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UNIT I - HIGH SPEED NETWORKS

Sl.No WEEK/ DATE TOPICS TO BE COVERED PAGE IN TEXTBOOK/REFERENCE

REMARKS

1. Introduction to HSN

2. Frame relay networks R1(82-88) ASSIGNMENT NO:1

3. Asynchronous transfer mode R1(91-92)

4. ATM protocol architecture andATM logical connection

R1(92-98)

5. ATM cell,ATM service categories ,

AAL

R1(98-117)

6. High speed LANs - Fast ethernet,gigabit Ethernet, Fiber channel

R1(121-144)

7. Wireless LANs– Applications&

Requirements

R1(144-147)

8. Architecture of 802.11 R1(147-151) SEMINAR NO:1

TEXT BOOK

1. Jean warland and Pravin Wadaja, “HIGH PERFORMANCE COMMUNICATION NETWORKS”, 2nd

Edition, Jean Harcourt Asia Pvt. Ltd., 2001.

REFERENCES

1. William Stallings, “High Speed Networks and Internet”, 2nd Edition, Pearson Education,2002.

2. Irvan Pepelnjk, Jim Guichard and Jeff Apcar, “Mpls and Vpn Architecture”,

Volume 1 and 2, Cisco Press, 2003



1.INTRODUCTION TO HIGH

SPEED NETWORKS



Introduction - Taxonomy

Circuit -Switched Packet -Switched

Virtual CircuitDatagram

Communication

Networks

TDMFDM

Frame Relay

ATM

The Internet

(TCP/IP)



Circuit-Switching

• Historically – long-haul telecom networksdesigned for voice and/or constant bit rateapplications

• Network resources dedicated to one “call”after circuit setup

• Shortcomings when used for data:

– Inefficient (high idle time) for “bursty” sources – Constant data rate not appropriate for varied

endpoint capabilities



Packet-Switching

• Historically – network technology designed for generaldata communications

• Basic technology is the same as in the 1970s

• One of the few effective technologies for long distancedata communications in use today

• Frame relay and ATM are variants of packet-switching(using virtual circuits)

•Advantages: – flexible, resource sharing, robust, responsive

• Disadvantages: – Time delays in distributed network, overhead penalties – Need for routing and congestion control



Packet-Switching

• Data transmitted in short blocks, or packets

• Packet length typically < 1000 octets

• Each packet contains user data plus control

info (routing)

• Store and forward



Use of Packets



A Simple Switching Network



Advantages over Circuit-Switching

• Greater line efficiency (many packets can

go over shared link)

• Data rate conversions

• Non-blocking (e.g. no “busy signals”) under

heavy traffic (but increased delays)

• Each packet can be handled based on a

priority scheme



Disadvantages relative to Circuit-

Switching• Packets incur delay with every node they pass through

Q * (d prop + dtrans + dqueue + d proc)

• Jitter: variation in end-to-end packet delay• Data overhead in every packet for routing

information, etc

• More processing overhead for every packetat every node traversed… circuit switchinghas little/no processing at each node



Switching Technique• Large are messages broken up into smaller

“chunks,” generically called packets

• Store and forward packet handling in core

•Two approaches to switching data: – Datagram

• Each packet sent independently of the others

• No call setup

• More reliable (can route around failed nodes or congestion)

– Virtual circuit

• Fixed route established before any packets sent

• No need for routing decision for each packet at each node



Packet Switching: Datagram

Approach

Advantages:

• No call setup•Flexible routes•Reliability



Packet Switching: Virtual-Circuit

Approach

Advantages:

• Network services•sequencing•error control

•Performance



Routing

• Key function of any packet-switchednetwork: forwarding packets to adestination

• Adaptive routing, routes are adjusted basedon: – Node/trunk failure

– Congestion• Nodes (routers/switches) must exchange

information about the state of the network



The Use of Virtual Circuits

Virtual end-to-end

circuits



X.25• First commercial packet switched network interfacestandard

• Motivates discussion of frame relay and ATMdesign

• X.25 defines 3 levels of functionalityL1 - Physical level (X.21, EIA-232, etc.): physical

connection of a station to the link

L2 - Link/frame level (LAPB, a subset of HDLC): logical,reliable transfer of data over the physical link

L3 - Packet level: network layer, provides virtual circuitservice to support logical connections between twosubscriber stations (multiplexing)



User Data and X.25 Protocol Control

Information

•Virtual circuit id#• Sequence #s

3 bytes ≤ 128 bytes

• Flags, address, control, FCS• Link layer framing• Reliable physical transfer



X.25 Features• Call control packets

– set up and tear down virtual circuits

– use same channel and VC as data

packets• Multiplexing of VCs at layer 3

• Layers 3 (packet) and 2 (frame) both

include extensive flow control anderror control mechanisms

ProcessingProcessing

OverheadOverhead(t(t

proc proc))

at eachat each

node!node!

RESULT:RESULT:64kbps64kbps

Max. dataMax. data

raterate



2.FRAME RELAY NETWORKS



Frame Relay Networks

• Most widely deployed WAN link-layer protocol inuse today

• Designed to eliminate much of the processing

overhead in X.25

• Designed to support “bandwidth on demand” for

modern, bursty applications

• Throughput is an order of magnitude higher than

X.25• ITU-T Recommendation I.233 indicates effective

rates of frame relay of up to 2 Mbps, but current

practice is much higher (up to T-3 equivalent, or

44.376 Mbps)



Frame Relay Networks

Important Improvement over X.25:• Call control signaling is on a separate logical

connection from user data

• Multiplexing/switching of logical connections is at

layer 2 (not layer 3)

• No hop-by-hop flow control and error control;

responsibility of higher layers

• Frames sizes can vary (up to 9000 bytes),supporting all current LAN frame sizes

• Direct support for TCP/IP packets, since no

network layer redundancy



Comparison of X.25 and Frame Relay

Protocol Stacks



Virtual Circuits and Frame Relay

Virtual Connections

X.25 Packet-Switching

network

(a) X.25 Packet Switching

(b) Frame Relay

Frame Relay network



Frame Relay Architecture

• X.25 has 3 layers: physical, link, network

• Frame Relay has 2 layers: physical and data

link (or LAPF)

• LAPF core: minimal data link control

– Preservation of order for frames

– Small probability of frame loss



LAPF Core

• Frame delimiting, alignment and

transparency

• Frame multiplexing/demultiplexing

• Inspection of frame for length constraints

• Detection of transmission errors

• Congestion control



LAPF-core Formats



User Data Transfer Frame

• No connection control fields, which arenormally used for: – Identifying frame type (data or control)

