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Chapter 1 Overview
4 Avaya M770 M-ACCF/SF ATM Access Modules User’s Guide
LAN Emulation Server (LES)
The LES coordinates and controls an Emulated LAN. It provides the central
“directory” service of an emulated LAN to which a LEC can turn to look up the
ATM address of another LEC. The LES directory contains a table of LAN
destinations (LAN destination refers to either a MAC address or a Route Descriptor)
together with the ATM addresses of the LECs that represent them. In order to
transmit a data frame to a particular LAN destination, the LEC sends the data frame
to the LEC that represents that LAN destination. If the LEC does not already know
the destination LEC’s address, it can send the LAN destination to the LES to look it
up (resolve). To populate the LES directory, the LECs may register the LAN
destination of LAN stations they represent with the LES. Every Route Descriptor
must be registered with the LES.
The LANE Service normally resides on a central ATM switch, such as the M770
ATM Switch, but may reside on an ATM end station instead.
Broadcast and Unknown Server (BUS)
The BUS is the LANE connection service which handles ATM traffic other than
direct transmissions between LECs. It handles the following:
• Data sent by a LEC to the broadcast MAC address
• All multicast traffic
• Initial unicast frames which are sent by a LEC before the data direct virtual
connection to the ATM address has been resolved
• Unknown traffic
• All broadcast, multicast and unknown traffic to and from a LEC passes through
a single BUS.
The BUS also handles ATM connections and manages its distribution group.
LAN Emulation Configuration Server (LECS)
The LECS assigns individual LAN Emulation Clients to different emulated LANs.
Based on its own programming, configuration database and information provided
by clients, it assigns any client which requests configuration information to a
particular emulated LAN service by giving the client the LES’s ATM address. This
method supports the ability to assign a client to an emulated LAN based on either
the physical location (ATM address) or the identity of a LAN destination which it is
representing (ELAN name). LECs obtain information from a LECS using the
configuration protocol.