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IP over ATM

IP over ATM. Integrated Network Services Almerindo Graziano. Introduction. Characteristics of IP and ATM IP over ATM - Overlay Model Data encapsulation CLIP NHRP LANE MPOA Conclusions. ATM. ATM is connection oriented IP is connectionless ATM has built-in QoS support

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IP over ATM

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  1. IP over ATM Integrated Network Services Almerindo Graziano

  2. Introduction • Characteristics of IP and ATM • IP over ATM - Overlay Model • Data encapsulation • CLIP • NHRP • LANE • MPOA • Conclusions

  3. ATM • ATM is connection oriented • IP is connectionless • ATM has built-in QoS support • IP uses best-effort • Two approaches • Connections established on demand • IP traffic is carried over pre-configured circuits • Both approaches have pros and cons

  4. IP over ATM • Overlay Model • ATM is treated as a Data Link layer on which IP runs • Classical IP over ATM (CLIP) • Next Hop Resolution Protocol (NHRP) • LAN Emulation (LANE) • Multiprotocol Over ATM (MPOA)

  5. CLIP • All members of a LIS (host or router) are under the same administrative control • A LIS is given ONE IP subnet address • CLIP

  6. Classical IP over ATM • The ATM network is divided into a number of Logical IP Subnet (LIS) • Systems within a LIS communicate through direct ATM connections • Each LIS has an ARP server called ATMARP • ARP queries are sent to the ATMARP server • Systems in different LIS communicate through a router • A router is a member of multiple LIS

  7. ATMARP server • There is one for each LIS • It holds a table of <IP address,ATM address> • A wants to communicate with B and it knows B’s IP address • A send an ARP_REQUEST to the ATMARP server • If the IP address is found an ARP_REPLY is sent • Otherwise an ARP_NACK packet is sent

  8. ATM Network LIS 3 R2 R3 H1 H6 H2 H3 R5 R4 LIS 1 H4 ATM ARP server ATM ARP server ATM ARP server R1 H5 LIS 2 Classical IP Over ATM

  9. Data Encapsulation • How do we carry different protocols • How do we identify different protocols • VC multiplexing • LLC/SNAP • TULIP • TUNIC

  10. VC multiplexing • VC multiplexing or null encapsulation • A different VC is required to carry each layer 3 protocol • One VC carries the IP protocol • One VC carries the IPX protocol etc.. • Not very suitable in a multiprotocol environment

  11. LLC/SNAP encapsulation • Similar to the IEEE 802 • Multiple protocols can be carried in the same VC • Less expensive • Can we do better than this? • Once established a VC, we don’t actually need the IP header

  12. TULIP/TUNIC • TULIP (TCP an UDP over Lightweight IP) • Only the layer 4 protocol identifier is kept • TUNIC (TCP and UDP over Nonexistent IP) Connection • The IP header is eliminated • A different VC is created for each layer 4 protocol

  13. CLIP Limitations • Inter-LIS communication has to go through a router • Both parties are attached to same ATM network • Can be a problem in an ATM WAN • NHRP • MPOA

  14. NHRP • NHRP (Next Hop Resolution Protocol) • NHRP servers and NHRP client • Each LIS has at least 1 NHRP server • A server can serve more than 1 LIS • A server has a table of <IP address,ATM address> • Every ES is a NHRP client

  15. NHRP • For intra-LIS communication, an NHRP server works as an ATMARP server • It resolves IP addresses into ATM addresses • For inter-LIS communication, NHSs are interconnected to exchange NHRP queries • When an NHS cannot solve an IP address, it forwards the query to another NHS • If the destination host is not part of the same ATM network, the NHS provides the address of the egress router • Intermediate NHSs store NHRP replies into their cache

  16. ATM Network LIS 3 NHS NHS R2 R3 H1 H6 H2 H3 R5 R4 LIS 1 H4 ATM ARP server ATM ARP server ATM ARP server R1 H5 LIS 2 NHRP

  17. LANE • LAN technologies such as Ethernet are widely used • However, new applications require higher bandwidth and QoS support • LANE (LAN Emulation) • Allows ATM to coexist with legacy LANs • Allows ATM to be gradually introduced into existing legacy LANs • Emulates IEEE 802 LANs without any change to upper layer protocols

  18. Legacy LANs • Connectionless MAC • ATM is connection oriented • Broadcast transmission • Difficult to achieve in ATM • No guaranteed QoS • In-built support in ATM

  19. LANE entities • LEC (LAN Emulation Client) • LES (LAN Emulation Server) • LECS (LAN Emulation Configuration Server) • BUS (Broadcast and Unknown Server)

  20. LEC • Runs on an ATM station and simulates an Ethernet or Token Ring network • Encapsulates upper layer protocols into ELAN frames • Decapsulate incoming ELAN frames into upper layer protocol data unit (e.g. IP packets)

  21. LES and BUS • Every ELAN has a LES • It acts as a coordinator and resolves MAC addresses into ATM addresses • LECs register with the LES giving <MAC address,ATM address> • BUS • Used to emulate broadcast feature of a legacy LAN • Packet sent to the BUS are sent to all LECs in the ELAN • It is used before a direct connection is established between two LECs

  22. LECS • More than one ELAN can run on an ATM network • A LECS assigns LECs to their ELAN • When a station starts up it queries the LECS to find out its LES • The station then registers with the LES • The BUS address is determined through an LE_ARP with a MAC address of all 1s

  23. Advantages and Disadvantages • Advantages • Higher speed (not completely true) • Allows the creation of multiple VLANs • Disadvantages • It hides QoS features of ATM • With LANEv2 a LEC can provide 8 levels of QoS to higher layers, each with a different VC

  24. MPOA • Communication over multiple sub-networks requires routers • Bottleneck • A connection is set up with router and then from the router to the destination • Combination of LANE and NHRP • Aims at optimal, direct communication between end systems without crossing any router

  25. MPOA • MPOA (Multi-Protocol Over ATM) • ATM hosts • Edge devices such as switches, routers etc.. • MPOA is built on top of LANE • Intra-LANE traffic follows LANE specification • Inter-LANE traffic is optimized by integrating NHRP functionalities

  26. MPOA • MPOA Client (MPC) • MPOA Server (MPS)

  27. MPOA R ATM Network H5 H6 H1 H2 H2 H3 H4 ELAN 1 ELAN 2

  28. Conclusions • Problems with IP over ATM • Overlay Model • Integration with legacy systems • LANE • CLIP, NHRP, MPOA

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