– Sequence numbers, used for error/flow control

• Implication: – Connection setup/teardown carried on separate

channel

– No flow and error control, must be handled byhigher layer in protocol stack



Frame Relay Call Control

• Frame Relay Call Control – Details of call control depend on the context of

its use – Assumes FR over ISDN

– Generally simpler for point-to-point use

• Data transfer involves:

– Establish logical connection and assign a uniqueDLCI

– Exchange data frames

– Release logical connection



Frame Relay Call Control

4 message types needed

• SETUP…request link establishment

• CONNECT…reply to SETUP withconnection accepted

• RELEASE…request to clear (tear down) a

connection• RELEASE COMPLETE… reply to SETUP

with connection denied, or response to

RELEASE



3.ASYNCHRONOUS TRANSFER

MODE(ATM)



Introduction

• ATM Protocol Architecture

• Logical connections

• ATM cell structure

• Service levels/categories

•ATM Adaptation Layer (AAL)



Introduction•

ATM evolved from B-ISDN development efforts – Frame Relay: high-speed WAN (1.5+ Mbps)

– ATM: very high speed WAN (155 Mbps and 622Mbps)

• ATM, like Frame Relay, was built on the assumptionthat the underlying physical media was reliable andflexible – minimal error and flow control capabilities

– even more streamlined, therefore faster, than Frame Relay

• Specifications developed by ITU-T and ATM Forum



ATM Protocol Architecture

• Fixed-size packets called cells – “cell switching” like packet switching

• 2 primary protocol layers relate to ATMfunctions: – Common layer providing packet transfers,

logical connections (ATM)

– Service dependent ATM adaptation layer (AAL)• AAL maps other protocols to ATM

– like IP (AAL5)



Protocol Model has 3 planes

• User – provides for user information

transfer and associated controls (flow

control, congestion control)• Control – performs call control and

connection control functions (signaling)

• Management – provides plane managementand layer management and coordination

functions



ATM Protocol Reference Model

Various data rates (155.52 Mbps,622.08 Mbps) over variousphysical media types (Fiber Optic,SONET, UTP, etc.)

Framing, cell structure

& Logical Connections

Map data tothe ATM cellstructure



User Plane Layers

AALAAL

ATMATM

Userinformation

Userinformation

AALAAL

ATMATM

PHYPHYPHYPHY

ATMATM

PHYPHY

ATMATM

PHYPHY

……

End systemEnd system End systemEnd system Network Network



User Plane LayersUser

informationUser

information



Logical Connections

• VCC (Virtual Channel Connection): a

logical connection analogous to a virtualcircuit in X.25, or Frame Relay data link connection – full-duplex flow between end users

– user-network control signaling

– network-network management/routing

• VPC (Virtual Path Connection): a bundle of

VCCs with the same end points (notnecessarily same end-users)

– and switched along the same path



ATM Connection Relationships

Virtual ChannelVirtual Channel: basic logical communications channel: basic logical communications channelVirtual PathVirtual Path: groups of “common” virtual channels: groups of “common” virtual channelsPhysical Transmission PathPhysical Transmission Path: physical communications link: physical communications link



VCC (logical connection) Uses• Exchange between end users

– user data

– control signaling (more later )

• Exchange between an end user and a network entity

– control signaling (more later )

• Exchange between 2 network entities – traffic management

– routing functions



Advantages of Virtual Paths

• Simplified network architecture – allows separation of functionality into into individual logical connections and related

groups of logical connections

• Increased network performance and reliability – network consists of fewer aggregated entities

• Reduced processing and short connection setup

time – complex setup tasks are in virtual paths, simplifies setup

of new virtual channels over existing virtual path• Enhanced network services – supports user-specified

closed groups/networks of VC bundles

Vi t l P th/Vi t l Ch l



Virtual Path/Virtual Channel

Terminology

Virtual ChannelVirtual Channel (VC) A generic term used to(VC) A generic term used todescribe unidirectional transportdescribe unidirectional transportof cells associated by a commonof cells associated by a commonunique identifierunique identifier

Virtual Channel IdentifierVirtual Channel Identifier (VCI) A unique numerical tag for a(VCI) A unique numerical tag for aparticular VC linkparticular VC link

Virtual Channel LinkVirtual Channel Link A means of unidirectional transportA means of unidirectional transportof cells between the point where aof cells between the point where aVCI is assigned and where it isVCI is assigned and where it is

translated or terminatedtranslated or terminatedVirtual Channel ConnectionVirtual Channel Connection (VCC) A concatenation of VC links(VCC) A concatenation of VC links

that extends between twothat extends between twoconnected ATM end-pointsconnected ATM end-points

Vi t l P th/Vi t l Ch l



Virtual Path/Virtual Channel

TerminologyVirtual PathVirtual Path (VP) A generic term which describes(VP) A generic term which describes

unidirectional transfer of cells thatunidirectional transfer of cells thatare associated with a common uniqueare associated with a common uniqueidentifieridentifier

Virtual Path IdentifierVirtual Path Identifier (VPI) Identifies a particular VP(VPI) Identifies a particular VP

Virtual Path LinkVirtual Path Link A group of VC links identified by aA group of VC links identified by acommon identifier between the pointcommon identifier between the pointwhere the identifier (VPI) is assignedwhere the identifier (VPI) is assignedand where it is translated orand where it is translated orterminatedterminated

Virtual Path ConnectionVirtual Path Connection (VPC) A concatenation of VP links that(VPC) A concatenation of VP links thatextends between ATM end-pointsextends between ATM end-pointswhere the VCIs are assigned andwhere the VCIs are assigned andwhere they are translated orwhere they are translated or

terminatedterminated



ATM Connection Relationships



VPC/VCC Characteristics

• Quality of Service (QoS)• Switched and semi-permanent virtual

channel connections

• Cell sequence integrity• Traffic parameter negotiation and usage

monitoring

– average rate, peak rate, burstiness, peak duration, etc.

