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Agenda

Agenda. ATM Technology Overview. ATM Technology Overview. ATM and the ATM Cell ATM Switching Technology ATM Protocol Stack ATM Standards. Asynchronous Transfer Mode (ATM). Originally developed in ITU (CCITT) as part of B-ISDN Initially designed for high-speed fiber optic lines

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Agenda

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  1. Agenda ATM Technology Overview

  2. ATM Technology Overview • ATM and the ATM Cell • ATM Switching Technology • ATM Protocol Stack • ATM Standards

  3. Asynchronous Transfer Mode (ATM) • Originally developed in ITU (CCITT) as part of B-ISDN • Initially designed for high-speed fiber optic lines • Worldwide support from: • computer vendors • data networking vendors • telecommunications vendors • network planners, designers, and administrators

  4. What is ATM? • ATM is packet switching! • Switched or permanent connections • Traffic type independent (voice, data, interactive video) • Fixed length packet - 53 bytes (cell) header payload Fixed length packet = cell

  5. What is ATM? Conventional LAN Conventional Telecom ATM Traffic Type Transmission Unit Switching Connection Type Delivery Access Rate & Media Data, Voice, Video Fixed Cell Cell Connection-oriented Defined Classes Dedicated Application Dependent Voice Fixed Frame Circuit Connection-oriented Guaranteed Dedicated Channel Dependent Data Variable Packet Packet Connectionless Best Effort Shared Protocol Dependent

  6. ATM Cell Relay:The Underlying Technology • Cell Features Benefit • Small Low latency to support real-time services like audio and video • Fixed Length Fast hardware switching and • scalability • Standardized Usable in all networks (LAN and WAN) Transmission Cable 5 Bytes 48 Bytes Header Data Payload

  7. ATM Technology Overview • ATM and the ATM Cell • ATM Switching Technology • ATM Protocol Stack • ATM Standards

  8. ATM Protocol Stack Upper Layers ATM Adaptation Layer ATM Layer Physical Layer

  9. ATM Physical Layer • CCITT SDH • • STM-1 (155 Mbps) • • STM-4 (622 Mbps) • • STM-16 (2.5 Gbps) • ANSI/Bellcore SONET • • OC-3 (155 Mbps) • • OC-12 (622 Mbps) • • OC-48 (2.5 Gbps) • ATM Forum • • SONET OC-3c (155 Mbps) • • UTP-5 and STP • • Multimode Fiber (155 Mbps) • • Multimode Fiber (100 Mbps) • • UTP-3 (51 Mbps) • DS-3 (45 Mbps) • • E-3 (34 Mbps) • • E-1 (2 Mbps) • • DS-1 (1.544 Mbps) • ATM 25 Consortium (led by IBM) • • UTP-3 (25 Mbps)

  10. SONET/SDH Hierarchy • SONET = Synchronous Optical Network (US) • SDH = Synchronous Digital Hierarchy (Europe) • SONET = SDH • OC-1 51.8 Mbps • OC-3 STM-1 155.52 Mbps • OC-12 STM-4 622.08 Mbps • OC-48 STM-12 2.488 Gbps • STS = physical framing • OC = optical implementation • OC-3c = OC-3 concatenated SONET SDH Rate

  11. The ATM Layer header payload Fixed length packet = cell

  12. Anatomy of an ATM Cell 8 7 6 5 4 3 2 1 • GFC (UNI) or VPI (NNI) VPI • VPI VCI • VCI • VCI PTI CLP • HEC Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Header 48 Bytes Payload VPI: Virtual Path Identifier CLP: Cell Loss Priority VCI: Virtual Channel Identifier HEC: Header Error Check PTI: Payload Type Indicator GFC: Generic Flow Control

  13. ATM Cell Header • PTI: Payload Type Indicator • Bit 1: User Indication (EPD in AAL5, marks last cell in packet) • Bit 2: indicates congestion up-stream (FECN) • Bit 3: discriminates between data & OAM cells • CLP: Cell Loss Priority • CLP bit is set to prioritize cell to be dropped (Policing) • HEC: Header Error Check • GFC: Generic Flow Control

