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Broadcast and Unknown Server (BUS)—Sends broadcasts, sequences cells, controls unicast flooding,
and distributes multicast packets.
•
Warning Notice that although LEC and LECS sound the same, they are completely different terms and
components in LANE.
LAN Emulation Client (LEC)
The LEC resides in every ATM end system. It provides services to emulate the Data Link layer interface that
allows communication of all higher−level protocols and applications to occur. It provides both ATM−attached
devices and ATM−capable Token Ring, Ethernet, and legacy LAN topologies the ability to coexist within an
ATM emulated LAN and WAN environment.
The LEC is the component responsible for passing traffic between separate VLANs on the Catalyst switches
and between ELANs on the ATM switch. You can configure multiple LECs for one or more ELANs on the
ATM modules. Prior to configuring a LEC on an ATM module, a VLAN must be configured on the switch,
and the LES/BUS or an ELAN must be configured on one or more ATM module subinterfaces.
The LEC forwards data to other LANE components in the ELAN and performs control functions. Each LEC
is a member of only one ELAN. In many instances, an Ethernet switch may have multiple LECs for each
ELAN. Examples of LEC implementations include servers, routers, switches, or other network hosts. The
LEC has the following functions:
Resolves MAC addresses•
Transfers data•
Performs address caching•
Interfaces with other LANE components•
Provides interface driver support•
LAN Emulation Server (LES)
The LES for an ELAN is the central piece of LANE. It gives the LECs the information they need to establish
ATM connections to other LECs in their ELAN. A single LES is responsible for address registry and
resolution for an ELAN. When a LEC joins an ELAN, it forms a connection with the LES. The LEC registers
its MAC and ATM addresses with the LES. The LES has the following functions:
Supports LECs•
Registers addresses from LECs•
Resolves addresses from LECs•
Interfaces to the LEC, LECS, and BUS•
The LES performs traffic control for all LECs connecting to an ELAN. This component provides the address
resolution, registration, broadcast, and unknown server information that guides communication among LECs.
When configuring each LEC, the LEC must request a connection from the LES. The request information
contains the ATM address of the LEC, a LAN identifier, and an optional MAC address. This component also
performs verification of each LEC during the initial connection with the server, checking to make sure that
each LEC has permission to join the requested ELAN.
Address registration is also a function of the LES. It must maintain a database to aid in resolving addresses.
This registration occurs after the LEC joins an ELAN. Each LEC provides the LES with one registered
address with a join request, and no separate registrations are required.
The LES with the ATM address database responds to all address resolution queries and attempts to locate
partnering LECs. The LES responds with the ATM addresses for the targeted ELANs. If no address can be
found, the LES attempts to forward the request to other LECs on other ELANs.
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