ECE544: Communication Networks-II, Spring 2007 D. Raychaudhuri Lecture 3 Includes tutorial materials...

ECE544: Communication Networks-II, Spring 2007

D. Raychaudhuri

Lecture 3

Includes tutorial materials from the ATM Forum & U VA

Today’s Lecture• Switched Networks

– Switched Ethernet• Concepts• Learning bridge, spanning tree

– ATM networks• Overview• Signaling• PNNI Routing (basics)

Ethernet Hub• Used to connect hosts to Ethernet LAN and to

connect multiple Ethernet LANs• Collisions are propagated

IP

LLC

802.3 MAC

IP

LLC

802.3 MACHubHub

EthernetHub

EthernetHub

HostHost

Bridges/LAN switches • We will use the terms bridge and LAN switch

(or Ethernet switch in the context of Ethernet) interchangeably. Interconnect multiple LAN, possibly with different type

• Bridges operate at the Data Link Layer (Layer 2)

BridgeIP

LLC

802.3 MAC 802.3 MAC 802.5 MAC

LLC

IP

LLC

802.5 MACLAN LAN

Token-ring

Bridge

Ethernet Hubs vs. Ethernet Switches• An Ethernet switch is a packet switch for

Ethernet frames • Buffering of frames prevents collisions. • Each port is isolated and builds its own collision domain

• An Ethernet Hub does not perform buffering:• Collisions occur if two frames arrive at the same time.

HighS

peedB

ackplane

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

OutputBuffers

InputBuffers

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

CSMA/CD

Hub Switch

Internet

A Switched Enterprise Network

Router

Switch

Need for Routing• What do bridges

do if some LANs are reachable only in multiple hops ?

• What do bridges do if the path between two LANs is not unique ?

LAN 2

Bridge 2

LAN 5

LAN 3

LAN 1

LAN 4

Bridge 5

Bridge 4Bridge 3

d

Bridge 1

Transparent Bridges

• Three principal approaches can be found:– Fixed Routing– Source Routing– Spanning Tree Routing (IEEE 802.1d)

• We only discuss the last one in detail.

• Bridges that execute the spanning tree algorithm are called transparent bridges

Transparent Bridges Three parts to transparent bridges:

(1) Forwarding of Frames(2) Learning of Addresses(3) Spanning Tree Algorithm

(1) Frame Forwarding• Each bridge maintains a forwarding

database with entries< MAC address, port, age>

MAC address: host name or group address

port: port number of bridgeage: aging time of entry

with interpretation: • a machine with MAC address lies in direction of the port number from the bridge. The entry is age time units old.

• Routing tables entries are set automatically with a simple heuristic:

The source field of a frame that arrives on a port tells which hosts are reachable from this port.

(2) Address Learning (Learning Bridges)

Port 1

Port 2

Port 3

Port 4

Port 5

Port 6

Src=x, Dest=y

Src=x, Dest=y

x is at Port 1y is at Port 5

Example

Bridge 2

Port1

LAN 1

A

LAN 2

CB D

LAN 3

E F

Port2

Bridge 2

Port1 Port2

•Consider the following packets: (Src=A, Dest=F), (Src=C, Dest=A), (Src=E, Dest=C)

•What have the bridges learned?

• Consider the two LANs that are connected by two bridges.

• Assume host n is transmitting a frame F with unknown destination.

What is happening?• Bridges A and B flood the frame

to LAN 2.• Bridge B sees F on LAN 2 (with

unknown destination), and copies the frame back to LAN 1

• Bridge A does the same. • The copying continues

Danger of Loops

LAN 2

LAN 1

Bridge BBridge A

host n

F

F F

FF

F F

Spanning Trees / Transparent Bridges

• A solution is to prevent loops in the topology

• IEEE 802.1d has an algorithm that organizes the bridges as spanning tree in a dynamic environment– Note: Trees don’t have loops

• Bridges that run 802.1d are called transparent bridges

• Bridges exchange messages to configure the bridge (Configuration Bridge Protocol Data Unit, Configuration BPDUs) to build the tree.

