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Introducing ATM Networking
LAN Emulation Configuration Server (LECS)A LECS usually resides within an ATM switch. When queried b y a
LEC over a Control Direct VC C, a LECS indicates what LAN(s) a LEC
can participate in based on input from a net work administrator.
LECs use the LECS to obtain the network address of the LES. A
temporary VCC, that tr ansports this informa tion, is the Configuration
Direct VCC.
LAN Emulation Server (LES)The LES maintains a table of all ATM nodes participating within a
LAN and can return appropriate values to querying nodes. The LES
usually resides within a node’s local switch and help s determine
node addresses.
To determine appropriate ATM addresses, a LEC maintains a table
of recently determined conversion values. When a value is not
within the table, a LEC contacts the LES using the LAN Emulation
Address Resolution Protocol (LEARP).
If a target node is an ATM end-station, the LES returns its address
and the process is complete. Otherwise the node is connected to a
legacy LAN which attaches to the ATM network using a transparent
bridge. If the LES does not have the appropriate MAC conversion
information to resolve addresses, the LES transmits associated
LEARP messages to the LES in any know n transparent bridg e using
Control Distribute VCCs. If a transparent bridge LEC recognizes the
specified MAC address, it provides the address to the original
requesting LEC and provides necessary message-passing facilities.
Broadcast and Unknown Server (BUS)Occasionally, app lications send LECs messages intended to be
broadcast to all LAN members. In this instance, th e LEC passe s th e
message to the BUS using a multicast VCC. The BUS then transmits
the message to each participating LAN node using a multicast using
ATM multicast facilities. Receiving LECs filter these messages using
the node address and pass surviving messages to intended
recipients.
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