IBM SC30-3681-08 manual Establishing Data Direct VCCs, Overview of Extensions for LAN Emulation

Overview of LAN Emulation

BUS processing requirements are increased and multicast frames must be transmitted twice (once on each Multicast Forward VCC). In general, IBUS operation is recommended; however, this option should be disabled in con®gurations that have source route bridges that join the ELAN as non-proxies.

Establishing Data Direct VCCs

Data Direct VCCs connect two LE clients, and are used to exchange unicast frames without involving the BUS. The LE client uses the address resolution procedures to determine the ATM address associated with the required LAN destination. If the LE client already has a Data Direct VCC to the ATM address (perhaps for another LAN destination represented by the target LE client), unicast data frames are subsequently transmitted on the existing VCC; otherwise, the LE client invokes the signaling protocol to establish a new VCC.

The LE client maintains an LE_ARP cache containing LAN destination-to-ATM address mappings. Entries in this cache are aged and must be periodically refreshed. The entries are refreshed when a data frame is received from the LAN destination. The LE client also attempts to refresh entries in the absence of data traffic.

Utilization of Data Direct VCCs is also monitored and the VCCs are released if there is no traffic for the VCC time-out period, which is con®gurable. Additionally, Data Direct VCCs are released in a least-recently used manner when establishment of a new Data Direct VCC fails due to insufficient resource availability.

Overview of Extensions for LAN Emulation

IBM has made value-add extensions to ATM Forum LAN Emulation available on the router. These extensions offer improved performance, reliability, security, and manageability:

Broadcast Manager (BCM)

This function can improve overall network performance by reducing ELAN broadcasts.

Redundancy

The redundancy mechanism improves reliability by allowing backup servers to take over if failures occur at primary servers.

Security

Security is improved by letting the LECS control ELAN memberships.

BUS Monitor

This function enhances manageability by identifying the top users of the

BUS.

The following sections describe each of these extensions.

Broadcast Manager

Broadcast Manager (BCM) is an extension to LAN emulation that consists of IBM enhancement of the LAN emulation BUS. Without BCM, the following events occur:

v A multicast frame sent to the BUS is forwarded to all LE clients on the ELAN.

Chapter 20. Overview of LAN Emulation 267