LAN 2

Bridge 2

LAN 5

LAN 3

LAN 1

LAN 4

Bridge 5

Bridge 4Bridge 3

d

Bridge 1

• Introduction• Physical Layers• ATM Layer• ATM Adaptation Layer• Interfaces• Management

ATM OverviewATM Overview

ATM Basic ConceptsATM Basic Concepts• Negotiated Service Connection

– End-to-end connections, called virtual circuits

– Traffic contract

• Switched Based– Dedicated capacity

• Cell Based– Small, fixed length

AA

Negotiated Service Connection

Negotiated Service Connection

Parameters Traffic

Characteristics Peak Cell Rate Sustainable

Cell Rate

Quality of Service Delay Cell Loss

Traffic Contract

Virtual Connection 1-QOS A

Virtual Connection 1-QOS B

Virtual Connection 1-QOS b

The ATM CellThe ATM Cell

• Small Size– 5 Byte Header– 48 Byte Payload

• Fixed Size• Header contains virtual circuit information• Payload can be voice, video or other data types

HeaderHeader

5 Bytes 48 Bytes48 Bytes

PayloadPayload

AA

ATM VisionATM Vision

• ATM network moves cells (fixed length packets) with low delay and low delay variation at high speeds

• Devices at ends translate (e.g., segment and reassemble) between cells and original traffic

The Ultimate Integrated Services The Ultimate Integrated Services NetworkNetwork

The Ultimate Integrated Services The Ultimate Integrated Services NetworkNetwork

DataData Voice VideoVideo

Voice

Voice

DataDataDataData

VideoVideo

VideoVideo

ATMATMNetworkNetwork

ATM System ArchitectureATM System Architecture

DataDataCellCell

VideoVideoCellCell

VoiceVoiceCellCell

AA

ATM Adaptation LayerATM Adaptation Layer

• Provides Mapping Of Applications To ATM Service Of The Same Type

• Segments/Reassembles Into 48 Payloads• Hands 48 Byte Payloads To ATM Layer

48 Bytes48 Bytes

AALAAL TypesTypes11 Circuit EmulationCircuit Emulation

-Constant Bit Rate (CBR) -Constant Bit Rate (CBR)

Low Bit Rate Voice (Real Time)Low Bit Rate Voice (Real Time)

-Variable Bit Rate (VBR)-Variable Bit Rate (VBR)

Time Invariant DataTime Invariant Data

““Simple” DataSimple” Data

22

3/43/4

55

AA

ATM LayerATM Layer

• Adds/Removes Header To 48 Byte Payload• Header Contains Connection Identifier• Multiplexes 53 Byte Cells Into Virtual

Connections• Sequential Delivery Within A Virtual

Connection

}}

48-Byte48-BytePayloadsPayloadsFrom AALFrom AAL 5-Byte Header5-Byte Header

Header Contains Virtual Header Contains Virtual PathPath

and Channel Identifiersand Channel Identifiers

53-Byte Cell53-Byte CellTo Physical LayerTo Physical Layer

AA

Physical LayerPhysical Layer

Speed MatchingSpeed Matchingand Framingand Framing

CableCablePlantsPlants

Wide Range of Wide Range of SpeedsSpeeds

LAN, MAN, LAN, MAN, WAN WAN CompatibilityCompatibility

Uses Existing Uses Existing MediaMedia

Twisted PairTwisted Pair

CoaxCoax

FiberFiber -Multimode -Multimode

-Single Mode-Single Mode

TransmissionTransmissionFrameFrame

AA

ATM System ArchitectureATM System ArchitectureATM Cell Creation TransmissionATM Cell Creation Transmission

AdaptationAdaptationLayerLayer

ATMATMLayerLayer

PhysicalPhysicalLayerLayer

Conversion Conversion to ATM Data to ATM Data Types, 48-Types, 48-

Byte LengthByte Length

Forward Forward Cell Cell

Through Through NetworkNetwork

Add 5-Byte Add 5-Byte HeaderHeader

Convert To Convert To Correct Correct

Electrical Electrical Or Optical Or Optical

FormatFormat

VoiceVoiceCellCell

DataDataCellCell

VideoVideoCellCell

Services

AA

Private UNI PHYATM Forum Physical Layer UNI InterfacesATM Forum Physical Layer UNI Interfaces

