3Com 7600 manual Bus

12-6CHAPTER 12: ATM, LAN EMULATION, AND VIRTUAL LANS

LE Service normally resides on a central ATM switch, such as the CELLplex 7000, but may reside on an ATM end station instead.

An ELAN is assigned a name (ELAN name) which is communicated to each LEC as the LEC joins the ELAN.

More than one emulated LAN can operate on the same ATM network. However, each of the emulated LANs is independent of the others and users cannot communicate directly across emulated LAN boundaries.

LAN Emulation Client The LEC is the LE connection service located in an ATM edge device which represents the device’s LAN users to the ATM network. A LEC has a unique LEC ID as well as an ATM address by which it is known in the emulated LAN. It handles the forwarding of its LAN users’ data frames over the ATM network to their destination, a task which also includes ascertaining the destination LEC address and setting up the connection between them.

Also provided is a MAC-level emulated Ethernet service interface to higher level software which implements the LAN Emulation User to Network Interface (LUNI).

LAN Emulation Server The LES is the central “directory” service of an emulated LAN to which a LEC can turn to look up the ATM address of another LEC. The LES directory contains a table of LAN station MAC addresses together with the ATM addresses of the LECs that represent them. In order to transmit a data frame to a particular destination MAC address, the LEC sends the data frame to the LEC that represents that destination MAC address. If the LEC does not already know the destination LEC’s address, it can send the destination MAC address to the LES to look it up (resolve). To populate the LES directory, the LECs may register the MAC addresses of LAN stations they represent with the LES.

Broadcast and The BUS is the LE connection service which handles ATM traffic other Unknown Server than direct transmissions between LECs. It handles the following:

(BUS)

QData sent by a LEC to the broadcast MAC address

QAll multicast traffic

QInitial unicast frames which are sent by a LEC before the data direct virtual connection to the ATM address has been resolved