• (VPC only) virtual channel identifier

restriction within a VPC



Call Establishment with Virtual Paths



ATM Signaling

X

X

X

X

X

X

X

X

X

Private

UNI

Public

UNI

NNI

Private

NNI

Private ATM

network

Public

UNIB-ICI

P u b l i

c U N I

Public ATM

network A

Public ATM

network B

Q-2931Q-2931

Q-2931Q-2931

PNNIPNNI

PNNIPNNI

PNNIPNNI



Control Signaling

• A mechanism to establish and release VPCsand VCCs (per ITU-T Rec. I.150)

• 4 methods for VCCs: – Semi-permanent VCC: no control signaling required –

Meta-signaling channel: permanent, low data ratechannel for setting up signaling channels – User-to-network signaling virtual channel: set up

between user and network – User-to-user signaling virtual channel: set up

between users within a VPC, allowing users to setup and tear down VCCs, without network intervention



Control Signaling• 3 methods for VPCs

– Semi-permanent: no control signaling required

– Customer controlled: customer uses a signaling

VCC to request VPC from the network

– Network controlled: Network establishes VPC for

its own control and signaling use



ATM Cells

• Fixed size

– 5-octet header

– 48-octet information field

• Small cells may reduce queuing delay for

high-priority cells (essential for low delay)

• Fixed size facilitates more efficientswitching in hardware (essential for very

high data rates)

ATM C ll F t



ATM Cell Format



Header Format

• Generic flow control (more ->)

• Virtual path identifier (VPI)

• Virtual channel identifier (VCI)

• Payload type (3 bits: identifies cell as user

data or network management cell, presence

of congestion, SDU type)

• Cell loss priority (0: high; 1: low)

• Header error control (more ->)



Generic Flow Control (GFC)• Control traffic flow at user to network interface (UNI)

to alleviate short term overload

• Two sets of procedures

– Uncontrolled transmission

– Controlled transmission

• Every connection either subject to flow control or not

• Subject to flow control

– May be one group (A) default – May be two groups (A and B)

• Flow control is from subscriber to network

– Controlled by network side



Single Group of Connections (1)

• Terminal equipment (TE) initializes twovariables

– TRANSMIT flag to 1

– GO_CNTR (credit counter) to 0• If TRANSMIT=1 cells on uncontrolled

connection may be sent any time

• If TRANSMIT=0 no cells may be sent (oncontrolled or uncontrolled connections)

• If HALT received, TRANSMIT set to 0 and

remains until NO HALT



Single Group of Connections (2)• If TRANSMIT=1 and no cell to transmit on

any uncontrolled connection: – If GO_CNTR>0, TE may send cell on controlled

connection

• Cell marked as being on controlled connection• GO_CNTR decremented

– If GO_CNTR=0, TE may not send on controlled

connection

• TE sets GO_CNTR to GO_VALUE upon

receiving SET signal

– Null signal has no effect

i l l ( ) i ld



Generic Flow Control (GFC) Field

Coding



Header Error Control

• 8-bit field - calculated based on the other 32 bits in the header – CRC based on x8 + x2 + x + 1 ->

generator is 100000111• error detection

• in some cases, error correction of single-biterrors in header

• 2 modes: – Error detection

– Error correction



HEC Operation at Receiver

Based on recognition of fact thatBased on recognition of fact that

bit errors occur in bursts. bit errors occur in bursts.



Effect of

Error in

Cell Header

I t f R d Bit E



Impact of Random Bit Errors on

HEC Performance



Use of HALT

• To limit effective data rate on ATM

• Should be cyclic

• To reduce data rate by half, HALT issued to

be in effect 50% of time

• Done on regular pattern over lifetime of

connection



ATM Service Categories• Real-time service

– Constant bit rate (CBR )

– Real-time variable bit rate (rt-VBR )

• Non-real-time service

– Non-real-time variable bit rate (nrt-VBR )

– Available bit rate (ABR )

– Unspecified bit rate (UBR )

– Guaranteed frame rate (GFR )



ATM SERVICE CATEGORIES

Class Description Example

CBR Constant Bit Rate T1 circuit

RT-VBR Real Time Variable Bit Rate Real-timevideoconferencing

NRT-VBR Non-real-time Variable BitRate

Multimedia email

ABR Available Bit Rate Browsing the Web

UBR Unspecified Bit Rate Background filetransfer



Real Time Services

• Amount of delay

• Variation of delay (jitter)



CBR

• Fixed data rate continuously available

• Tight upper bound on delay

• Uncompressed audio and video

– Video conferencing

– Interactive audio

– A/V distribution and retrieval

rt VBR



rt-VBR • Time sensitive application

– Tightly constrained delay and delay variation

• rt-VBR applications transmit at a rate that

varies with time

• e.g. compressed video

– Produces varying sized image frames

– Original (uncompressed) frame rate constant

– So compressed data rate varies

• Can statistically multiplex connections

nrt VBR



nrt-VBR • May be able to characterize expected traffic

flow

• Improve QoS in loss and delay

• End system specifies:

– Peak cell rate

– Sustainable or average rate

– Measure of how bursty traffic is

• e.g. Airline reservations, banking

transactions



UBR • May be additional capacity over and above

that used by CBR and VBR traffic

– Not all resources dedicated

– Bursty nature of VBR

• For application that can tolerate some cell

loss or variable delays

– e.g. TCP based traffic

• Cells forwarded on FIFO basis

• Best efforts service



ABR

• Application specifies peak cell rate (PCR)

and minimum cell rate (MCR)

• Resources allocated to give at least MCR • Spare capacity shared among all ARB

sources

• e.g. LAN interconnection

Guaranteed Frame Rate (GFR)



• Designed to support IP backbone sub networks

• Better service than UBR for frame based traffic

– Including IP and Ethernet• Optimize handling of frame based traffic passing

from LAN through router to ATM backbone – Used by enterprise, carrier and ISP networks

– Consolidation and extension of IP over WAN• ABR difficult to implement between routers over

ATM network

• GFR better alternative for traffic originating on

Ethernet – Network aware of frame/packet boundaries

– When congested, all cells from frame discarded

– Guaranteed minimum capacity

– Additional frames carried of not congested



ATM Bit Rate Service Levels



AAL



ATM Adaptation Layer (AAL)

• Support higher-level protocols and/or native

applications

– e.g., PCM voice, LAPF, IP• AAL Services

– Handle transmission errors

– Segmentation/reassembly (SAR ) – Handle lost and misinserted cell conditions

– Flow control and timing control

Voice ATM Adaptation Layers



A/D

s1 , s2 …

Digital voice samples

A/D

Video

… Compression

compressed

frames picture frames

Data

Bursty variable-length

packets

cells

cells

cells

Figure 9.3Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

AAL

AAL

AAL

p y



ATM ADAPTATION LAYER ATM ADAPTATION LAYER

(AAL)(AAL)

• Specifically, the AAL receives packets from upper-Specifically, the AAL receives packets from upper-

level protocols and breaks them into the 48-bytelevel protocols and breaks them into the 48-byte

segments that form the payload field of an ATMsegments that form the payload field of an ATM

cell.cell.