Frame FormatFrame Format Bit Rate/Line RateBit Rate/Line Rate Transmission MediaTransmission Media

Cell StreamCell Stream

STS-1STS-1

FDDIFDDI

STS-3c, STM-1STS-3c, STM-1


Cell StreamCell Stream


STS-12, STM-4STS-12, STM-4

25.6 Mb/s / 32 Mbaud25.6 Mb/s / 32 Mbaud

51.84 Mb/s51.84 Mb/s

100 Mb/s / 125 Mbaud100 Mb/s / 125 Mbaud

155.52 Mb/s155.52 Mb/s

155.52 Mb/s155.52 Mb/s

155.52 Mb/s / 194.4 Mbaud155.52 Mb/s / 194.4 Mbaud

155.52 Mb/s155.52 Mb/s

622.08 Mb/s622.08 Mb/s

UTP-3UTP-3

UTP-3UTP-3

MMFMMF

UTP-5, STPUTP-5, STP

SMF, MMF, Coax pairSMF, MMF, Coax pair

MMF/STPMMF/STP

UTP-3UTP-3

SMF-Single Mode FiberSMF-Single Mode FiberMMF-Multimode FiberMMF-Multimode Fiber

SMF, MMFSMF, MMF

STS-48, STM-16*STS-48, STM-16* 2,488.32 Mb/s2,488.32 Mb/s SMFSMF

*-Under Development*-Under DevelopmentUTP-Unshielded Twisted PairUTP-Unshielded Twisted PairSTP-Shielded Twisted PairSTP-Shielded Twisted PairDS1 and DS3-Also Private SpeedsDS1 and DS3-Also Private Speeds BB

Public UNI PHYPublic UNI PHYATM Forum Physical Layer UNI InterfacesATM Forum Physical Layer UNI Interfaces

Frame FormatFrame Format Bit RateBit Rate Transmission MediaTransmission Media

DS3DS3


E1E1

E3E3

J2J2

N X T1N X T1

1.544 Mb/s1.544 Mb/s

44.736 Mb/s44.736 Mb/s

155.520 Mb/s155.520 Mb/s

2.048 Mb/s2.048 Mb/s

34.368 Mb/s34.368 Mb/s

6.312 Mb/s6.312 Mb/s

N X 1.544 Mb/sN X 1.544 Mb/s

Twisted PairTwisted Pair

Coax PairCoax Pair

SMFSMF

Twisted Pair, Coax PairTwisted Pair, Coax Pair

Coax pairCoax pair

Coax pairCoax pair

Twisted pairTwisted pair

*-Under Development*-Under DevelopmentSMF-Single Mode FiberSMF-Single Mode FiberPLCP-Physical Layer Convergence ProtocolPLCP-Physical Layer Convergence Protocol

DS1DS1

N X E1N X E1 N X 2.048Mb/sN X 2.048Mb/s Twisted pairTwisted pair

BB

ATM PHY: Two SublayersATM PHY: Two SublayersTransmission Convergence Transmission Convergence

SublayerSublayer

Physical Layer Medium Dependent Physical Layer Medium Dependent SublayerSublayer

• PMD:– Medium, line code, connectors– Probably use existing standards and technology

• TCS:– Specific to the PMD– Cell delineation– Cell rate decoupling (inserting empty cells during idle periods)

155 Mbps, SONET STS-3c/SDH STM-1

155 Mbps, SONET STS-3c/SDH STM-1

99

RRoowwss

270 columns270 columns

9 bytes9 bytes

MaintenanceMaintenanceandand

operationsoperations

1 Synchronous1 SynchronousPayload EnvelopePayload Envelope

(1 column of overhead)(1 column of overhead)

• 9 260 8/125 sec = 149.76 Mbps payload

. . .

125125 secsec

AA

HEC Cell Delineation (For SONET, etc...)

HEC Cell Delineation (For SONET, etc...)

