SMTP, SNMP, FTP, Telnet, FTAM, APPC, X.400, X.500, NCP, Appletalk, AFP, DAP

6 - Presentation TDI, XDR, SNMP, FTP, Telnet, SMTP, NCP, AFP

5 - Session NWLink, NBT, Named Pipes, NetBIOS, ASP, ADSP, ZIP, PAP, DLC

4 - Transport TCP, UDP, SPX, NetBEUI, ATP, NBP, AEP, RTMP

3 - Network IP, IPX, NWLink, NetBEUI, DDP

2 - Data Link Ethernet, Token Ring, PPP, ODI, NDIS, LocalTalk, TokenTalk, EtherTalk

1 - Physical RS-232, ISDN, 10BASE-T, electricity, radio

Review - Functions of the OSI LayersReview - Functions of the OSI Layers

Layer 1 (physical): Transmission of bitsLayer 1 (physical): Transmission of bits

Layer 2 (data link): Transmission of frames on Layer 2 (data link): Transmission of frames on one given linkone given link

Layer 3 (network): Routing of packets through Layer 3 (network): Routing of packets through the networkthe network

Layer 4 (transport): End-to-end delivery of Layer 4 (transport): End-to-end delivery of messagesmessages

Review - Functions of the OSI LayersReview - Functions of the OSI Layers

Layer 5 (session): Setup and management of end-to-Layer 5 (session): Setup and management of end-to-end conversation, synchronizationend conversation, synchronization

Layer 6 (presentation): Formatting, encryption, and Layer 6 (presentation): Formatting, encryption, and compression of datacompression of data

Layer 7 (application): user applicationsLayer 7 (application): user applications

Introduction to TCP/IP

What is TCP/IPWhat is TCP/IP

Transmission Control Protocol/Internet Protocol

TCP/IP refers to an entire suite of networking protocols, developed for use on the Internet

TCP and IP are certainly two of the most important

TCP/IP Protocol SuiteTCP/IP Protocol Suite

Advanced Research Project Agency (ARPA) of DoD Advanced Research Project Agency (ARPA) of DoD sponsored the development of ARPANET in 1970s. sponsored the development of ARPANET in 1970s.

TCP/IP has been adopted as the ARPANET protocol TCP/IP has been adopted as the ARPANET protocol suitesuite

TCP/IP became popular by the inclusion of this TCP/IP became popular by the inclusion of this protocol in BSD Unix system (a version of Unix protocol in BSD Unix system (a version of Unix developed by University of California @ Berkley)developed by University of California @ Berkley)

TCP/IP (cont.)TCP/IP (cont.)Transport Layer-TCP (Transmission Control Protocol)Transport Layer-TCP (Transmission Control Protocol)

•Provides fully reliable, connection-oriented serviceProvides fully reliable, connection-oriented service

•Byte-stream transmissionByte-stream transmission

Network Layer- IP (Internet Protocol)Network Layer- IP (Internet Protocol)

•IP provides datagram service (used in packet IP provides datagram service (used in packet switching)switching)

•It is connectionless unreliable serviceIt is connectionless unreliable service

•IP handles routingIP handles routing

TCP/IP CharacteristicsTCP/IP Characteristics

TCP/IP provides the services necessary to interconnect computers and to interconnect networks, creating the Internet