• AALprotocol model consists of a Segmentation andAALprotocol model consists of a Segmentation and

Reassembly (SAR) sublayer and ConvergenceReassembly (SAR) sublayer and Convergence

Sublayers (CPCS and SSCS).Sublayers (CPCS and SSCS).

• Convergence Sublayers further subdivided asConvergence Sublayers further subdivided as

Common part & Service SpecificCommon part & Service Specific

•The ATM Adaptation Layer (AAL) provides support for higher-layer

services such as signaling, circuit emulation, voice, and video.

AALs also support packet-based services, such as IP, LANs, and

Frame Relay



AAL Protocols• AAL layer has 2 sublayers:

– Convergence Sublayer (CS)• Supports specific applications/protocols using AAL

• Users attach via the Service Access Point (like a port

number)• Common part (CPCS) and application service-

specific part (SSCS)

– Segmentation and Reassembly Sublayer (SAR)

• Packages data from CS into ATM cells and unpacksat other end



AAL AAL



ATM Adaptation Layer (AAL)



AAL Types AAL Types



Applications of AAL and ATM

• Circuit emulation (e.g., T-1 synchronous

TDM circuits)

• VBR voice and video• General data services

• IP over ATM

• Multiprotocol encapsulation over ATM

(MPOA)

• LAN emulation (LANE)



AAL Protocol and Services

Basis for classification:Basis for classification:

• requirement for a timing relationship betweenrequirement for a timing relationship betweensource and destinationsource and destination

• requirement for a constant bit rate data flowrequirement for a constant bit rate data flow• connection or connectionless transferconnection or connectionless transfer



AAL Protocols and PDUs

AAL Protocol Descriptions



AAL Protocol Descriptions



Service Classes

and AAL typesClass A Class B Class C Class D

Timing

Relation

between

source &

destination

Required Not Required

Bit Rate Constant Variable

Connection

Mode

Connection Oriented Connectio

nless

AAL Types AAL1 AAL2 AAL 3/

4, 5

AAL 3/ 4



AAL Type 1

• Constant-bit-rate source

• SAR simply packs bits into cells and

unpacks them at destination• One-octet header contains 3-bit SC field to

provide an 8-cell frame structure

• No CS PDU structure is defined since CSsublayer primarily for clocking and

synchronization



AAL 1 AAL 1

• AAL1, a connection-oriented service, is suitable for handling constant bitAAL1, a connection-oriented service, is suitable for handling constant bitrate sources (CBR), such as voice and videoconferencing.rate sources (CBR), such as voice and videoconferencing.

• The sequence number field (SN) and sequence number protection (SNP)The sequence number field (SN) and sequence number protection (SNP)fields provide the information that the receiving AAL1 needs to verify thatfields provide the information that the receiving AAL1 needs to verify that

it has received the cells in the correct order. The rest of the payload field isit has received the cells in the correct order. The rest of the payload field isfilled with enough single bytes to equal 48 bytes.filled with enough single bytes to equal 48 bytes.

• AAL1 requires timing synchronization between the source and destinationAAL1 requires timing synchronization between the source and destinationand, for that reason, depends on a media that supports clocking, such asand, for that reason, depends on a media that supports clocking, such asSONET. The standards for supporting clock recovery are currently beingSONET. The standards for supporting clock recovery are currently beingdefined.defined.



AAL 1 AAL 1



Structured mode AAL1 SAR and CSStructured mode AAL1 SAR and CS



AAL Type 1

AAL 1



…Higher layer User data stream

Convergence

sublayer

SAR sublayer

ATM layer

CS PDUs

SAR PDUs

ATM Cells

47 47 47

1 47 1 47 1 47

H H H

5 48

H

5 48

H

5 48

H

b1 b2 b3

Figure 9.10

AAL 1

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies



AAL Type 2

• Intended for variable bit rate applications thatgenerate bursty data and demand low loss

• Originally, connectionless (AAL4) or connection

(AAL3) oriented, now combined into single format(AAL 3/4)• Provides comprehensive sequencing and error

control mechanisms

AAL Type 3/4 AAL Type 3/4

Intended for use with applications withIntended for use with applications withvariable bit-rate service on multiplevariable bit-rate service on multiplechannels (multiplexing), or low bit rate,channels (multiplexing), or low bit rate,short-frame trafficshort-frame traffic



AAL 2 AAL 2• Designed to support Variable Bit Rate (“Bandwidth on Demand”)Designed to support Variable Bit Rate (“Bandwidth on Demand”)• Provides for partial payloads to support low rate dataProvides for partial payloads to support low rate data

• Error protection over full PDUError protection over full PDU

• Simple flag to indicate position in messageSimple flag to indicate position in message

• Also AAL 2 was designed to multiplex a number of such low variableAlso AAL 2 was designed to multiplex a number of such low variable bit rate data streams on to a single ATM connection. bit rate data streams on to a single ATM connection.



AAL2 Operation AAL2 OperationCPS packet



CPS packetCPS packet• Channel identifier (CID)Channel identifier (CID): CPS can multiplex several streams onto a single: CPS can multiplex several streams onto a single

ATM connection. The CID identifies each channel. CID values areATM connection. The CID identifies each channel. CID values areallocated as follows: the 0 value is used as padding, and the 8 to 255 valuesallocated as follows: the 0 value is used as padding, and the 8 to 255 valuesare valid CID values used to identify channels.are valid CID values used to identify channels.

• Length indicator (LI) Length indicator (LI): Its value is one less than the number of bytes in the: Its value is one less than the number of bytes in the

CPSpacket payload. The default maximum length of the CPS-packetCPSpacket payload. The default maximum length of the CPS-packet payload is 45 bytes. payload is 45 bytes.

• Header error control (HEC) Header error control (HEC): It use the pattern: It use the pattern x x5 +5 + x x2 + 1. The receiver 2 + 1. The receiver uses the contents of the HEC to detect errors in the header.uses the contents of the HEC to detect errors in the header.

• User-to-user-indication (UUI)User-to-user-indication (UUI): used for transferring information between: used for transferring information betweenthe peer CPS users. The CPS transports this information transparently.the peer CPS users. The CPS transports this information transparently.



AAL2 Operation AAL2 Operation

• (CPS) PDU format(CPS) PDU format



CPS-PDUCPS-PDU

• Parity (P) Parity (P): A 1-bit field used to detect errors in the STF.: A 1-bit field used to detect errors in the STF.

• Sequence numbers (SN)Sequence numbers (SN): A 1-bit field used to number modulo 2 the: A 1-bit field used to number modulo 2 the

successive CPSPDUs.successive CPSPDUs.