Peek ahead at the cell Peek ahead at the cell formatformat

Header Payload

HEC (Header Error Check)

Coverage of the 1 byte HEC

Receiver locks on 5 byte blocks that Satisfy the HEC calculation Are separated by 48 bytes

HEC includes coset so that empty cell (first 4 bytes of header = 0) does not make HEC = 0

Receiver locks on 5 byte blocks that Satisfy the HEC calculation Are separated by 48 bytes

HEC includes coset so that empty cell (first 4 bytes of header = 0) does not make HEC = 0

AA

1.5 Mbps, DS11.5 Mbps, DS1

• (24 bytes x 8 bits/byte)/125 sec=1.536 Mbps of payload

• Cell delineation by HEC detection as with SONET

• Cell payload=1.536 Mbps x (48/53)=1.391 Mbps

. . . F B B . . . B F B . . . B F . . .. . . F B B . . . B F B . . . B F . . .

125 125 secsec

Framing BitFraming Bit

24 bytes24 bytes

25.6 Mbps UTP-325.6 Mbps UTP-3• Based on IEEE 802.5 physical layer with 4B/5B Based on IEEE 802.5 physical layer with 4B/5B

coding plus scramblingcoding plus scrambling• 32 Mbaud x 4/5 = 25.6 Mbps32 Mbaud x 4/5 = 25.6 Mbps• Cells delineated by special symbol pairsCells delineated by special symbol pairs

xx CellCellxx

Reset ScrambleReset Scramble

xx CellCell44

No Scramble ResetNo Scramble Reset

oror

AA

ATM UNI CellATM UNI Cell

CLP = Cell Loss PriorityCLP = Cell Loss Priority

5 Bytes5 Bytes

48 Bytes48 Bytes

Virtual Channel Virtual Channel IdentifierIdentifier

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Payload Type Payload Type IdentifierIdentifier CLPCLP

Generic Flow Generic Flow ControlControl

Virtual Path Virtual Path IdentifierIdentifier



Virtual ChannelVirtual ChannelIdentifierIdentifier

Header ErrorHeader ErrorCheckCheck

PayloadPayload(48 bytes)(48 bytes)


Why 53 Bytes?Why 53 Bytes?

64 + 564 + 5 32 + 432 + 4

48 + 548 + 5

• Compromise reached in ITU-TS Study Group XVIII in June 1989

Packetization Delay Advantage of Small Cells

Packetization Delay Advantage of Small Cells

Percent Overhead and Packetization DelayPercent Overhead and Packetization Delayfor 64 Kbps Voicefor 64 Kbps Voice

Payload (Bytes)Payload (Bytes)

00

2020

4040

6060

8080

100100

00 2020 4040 6060 808000

22

44

66

88

1010DelayDelay

OverheadOverhead

Dela

y (

ms)

Dela

y (

ms)

% O

verh

ead

% O

verh

ead

Queuing Advantage of Small Cells

Queuing Advantage of Small Cells

••••••

100 byte message100 byte message

100 other active100 other activeconnectionsconnections 45 Mbps45 Mbps

Delay and delay variation are small for small messages e.g., a digitized voice sample

High overheadHigh overhead Wait for other cellsWait for other cells

Just fits in one cellJust fits in one cell

Payload (bytes)Payload (bytes)

MaxMax

DelayDelay

(ms)(ms)

0022446688

10101212

11 5050 100100 150150 200200 250250 300300

AA

Virtual ConnectionsVirtual Connections

PortPort VPI/VCIVPI/VCI PortPort VPI/VCIVPI/VCI 11 0/370/37 33 0/760/76 11 0/420/42 55 0/520/52 22 0/370/37 66 0/220/22 22 0/780/78 44 0/880/88

