第五章-ATM技术.pdf

1Page 1第五章：ATM宽带交换技术牛志升清华大学电子工程系宽带信息网络宽带信息网络Content?Why ATM:Background and Motivation?Whats ATM:Key TechnologiesIntroductionPhysical LayersATM LayerATM Adaptation LayerInterfacesTraffic Control and Management?Wheres ATM:Application and Future Trend2Page 2Why ATM:Technology DrivenScalability&FlexibilityATMSimplifiedNetworkInfrastructureAccommodation of mixedmedia trafficAdvantages of ATMATMDeviceServerATMATME-netTRATMDeviceServerATMATME-netTRWANCampus/MANLAN/DesktopLAN=MAN=WANATM SwitchATM SwitchAdvantages:Simplified Network Infrastructure3Page 3Advantages:Scalability and FlexibilityServerATM Switch“A”Mb/s“B”Mb/sMedical ImagingResearchAccountingRXProposed newPharmacy“C”Mb/s“C”Mb/sE-netTRTo ATM Wide Area NetworkAdvantages:Accommodation of Mixed Media Traffic Types4Page 4?Introduction?Physical Layers?ATM Layer?ATM Adaptation Layer?Interfaces?Switching and routing?ManagementWhats ATM:Key TechnologiesATM 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 trafficThe Ultimate Integrated Services NetworkDataVoiceVideoVoiceVoiceDataDataVideoVideoATMNetwork5Page 5ATM=Asynchronous TDMABCDData to be sentt1 t2 t3A1B1C1D1C2D2A2B21stcycle2ndcycleSynchronous TDMwaste bandwidthA1B1C2B21stcycle2ndcycleStatistical TDMextra bandwidthavailableATM vs Synchronous(Phone)Networks?Phone networks are synchronous(periodic).ATM=Asynchronous Transfer Mode?Phone networks use circuit-switching.ATM networks use“Packet”or“cell”Switching?In phone networks,all rates are multiple of 64 kbps.With ATM service,you can get any rate,and you can vary your rate with time.?With current phone networks,all high speed circuits are manually setup.ATM allows“dialing”any speed&rapid provisioning6Page 6Asynchronous Transfer is FlexibleAsynchronous Transfer is Flexible7Page 7Asynchronous Transfer is FlexibleATM is Statistical Multiplexing?Transfer Mode=transmission+multiplexing+switching?ATM is Statistical Multiplexing and Virtual NetworkingDeterministic MultiplexingStatistical Multiplexing8Page 8ATM vs Data Networks(Internet)?ATM is“virtual circuit”based:the path(and optionally resources on the path)is reserved before transmissionInternet Protocol(IP)is connectionless,and end-to-end resource reservations not possibleRSVP is a new signaling protocol in the Internet?ATM Cells:Fixed/small size:tradeoff between voice/dataIP packets:variable size?ATM provides QoS routing coupled to signaling(PNNI)Internet provides“best-effort”routing(combination of RIP/OSPF/IS-IS/BGP-4),aiming only for connectivity?Addressing:ATM uses 20-byte global NSAP addresses for signaling and 32-bit locally-assigned labels in cellsIP uses 32-bit global addresses in all packets?ATM offers sophisticated traffic managementTCP/IP:congestion control is packet-loss-basedATM is Fast Packet Switching?Simplified transfer protocolCell relay only inside the networkError control at the endsBased on optical fiber?Fixed size cell for hardware switchingSelf-routingsmall delay jitter(predictable time delay)easy cell delineation9Page 9ATM is Connection-Oriented?Connectionless Datagramflexible and efficientlow speed(store-and-forward)no QoS guarantee?Permanent Virtual CircuitQoS guaranteeshort setup timesmall control overhead?Switched Virtual CircuitQoS guaranteebandwidth on demandlong setup/release timecontrol overheadConnectionless vs Connection-oriented10Page 10Connectionless vs Connection-orientedATM Concepts:Fixed-size packets?ProsSimpler buffer hardware-packet arrival and departure requires us to manage fixed buffer sizesSimpler line scheduling-each cell takes a constant chunk of bandwidth to transmitEasier to build large parallel packet switches?Consoverhead for sending small amounts of datasegmentation and reassembly costlast unfilled cell after segmentation wastes bandwidth11Page 11ATM Cell is a Small Packet?Small packet for short delay and jitter?Why 53 bytes?longer for efficiency;shorter for realtimejust a compromise(32+64)/2=48,48+5=53)!?Rationale for the Cell SizeDelay-packetization:48x8/32Kbps=12ms;propagation:2ms for 500km-switching:72us for 3 switches;queueing:225us for 3 switchesOverhead-5/48=10.4%in ATM vs 2/512=0.39%in frame relayReliability-at least 6 bits are needed to correct a single bit error for 40 bits header,and 8 bits can detect 84%of multiple bit errorsPacketization Delay Advantage of Small CellsPercent Overhead and Packetization Delayfor 64 Kbps VoicePayload(Bytes)0204060801000204060800246810DelayOverheadDelay(ms)%Overhead12Page 12Queuing Advantage of Small Cells100 byte message100 other activeconnections45 MbpsDelay and delay variation are small for small messages e.g.,a digitized voice sampleHigh overheadWait for other