• Offset field (OSF)Offset field (OSF): The CPS-PDU payload can carry CPS packets in a: The CPS-PDU payload can carry CPS packets in avariety of different arrangements. To extract the CPS-packets from thevariety of different arrangements. To extract the CPS-packets from theCPS-PDU payload, a 6-bitCPS-PDU payload, a 6-bit offset field (OSF)offset field (OSF) is used to indicate theis used to indicate thestart of a new CPS-packet in the CPS-PDU payload. Specifically, OSFstart of a new CPS-packet in the CPS-PDU payload. Specifically, OSF

gives the number of bytes between the end of the STF and the start of gives the number of bytes between the end of the STF and the start of the first CPS-packet in the CPS-PDU payload.the first CPS-packet in the CPS-PDU payload.




AAL2 Operationp



AAL 3/4 AAL 3/4

• AAL3/4 supports both connection-oriented and connectionless data. ItAAL3/4 supports both connection-oriented and connectionless data. It

was designed for network service providers and is closely aligned withwas designed for network service providers and is closely aligned with

Switched Multimegabit Data Service (SMDS). AAL3/4 is used toSwitched Multimegabit Data Service (SMDS). AAL3/4 is used to

transmit SMDS packets over an ATM network.transmit SMDS packets over an ATM network.

• Originally 2 separate AALs:Originally 2 separate AALs:

– – AAL3: Connection-oriented packet svcs (X.25)AAL3: Connection-oriented packet svcs (X.25)

– – AAL4: Connectionless svcs (IP)AAL4: Connectionless svcs (IP)

•• Eventually combined into a single type for all data serviceEventually combined into a single type for all data service



AAL3/4 CS PDU AAL3/4 CS PDU



AAL3/4 SAR PDU AAL3/4 SAR PDU



AAL3/4 Operation AAL3/4 Operation

AAL 3/4



AAL 3/4

AAL 3/4



Higher layer

Common part

convergencesublayer

SAR sublayer

ATM layer

Service specific

convergence

sublayer

Information

Assume null

TPAD

User message

Pad message to multiple

of 4 bytes. Add header and trailer.

Each SAR-PDU consists

of 2-byte header, 2-byte

trailer, and 44-byte payload.

H

4 4

2 44 2 2 44 2 2 44 2

…

…

Information

Figure 9.15

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies



AAL Type 5

• Streamlined transport for connection

oriented protocols

– Reduce protocol processing overhead – Reduce transmission overhead

– Ensure adaptability to existing transport

protocols

– primary function is segmentation and

reassembly of higher-level PDUs



AAL5AAL5• AAL 5 is used for the transfer of data. Due to its simplicity, it is the mostAAL 5 is used for the transfer of data. Due to its simplicity, it is the most

popular adaptation layer. popular adaptation layer.

• AAL5 is a Simple Efficient Adaptation Layer (SEAL). The Common PartAAL5 is a Simple Efficient Adaptation Layer (SEAL). The Common Part(CP) AAL5 supports Variable Bit Rate (VBR) traffic, both connection-(CP) AAL5 supports Variable Bit Rate (VBR) traffic, both connection-oriented and connectionless.oriented and connectionless.

• It is used to transfer most non-SMDS data, such as classical IP over ATMIt is used to transfer most non-SMDS data, such as classical IP over ATMand LAN Emulation (LANE).and LAN Emulation (LANE).

• Efficiency: Efficiency:

AAL3/4: 4 bytes per message + 4 bytes per cell => 44 User Data BytesAAL3/4: 4 bytes per message + 4 bytes per cell => 44 User Data Bytes/ Cell/ Cell

AAL5: 8 bytes per message => 48 User Data Bytes / Cell, 8%AAL5: 8 bytes per message => 48 User Data Bytes / Cell, 8%improvementimprovement



AAL5 CS PDU AAL5 CS PDU



AAL5 CS PDU AAL5 CS PDU • Padding (Pad) Padding (Pad): It can be between 0 and 47 bytes long, and is added so that: It can be between 0 and 47 bytes long, and is added so thatthe entire CPS-PDU including the padding and the remaining fields in thethe entire CPS-PDU including the padding and the remaining fields in the

trailer becomes an integer multiple of 48 bytes.trailer becomes an integer multiple of 48 bytes.

• CPS user-to-user indication (CPS-UU)CPS user-to-user indication (CPS-UU): A 1-byte field used to transfer : A 1-byte field used to transfer transparently CPS user-to-user information.transparently CPS user-to-user information.

• Common part indicator (CPI)Common part indicator (CPI): A 1-byte field to support future AAL 5: A 1-byte field to support future AAL 5functions.functions.

• Length Length: A 2-byte field used to indicate the length in bytes of the CPS-: A 2-byte field used to indicate the length in bytes of the CPS-

PDU payload .PDU payload .

• CRC-32CRC-32: This 4-byte field contains the FCS calculated by the transmitting: This 4-byte field contains the FCS calculated by the transmittingCPS over the entire contents of the CPS-PDU The pattern used is:CPS over the entire contents of the CPS-PDU The pattern used is: x x32 +32 + x x26 +26 + x x23 +23 + x x22 +22 + x x16 +16 + x x12 +12 + x x11 +11 + x x10 +10 + x x8 +8 + x x7 +7 + x x5 +5 + x x4 +4 + x x2 +2 + x x + 1.+ 1.



AAL5 SAR AAL5 SAR

• Simply breaks CS PDU into 48-byte chunks and passes them to ATMSimply breaks CS PDU into 48-byte chunks and passes them to ATM

Layer.Layer.

• No overhead bytes added. No overhead bytes added.




AAL5



AAL5

AAL 5



Higher layer

Common part

convergence

sublayer

SAR sublayer

ATM layer

PTI = 0

Service specific

convergence

sublayer Assume null

48

(1)

Information

TPAD

…

…

Information

48

(0)

48

(0)

PTI = 0PTI = 1

Figure 9.18

Leon-Garcia & Widjaja: Communication Networks

Copyright ©2000 The McGraw Hill Companies



S

A

R

C

S

AAL

ATM Adaptation Layer—AALPBX

ATMATM

Adaptation Layer Adaptation Layer

(AAL)(AAL)

ATM Layer ATM Layer

Physical Layer Physical Layer

AAL = CS + SAR • CS—cell tax

• SAR—cell <-> packet

AAL Cell Tax



1 Byte1 Byte

5 Byte5 ByteHeader Header

47 Byte47 Byte

PayloadPayload

1–481–48

BytesBytes

5 Byte5 ByteHeader Header

1–47 Byte1–47 Byte

PayloadPayload

5 Byte5 Byte

Header Header

44 Byte44 BytePayloadPayload

4 Bytes4 Bytes

5 Byte5 Byte

Header Header

48 Byte48 BytePayloadPayload

nono

taxtax

AAL-1 Cell Tax AAL-2 Cell Tax

AAL-3/4 Cell Tax AAL-5 Cell Tax

AAL Cell Tax



HIGH SPEED LAN

• Range of technologies

– Fast and Gigabit Ethernet

– Fibre Channel – High Speed Wireless LANs

Why High Speed LANs?



