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					    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
•   IP uses best-effort
•   Two approaches
    – Connections established on demand
    – IP traffic is carried over pre-configured circuits
• Both approaches have pros and cons
               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)
                   CLIP
• All members of a LIS (host or router) are
  under the same administrative control
• A LIS is given ONE IP subnet address
• CLIP
       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
           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
             Classical IP Over ATM
                       ATM Network

        R2                                  LIS 3
                                                    ATM
                                                     ARP
                                                    server
        H1                    R3
                                                             H6
 H2          ATM
              ARP
H3           server                     ATM                       R5
                                         ARP         R4
                                        server

     LIS 1               H4
                  R1               H5

                                           LIS 2
         Data Encapsulation
• How do we carry different protocols
• How do we identify different protocols
  – VC multiplexing
  – LLC/SNAP
  – TULIP
  – TUNIC
            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
     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
             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
           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
                   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
                   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
                             NHRP
                         ATM Network                   LIS 3

        R2             NHS                   NHS
                                                           ATM
                                                            ARP
                                                           server
        H1                        R3
                                                                    H6
 H2          ATM
              ARP
H3           server                         ATM                          R5
                                             ARP               R4
                                            server

     LIS 1                   H4
                  R1                   H5

                                               LIS 2
                  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
             Legacy LANs
• Connectionless MAC
  – ATM is connection oriented
• Broadcast transmission
  – Difficult to achieve in ATM
• No guaranteed QoS
  – In-built support in ATM
           LANE entities
• LEC (LAN Emulation Client)
• LES (LAN Emulation Server)
• LECS (LAN Emulation Configuration
  Server)
• BUS (Broadcast and Unknown Server)
                  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)
              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
                    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
 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
                   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
                    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
              MPOA
• MPOA Client (MPC)
• MPOA Server (MPS)
                   MPOA
                        R

               ATM Network




                                 H5   H6

H1   H2       H2   H3       H4

     ELAN 1
     ELAN 2
              Conclusions
• Problems with IP over ATM
• Overlay Model
• Integration with legacy systems
  – LANE
• CLIP, NHRP, MPOA

				
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posted:5/24/2013
language:Latin
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