Connection TableConnection Table

3737 4242

3737 7878

7676

5252

2222

8888

11

22

33

44

55

66

VideoVideo DataData

Voice

VideoVideo

DataData

Voice

VideoVideo

DataData

Voice

VideoVideo

VideoVideo

VideoVideo

77 66 55 44 33 22 11 00






CLPCLP




Payload Type Payload Type IdentifierIdentifier

Virtual Paths and Virtual Channels

Virtual Paths and Virtual Channels Physical LinkPhysical Link

Virtual PathVirtual Path

Virtual ChannelVirtual Channel

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CLPCLP





VPI = 1VPI = 1

VPI = 2VPI = 2

VPI = 3VPI = 3

VPI = 4VPI = 4

VPI = 5VPI = 5

VPI = 6VPI = 6

VCI = 31VCI = 31VCI = 32VCI = 32

VCI = 31VCI = 31VCI = 40VCI = 40

VCI = 96VCI = 96VCI = 97VCI = 97

VCI = 55VCI = 55VCI = 57VCI = 57

VCI = 99VCI = 99VCI = 32VCI = 32

VCI = 96VCI = 96VCI = 97VCI = 97

ATM Switch or NetworkATM Switch or Network

• Bundles of Virtual Channels are switched via Virtual Paths

• Virtual Path service from a carrier allows reconfiguration of Virtual Channels without service orders to carrier

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CLPCLP





Virtual Paths and Virtual Virtual Paths and Virtual ChannelsChannelsVirtual Paths and Virtual Virtual Paths and Virtual ChannelsChannels

Cell Loss PriorityCell Loss Priority• Cells with bit set should be discarded

before those with bit not set• Can be set by the terminal• Can be set by ATM switches for internal

network control– Virtual channels/paths with low quality of

service– Cells that violate traffic management contract

• Key to ATM Traffic Management

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CLPCLP





Generic Flow ControlGeneric Flow Control

• Used for UNI only - Not NNI• Currently undefined

• Set to 0000B

• Proposed future uses– Flow control– Shared media multiple access

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CLPCLP





B

Header Error CheckHeader Error Check• Header error control

– Detection mode:• Protects header only (all five bytes)• Discards cell when header error

– Correction mode (optional): Correct 1 bit errors else discard when error detected• Reduced cell loss in face of single bit errors• Reduced error detection for multiple bit errors

• Cell delineation for SONET, SDH, etc...• Recalculated link-by-link because of VPI/VCI

value changes

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CLPCLP





B

Permanent Virtual CircuitsPermanent Virtual Circuits

• Long setup time (especially with human intervention) means that connections are left active for long periods of time e.g., days, weeks

• VPI/VCI tables setup in terminals and switches

NetworkNetworkManagementManagement

SystemSystem

VPI/VCIVPI/VCI

VPI/VCIVPI/VCIVPI/VCIVPI/VCI

VPI/VCIVPI/VCI

B

Switched Virtual CircuitsSwitched Virtual Circuits

ATM SwitchATM Switch

Signalling ChannelSignalling Channel(VPI/VCI = 0/5)(VPI/VCI = 0/5)

Signalling ChannelSignalling Channel(VPI/VCI = 0/5)(VPI/VCI = 0/5)

• Switch and terminal exchange signalling messages using the predefined signalling channel, VPI/VCI = 0/5

CallCallProcessingProcessing

B

Point-to-Point Connection

Point-to-Point Connection

• Data may flow in one or both directions (unidirectional or bidirectional)

• Bandwidth may be:– Same in both directions (symmetric), or– Different in each direction (asymmetric)

• Data may flow in one or both directions (unidirectional or bidirectional)

• Bandwidth may be:– Same in both directions (symmetric), or– Different in each direction (asymmetric)

Point-to-Multipoint Connection

Point-to-Multipoint Connection

• Data are replicated by the network

• Data flow only from Root to Leaves

• Data are replicated by the network

• Data flow only from Root to Leaves

““Root”Root”

““Leaves”Leaves”

Why SVCs?Why SVCs?

•Universal connectivity•More efficient resource

utilization

•Universal connectivity•More efficient resource

utilization

AA

Call Control SignallingCall Control SignallingCall control protocol is used to establish, maintain, and clear

virtual channel connections between a user and networkCall control protocol is used to establish, maintain, and clear

virtual channel connections between a user and network

UserUser NetworkNetwork

UNIUNI

UNI or NNIUNI or NNI

UNI or NNIUNI or NNI

VirtualVirtualChannelChannelConnectionsConnections

InterfaceInterface

Call ControlSignalling

Call ControlSignalling

Signalling 4.0Signalling 4.0

• Delta from Q.2931 etc.• Extensions for parameterized QoS,

ABR, LIJ• Some restrictions

• Delta from Q.2931 etc.• Extensions for parameterized QoS,

ABR, LIJ• Some restrictions

Signalling Protocol StackSignalling Protocol Stack

Q.931Q.931 Q.2931Q.2931

Q.921Q.921LAPDLAPD

I.430/431I.430/431

SSCOPSSCOP

ATMATM

SONET/DS3SONET/DS3

UNI 4.0UNI 4.0

ATM UNIATM UNIISDN UNIISDN UNI

Setting Up a Call - 1Setting Up a Call - 1

SetupSetup

CallCallProceedingProceeding

AA BB

A wants to communicate with BA wants to communicate with B

• Setup message– Call reference– Called party address– Calling party address– Traffic characteristics– Quality of service

