第五章_ATM技术.pdf

1 Page 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 What s ATM Key Technologies Introduction Physical Layers ATM Layer ATM Adaptation Layer Interfaces Traffic Control and Management Where s ATM Application and Future Trend 2 Page 2 Why ATM Technology Driven Scalability shorter for realtime just a compromise 32 64 2 48 48 5 53 Rationale for the Cell Size Delay packetization 48x8 32Kbps 12ms propagation 2ms for 500km switching 72us for 3 switches queueing 225us for 3 switches Overhead 5 48 10 4 in ATM vs 2 512 0 39 in frame relay Reliability 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 errors Packetization Delay Advantage of Small Cells Percent Overhead and Packetization Delay for 64 Kbps Voice Payload Bytes 0 20 40 60 80 100 020406080 0 2 4 6 8 10 Delay Overhead Delay ms Overhead 12 Page 12 Queuing Advantage of Small Cells 100 byte message 100 other active connections 45 Mbps Delay and delay variation are small for small messages e g a digitized voice sample High overheadWait for other cells Just fits in one cell Payload bytes Max Delay ms 0 2 4 6 8 10 12 150100150200250300 A Why 53 Bytes 64 532 4 48 5 Compromise reached in ITU TS Study Group XVIII in June 1989 13 Page 13 ATM Cell simplified Header 5 bytes48 bytes Header contains information to allow cell to be forwarded to its destination PayloadHeader ATM UNI Cell CLP Cell Loss Priority 5 Bytes 48 Bytes Virtual Channel Identifier 76543210 Payload Type Identifier CLP Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier Header Error Check Payload 48 bytes Virtual Channel Identifier 14 Page 14 NNI Supports 212Virtual 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 Priority Cell Format Virtual Channel Identifier 76543210 Payload Type Identifier CLP Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier Header Error Check Payload 48 bytes Virtual Path Identifier Virtual Path Identifier C ATM 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 relay two layer addresses for easy management 2 8 256VPs at UNI and 2 12 4096VPs at NNI 2 16 65536 VCs in a VP switching by address swapping and self routing 15 Page 15 Generic Flow Control Used for UNI only Not NNI Currently undefined Set to 0000B Proposed future uses Flow control Shared media multiple access 76543210 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier CLP Header Error Check Payload 48 bytes Virtual Channel Identifier Payload Type Identifier B What s ATM Virtual Networking PortVPI VCIPortVPI VCI 10 3730 76 10 4250 52 20 3760 22 20 7840 88 Connection Table 3742 3778 76 52 22 88 1 2 3 4 5 6 Video Data Voice Video Data Voice Video Data Voice Video Video Video 76543210 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier CLP Header Error Check Payload 48 bytes Virtual Channel Identifier Payload Type Identifier 16 Page 16 Two Layered Virtual networking Virtual Paths and Virtual Channels Physical Link Virtual Path Virtual Channel 76543210 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier CLP Header Error Check Payload 48 bytes Virtual Channel Identifier Payload 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 carrier VPI 1 VPI 2 VPI 3 VPI 4 VPI 5 VPI 6 VCI 31 VCI 32 VCI 31 VCI 40 VCI 96 VCI 97 VCI 55 VCI 57 VCI 99 VCI 32 VCI 96 VCI 97 ATM Switches 76543210 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier CLP Header Error Check Payload 48 bytes Virtual Channel Identifier Payload Type Identifier Virtual Path Switching and Virtual Channel Switching 17 Page 17 Permanent 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 switches Network Management System VPI VCI VPI VCI VPI VCI VPI VCI B Switched Virtual Connections ATM Switch Signalling 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 5 Call Processing B 18 Page 18 Setting Up a Call 1 Setup Call Proceeding AB A 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 Setting Up a Call 2 Internal network processing Resource availability checking Virtual channel or path routing Function of the Network Node Interface NNI Setup Call Proceeding B 19 Page 19 Setting Up a Call 3 Setup Call Proceeding Setup Call Proceeding Setup message Call reference Called party address Calling party address Traffic characteristics Quality of service VPI VCI Call Proceeding Call reference Called user deciding to accept call B Setting Up a Call 4 Setup Call Proceeding Setup Call Proceeding Connect Ack Connect Connect message Call reference Indicates call acceptance Connect