PDF of this tutorialATM–based Ethernet switches and ATM workgroup switches are being deployed by end users at various corporate sites. The most widely used set of standards in local ATM environments is ATM LAN emulation (LANE) (see Figure 4). ATM LAN emulation is used to make the ATM SVC network appear to be a collection of virtual-Ethernet/IEEE 802.3 and token-ring/IEEE802.5 LANs. The replication of most of the characteristics of existing LANs means that LAN emulation enables existing LAN applications to run over ATM transparently, this latter characteristic leading to its wide deployment. In ATM LAN emulation, most unicast LAN traffic moves directly between clients over direct ATM SVCs, while multicast traffic is handled via a server functionality. Bridging is used to interconnect real LANs and emulated LANs running on ATM, while routing is used to interconnect ATM–emulated LANs and other WAN or LAN media for purposes of routing scalability, protocol spoofing, or security firewalls.
Figure 4. ATM LAN Emulation (LANE)
The ATM Forum LANE implementation agreement specifies two types of LANE network components connected to an ATM network.
- LANE clients which function as end systems, such as computers with ATM interfaces that operate as file servers; end-user workstations or personal computers; Ethernet or token-ring switches that support ATM networking; and routers, bridges, and ATM ENS with membership in an emulated ATM LAN
- LANE servers that support ATM LANE service for configuration management, multicast support, and address resolution
The LAN–emulation service may be implemented in the same devices as clients or involve other ATM network devices. The communications interface, LAN emulation user-network interface (LUNI), is the sequence and contents of the messages that the clients ultimately use to transfer traffic of the type expected on IEEE 802.3/5 LANs. The component of the LAN–emulation service that deals with initialization (i.e., emulates plugging the terminal into a LAN hub), is the LAN emulation configuration server (LECS). It directs a client to connect to a particular LAN emulation server (LES). The LES is the component of the LAN–emulation service that performs the address registration and resolution. The LES is responsible for mapping IEEE 48-bit MAC addresses and token-ring route descriptors to ATM addresses. One very important MAC address for clients is the MAC–layer broadcast address that is used to send traffic to all locations on a LAN. In LAN emulation, this function is performed by the broadcast and unknown server (BUS). ATM LANE is a comprehensive set of capabilities which has been widely deployed in ATM networks.
ATM LANE is an element of the multiple protocol over ATM (MPOA) architecture that is being defined by the ATM Forum. This work is addressing encapsulation of multiple protocols over ATM, automatic address resolution, and the routing issues associated with minimizing multiple router hops in ATM networks.