Independence from underlying network topology, physical network hardware, and OS

Unique IP Address

Universal connectivity throughout the network

Standardize high-level protocols

TCP/IP Protocol Architecture ModelTCP/IP Protocol Architecture Model

Application

TCP

Application

TCP

IP

NetworkAccess

IP

NetworkAccess

Physical Physical

Source Transmitter

Trans-MissionSystem

Receiver Destination

Source System Destination System

Network

A ComparisonA Comparison

Application

Session

Transport

Network

Physical

Presentation

Data Link

IP

NetworkAccess

Physical

Application

Transport

Hardware

Firmware

Software

UserSpace

OperatingSystem

TCP/IP Network Structure

hardwareinterface

TCP

IP

UDP

userprocessor

userprocessor OSI Layer 5-7

OSI Layer 4

OSI Layer 3

OSI Layer 1-2

ARPICMP RARP

UDP: User Datagram Protocol ICMP: Internet Control Message Protocol

IP: Internet Protocol

ARP: Address Resolution Protocol

RARP: Reverse ARP

Port Number

userproc.A

userproc.B

userproc.C

userproc.D

userproc.E

userproc.F

userproc.G

IDPIP

SPPPEXTCPUDP

Ethernetinterface

Ethernetinterface

Ethernetinterface

Ethernetinterface

TCP/IPprotocol suite

XNSprotocol suite

Ethernet cable 2

Ethernet cable 1

Port AssignmentsPort Assignments

Servers are known by ports numberFTP 20, TELNET 23, SMTP 25, HTTP 80

Port numbers are generally allocated by0 --not used

1-255 --Reserved ports for well-known services

256-1023 --Other reserved ports

1024-65535 --user-defined server ports

Unix stores general used ports in /etc/services directory

Applications

Transport

Network access

1 2 3 4( ) ( ) ( ) ( )

Hierarchical Addressing SchemeHierarchical Addressing Scheme

Connection defines the communication link between two processes

data

dataUDPheader

dataUDPheader

IPheader

UDPheader dataIP

headerEthernettrailer

Ethernetheader

16-bit UDP source port #16-bit UDP dest. port #

protocol = UDPinternet 32-bit source addrinternet 32-bit dest. addr

frame type = IPEthernet 48-bit source addrEthernet 48-bit dest. addr

Ethernet frame

UDP = User Datagram Protocol

TCP/IP InternetworkingTCP/IP Internetworking

TokenRing

FDDI

Private Netsand Internet

Router

LAN and DevicesLAN and Devices

LANs are designed to :

Operate within a limited geographic area Allow multi-access to high-bandwidth media Control the network privately under local administration Provide full-time connectivity to local services Connect physically adjacent devices

ATMSwitch

EthernetSwitchBridge Hub Router

Wide-Area Networks and DevicesWide-Area Networks and DevicesWANs are designed to :

Operate over geography of telecommunications carriers Allow access over serial interfaces operating at lower speeds Control the network subject to regulated public services Provide full-time and part-time connectivity Connect devices separated over wide, even global areas

ATMSwitchRouter

ModemCSU/DSUTA/NT1

S

X.25 orFrame Relay

Switch

Comm.Server Multiplexor

statmux

TCP/IP Architectural LayersTCP/IP Architectural Layers

ApplicationApplication

TransportTransport

InternetInternet

NetworkNetwork

PhysicalPhysical

NetworkApplications

End-to-endServices

Routing

Transmission

Network Interface

Layer HardwareLayer Hardware

Routers, PAD’s, X.25 switches

Bridges, LAN switches, ATM switches and terminal servers

Transceivers, repeaters, hubs, FDDI concentrators, modems, terminal adapters, DSU’s, CSU’s, MUX and NIC’s

ApplicationApplication

TransportTransport

InternetInternet

NetworkNetwork

PhysicalPhysical

TransceiversTransceivers

•A transceiver connects a network device to the network cable

•A transceiver listens to the bus to determine if it is being used by another station

•A transceiver determines if the bus is being used by another station

•A transceiver alerts the connected device when there is a collision during transmission

•A transceiver may have DIP switches for controlling the exchange of SQE or heartbeat signals with the directly connected device.

TransceiversTransceivers

Attachment Interface Unit (AUI): The portion of the Ethernet standard that specifies how a cable is to be connected to an Ethernet card. AUI specifies a coaxial cable connected to a transceiver that plugs into a 15-pin socket on the network interface card (NIC).

RepeatersRepeaters

•A repeater is used to connect two segments of the same network

•A repeater receives a signal from one segment, cleans and boosts the signal and sends it to the other segment

•A repeater is responsible for ensuring that a collision is propagated to all attached segments

•A repeater may be used to extend the network beyond the limitations of the network’s architecture by increasing segment length

•Cannot add an infinite number of repeaters as this would adversely affect collision propagation.

HubsHubs

•A hub often attaches at least four nodes and many hubs include connectors for linking to other hubs

•A hub provides connectivity by passing incoming signals to connected nodes

•Hubs may be cascaded together to allow small workgroups with low-intensity applications to be formed

•Hubs typically have LEDs to indicate the status of each port

•Hubs may do partitioning to allow isolation of a non-functioning node

•Hubs allow connection to different physical media.

NIC’sNIC’s

•A NIC is an internetworking device that is a component part of a much larger host

•NICs are used to connect the systems to the network

•NICs will be different for each type of host system and type of network topology (and for each bus type)

•Remote access is achieved through remote access to the host system

•When installing a NIC it is important to consider the network topology, cabling and electrical considerations to avoid network disruption.

