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LAN Emulation

ATM LAN emulation (LANE) is used to make the ATM network appear to be a collection of virtual Ethernet and Token Ring LANs. The replication of most of the characteristics of existing LANs means that LANE enables the LAN applications to run over ATM transparently. LANE is independent of particular LAN protocols, so that other protocols can use ATM-emulated LANs.

ATM LANE advantages include:

  An Ethernet or Token Ring network interface card (NIC) can be replaced by an ATM NIC with no impact on the network applications in use in the workstation.
  Most unicast LAN traffic moves directly between clients over direct ATM virtual circuits (VCs), while multicast traffic is handled via a server.
  Bridges are used to interconnect real LANs and emulated LANs running on ATM.
  Source routing bridges can interconnect a real Token Ring LAN and an emulated Token Ring LAN.
  Routers can interconnect ATM emulated LANs and other wide-area or LAN media for purposes of routing scalability, protocol spoofing, or security firewalls.

The ATM Forum LANE implementation agreement discusses client devices and end systems connected to an ATM network, including:

  Computers with ATM interfaces that operate as file servers.
  End-user workstations or personal computers.
  Ethernet or Token Ring switches that support ATM networking.
  Routers and bridges with membership in an emulated ATM LAN server supporting ATM LANE service.

To the extent that desktop ATM penetrates the market, four existing or emerging protocol stack/application standards are relevant:

  LAN emulation client.
  Native ATM.
  ATM adaptation of voice/data/video pipes.
  Classic IP and multiprotocol over ATM (MPOA) clients.

These application environments can co-exist in any given workstation by using different ATM virtual circuits supporting the appropriate class of service.

Routing Requirements

Routing is required to support communication with the installed base of shared-media LAN bridge/router networks and to manage broadcasts and unknown address flooding over the wide area. Applications using ATM LAN emulation require multiprotocol routing to support connectivity between emulated LANs, while classic IP requires multiprotocol routing, at least in the context of address resolution. In contrast, ATM switching provides high-speed connectivity for classic IP, MPOA, and ATM LAN emulation and for emerging native ATM applications. It will provide circuits for the network consolidation of voice, data, and video.

The introduction of Ethernet or Token Ring switches into wiring closets will maximize application performance in the local area, and be an important next step in the process of reducing administrative complexity in the local environment. An important enterprise networking issue is how ATM switching will extend application performance across the wide area. The objective is to make network capacity more scalable, simplify the network management, and improve bandwidth price performance (through consolidation of other traffic including voice and video), while allowing routing to co-exist and evolve to leverage the inherent advantages of switching.

Classic IP and MPOA

RFC 1483 defines an encapsulation technique for carrying IP traffic over ATM VCs, which is used in three types of environments:

  For ATM PVCs between routers.
  To carry LAN traffic transparently between bridges.
  For individual workstations to use ATM to carry IP traffic in IP virtual LANs. This is an important ATM application because these users need the larger capacity provided by ATM.

RFC 1577 describes how to construct a logical IP subnet (LIS) so that high-performance workstations and supercomputers can use ATM as a virtual LAN. In this process:

  A protocol supporting automatic address resolution of IP addresses is defined.
  Each LIS supports a single ATM ARP server.
  Each LIS client is configured with the unique address of the ATM ARP server.
  A subset of the IP protocol suite is supported.

The MPOA subcommittee of the ATM Forum is defining standards to provide RFC 1577 capabilities in a protocol-independent manner and to address the routing issues associated with minimizing multiple router hops in ATM networks.


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