• Call proceeding message– Call reference– VPI/VCI

B


• Internal network processing– Resource

availability checking

– Virtual channel or path routing

– Function of the Network Node Interface (NNI)

SetupSetup


B


SetupSetup


SetupSetup

Call Call ProceedingProceeding

• Setup message– Call reference– Called party address– Calling party address– Traffic characteristics– Quality of service– VPI/VCI

Call ProceedingCall Proceeding Call referenceCall reference

Called user Called user deciding to accept deciding to accept callcall

B


SetupSetup


SetupSetup


Connect AckConnect Ack

Connect Connect • Connect message

– Call reference– Indicates call

acceptance

• Connect Acknowledge– Call reference

B


SetupSetup


SetupSetup



Connect Connect


Connect Connect

• Calling party informed that call is available for user information exchange

B

ATM AddressingATM Addressing• Private networks

– 20 byte address– Format modeled after OSI NSAP (Network Service Access

Point)– Mechanisms for administration exist– Hierarchical structure will facilitate virtual connection

routing in large ATM networks

• Public networks– E.164 numbers (telephone numbers)– Up to 15 digits

• Private networks– MAC address will be encapsulated within NSAP

B

Address to EndstationAddress to Endstation

PrivatePrivateUNIUNI PublicPublic

UNIUNI

ATM End ATM End System System Address Address FormatFormat

Native Native E.164 orE.164 or

AESAAESA

Private ATM SwitchPrivate ATM Switch

Public ATM

Network

ATM End System AddressATM End System Address

• Selector (Not used by Network for Routing)

• Selector (Not used by Network for Routing)

PrivatePrivateUNIUNI

AESAAESAFormatFormat Network-Network-

SuppliedSupplied

EndEndSystem-System-SuppliedSupplied

SELSEL

SELSEL

4747 SELSELHO-DSPHO-DSP End System IDEnd System ID

4545 E.164 NumberE.164 Number HO-DSPHO-DSP End System IDEnd System ID SELSEL

3939 SELSELDCCDCC HO-DSPHO-DSP End System IDEnd System ID

IDCIDC

Based on ISO NSAP FormatBased on ISO NSAP Format

Private Address Formats

Private Address Formats

Data Country CodeData Country Code

International Code DesignatorInternational Code Designator

E.164 Private AddressE.164 Private Address

3939

4747

4545

DCCDCC

ICDICD

Routing FieldsRouting Fields End System IDEnd System ID SELSEL

SELSEL

SELSEL

Routing FieldsRouting Fields End System IDEnd System ID

Routing FieldsRouting Fields End System IDEnd System IDE.164 NumberE.164 Number

D

Address RegistrationAddress Registration• Allows automatic configuration

• Required at the private UNI

• Optional at the public UNI

• Network supplies the network prefix

• User supplies the user part

• Allows automatic configuration

• Required at the private UNI

• Optional at the public UNI

• Network supplies the network prefix

• User supplies the user part

Subaddress UseSubaddress Use

Private UNIAddress: AESA

Subaddress: NSAP or Not Used

Private UNIAddress: AESA

Subaddress: NSAP or Not Used

Public UNIPublic UNI

Address: E.164 Public Network AddressAddress: E.164 Public Network Address

Subaddress: AESASubaddress: AESA

Subaddress IE: Only present if used for NSAP at Subaddress IE: Only present if used for NSAP at Private UNIPrivate UNI