• Office LANs used to provide basic connectivity – Connecting PCs and terminals to mainframes and

midrange systems that ran corporate applications

– Providing workgroup connectivity at departmental level

– Traffic patterns light• Emphasis on file transfer and electronic mail

• Speed and power of PCs has risen – Graphics-intensive applications and GUIs

• MIS organizations recognize LANs as essential –

Began with client/server computing• Now dominant architecture in business environment

• Intranetworks

• Frequent transfer of large volumes of data

Applications Requiring High



Speed LANs• Centralized server farms

– User needs to draw huge amounts of data from multiple centralizedservers

– E.g. Color publishing

• Servers contain tens of gigabytes of image data

• Downloaded to imaging workstations

• Power workgroups

• Small number of cooperating users

– Draw massive data files across network

– E.g. Software development group testing new software version or computer-aided design (CAD) running simulations

• High-speed local backbone

– Processing demand grows

– LANs proliferate at site

– High-speed interconnection is necessary



Classical Ethernet

• Bus topology LAN

• 10 Mbps

• 2 problems: – A transmission from any station can be received

by all stations

– How to regulate transmission



Solution to First Problem

• Data transmitted in blocks called frames:

– User data

– Frame header containing unique address of destination station



Figure 6.1

/



CSMA/CD

Carrier Sense Multiple Access/ Carrier Detection

1. If the medium is idle, transmit.

2. If the medium is busy, continue to listen until thechannel is idle, then transmit immediately.

3. If a collision is detected during transmission,immediately cease transmitting.

4. After a collision, wait a random amount of time,then attempt to transmit again (repeat from step1).

i



Figure 6.2

Fi 6 3



Figure 6.3

M di O i 10Mb



Medium Options at 10Mbps

• <data rate> <signaling method> <max length>

• 10Base5

– 10 Mbps

– 50-ohm coaxial cable bus

– Maximum segment length 500 meters

• 10Base-T

– Twisted pair, maximum length 100 meters – Star topology (hub or multipoint repeater at central point)

10Mb S ifi i (E h )



10Mbps Specification (Ethernet)

10BASE5 10BASE2 10BASE-T 10BASE-FP

Transmission

medium

Coaxial cable (50

ohm)

Coaxial cable (50

ohm)

Unshielded twisted

pair

850-nm optical fiber

pair

Signaling

technique

Baseband

(Manchester)

Baseband

(Manchester)

Baseband

(Manchester)

Manchester/on-off

Topology Bus Bus Star Star

Maximum segment

length (m)

500 185 100 500

Nodes per segment 100 30 — 33

Cable diameter

(mm)

10 5 0.4 to 0.6 62.5/125 µm

100Mbps Fast Ethernet



• Use IEEE 802.3 MAC protocol and frame format

• 100BASE-X use physical medium specificationsfrom FDDI – Two physical links between nodes

• Transmission and reception

– 100BASE-TX uses STP or Cat. 5 UTP• May require new cable

– 100BASE-FX uses optical fiber

– 100BASE-T4 can use Cat. 3, voice-grade UTP• Uses four twisted-pair lines between nodes

• Data transmission uses three pairs in one direction at a time

• Star-wire topology – Similar to 10BASE-T

100Mb F E h



100Mbps Fast Ethernet

100BASE-TX 100BASE-FX 100BASE-T4

Transmission

medium

2 pair, STP 2 pair, Category

5 UTP

2 optical fibers 4 pair, Category

3, 4, or 5 UTP

Signalingtechnique

MLT-3 MLT-3 4B5B, NRZI 8B6T, NRZ

Data rate 100 Mbps 100 Mbps 100 Mbps 100 Mbps

Maximum

segment length

100 m 100 m 100 m 100 m

Network span 200 m 200 m 400 m 200 m

100BASE X



100BASE-X

• uses a unidirectional data rate 100 Mbps over singletwisted pair or optical fiber link

• encoding scheme same as FDDI

– 4B/5B-NRZI

• two physical medium specifications

– 100BASE-TX

• uses two pairs of twisted-pair cable for tx & rx

• STP and Category 5 UTP allowed

• MTL-3 signaling scheme is used

– 100BASE-FX

• uses two optical fiber cables for tx & rx

• convert 4B/5B-NRZI code group into optical signals

100BASE T4



100BASE-T4

• 100-Mbps over lower-quality Cat 3 UTP – takes advantage of large installed base

– does not transmit continuous signal between packets

– useful in battery-powered applications

• can not get 100 Mbps on single twisted pair

– so data stream split into three separate streams

– four twisted pairs used

– data transmitted and received using three pairs

– two pairs configured for bidirectional transmission

• use ternary signaling scheme (8B6T)

100BASE-X Data Rate and



Encoding

• Unidirectional data rate 100 Mbps over

single link

– Single twisted pair, single optical fiber • Encoding scheme same as FDDI

– 4B/5B-NRZI

– Modified for each option

100BASE-X Media• Two physical medium specifications



Two physical medium specifications

• 100BASE-TX

– Two pairs of twisted-pair cable

– One pair for transmission and one for reception

– STP and Category 5 UTP allowed

– The MTL-3 signaling scheme is used

• 100BASE-FX – Two optical fiber cables

– One for transmission and one for reception

– Intensity modulation used to convert 4B/5B-NRZI codegroup stream into optical signals

– 1 represented by pulse of light

– 0 by either absence of pulse or very low intensity pulse

100BASE-T4• 100-Mbps over lower-quality Cat 3 UTP– Taking advantage of large installed base



Taking advantage of large installed base

– Cat 5 optional

– Does not transmit continuous signal between packets – Useful in battery-powered applications

• Can not get 100 Mbps on single twisted pair – Data stream split into three separate streams

• Each with an effective data rate of 33.33 Mbps

– Four twisted pairs used

– Data transmitted and received using three pairs

– Two pairs configured for bidirectional transmission

• NRZ encoding not used – Would require signaling rate of 33 Mbps on each pair

– Does not provide synchronization

– Ternary signaling scheme (8B6T)