  14. Physical Transmission Link VCs VCs VP VP VCs VCs VP VP Virtual Paths &Virtual Channels • VPI: Virtual Path Identifier • VCI: Virtual Channel Identifier • Unique on a link-by-link basis • Virtual channels are contained within virtual paths • Interpreted at each switch to: • determine output link • determine outgoing VPI/VCI • Two-level structure: • allows “trunking” of virtual channels as one virtual path • virtual path can be switched • both used to route cells through network

  15. Virtual Paths &Virtual Channels VC1 VC2 VC3 VC4 VC5 VC6 VC1 VC2 VC3 VC4 VC5 VC6 VC1 VC2 VC3 VC4 VC5 VC6 VC1 VC2 VC3 VC4 VC5 VC6 VC1 VC2 VC3 VC4 VC5 VC6 VC1 VC2 VC3 VC4 VC5 VC6 VP1 VP1 ATM Switch ATM Switch ATM Switch

  16. ATM Network Interfaces WAN B-ICI Public NNI WAN Service Provider Public UNI Customer Premises Private UNI Private NNI Private UNI

  17. ATM Addressing • Required for interoperability • Public-switched networks use E.164 addresses: • 4-bit type indicator • 60-bit address container • (15 BCD digit phone numbers) • ATM Forum and IETF • E.164 + 48-bit address (use one or both) • OSI NSAP (can encapsulate any address) • Address administration is handled by ILMI

  18. ATM Signaling • ATM is connection oriented. A virtual connection must be established before cells can be sent. • Connections can be established: • administratively as Permanent Virtual Circuits (PVC) (telephone switchboard operator) • dynamically as Switched Virtual Circuits (SVC) (automatic, like today’s telephone switches) • Connection establishment includes: • route set-up (path) • resource allocation (QoS - bandwidth)

  19. Traffic Management Types of Traffic • CBR (Constant Bit Rate) • VBR (Variable Bit Rate) • ABR (Available Bit Rate) Traffic Management Function • Traffic Shaping • Traffic Policing • Congestion Control

  20. Traffic Management Adapter Switch Work Station Work Station Peak Average Shaping Policing • Switch polices traffic (UPC) • Dual Leaky Buckets • CLP bit • Bursty traffic • Adapters shape traffic

  21. Traffic Management Switch Switch Work Station Work Station Transmit Transmit Transmit Output contention may cause switch to set cell FECN bit End station sees FECN bit and sends a RM cell to other end station End station receives RM cell and reduces transmission rate

  22. ATM Service Types Desktop & MPEG Video Not Defined Not Widely Used Class A Class B Class C Class D Class X Voice Legacy Video Private Line Video Playback Compressed Voice Frame Relay SMDS Cell Relay Service AAL1 AAL2 AAL 3/4 AAL5 ATM Adaptation Layer CBR ATM Traffic Type CBR/VBR/UBR/ABR N/A UBR/ABR UBR/ABR

  23. ATM Internetworking Network Configuration (ILMI) LAN Emulation • MAC address registration • Address resolution IP-over-ATM (Classical IP) • IP address registration • ARP (RFC 1577) Q.2931 Signaling • Call setup • End of connection

  24. ATM Technology Overview • ATM and the ATM Cell • ATM Switching Technology • ATM Protocol Stack • ATM Standards

  25. ATM Switching • Connections (routes) set up by software • Routing (path through multiple-switch network) and resource allocation is performed once per connection by switch control CPU • Cells are switched by hardware • Hardware (table lookup + switching fabric) switches each incoming cell to appropriate output port • Once a connection is established, cells are not touched by software • ATM LANs grow by adding more switches • More aggregate bandwidth • Negligible additional latency (10-50 microseconds per switch hop vs. 10000 microseconds per router hop)

  26. ATM Switching: Architectures • Switch fabric architecture is critical because it affects: • aggregate throughput capacity • cell transit delay • cell blocking probabilities • port speeds • complexity of routing tables and switch controller interface • required fabric logic speeds • Many forms and variants of switching architectures are possible; each has advantages and disadvantages • Two commercially-implemented ATM switch architectures: • matrix • contentionless, time division

  27. 16x16 Matrix Architecture Port 0 Port 1 Port 0 Port 1 4 Port 2 Port 3 Port 2 Port 3 Port 4 Port 5 Port 4 Port 5 5 Port 6 Port 7 Port 6 Port 7 Port 8 Port 9 Port 8 Port 9 Port 10 Port 11 Port 10 Port 11 Port 12 Port 13 Port 12 Port 13 Port 14 Port 15 Port 14 Port 15