TCP/IP Networking SoftwareTCP/IP Networking Software

TCP/IP protocol suites define a set of universal communication services

Services can be implemented in a standardized manner in the networking software, normally bundled with OS

TCP/IP Comm. Software

InternetTCP/IP Comm. Software

TCP/IP and InternetTCP/IP and Internet

1957 USSR sputnik, USA established ARPA

1969 ARPA funded ARPANET

1971 Network with 15 nodes

1974 Cerf/Kahn Protocol

1973 Ethernet (Ph.D Dissertation Bob Metcalfe)

1982/83 TCP/IP as a core protocol

1983 4.2 BSD Unix with TCP/IP from UCB (univ. of California @ Berkley)

TCP/IP StandardsTCP/IP Standards

TCP/IP Standards

The standards for TCP/IP are published in a series of documents called Request for Comments

(RFCs). RFCs describe the internal workings of the Internet. Some RFCs describe network services or

protocols and their implementations, whereas others summarize policies. TCP/IP standards are always

published as RFCs, although not all RFCs specify standards.

TCP/IP standards are not developed by a committee, but rather by consensus. Anyone can submit a document for publication as an RFC. Documents are reviewed by a technical expert, a task force, or the RFC editor, and then assigned a status. The status specifies whether a document is being considered as a standa

Internet Technical BodiesInternet Technical Bodies

ISOC - Internet Society. Professional society to promote the use of Internet for research and scholar communication and collaboration

IAB - Internet Architecture Board. Technical oversight

and coordination, falls under ISOC

IETF - Internet Engineering Task force. Current protocols and specifications for standardization. Meets 3 times a year, organized in working groups

IRTF - Internet Research Task force. Research oriented for future.

Internet AdministrationsInternet AdministrationsDDN - the USA Defense Data Network is the government organization that has overall responsibilty for administrating the Internet

DDN NIC (Network Information Center)assigns unique names and addresses

collects and distributes information about TCP/IP protocols

IANA Internet Assigned Numbers Authorityassigns value for network parameters, name of services, identifiers

NOC (Network Operations Center)manages communication links

Internet Standards Internet Standards

RFC

Internet Draft

Proposed Standard

Draft Standard

Official Standard

Circulated technical documents call Request For Comments

Revision RFC

protocol specifications should be stable technically and should have no bugs or holes.

at least 2 independent and interoperable implementations that test all specification funcions

have had significant field use and clear community interest in production use.

Protocol Status LevelsProtocol Status Levels

TCP/IP protocols have one of the following five status levels:

Required

Recommended

Elective

Limited use

Not recommended

Internet documentsInternet documentsRFC

number with RFC XXXX, more than 1700 now

updated RFCs are published with new RFC numbers

not all RFCs describe protocols. not all RFCs are used

ftp://ds.internic.net

STD (STandDard)official Internet standard

FYI (For Your Information)RFC series that do not contain protocol specifications

Sample DocumentsSample DocumentsRFC

2030 I D. Mills, "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI", 10/30/1996. (Pages=18) (Format=.txt) (Obsoletes RFC1769)

1879 I B. Manning, "Class A Subnet Experiment Results and Recommendations", 01/15/1996. (Pages=6) (Format=.txt)

FYI0023 Guide to Network Resource Tool. EARN Staff. March 1994. (Format:TXT=235112 bytes) (Also RFC1580)

0028 Netiquette Guidelines. S. Hambridge. October 1995. (Format: TXT=46185 bytes) (Also RFC1855)

Wireless LANsWireless LANs

Wireless LANsWireless LANs

•Why RF?

•IEEE 802.11 activities

•RF Technologies - 2.4GHz/5GHz

•Wireless LAN Topology Basics

•Customers WLAN requirements

•Building-to-Building Bridges

IEEE802.11IEEE802.11IEEE 802.11 or WiFi denotes a set of Wireless LAN standards developed by working group 11 of IEEE 802. The current IEEE standard is 802.11b. Network cards for this standard are becoming a commodity (as of Sept 2001), thus for the first time wireless computer networks, previously only a niche market, are becoming practical. Now with the proliferation of cable modems and DSL, there is an ever-increasing market of people who wish to establish small networks in their homes to share their high speed Internet connection. There are also efforts by volunteer groups to establish wireless community networks to provide free wireless connectivity to the public.