PrivateNetwork

Public

Network

PrivateNetwork

• Subaddress:– Used to convey an AESA across a public network which

supports only E.164 addresses– Also can be used for NSAP

• Subaddress:– Used to convey an AESA across a public network which

supports only E.164 addresses– Also can be used for NSAP

AA

Messages and Information Elements

• Very flexible and extensible encoding• 19 message types• Around 35 IEs

Type LengthType Length TypeTypeLengthLength ValueValue TypeType

LengthLength ValueValue TypeTypeLengthLength

……..Message Message HeaderHeader

Message Message HeaderHeader

IE1IE1 IE2IE2 IE3IE3

AAL1: Adaptive Clock MethodAAL1: Adaptive Clock Method

Water MarkWater Mark

Speed up Speed up bit clockbit clock

Slow down bit Slow down bit clockclock

Received CellsReceived Cells

Substitute Substitute CellsCells

Continuous Bit Continuous Bit StreamStream

• Bit stream rate is independent of ATM network and (theoretically) can be any value

• Cell delay variation is critical to buffer sizing and bit clock jitter

Reconstructing the bit streamReconstructing the bit stream

B

User 1User 1 User 2User 2 User 3User 3 User 1User 1 User 3User 3

ATM CellATM Cell

Cell HeaderCell Header(5 Octets)(5 Octets)

AAL2 HeaderAAL2 Header(3 Octets)(3 Octets)

AAL2 PayloadAAL2 Payload(variable)(variable)

AAL2• Small payload to reduce packetization delaySmall payload to reduce packetization delay

B

MM

IIDD

AAL3/4AAL3/40 - 655350 - 65535 BytesBytes

BytesBytes44 4 or 84 or 8

ErrorErrorCheckingChecking

ErrorErrorCheckingChecking

4444

4444

4444

4444

PadPad

• 44 Bytes of Data per Cell• CRC Checking per Cell• Message Identifier (MID) Allows

Multiple Interleaved Packets on a Virtual Connection

User DataUser DataMMIIDD

2222

2222

2222CCRRCC

DataData


CCRRCC


CCRRCC

CCRRCC

D

PadPad

AAL 5AAL 50 - 655350 - 65535

2222 44 BytesBytes

BytesBytes

Not drawn to scaleNot drawn to scale

Error detection fieldsError detection fields

. . .. . .

Last cell flagLast cell flag

• 48 Bytes of Data per Cell

• Uses a PTI Bit to Indicate Last Cell

• Only One Packet at a Time on a Virtual Connection

4848

4848

0

1

DataData0-470-47

00LLeenn

CCRRCC

C

Quality-of-ServiceQuality-of-Service

• Problem: Providing quality of service– How should ATM network resources be allocated to

ensure good performance including preventing congestion, e.g., how many virtual channels should be assigned to a particular transmission link?

• Solution: Traffic Management– Specify the traffic "contract" on each virtual channel/path– Route (including rejecting setup request) each virtual

channel/path along a path with adequate resources (Admission Control)

– Mark (via Cell Loss Priority bit) for loss all cells that violate the contract (Traffic Policing)

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CLPCLP





ATM Service CategoriesATM Service Categories• CBR

– Constant Bit Rate– Continuous flow of data with tight bounds on delay and delay variation

• rt-VBR– Real-Time Variable Bit Rate

– Variable bandwidth with tight bounds on delay and delay variation

• nrt-VBR– Non-Real-Time Variable Bit Rate– Variable bandwidth with tight bound on cell loss

• UBR– Unspecified Bit Rate– No guarantees (i.e., best effort delivery)

• ABR– Available Bit Rate– Flow control on source with tight bound on cell loss

Quality of Service Parameters

• End to end transit delay• Acceptable CDV (Forwards, Backwards)• Cumulative CDV (Forwards,

Backwards) • Cell Loss Ratio (Forwards, Backwards)• Encoded as two IEs• QoS Classes may also be indicated for

backwards compatibility

Generic Cell Rate Algorithm

Generic Cell Rate Algorithm

• For a sequence of cell arrival times, {tk}, determines which cells conform to the traffic contract

• A counter scheme based on two parameters denoted GCRA(I,L)– Increment parameter: I

• affects cell rate

– Limit parameter: L• affects cell bursts

• “Leaky bucket”– A cell that would cause the bucket to

overflow is non-conforming

One unit leak One unit leak per unit of timeper unit of time

I for each cell I for each cell arrivalarrival

L + IL + I

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CLPCLP





Payload Type IdentifierPayload Type Identifier• Bit 3: Used to discriminate data cells

from operation, administration, maintenance cells.