  28. ATM Switching: Matrix • Advantages • Symmetric structure uses array of identical • elements (potential economies of scale) • Disadvantages • Blocking—probability of losing cells is not zero • Long transit delays—multiple stages require higher logic • speeds (2X) than actual switch throughput capacity • Port speed changes require matrix element changes • Multicast implemented by copying cells

  29. Cell Copying Multicast (Congestion-Prone) Source Cell Copying ATM Switch ATM Switch Multiple Cells Transported Through Switch Fabric

  30. ATM Switching:Contentionless Time Division Ports 1-4 622 Mbps (OC-12) 2.5 Gbps Switch Fabric Ports 13-16 Ports 5-8 Benefits: 4 x 155 Mbps OC-3c or 6 x 100 Mbps TAXI with Multiple Priority Output Buffers • Non-blocking • Deterministic performance • Flexible port speeds • Congestionless hardware multicast • Lowest transit delays Ports 9-12

  31. ATM Switching:Contentionless Time Division • Advantages • Non-blocking • Deterministic performance—probability of cell loss = 0 • Flexible port speeds • (DS-1, E-1, DS-3, E-3, 100M, 155M, 622M) • Hardware multicast without increasing fabric cell traffic • Low transit delays • Disadvantages • Limited scalability on single TDM fabric • Use time-space-time to expand

  32. CongestionlessMulticast Connections No Source Cell Copying Single Cell Through Switch Fabric Single Cell Transported Benefit: Eliminates Congestion within Switching Fabric and Network

  33. ILMI: Network Configuration ASX-200 ASX-200 ATM ATM ATM ATM End Station ATM End Station ATM Switch ATM Switch Host makes physical connection SNMP Cold Start Trap VC = 16 NSAP Prefix NSAP Prefix + End System Identifier • Automatically configure link • •UNI vs. NNI (version) • • Public vs. private • • ATM address registration • • ATM layer parameters • Discovery of IP address for network management

  34. Q.2931:Establish SVC ASX-200 ASX-200 ATM ATM ATM ATM End Station ATM End Station ATM Switch ATM Switch Setup VC=5 1. 2. 3. 4. 5. 6. 7. Setup (VPI/VCI) Setup (VPI/VCI) Connect Connect ACK Connect Connect Connect ACK Connect ACK VC is set up

  35. Q.2931:Tear Down SVC ASX-200 ASX-200 ATM ATM ATM ATM End Station ATM End Station ATM Switch ATM Switch Data is sent Release 1. 2. 3. 4. Release complete Release Release Release complete Release complete

  36. Features of IP-over-ATM • Interoperability with existing IP networks • Simplified network administration (virtual IP network) • Seamless connection to ATM from Ethernet, Token Ring, and FDDI LANs • Transparently handles the differences between connectionless (conventional LANs) and connection-oriented (ATM) networks • Data encapsulation and transmission (RFC 1483) • Address resolution—translates between the 4-Byte IP address and the 20-Byte ATM address • Multicast group management (only with SPANS)

  37. IP-over-ATM: Status TCP/IP in ATM LANs • Operational today in FORE ATM LANs (SVC-based) • Encapsulate IP packets over ATM (RFC 1483) • Interoperable with other vendors over PVCs* and SVCs* • SVC interoperability based on ATM Forum Q.2931 TCP/IP in extended ATM LAN/WANs • Single ARP server is inadequate • Must use distributed “address-lookup” or “routing” solution for scalability and fault tolerance *PVC-Permanent Virtual Circuit *SVC-Switched Virtual Circuit

  38. Typical LAN Structure Bridge/Router Ethernet LAN Host LAN Host Higher Layer Applications Higher Layer Applications IP IP IP IP R B LAN MAC LAN MAC LAN MAC LAN MAC LAN PMD LAN PMD LAN PMD LAN PMD

  39. IP-over-ATMStructure ASX-200 LAX-20 ATM ATM Ethernet Server ATM End Station LAN Host ATM Switch LAN Access Switch Higher Layer Applications Higher Layer Applications IP IP IP IP LAN MAC LAN MAC RFC 1577 RFC 1577 AAL 5 AAL 5 ATM Layer ATM Layer ATM Layer Physical Layer Physical Layer Physical Layer LAN PMD LAN PMD