100BASE T O ti



100BASE-T Options

Full Duplex Operation• Traditional Ethernet half duplex



p – Either transmit or receive but not both simultaneously

• With full-duplex, station can transmit and receivesimultaneously

• 100-Mbps Ethernet in full-duplex mode, theoreticaltransfer rate 200 Mbps

• Attached stations must have full-duplex adapter cards

• Must use switching hub – Each station constitutes separate collision domain

– In fact, no collisions

– CSMA/CD algorithm no longer needed

– 802.3 MAC frame format used

– Attached stations can continue CSMA/CD

Mixed Configurations• Fast Ethernet supports mixture of existing 10-Mbps



Fast Ethernet supports mixture of existing 10 Mbps

LANs and newer 100-Mbps LANs

• E.g. 100-Mbps backbone LAN to support 10-Mbps

hubs

– Stations attach to 10-Mbps hubs using 10BASE-T

– Hubs connected to switching hubs using 100BASE-T• Support 10-Mbps and 100-Mbps

– High-capacity workstations and servers attach directly to

10/100 switches

– Switches connected to 100-Mbps hubs using 100-Mbpslinks

– 100-Mbps hubs provide building backbone

• Connected to router providing connection to WAN

Gigabit Ethernet Configuration



g g

Gigabit Ethernet – Physical



• 1000Base-SX – Short wavelength, multimode fiber

• 1000Base-LX – Long wavelength, Multi or single mode fiber

• 1000Base-CX – Copper jumpers <25m, shielded twisted pair

• 1000Base-T

– 4 pairs, cat 5 UTP

• Signaling - 8B/10B

Gbit Ethernet Medium Options

(l l )



(log scale)

10Gbps Ethernet - Uses• High-speed, local backbone interconnection between large-



capacity switches

• Server farm• Campus wide connectivity

• Enables Internet service providers (ISPs) and network

service providers (NSPs) to create very high-speed links at

very low cost• Allows construction of (MANs) and WANs

– Connect geographically dispersed LANs between campuses or

points of presence (PoPs)

• Ethernet competes with ATM and other WAN technologies

• 10-Gbps Ethernet provides substantial value over ATM

10Gbps Ethernet - AdvantagesN i b d idth i i



• No expensive, bandwidth-consuming conversion

between Ethernet packets and ATM cells• Network is Ethernet, end to end

• IP and Ethernet together offers QoS and traffic

policing approach ATM

• Advanced traffic engineering technologies

available to users and providers

• Variety of standard optical interfaces (wavelengths

and link distances) specified for 10 Gb Ethernet• Optimizing operation and cost for LAN, MAN, or

WAN

10Gbps Ethernet - Advantages• Maximum link distances cover 300 m to 40 km

• F ll d ple mode onl



• Full-duplex mode only

• 10GBASE-S (short): – 850 nm on multimode fiber

– Up to 300 m

• 10GBASE-L (long) – 1310 nm on single-mode fiber

– Up to 10 km• 10GBASE-E (extended)

– 1550 nm on single-mode fiber

– Up to 40 km

• 10GBASE-LX4: – 1310 nm on single-mode or multimode fiber

– Up to 10 km

– Wavelength-division multiplexing (WDM) bit stream across four light waves

Figure 6 11



Figure 6.11

Fibre Channel - Background



• I/O channel

– Direct point to point or multipoint comms link

– Hardware based

– High Speed

– Very short distance – User data moved from source buffer to destination buffer

• Network connection

– Interconnected access points

– Software based protocol

– Flow control, error detection &recovery

– End systems connections

Fibre Channel



Fibre Channel

• 2 methods of communication with processor: – I/O channel

– Network communications• Fibre channel combines both

– Simplicity and speed of channel

communications – Flexibility and interconnectivity of network communications

Fibre Channel I/O channel Oriented



Facilities• Data type qualifiers for routing payload

• Link-level constructs for individual I/Ooperations

• Protocol specific specifications to supporte.g. SCSI

Fibre Channel Network-Oriented



Facilities

• Full multiplexing between multiple

destinations

• Peer-to-peer connectivity between any pair of ports

• Internetworking with other connection

technologies

Fibre Channel Requirements



Fibre Channel Requirements

• Full duplex links with 2 fibres/link • 100 Mbps – 800 Mbps• Distances up to 10 km• Small connectors• high-capacity• Greater connectivity than existing multidrop

channels• Broad availability

• Support for multiple cost/performance levels• Support for multiple existing interface command

sets

Fibre Channel Elements



Fibre Channel Elements

• End systems - Nodes

• Switched elements - the network or fabric

• Communication across point to point links

Fibre Channel Network



Fibre Channel Network

Fibre Channel Protocol Architecture



Fibre Channel Protocol Architecture

• FC-0 Physical Media

• FC-1 Transmission Protocol

• FC-2 Framing Protocol• FC-3 Common Services

• FC-4 Mapping

Fibre Channel ProtocolArchitecture (1)



Architecture (1)• FC-0 Physical Media

– Optical fiber for long distance

– coaxial cable for high speed short distance

– STP for lower speed short distance

• FC-1 Transmission Protocol – 8B/10B signal encoding

• FC-2 Framing Protocol

– Topologies

– Framing formats

– Flow and error control

– Sequences and exchanges (logical grouping of frames)

Fibre Channel Protocol



• FC-3 Common Services

– Including multicasting

• FC-4 Mapping – Mapping of channel and network services onto

fibre channel

• e.g. IEEE 802, ATM, IP, SCSI

Architecture (2)

Fibre Channel Physical Media



Fibre Channel Physical Media

• Provides range of options for physical

medium, the data rate on medium, and

topology of network

• Shielded twisted pair, video coaxial cable,

and optical fiber

• Data rates 100 Mbps to 3.2 Gbps• Point-to-point from 33 m to 10 km

Topologies

• Point to point topology



• Point-to-point topology

– Only two ports – Directly connected, with no intervening switches

– No routing

• Arbitrated loop topology – Simple, low-cost topology

– Up to 126 nodes in loop

– Operates roughly equivalent to token ring• Topologies, transmission media, and data

rates may be combined

Fibre Channel Fabric• General topology called fabric or switched topology



p gy p gy

• Arbitrary topology includes at least one switch to interconnect number

of end systems• May also consist of switched network

– Some of these switches supporting end nodes

• Routing transparent to nodes

– Each port has unique address

– When data transmitted into fabric, edge switch to which node

attached uses destination port address to determine location

– Either deliver frame to node attached to same switch or transfers

frame to adjacent switch to begin routing to remote destination

Fabric Advantages



• Scalability of capacity

– As additional ports added, aggregate capacity of network increases

– Minimizes congestion and contention

– Increases throughput

• Protocol independent• Distance insensitive

• Switch and transmission link technologies maychange without affecting overall configuration

• Burden on nodes minimized – Fibre Channel node responsible for managing point-to-

point connection between itself and fabric

– Fabric responsible for routing and error detection

Five Applications of Fibre

Channel



Channel

WLANs – Wireless LANs



WLANs Wireless LANs

• Rely upon wireless transmission media

• Infrared, spread spectrum, narrowband

microwave• Follow IEEE 802.11 standard

– Services include managing associations,

delivering data, and security

WLAN Advantages



WLAN Advantages

• Mobility – enable users to access data while

they are on the move

• Ease and speed of deployment – older building difficult to wire, cable installation

costs, etc.

