Avaya M-ACCF/SF User Manual page 29

Figure 1.7
Hosts with
MAC Addresses
Avaya M770
Multifunction Switch
ATM Port with
16 LAN Emulation Clients (LECs)
each with an ATM Address
ATM Access
Module
These clients represent (act as a proxy for) devices connected to the Ethernet ports.
Whenever an Ethernet device wants to communicate with another device over the
ATM network, the LEC must first discover the ATM address of the LEC that is
acting as a proxy for the destination MAC address. The LEC must do this for each
unicast Ethernet frame sent. The process is known as Address Resolution.
Address Resolution
The process by which a LEC associates a LAN destination address with the ATM
address of another LEC (or the BUS) is known as Address Resolution.
Each LEC keeps a LAN Emulation ARP Table (which should not to be confused with
the IP ARP Table). The ARP Table lists the remote destination MAC addresses and
the ATM address of the LEC through which each destination MAC address can be
reached.
Prior to sending a frame with a known destination, the LEC checks the ARP Table to
see if the destination MAC address of the frame is listed in the ARP Table. The
action the LEC then takes depends on whether the MAC address is listed in the ARP
Table:
• If the destination MAC address is listed in the ARP Table:
— and there is an ATM connection to that LEC, the frame is sent directly to
that LEC.
— and an ATM connection has not already been set up, the LEC sets up an
ATM connection.
• If the destination MAC address is not listed in the ARP Table:
the LEC sends the frame to the BUS. The BUS then sends the frame to all LECs
on the Emulated LAN.
Sending a frame to every LEC is an inefficient use of resources, so the LEC also tries
to locate the MAC address for future use.
To discover the correct address, the LEC uses a process called LAN Emulation
Address Resolution Protocol (LE_ARP).
Avaya M770 M-ACCF/SF ATM Access Modules User's Guide
LAN Emulation Clients and Ethernet Hosts
Chapter 1 Overview
13