cellsJust fits in one cellPayload(bytes)MaxDelay(ms)024681012150100150200250300AWhy 53 Bytes?64+532+448+5?Compromise reached in ITU-TS Study Group XVIII in June 198913Page 13ATM Cell(simplified)Header5 bytes48 bytes?Header contains information to allow cell to be forwarded to its destinationPayloadHeaderATM UNI CellCLP=Cell Loss Priority5 Bytes48 BytesVirtual Channel Identifier76543210Payload Type IdentifierCLPGeneric Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierHeader ErrorCheckPayload(48 bytes)Virtual ChannelIdentifier14Page 14NNI?Supports 212Virtual Paths?Supports virtual connection routingDistribution of topology informationDistribution of resource availability information?Public version being standardized by ITU TS?Private version specified by ATM Forum Technical Working GroupCLP=Cell Loss PriorityCell FormatVirtual Channel Identifier76543210Payload Type IdentifierCLPVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierHeader ErrorCheckPayload(48 bytes)Virtual Path IdentifierVirtual Path IdentifierCATM Cell Structure?GFC(generic flow control)appear at UNI only(for multiplexing and flow control)?VPI and VCI(virtual path/connection identifier)local logical addresses for connection identification-like LCN in X.25 or DLCI in frame relaytwo-layer addresses for easy management-28=256VPs at UNI and 212=4096VPs at NNI-216=65536 VCs in a VPswitching by address swapping and self routing15Page 15Generic Flow Control?Used for UNI only-Not NNI?Currently undefined?Set to 0000B?Proposed future usesFlow controlShared media multiple access 76543210Generic Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierCLPHeader ErrorCheckPayload(48 bytes)Virtual Channel IdentifierPayload Type IdentifierBWhats ATM:Virtual NetworkingPortVPI/VCIPortVPI/VCI10/3730/7610/4250/5220/3760/2220/7840/88Connection Table3742377876522288123456VideoDataVoiceVideoDataVoiceVideoDataVoiceVideoVideoVideo76543210Generic Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierCLPHeader ErrorCheckPayload(48 bytes)Virtual Channel IdentifierPayload Type Identifier16Page 16Two Layered Virtual networking:Virtual Paths and Virtual ChannelsPhysical LinkVirtual PathVirtual Channel76543210Generic Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierCLPHeader ErrorCheckPayload(48 bytes)Virtual Channel IdentifierPayload Type Identifier?Bundles of Virtual Channels are switched via Virtual Paths?Virtual Path service from a carrier allows reconfiguration of Virtual Channels without service orders to carrierVPI=1VPI=2VPI=3VPI=4VPI=5VPI=6VCI=31VCI=32VCI=31VCI=40VCI=96VCI=97VCI=55VCI=57VCI=99VCI=32VCI=96VCI=97ATM Switches76543210Generic Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierCLPHeader ErrorCheckPayload(48 bytes)Virtual Channel IdentifierPayload Type IdentifierVirtual Path Switching and Virtual Channel Switching17Page 17Permanent Virtual Connections?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 switchesNetworkManagementSystemVPI/VCIVPI/VCIVPI/VCIVPI/VCIBSwitched Virtual ConnectionsATM SwitchSignalling Channel(VPI/VCI=0/5)Signalling Channel(VPI/VCI=0/5)?Switch and terminal exchange signalling messages using the predefined signalling channel,VPI/VCI=0/5CallProcessingB18Page 18Setting Up a Call-1SetupCallProceedingABA wants to communicate with B?Setup messageCall referenceCalled party addressCalling party addressTraffic characteristicsQuality of service?Call proceeding messageCall referenceVPI/VCIBSetting Up a Call-2?Internal network processingResource availability checkingVirtual channel or path routingFunction of the Network Node Interface(NNI)SetupCallProceedingB19Page 19Setting Up a Call-3SetupCallProceedingSetupCall Proceeding?Setup messageCall referenceCalled party addressCalling party addressTraffic characteristicsQuality of serviceVPI/VCI?Call Proceeding?Call reference?Called user deciding to accept callBSetting Up a Call-4SetupCallProceedingSetupCall ProceedingConnect AckConnect?Connect messageCall referenceIndicates call acceptance?Connect AcknowledgeCall referenceB20Page 20Setting Up a Call-5SetupCallProceedingSetupCall ProceedingConnect AckConnect Connect AckConnect?Calling party informed that call is available for user information exchangeBATM Connection Release21Page 21ATM Connection Release(contd)ATM Addressing in a Pure ATM Network?Private networks20 byte addressFormat modeled after OSI NSAP(Network Service Access Point)Mechanisms for administration existHierarchical structure will facilitate virtual connection routing in large ATM networks?Public networksE.164 numbers(telephone numbers)Up to 15 digits?Private networksLAN Mac address will be encapsulated within NSAPB22Page 