Acknowledge Call reference B 20 Page 20 Setting Up a Call 5 Setup Call Proceeding Setup Call Proceeding Connect Ack Connect Connect Ack Connect Calling party informed that call is available for user information exchange B ATM Connection Release 21 Page 21 ATM Connection Release contd ATM Addressing in a Pure ATM Network 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 LAN Mac address will be encapsulated within NSAP B 22 Page 22 Private Address Formats Data Country Code International Code Designator E 164 Private Address 39 47 45 DCC ICD Routing FieldsEnd System IDSEL SEL SEL Routing FieldsEnd System ID Routing FieldsEnd System IDE 164 Number D Address Registration Supplied by ATM NetworkSupplied by Terminal 39 47 45 DCC ICD Routing FieldsEnd System IDSEL SEL SEL Routing FieldsEnd System ID Routing FieldsEnd System IDE 164 Number Information Exchanged through ILMI Messages SEL Byte Ignored by ATM Network and Carried Transparently Integrated Layer Management Interface C 23 Page 23 ATM 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 only correct one bit errors and discard multiple bit errors cell delineation Payload 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 Payload Type Identifier 76543210 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier CLP Header Error Check Payload 48 bytes Virtual Channel Identifier C 24 Page 24 Cell 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 76543210 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier CLP Header Error Check Payload 48 bytes Virtual Channel Identifier Payload Type Identifier CLP 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 25 Page 25 Cell Loss Priority CLP and Tagging 1 Network Ignores CLP Does not mark it or look at it Available for CBR VBR and UBR GCRA conformance on all cells CLP 0 and 1 2 Network may selectively discard CLP 1 cells Available for CBR VBR ABR and UBR Network Tagging permitted for VBR and UBR There are two basic modes of operation supported B Header 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 76543210 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual Channel Identifier CLP Header Error Check Payload 48 bytes Virtual Channel Identifier Payload Type Identifier B 26 Page 26 Introduction Physical Layers ATM Layer ATM Adaptation Layer Interfaces Management What s ATM Key Technologies B ATM System Architecture End StationEnd StationSwitch Voice Data Video A A L P H Y P H Y A T M P H Y A T M P H Y A T M A A L Voice Data Video Cells 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 format 27 Page 27 ATM 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 ATM Forum Service Categories B Notes 1 CVDT is not signalled it is network specific n a CLR CTD and CDV PCR and CDVT SCR and BT CBRrt VBRnrt VBR specified network specific n a specified specified specifiedspecified unspecified 1 UBR Attribute ATM Layer Services Categories specifiedunspecified Feedback unspecified specified unspecified unspecified ABR unspecified n a specifiedn a MCR 28 Page 28 CCITT Service Classifications Class Connection mode Bit rate End to end timing DACB Required Con stant Not Required Variable Connectionless Connection oriented Examples 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 C ATM Fundamental Concept All communications are bursty and of realtime Voice Energy Time Speaking Pause Listening Speaking Pause Therefore a high performance packet switching network can carry all communications 29 Page 29 AAL1 for Class A Payload 47 Bytes Header functions include Lost cell detection Used by Adaptive Clock Method Byte alignment Allows channelized circuit emulation e g channelized DS1 E1 etc Time stamp Used for end to end clock synchronization e g Synchronous Residual Time Stamp method 1 Byte AAL1 Header B AAL1 Adaptive Clock Method Water Mark Speed up bit clock Slow down bit clock Received Cells Substitute Cells Continuous Bit Stream 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 stream B 30 Page 30 M I D AAL3 4 for Classes C and D 0 65535Bytes Bytes44 or 8 Error Checking Error Checking 44 44 44 44 Pad 44 Bytes of Data per Cell CRC Checking per Cell Message Identifier MID Allows Multiple Interleaved Packets on a Virtual Connection User Data M I D 22 22 22 C R C Data User Data M I D C R C User Data M I D C R C C R C D Pad AAL 5 for Classes C and D 0 65535 224Bytes Bytes Not drawn to scale Error detection fields Last 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 