  40. IP-over-ATMAddress Registration ASX-200 LAX-20 ATM ATM Ethernet Server ATM End Station LAN Host ATM Switch LAN Access Switch IP drivers in end stations set up connection (using Q.2931) to a manually configured server ATM address. ATM connection InARP request InARP reply

  41. IP-over-ATMARP ASX-200 LAX-20 ATM ATM Ethernet Server ATM End Station LAN Host ATM Switch LAN Access Switch ATMARP request Host checks ARP cache for ATM address. If no ATM address, sends ATMARP request. ATMARP reply Host looks for existing VC to ATM address. If it finds VC, sends data; If no VC, uses Q.2931 to set up VC. ATM connection

  42. ASX-200 LAX-20 ATM ATM Ethernet Server ATM End Station LAN Host ATM Switch LAN Access Switch Data Is Sent Data is sent Cells Cells IP Packets Broadcast Packets decoded from Ethernet frame Cells are reassembled into packets, then put in Ethernet frame Cells are policed, buffered, and congestion controlled IP packets are segmented into cells which are then shaped

  43. Features of LAN Emulation • Interoperability with existing protocols • Immediately supports existing applications running over IP, IPX, Banyan Vines, DECnet, AppleTalk • Seamless connection to ATM from Ethernet, Token Ring, and FDDI LANs • Transparently handles the differences between connectionless (conventional LANs) and connection-oriented (ATM) networks • Data encapsulation and transmission • Address resolution—translates between the 48-bit MAC address and the 20-byte ATM address • Multicast group management • Simplified network administration • Components • LAN emulation driver—ARP and point-to-point connectivity • LAN emulation server—provide ARP information

  44. ATM Forum LAN Emulation Model • LAN emulation User-to-Network Interface (LUNI) • Current model • LAN Emulation Clients (LEC) • LAN Emulation Servers (LES) • LAN Emulation Configuration Servers (LECS) • Broadcast and Unknown Servers (BUS) • LAN Emulation Network-to-Network Interface (LENNI) • Future definition by the Forum

  45. ATM LAN EmulationStructure LAX-20 ASX-200 ATM ATM Ethernet ATM End Station (LEC) LAN Access Switch (LEC) LES LAN Host ATM Switch Higher Layer Applications Higher Layer Applications IP IPX etc. IP IPX etc. IP IP NDIS ODI NDIS ODI LAN Emulation LAN Emulation LAN MAC LAN MAC RFC 1483 RFC 1483 AAL 5 AAL 5 ATM Layer ATM Layer ATM Layer Physical Layer Physical Layer Physical Layer LAN PMD LAN PMD

  46. ASX-200 ForeRunner ATM Switch LAX-20 ForeRunner LAN Access Switch LAN EmulationAddress Registration BUS Ethernet A LES ATM End station LECS SVC to LECS X LAN Emulation drivers in end stations set up connection (using Q.2931). Initialization Request Initialization Response SVC to LES Address Registration Request Address Registration Response

  47. ASX-200 ForeRunner ATM Switch LAX-20 ForeRunner LAN Access Switch LAN EmulationLES Address Resolution BUS Ethernet A ATM End station LES 1. B X Address Request ATM End station Address 2a. (Direct via the LAN Emulation Server) -OR- Address Request 2b. Address (Request Forwarded) (Bridge responds via the LAN Emulation Server)

  48. ASX-200 ForeRunner ATM Switch LAX-20 ForeRunner LAN Access Switch LAN EmulationCommunication using BUS BUS Ethernet A ATM End station LES 1. B X Address Request 2a. Address -OR- Data Sent Floods 2b.

  49. Benefits of LAN Emulation • Multiple Emulated LANs (VLANs) • Distinct emulated LANs • Broadcast traffic seen on one emulated LAN is not seen on different emulated LANs • LAN Emulation Configuration Service (LECS) • Addition of dynamic configuration capabilities • Physical connections no longer define LAN membership • Simplified network management • Support of Conventional Systems • Allows existing protocols and applications to run unmodified over an ATM network • Provides conventional LAN-to-ATM connectivity

  50. ATM Technology Overview • ATM and the ATM Cell • ATM Switching Technology • ATM Protocol Stack • ATM Standards

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