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ATM and Other Protocols

ATM and Other Protocols. Philip Branch Centre for Telecommunications and Information Engineering (CTIE) Monash University http://www.anspag.monash.edu.au/~pbranch/masters.ppt. Outline. Interworking between ATM and other networks Classical IP over ATM LAN Emulation Multiprotocol over ATM

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ATM and Other Protocols

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  1. ATM and Other Protocols Philip Branch Centre for Telecommunications and Information Engineering (CTIE) Monash University http://www.anspag.monash.edu.au/~pbranch/masters.ppt

  2. Outline • Interworking between ATM and other networks • Classical IP over ATM • LAN Emulation • Multiprotocol over ATM • Label Switching

  3. Heterogeneous Networks • Large installed base of Ethernet • No need for ATM to desktop • ATM backbone / Ethernet clients • Internet based applications

  4. Interworking Between ATM and Other Networks • Connection oriented ATM / connectionless LANs and IP • Addressing • Routing • IP routing / ATM PNNI • Quality of Service

  5. LAN Emulation (LANE) • Emulates a MAC service 802.3 or 802.5 • Basic functionality of Ethernet or Token Ring • Attempts to hide ATM from application • Emulated LANs (ELANs) connected via routers

  6. Motivation for LANE • Most networks are multiprotocol • IP, IPX, NetBUI, AppleTalk • No mapping to ATM • Integration of ATM with existing networks • Through bridges, routers, Ethernet switches and hubs • Huge base of applications not ATM aware, but are Ethernet (or Token Ring) aware

  7. LAN Emulation Issues • ATM non-broadcast multiple access (NBMA) • Ethernet broadcast based • LAN segments connected by bridges and routers • ATM networks connected by switches • LANE simulates broadcast where necessary • No provision for Quality of Service

  8. Trivial Solution for LAN Emulation • ‘Flooding Forwarder’ • Forwarder has point to multipoint connection to every member of the emulated LAN • All messages forwarded to ‘flooding forwarder’ which then transmits to every other member of emulated LAN

  9. Problems of Flooding Forwarder Solution • Overhead on end systems • Flooding forwarder a bottleneck • Flooding forwarder fails to use point-to-point of ATM • most traffic is point to point

  10. LAN Emulation Solution • LAN Emulation Client Software • replaces Ethernet drivers • A number of centralised servers • Broadcast and Unknown Server (BUS) • LAN Emulation Server (LES) • LAN Emulation Configuration Server (LECS) • Typically BUS, LECS and LES on the ATM switch

  11. LAN Emulation Architecture LAN Emulation Service LAN Emulation Clients (LEC) LAN Emulation Configuration Server (LECS) Ethernet Switch/Hub Control Direct & Distribute VCCs LAN Emulation Server (LES) ATM Data Direct VCCs b/t Clients Broadcast & Unknown Server (BUS) Multicast Send & Forward VCCs Ethernet Clients

  12. Broadcasts • Use the BUS • BUS is a ‘flooding forwarder’ • Each LEC connected to BUS by two virtual channel connections (VCCs) • point to point multicast send VCC from LEC to BUS • point to multipoint multicast VCC from BUS to each LEC

  13. LAN Emulation Clients (LECs) • Establish a mesh of point-to-point VCCs with other LECs • Use BUS only when necessary

  14. LAN Emulation Server (LES) • Enable LECs to find unknown ATM address associated with MAC addresses • There are two point-to-point VCCs between each LEC and the LES • control direct to the LES • control distribute from the LES

  15. LAN Emulation Configuration Server (LECS) • Enables automatic configuration of the LES • ‘plug and play’ • Sets up a ‘configure direct’ VCC between the LEC and LECS during initialisation

  16. Configuring the LEC • LEC discovers ATM address of LECS • ILMI, fixed LECS ATM address or well known PVC • LEC sends configure request to LECS • contains LEC ATM address, MAC address, frame size, LAN type etc • LECS sends ATM address of LES • LEC now configured and can join ELAN

  17. Joining the Emulated LAN (ELAN) • LEC establishes control direct VCC to LES • Sends join request to LES • LES establishes control direct VCC to LEC • Sends join response to LEC • contains LECID

  18. Connecting to BUS • LEC sends LE-ARP to LES • LES responds with BUS ATM address • LEC establishes multicast send VCC to BUS • BUS establishes multicast forward VCC to LEC • LEC now fully operational!