IEEE 802.11IEEE 802.11

The IEEE 802.11 standard defines the protocol for two types of networks; Ad-hoc and client/server networks. An Ad-hocnetwork is a simple network where communications are established between multiple stations in a given coverage areawithout the use of an access point or server. The standard specifies the etiquette that each station must observe so thatthey all have fair access to the wireless media. It provides methods for arbitrating requests to use the media to ensure thatthroughput is maximized for all of the users in the base service set.

IEEE802.11IEEE802.11

The IEEE802 standards committee formed the 802.11 Wireless Local Area Networks Standards Working Group in 1990.The 802.11-working group took on the task of developing a global standard for radio equipment and networks operatingin the 2.4GHz unlicensed frequency band for data rates of 1 and 2Mbps.

The standard does not specify technology or implementation but simply specifications for the physical layer and Media Access Control (MAC) layer. The standard allows for manufacturers of wireless LAN radio equipment to build interoperable network equipment.

IEEE802.11IEEE802.11

The membership of the committee consists of individuals from a number of companies and universities, who research, manufacture, install and use products in wireless LAN network applications. Manufacturers of semiconductors, computers, radio equipment, WLAN systems solution providers, University research labs and end-users make up the core group. Companies globally represent the working group from the United States, Canada, Europe, Israel and the Pacific Rim.

IEEE 802.11 Standard ActivitiesIEEE 802.11 Standard Activities•802.11a - 5GHz- Ratified in 1999

•802.11b - 11Mb 2.4GHz- ratified in 1999

•802.11d - Additional regulatory domains

•802.11e - Quality of Service

•802.11f - Inter-Access Point Protocol (IAPP)

•802.11g - Higher Datarate (>20mBps) 2.4GHz

•802.11h - Dynamic Frequency Selection and Transmit Power Control mechanisms

•802.11i - Authentication and security

IEEE802.11IEEE802.11

Physical Layer Implementation ChoicesThe Physical Layer in any network defines the modulation and signaling characteristics for the transmission of data. At the physical layer, two RF transmission methods and one infrared are defined. Operation of the WLAN in unlicensed RF bands requires the of spread spectrum modulation to meet the requirements for operation in most countries. The RF transmission techniques in the standard are Frequency Hopping (FH) and Direct Sequence (DS) spread spectrum.

IEEE802.11IEEE802.11Both architectures are defined for operation in the 2.4GHz (ISM) frequency band. Each occupies 83Mhz of bandwidth ranging from 2.400 GHz to 2.483 GHz.

Differential BPSK (DBPSK) and DQPSK is the modulation for the direct sequence.

Frequency hopping uses 2-4 level Gaussian FSK as the modulation signaling method.

The radiated RF power at the antenna is set by the rules governed by FCC part 15 for operation in the United States.

Antenna gain is also limited to 6 dBi maximum.

Range of a Radio LinkRange of a Radio Link

•The range of a RF radio link can be calculated by using the following items:

Transmitter power

Receiver sensitivity (at a given data rate)

Path loss in free space (increases as Frequency increases)

Antenna system gain (includes cable losses)

IEEE802.11IEEE802.11 Operating Frequency Ranges

Lower Limit Upper Limit Regulatory Range Geography2.402 GHz 2.480 GHz 2.400-2.4835 GHz North America*2.402 GHz 2.480 GHz 2.400-2.4835 GHz Europe*2.473 GHz 2.495 GHz 2.471-2.497 GHz Japan*2.447 GHz 2.473 GHz 2.445-2.475 GHz Spain*2.448 GHz 2.482 GHz 2.4465-2.4835 GHz France*

The radiated power is limited to 1W for the United States, 10mW per 1Mhz in Europe and 10mW for Japan. There are different frequencies approved for use in Japan, United States and Europe and any WLAN product must meet the requirements for the country in which it is sold.

IEEE802.11IEEE802.11The MAC LayerThe MAC layer specification for 802.11 has similarities to the 802.3 Ethernet wired line standard. The protocol for 802.11 uses a protocol scheme know as carrier-sense, multiple access, collision avoidance (CSMA/CA). This protocol avoids collisions instead of detecting a collision like the algorithm used in 802.3. It is difficult to detect collisions in a RF transmission network and it is for this reason that collision avoidance is used. The MAC layer operates together with the physical layer by sampling the energy over the medium transmitting data.

