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Broadcast and Unknown Server<br />

The Broadcast and Unknown Server (BUS) addresses ATM's inability<br />

<strong>to</strong> handle Layer 3 broadcast datagrams. It is responsible for sending<br />

broadcast and local multicast traffic <strong>to</strong> all LANE clients within a specific<br />

ELAN. It also performs Layer 2 broadcast functions such as LEARP<br />

queries. The BUS sends address queries, such as broadcast and<br />

multicast datagrams <strong>to</strong> LANE clients, in most cases through a<br />

unidirectional multicast VCC. Like <strong>the</strong> LES, each ELAN must have its<br />

own BUS.<br />

LAN Emulation Configuration Server<br />

The LAN Emulation Configuration Server (LECS) provides<br />

configuration for <strong>the</strong> LANE clients. The LECS is essentially a database<br />

server that contains information about all <strong>the</strong> ELANS in existence for a<br />

given ATM <strong>network</strong>. The LECS also has configuration information for<br />

all <strong>the</strong> LANE clients: which ELAN <strong>the</strong>y belong <strong>to</strong>, <strong>the</strong> ELAN type and<br />

MAC address, <strong>the</strong> address of <strong>the</strong> LES, and so on. When <strong>the</strong> LANE client<br />

starts up, it establishes a configuration VCC with <strong>the</strong> LECS. If <strong>the</strong> LECS<br />

has configuration information for <strong>the</strong> requesting client, it provides <strong>the</strong><br />

client with <strong>the</strong> needed information. If no configuration information<br />

exists, <strong>the</strong> LANE client configuration fails. A single LECS is all that is<br />

required <strong>to</strong> provide configuration information for all <strong>the</strong> ELANS within<br />

an ATM <strong>network</strong>.<br />

The LAN Emulation Client<br />

The LAN Emulation Client (LEC) exists on each ATM endpoint involved<br />

in <strong>the</strong> ELAN. A separate LEC must exist for each ELAN with which <strong>the</strong><br />

ATM endpoint is involved. The LEC (with <strong>the</strong> assistance of <strong>the</strong> LAN<br />

emulation server) is responsible for performing ATM-<strong>to</strong>-MAC address<br />

translations. Each LEC client has both an ATM and emulated MAC<br />

(E<strong>the</strong>rnet or Token Ring) address for each connected ELAN. The LEC<br />

on ATM-equipped end-stations provides <strong>the</strong> interface used by <strong>the</strong><br />

Layer 3 pro<strong>to</strong>col <strong>to</strong> interact with o<strong>the</strong>r connected end-stations. LEC<br />

functionality is part of <strong>the</strong> ATM NIC, LAN switch, or router interface.<br />

In order for <strong>the</strong> LEC <strong>to</strong> participate in <strong>the</strong> ELAN, three events must<br />

occur. First, <strong>the</strong> LEC needs <strong>to</strong> be configured for operation within a<br />

specific ELAN. This is accomplished by <strong>the</strong> LEC establishing a<br />

bidirectional configuration VCC with <strong>the</strong> LANE configuration server

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