• Bit 2: Used to indicate congestion in data cells (Bit 3 = 0)– Set by Switches– Source and Destination Behavior Defined for Available

Bit Rate Flow Control VCC’s

• Bit 1: Carried transparently end-to-end in data cells– Used by AAL5


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CLPCLP




CC

SourceSource DestinationDestination

++ ++ ++Forward RM* CellsForward RM* Cells

CongestionCongestionIndicationIndication

++ ++RateRate

IndicationIndicationRate & CongestionRate & Congestion

IndicationIndication

*- Resource Management*- Resource Management

Backward RM* CellsBackward RM* Cells

B

ABR Feedback

• Source sets Actual Cell Rate Source sets Actual Cell Rate based on rate & congestion based on rate & congestion feedbackfeedback


77 66 55 44 33 22 11 00






CLPCLP




Example Source Cell Rate Profile

PeakCell Rate

MinimumCell Rate

Act

ual

Cell

Rate

Time

Netw

ork

Con

gest

ion

Netw

ork

Con

gest

ion

C

Bandwidth NegotiationBandwidth Negotiation

Setup Setup (20 Mb/s)(20 Mb/s)

UNIUNI NNINNI UNIUNI

Connect Connect (10 Mb/s)(10 Mb/s)





Other ATM InterfacesOther ATM Interfaces

PrivatePrivateUNIUNI

PrivatePrivateNNINNI

PublicPublicUNIUNI

ATMATMDXIDXI

B-ICIB-ICI

UNI User Network InterfaceNNI Network Node InterfaceB-ICI BISDN Inter-Carrier InterfaceATM DXI Data eXchange InterfaceFUNI ATM Frame Based UNI Interface

Metropolis Data Metropolis Data Services Inc.Services Inc.

Country Wide Country Wide Carrier ServicesCarrier Services

PublicPublicNNINNI

FUNIFUNI

FUNIFUNI

D

NNINNI

• Supports 212 Virtual Paths• Supports virtual connection

routing– Distribution of topology

information– Distribution of resource

availability information• Public version being

standardized by ITU TS• Private version specified by

ATM Forum Technical Working Group

CLP = Cell Loss PriorityCLP = Cell Loss Priority

Cell FormatCell Format


77 66 55 44 33 22 11 00

Payload Type Payload Type IdentifierIdentifier CLPCLP








C

B-ICIB-ICI• For interfaces between public carriers• Based on carrier digital transmission

– DS3, 44.736 Mbps– STS-3c, 155.52 Mbps– STS-12c, 622.08 Mbps

• Supports multiple carrier services– Cell Relay Service (PVC)– Circuit Emulation Service (Synchronous Residual

Time Stamp, PVC)– Frame Relay Service (PVC)– Switched Multi-megabit Data Service

D

ATM Network ManagementATM Network Management

UNIUNI

M1M1 M2M2

M3M3

M4M4 M4M4

M5M5

UNIUNI BICIBICI

ManagementManagementSystemSystem

ATMATMDeviceDevice

PrivatePrivateATMATM

NetworkNetwork

PublicPublicATMATM

NetworkNetwork

PublicPublicATMATM

NetworkNetwork



ILMI:Integrated Layer

Management Interface

C

78

Today’s Homework• Peterson & Davie, Chap 3

-3.1 (v2) 3.1 (v3)-3.4 (v2) 3.5 (v3)-3.6,7 (v2) 3.7,8 (v3)-3.12 (v2) 3.13 (v3)-3.23 (v2) 3.26 (v3)-3.27 (v2) 3.30 (v3)Download and browse ATM UNI4.0 and PNNI1.0 specs

Due next Fri (2/9)

ECE544: Communication Networks-II, Spring 2007 D. Raychaudhuri Lecture 3 Includes tutorial materials...

Documents

Transcript of ECE544: Communication Networks-II, Spring 2007 D. Raychaudhuri Lecture 3 Includes tutorial materials...