  19. Address Resolution • LE-ARP cache in LEC • table of MAC/ATM address pairs • Unknown MAC address sent to LES • LE-ARP request • LES responds with ATM address • LE-ARP response • LEC establishes VCC to unknown LEC

  20. Data transfer • Broadcast and multicast data sent to BUS • Unicast data sent across VCC identified in the LE-ARP cache

  21. Limitations of LAN Emulation • Scales poorly • mesh of unicast connections • LES and BUS bottlenecks • No quality of service • Still need routers to connect emulated LANs even when on the same ATM network

  22. Classical IP over ATM (CLP) • IETF RFC1577 • Uses ATM to emulate IP subnet • Logical IP subnetwork (LIS) • LIS a collection of ATM attached hosts and ATM attached IP routers

  23. Address Resolution in CLP • Each LIS has an ARP server • Clients register with ARP server • Similar to LANE except IP addresses • Multicast Address Resolution Protocol (MARS)

  24. Weaknesses of Classical IP over ATM • Multiple subnets on the one ATM network • traffic between them must go through a router • No quality of service across IP subnets • IP / ATM routers expensive

  25. Multiprotocol over ATM (MPOA) • Attempts to provide direct (cut-through) routes over ATM • Essentially an address resolution scheme • Separates route finding from connections • Based on client / server model • Can support QoS

  26. MPOA Components • MPOA Clients (MPC) • Edge devices • Either an ATM attached host or a ATM attached switch / router • MPOA Server (MPS) • Provides ATM address of edge devices based on layer 3 address

  27. MPOA Procedure for Routing • Source edge device examines address packet • Sends address to route server • Route server returns address of destination ATM edge device • Source edge device sets up ATM connection to destination • Source caches ATM address for future transfers

  28. MPOA Routing • MPOA does not define a routing protocol • Routing request information carried in Next Hop Resolution Protocol (NHRP) • MPS can obtain destination addresses using • IETF OSPF or RIP • ATM Forum IPNNI

  29. Virtual Router Concept • MPOA makes whole ATM switching network into a ‘virtual router’ • Edge devices analogous to router interface cards • Route server analogous to control processor • ATM switching fabric analogous to the router backplane

  30. Label Switching Routers • Labels behave like VPI/VCI for IP packets • local significance only • change on a hop-by-hop basis

  31. Main Label Switching Proposals • Ipsilon (only one actually implemented) • IP switching • CISCO • tag switching • Toshiba • Cell Switching Router • Multi-protocol label switching • MPLS

  32. Ipsilon IP switching • IP over ATM complex • IP switching solution is the removal of ATM control plane • ATM ARP, PNNI, Q.2931 removed • Replaced by IP level label binding protocol • IPSILON Flow Management Protocol (IFMP) • Direct control of ATM hardware by IP layer • General Switch Management Protocol (GSMP)

  33. IP Switching operation • Traffic flows between IP switches on default VPI/VCI • Flow classification module identifies flows likely to benefit from being label switched • Uses IFMP to inform neighbouring switches • issues a redirection message • IP packets segmented to cells with new VPI/VCI

  34. Flow classification • Packet rate • examine rate of packets for destination • Identify flow type • eg FTPs likely to be long-lived flow

  35. IFMP • Point to point protocol between IP switches • IFMP traffic on well known VCI/VPI value • Softstate protocol • will timeout unless refreshed

  36. Tag Switching • Similar to IP switching • Tag distribution protocol • Tag edge routers • affix tag to IP packets • Tag switches • operate within the network

  37. Differences to IP switching • Can be used at layer 3 or layer 2 • flow label field in IPv6 (layer 3) • VPI/VCI in ATM (layer 2) • Hierarchy of routing knowledge • segment domains into a hierarchy • improved scalability • Aims at link layer independence • not just ATM

  38. Multi Protocol Label Switching • An attempt to standardise label switching • IETF working group • Based on Tag Switching • Much effort devoted to MPLS over ATM • Label Distribution Protocol • uses TCP to distribute label messages

  39. Summary • Classical IP over ATM • LAN Emulation • Multiprotocol over ATM • Label Switching

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