48 48 0 1 Data 0 47 0 L e n C R C C 31 Page 31 User 1User 2User 3User 1User 3 ATM Cell Cell Header 5 Octets AAL2 Header 3 Octets AAL2 Payload variable AAL2 for Class B Small payload to reduce packetization delay B Introduction Physical Layers ATM Layer ATM Adaptation Layer Interfaces Management What s ATM Key Technologies C 32 Page 32 ATM Networking and Interfaces Private UNI Private NNI Public UNI ATM DXI B ICI UNIUser Network Interface NNINetwork Node Interface B ICIBISDN Inter Carrier Interface ATM DXIData eXchange Interface FUNIATM Frame Based UNI Interface Metropolis Data Services Inc Country Wide Carrier Services Public NNI FUNI FUNI D ATM DXI DTE e g router DCE e g CSU DSU UNIDXI FrameCells Provides access to ATM for installed equipment ATM Wide Area Public Private Network HDLC Frames HSSI V 35 Physical Layer Segmentation Reassembly Hardware Traffic Shaping Hardware Cells DS3 PHY SONET SDH B 33 Page 33 ATM Frame Based UNI FUNI The FUNI centralizes the SAR function by moving it from the customer premises to the ATM switch The FUNI provides improved efficiency for the access line bandwidth when compared to the cell based access line of the ATM DXI Full and Fractional T1 E1 data rates are supported Standard SNMP and MIBs are supported ATM FUNI Customer Premises ATM FUNI Frames Router w HDLC Interface ATM ATM FUNI Interface SAR D B 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 34 Page 34 Private UNI ATM Forum Physical Layer UNI Interfaces Frame FormatBit Rate Line RateTransmission Media Cell Stream STS 1 FDDI STS 3c STM 1 STS 3c STM 1 Cell Stream STS 3c STM 1 STS 12 STM 4 25 6 Mb s 32 Mbaud 51 84 Mb s 100 Mb s 125 Mbaud 155 52 Mb s 155 52 Mb s 155 52 Mb s 194 4 Mbaud 155 52 Mb s 622 08 Mb s UTP 3 UTP 3 MMF UTP 5 STP SMF MMF Coax pair MMF STP UTP 3 SMF Single Mode Fiber MMF Multimode Fiber SMF MMF STS 48 STM 16 2 488 32 Mb s SMF Under Development UTP Unshielded Twisted Pair STP Shielded Twisted Pair DS1 and DS3 Also Private Speeds B Public UNI ATM Forum Physical Layer UNI Interfaces Frame FormatBit RateTransmission Media DS3 STS 3c STM 1 E1 E3 J2 N X T1 1 544 Mb s 44 736 Mb s 155 520 Mb s 2 048 Mb s 34 368 Mb s 6 312 Mb s N X 1 544 Mb s Twisted Pair Coax Pair SMF Twisted Pair Coax Pair Coax pair Coax pair Twisted pair Under Development SMF Single Mode Fiber PLCP Physical Layer Convergence Protocol DS1 N X E1N X 2 048Mb sTwisted pair B 35 Page 35 Two Sublayers Transmission Convergence Sublayer Physical Layer Medium Dependent Sublayer 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 9 R o w s 270 columns 9 bytes Maintenance and operations 1 Synchronous Payload Envelope 1 column of overhead 9 260 8 125 sec 149 76 Mbps payload 125 sec A 36 Page 36 HEC Cell Delineation For SONET etc Peek ahead at the cell format 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 A 1 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 125 sec Framing Bit 24 bytes 37 Page 37 44 Mbps DS3 Bits Framing and maintenance Payload 106 4 sec frame 7 8 84 106 4 sec 44 21 Mbps of payload TCS must delimit 53 byte cells within payload bits 841841841841841841841841 DS3 Cell Delineation PLCP Mapped F F F F 11 10 0 1 C Cell Cell Cell Cell 21153Bytes 125 sec F is framing pattern 12 cells 125 sec means 96 000 cells per second or 36 864 Mbps of cell payload Stuff is either 13 or 14 nibbles and is indicated by C HEC Delineation instead of PLCP is also specified Stuff 38 Page 38 2 048 Mbps E1 32 x 8 125 s 2 048 Mbps HEC cell delineation used Framing and Overhead Bytes Cell Carrying Bytes 32 Bytes 125 s 012 151617 31 Bytes A 34 368 Mbps E3 59 x 9 6 x 8 125 s 34 368 Mbps HEC cell delineation used Framing and Overhead Bytes 59 Columns 9 Rows 125 s Frame 39 Page 39 6 3 Mbps J2 Coding F F F F 789 bits 125 s PayloadReservedFraming and Maintenance 6 312 Mbps 98 Continuous Time Slots 8 bits and 5 F bits 789 bits 98 Octets of Payload F is Framing Pattern and OAM Functions B 25 6 Mbps UTP 3 Based on IEEE 802 5 physical layer with 4B 5B coding plus scrambling 32 Mbaud x 4 5 25 6 Mbps Cells delineated by special symbol pairs xCellx Reset Scramble xCell4 No Scramble Reset or A 40 Page 40 T1 E1 3 T1 E13 T1 E1 Inverse Multiplexing with ATM IMA Uses n parallel T1 E1 links Preserves cell order Provides finer granularity of bandwidth use over the WAN A Introduction Physical Layers ATM Layer ATM Adaptation Layer Interfaces Switching and routing Traffic Control and Management What s ATM Key Technologies C 41 Page 4