• Flexibility – no need to re-cable or reconfigure network when someone

changes offices

• Cost

WLAN applications



WLAN applications

• LAN extension - extension of an existing

wired LAN

– for large open areas; historical buildings; small

offices, etc.

• Cross-Building Interconnect

– Connect two buildings without wires

• Nomadic access

• Ad hoc networking

Multi-Cell Wireless LAN

C fi i



Configuration

Infrastructure Wireless LAN



Infrastructure Wireless LAN

Applications –

Ad H N ki



Ad Hoc Networking

• Peer-to-peer network

• Set up temporarily to meet some immediate

need• E.g. group of employees, each with laptop

or palmtop, in business or classroom

meeting• Network for duration of meeting

Wireless LAN Requirements• Same as any LAN



– High capacity, short distances, full connectivity, broadcastcapability

• Throughput: efficient use wireless medium

• Number of nodes:up to hundreds of nodes across multiplecells

• Connection to backbone LAN: Use control modules to

connect to both types of LANs

• Service area: 100 to 300 m

• Low power consumption:Need long battery life on mobilestations

– Mustn't require nodes to monitor access points or frequenthandshakes

• Transmission robustness and security:Interference proneand easily eavesdropped

• Collocated network operation:Two or more wireless LANs

WLAN Technology• Infrared (IR) LANs: Individual cell of IR LAN



limited to single room – high speed

– IR light does not penetrate opaque walls – High security for a small area, and no interference from

other IR LANs in other rooms

– Can’t use outdoors – need to

•Spread spectrum LANs: Mostly operate in ISM(industrial, scientific, and medical) bands – No Federal Communications Commission (FCC)

licensing is required in USA

• Narrowband microwave: Microwave frequencies

but do not use spread spectrum – just wide enoughto transmit – Some require FCC licensing, which guarantees no

channel interference

IEEE 802.11 Architecture



80 . c ec u e

802.11 Nomenclature and Design



g

• Access Points – perform the wireless to

wired bridging function between networks

• Wireless medium – means of movingframes from station to station

• Station – computing devices with wireless

network interfaces• Distribution System – backbone network

used to relay frames between access points

Access and Privacy Services -

Authentication• On wireless LAN, any station within radio range of other devices can



transmit

• Any station within radio range can receive• “Wireless Ethernet”

• Authentication: Used to establish identity of stations to each other

– Wired LANs assume access to physical connection conveysauthority to connect to LAN

– Not valid assumption for wireless LANs• Connectivity achieved by having properly tuned antenna

– Authentication service used to establish station identity

– 802.11 supports several authentication schemes

– Does not mandate any particular scheme

– Range from relatively insecure handshaking to public-keyencryption schemes

– 802.11 requires mutually acceptable, successful authentication before association

Medium Access Control



• MAC layer covers three functional areas

– Reliable data delivery

– Access control

– Security

• Beyond our scope

Reliable Data Delivery• 802.11 physical and MAC layers subject to unreliability



• Noise, interference, and other propagation effects result in

loss of frames• Even with error-correction codes, frames may not

successfully be received

• Can be dealt with at a higher layer, such as TCP

– However, retransmission timers at higher layerstypically order of seconds

– More efficient to deal with errors at the MAC level

• 802.11 includes frame exchange protocol

– Station receiving frame returns acknowledgment (ACK)frame

– Exchange treated as atomic unit

• Not interrupted by any other station

– If noACK within short period of time, retransmit

Distributed Coordination Function



• DCF sublayer uses CSMA

• If station has frame to transmit, it listens to medium

• If medium idle, station may transmit

• Otherwise must wait until current transmission complete

• No collision detection – Not practical on wireless network

– Dynamic range of signals very large

– Transmitting station cannot distinguish incoming weak

signals from noise and effects of own transmission• DCF includes delays

– Amounts to priority scheme



IEEE 802.11Medium

Access

ControlLogic

802.11 Physical Layer • Issued in four stages



• First part in 1997 – IEEE 802.11

– Includes MAC layer and three physical layer specifications

– Two in 2.4-GHz band and one infrared

– All operating at 1 and 2 Mbps

• Two additional parts in 1999 – IEEE 802.11a

• 5-GHz band up to 54 Mbps

– IEEE 802.11b• 2.4-GHz band at 5.5 and 11 Mbps

• Most recent in 2002 – IEEE 802.g extends IEEE 802.11b to higher data rates

Original 802.11 Physical Layer -



DSSS• Three physical media

• Direct-sequence spread spectrum

– 2.4 GHz ISM band at 1 Mbps and 2 Mbps – OR

• FHSS

– 2.4 GHz ISM band at 1 Mbps and 2 Mbps – OR

• Infrared

At 1 and 2 Mb s

802.11a• 5-GHz band

U th l f di i i



• Uses orthogonal frequency division

multiplexing (OFDM) – Not spread spectrum

• Also called multi-carrier modulation

• Multiple carrier signals at differentfrequencies

• Some bits on each channel

– Similar to FDM but all subchannels dedicated tosingle source

• Data rates 6, 9, 12, 18, 24, 36, 48, and 54Mbps

802.11b



• Extension of 802.11 DS-SS scheme

• 5.5 and 11 Mbps

802.11g



g

• Higher-speed extension to 802.11b

• Combines physical layer encoding

techniques used in 802.11a and 802.11b to provide service at a variety of data rates

Chapter 17 – Review Questions



• Discuss the advantages of wireless LANS

• Discuss how a WLAN can be employed to connectLANs from separate buildings

• Describe the purpose of peer-to-peer (ad hoc)networking. Provide examples.

• Describe the WLAN requirements

• Describe an infrared LAN. What are its strengths

and weaknesses?

unit i complete

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