IEEE802.11IEEE802.11

The physical layer uses a clear channel assessment (CCA) algorithm to determine if the channel is clear. This is accomplished by measuring the RF energy at the antenna and determining the strength of the received signal. This measured signal is commonly known as RSSI. If the received signal strength is below a specified threshold the channel is declared clear and the MAC layer is given the clear channel status for data transmission. If the RF energy is above the threshold, data transmissions are deferred in accordance with the protocol rules. The standard provides another option for CCA that can be alone or with the RSSI measurement. Carrier sense can be used to determine if the channel is available.

IEEE802.11IEEE802.11802.11b has a range of about 150 feet (50 meters) and a theoretical maximum throughput of 11 Megabits per second (Mbps); in practice the maximum throughput is about 7 Mbps. Particularly thick walls, and large amounts of concrete can decrease the range drastically. 802.11 runs in the 2.4 GHz spectrum and uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as its media access method. With high-gain external antennas, the protocol can also be used in fixed point-to-point scenarios (5 miles (8 kilometers), reports of up to 50-75 miles (80-120 kilometers) line of sight) to replace costly leased lines, or in place of very cumbersome microwave communications gear. Current cards can operate at 11 Mbps, but will scale back to 5.5, then 2, then 1, if signal strength is an issue. The next 802.11 protocol, 802.11a, is now complete. It offers raw throughput of up to 54Mbps and operates in 5GHz frequency bands. 802.11a may be less useful than 802.11b for home users, as internal walls absorb the higher frequency 11a signals more than the 2.4GHz signals of 11b.

Comparing Radio specsComparing Radio specs5Ghz vs. 2.4GHz5Ghz vs. 2.4GHz

2.4Ghz (Cisco 350) 5Ghz (802.11a)

TX Power 20dBm (11Mbps) (100mW)

12dBm (6Mbps) (16mW)

RX Sens. -85dBm (11Mbps) -79dBm (6Mbps)

Results= 14dBm less for 5Ghz than 2.4 @similar rates.

14dB less > 50% range reduction

5GHz vs.. 2.4GHz5GHz vs.. 2.4GHz

50'

150'

2.4GHz 5GHz1 32

4 5

67

2.4GHz Range

•Range of 5GHz is MUCH MUCH less. About 30%.

•Overall investment of infrastructure is much higher (more APs)

Shared Local Area Network (LAN)Shared Local Area Network (LAN)

ServerEthernet

Shared Hub

Internet

Wireless Local Area Network Wireless Local Area Network (WLAN)(WLAN)

Access Point

ServerEthernet

Internet

Remember: An Access Point is a SHARED device and has similar

performance to a SHARED Ethernet HUB.

Typical Single Cell ConfigurationTypical Single Cell Configuration

LANBackbone

WirelessClients

WirelessCell

WirelessCell

Typical Multi-cell ConfigurationTypical Multi-cell Configuration

Access PointAccess Point

LAN BackboneLAN Backbone

WirelessCell

WirelessCell

Channel 1Channel 1 Channel 6Channel 6

WirelessClients

WirelessClients

WirelessCell

WirelessCell

Typical Multi-cell ConfigurationTypical Multi-cell Configuration

Access PointAccess Point

LAN BackboneLAN Backbone

WirelessCell

WirelessCell

Channel 1Channel 1 Channel 6Channel 6

WirelessClients

WirelessClients

WirelessCell

WirelessCell

Wireless RepeaterWireless Repeater

Channel 1Channel 1

Channel 1Channel 1

AccessPoint

AccessPoint

WirelessClients

WirelessClients

LAN BackboneLAN Backbone

WirelessRepeaterCell

WirelessRepeaterCell

Standard Office ApplicationStandard Office Application

•Use three non-overlapping channels

•Rotate channels to fill in

•Reduce Cell size

•Reduce Antenna gain or Transmitter power to create smaller cell size

•Enable Load Balancing

Mixed Antenna ExampleMixed Antenna ExampleMaximum CoverageAutorate Negotiation

Wireless for StudentsDiPole Indoor, Patch Outdoor

Class 1 Class 3

Hallway

1000’

850’

Class 4Class 2

Class 8 Class 10 Class 11Class 9

Building Courtyard

1000’

Channel 1Channel 1

Channel 1Channel 1

Channel 11

Channel 11

Channel 6Channel 6

Channel 6Channel 6

END Class 2END Class 2