22Private Address FormatsData Country CodeInternational Code DesignatorE.164 Private Address394745DCCICDRouting FieldsEnd System IDSELSELSELRouting FieldsEnd System IDRouting FieldsEnd System IDE.164 NumberDAddress RegistrationSupplied by ATM NetworkSupplied by Terminal394745DCCICDRouting FieldsEnd System IDSELSELSELRouting FieldsEnd System IDRouting FieldsEnd System IDE.164 Number?Information Exchanged through ILMI*Messages?SEL Byte Ignored by ATM Network and Carried Transparently*-Integrated Layer Management InterfaceC23Page 23ATM Cell Structure?PTI(payload type identifier)indicate the type of payload(user data or not?)congestion notification(like FECN and BECN)?CLP(cell loss priority)congestion control by selective discarding?HEC(header error check)error detection/correction for header onlycorrect one-bit errors and discard multiple-bit errors cell delineationPayload 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 SwitchesSource and Destination Behavior Defined for Available Bit Rate Flow Control VCCs?Bit 1:Carried transparently end-to-end in data cellsUsed by AAL5Payload Type Identifier76543210Generic Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierCLPHeader ErrorCheckPayload(48 bytes)Virtual Channel IdentifierC24Page 24Cell 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 controlVirtual channels/paths with low quality of serviceCells that violate traffic management contract?Key to ATM Traffic Management76543210Generic Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierCLPHeader ErrorCheckPayload(48 bytes)Virtual Channel IdentifierPayload Type IdentifierCLP-Cell Loss Priority Control?CLP=0 cells are guaranteed a CLR no higher than that of CLP=1 cells.?Priority control(also known as selective discard)is a mechanism by which network elements selectively discard CLP=1 cells in order to guarantee a lower CLR to the CLP=0 cells.?Tagging is when the network marks non-conformant cells as CLP=1 rather than immediately discarding them.25Page 25Cell Loss Priority(CLP)and Tagging1.Network Ignores CLP.Does not mark it or look at it.Available for CBR,VBR,and UBRGCRA conformance on all cells,CLP 0 and 1.2.Network may selectively discard CLP=1 cells.Available for CBR*,VBR,ABR,and UBRNetwork Tagging permitted for VBR and UBRThere are two basic modes of operation supported:BHeader Error Check?Header error controlDetection mode:-Protects header only(all five bytes)-Discards cell when header errorCorrection 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 changes76543210Generic Flow ControlVirtual Path IdentifierVirtual Path IdentifierVirtual Channel IdentifierVirtual ChannelIdentifierCLPHeader ErrorCheckPayload(48 bytes)Virtual Channel IdentifierPayload Type IdentifierB26Page 26?Introduction?Physical Layers?ATM Layer?ATM Adaptation Layer?Interfaces?ManagementWhats ATM:Key TechnologiesBATM System ArchitectureEnd StationEnd StationSwitchVoiceDataVideoAALPHYPHYATMPHYATMPHYATMAALVoiceDataVideoCells?Adaptation Layer(AAL):Inserts/extracts information into 48 byte payload?ATM Layer:Adds/removes 5 byte header to payload?Physical Layer:Converts to appropriate electrical or optical format27Page 27ATM Service Categories?CBRConstant Bit RateContinuous flow of data with tight bounds on delay and delay variation?rt-VBRReal-Time Variable Bit RateVariable bandwidth with tight bounds on delay and delay variation?nrt-VBRNon-Real-Time Variable Bit RateVariable bandwidth with tight bound on cell loss?UBRUnspecified Bit RateNo guarantees(i.e.,best effort delivery)?ABRAvailable Bit RateFlow control on source with tight bound on cell lossATM Forum Service Categories BNotes:?1.CVDT is not signalled,it is network specific.n/aCLRCTD and CDVPCR and CDVTSCR and BTCBRrt-VBRnrt-VBR specifiednetwork specificn/aspecifiedspecifiedspecifiedspecifiedunspecified1UBRAttributeATM Layer Services CategoriesspecifiedunspecifiedFeedbackunspecifiedspecifiedunspecifiedunspecifiedABRunspecifiedn/aspecifiedn/aMCR28Page 28CCITT Service ClassificationsClassConnection modeBit rateEnd-to-end timingDACBRequiredCon-stantNotRequiredVariableConnectionlessConnectionorientedExamples?Class A:64 Kbps digital voice?Class B:Variable bit rate encoded video?Class C:Frame Relay over ATM?Class D:CCITT I.364(SMDS)over ATM?Class X:Raw cell service(e.g.,proprietary AAL)CATM Fundamental ConceptAll communications are bursty and of realtime.VoiceEnergyTimeSpeakingPauseListeningSpeakingPauseTherefore,a high performance packet switching network can carry all communications.29Page 29AAL1 for Class APayload47 Bytes?Header functions include:Lost cell detection-Used by Adaptive Clock MethodByte alignment-Allows channelized circu