LAN emulation (LANE)
In order to enable a transition-free integration of existing local networks on ATM technology, an ATM emulation specification was developed by the ATM Forum. LAN emulation is a procedure for using connectionless LAN protocols in ATM networks. The principle of LAN emulation is based on the mapping ofMAC addresses to ATM addresses, which makes this procedure completely transparent for layer 3 protocols.
Using LAN emulation, ATM switching units are able to emulate the MAC layer of standardized local area networks.
LAN emulation as client-server architecture
An emulated LAN has a client- server architecture and consists of four components that must be implemented on one or more computers or network nodes: The LAN Emulation Client( LEC), the LAN Emulation Server( LES), the LAN Emulation Configuration Server( LECS) and the Broadcast and Unknown Server( BUS)
Since classic LANs such as Ethernet, Token Ring or FDDI operate connectionless, but ATM functionality is connection-oriented, the LAN emulation must ensure that all end devices (LEC) on the ATM network that want to communicate with each other receive a connection. At the same time, not all devices need to be connected to each other at all times. The devices that want to communicate with each other are on a virtual network that provides the connections necessary for that communication. End devices that need to communicate with each other frequently or that require time transparency for their communication are given their own connections.
End devices that communicate with each other less frequently and do not require time transparency communicate via the LAN emulation server. This applies to point-to-point connections. For broadcast connections, there is the broadcast and unknown server, which has connections to all end devices.
LAN emulation and internetworking
In LAN emulation, the Internetworking components and the ATM switches must transparently transmit the structures of the LANs along with the MAC address.
In addition, LAN emulation must provide for the conversion of certain LAN data to ATM format. Since LAN-specific protocols such as the IP protocol, the Internetwork Packet Exchange Protocol( IPX) or OSI protocols are not optimized for cell-oriented ATM, these protocols must be packed into the ATM cells with the highest possible efficiency, for example by encapsulation. It must be taken into account that the MAC information of the existing LANs must be transferred via the ATM network. Since no uniform standards have yet been developed for this, there are different manufacturer approaches that support proprietary solutions. In addition, LAN emulation should support the configuration of virtual networks.