Cisco RJ-45-to-AUX Brochure page 189

In the ATM LANE communications process, when a client wants to join an ELAN, the client must build a
table that links ATM addresses to Ethernet MAC addresses. Let's take a close look at this process:
1. The LEC first sends a LAN Emulation ARP (LE_ARP) message to the LES that is using a
point−to−point configure direct VCC. This query is made to the ATM switch containing the LECS,
using ILMI. The query is a request for the ATM address of the LES for its emulated LAN. The switch
contains a Management Information Base (MIB) variable containing the requested ATM address. The
LEC will attempt to locate the LES using these steps:
a. Uses ILMI to connect to the LECS
b. Checks to see if any locally configured ATM addresses exist
c. Checks to see if it has received a fixed address defined by the MIB variable using UNI
d. Checks to see if this is a well−known permanent virtual circuit
2. The LES forwards the LE_ARP to all clients on the ELAN using a point−to−multipoint control
distribute VCC.
3. The LECS responds across the established connection with the ATM address and name of the LES for
the LEC's ELAN. The LEC can establish a connection with the LES based on the configuration data
received. This connection is a bidirectional point−to−point control direct VCC; it remains open
throughout the remainder of the communications process.
4. The LES forwards the response using a point−to−multipoint control distribute VCC to the LEC.
While the connection is established with the LEC requesting entry to the ELAN, the LES attempts to
make a bidirectional connection to the LECS to request verification that the requesting LEC may
enter the ELAN. After this verification is completed, the server configuration that was received in the
first connection is verified against the LECS database; if authentication is approved, the client gains
membership in the ELAN.
5. The LEC creates another packet with the correct ATM address for the LES and establishes a control
direct VCC to make the connection. The LEC sends out a LE_JOIN_REQUEST to the LES
containing the LEC ATM address as well as the MAC address, in order to register with the ELAN.
6. The LES checks with the LECS to verify the LEC. The LES receives the data, creates a new entry in
the cache for the LEC, and sends a LE_JOIN_RESPONSE back to the LEC.
7. The LES replies to the LEC using the existing configure direct VCC. This process is completed by
either allowing or denying membership in the ELAN. If the LES rejects the LEC's request, the
session is terminated.
8. If the LES connection is allowed, the LEC is added to the point−to−multipoint control distribute VCC
connection. The LEC is granted a connection using the point−to−point control VCC to the
corresponding LEC, and the higher−level protocols take over.
9. If permission is granted by the LES, the LEC must determine the ATM address for the BUS in order
to become a member of the broadcast group.
10. The LEC must locate the BUS, so it sends an LE_ARP_REQUEST packet containing the MAC
address 0xFFFFFFFF. This packet is sent down the control direct VCC to the LES, which understands
the request for the BUS. The LES responds with the ATM address for the BUS.
11. When the BUS is located, the LEC can become a member of the ELAN.
LE Messages
An LE_ARP message is used to allow a LEC to indicate that a particular MAC address resides on a local node
on the local network. This message can then be redistributed to all other LECs in the ELAN to allow those
LECs to update their address cache.
Once a client has joined an ELAN and built an address cache based on the LE_ARP messages received, the
client can establish a VCC to the desired destina−tion and transmit packets to the ATM address mapped to the
physical MAC address using a bidirectional point−to−point data direct VCC. Let's take a look at four types of
packets:
173