IBM SC30-3681-08 manual Addressing in ATM, Broadcast and Unknown Server BUS

Overview of LAN Emulation

Broadcast and Unknown Server (BUS)

A LAN emulation service component responsible for the delivery of multicast and unknown unicast frames.

The LES, BUS, and LECS are collectively referred to as the LE service components. Each ELAN has a dedicated LES and BUS. LE clients reside in end systems, either in ATM-attached hosts or in bridges or LAN switches. The bridges or LAN switches represent hosts that are connected to Ethernet or Token-Ring LANs. LE clients provide a MAC-level service to higher level software. Either Ethernet IEEE 802.3 or IEEE 802.5 Token-Ring LANs can be emulated, but all stations on an ELAN must be of the same type.

The function that bridges between Token-Ring or Ethernet LAN segments and ELANs is called a Proxy LEC. To emulate a LAN, LE clients request services from the LECS, LES, and BUS. The following sections brie¯y review ATM addressing and pertinent Interim Local Management Interface (ILMI) functions. You need to understand these concepts before you can understand how the LE components function in the network.

Addressing in ATM

ATM uses 20-byte hierarchical addressing:

			End System
		~‡	Identifier ‡‡€		~ Selector
~‡‡‡‡‡‡‡‡‡ Network Prefix‡‡‡‡‡‡‡‡‡‡‡‡€		ˆ	(ESI)	ˆ	ˆ
1	13	14		19	20

~‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡ƒ‡‡‡‡‡‡‡‡‡‡‡￿‡‡‡‡‡‡ƒ‡‡€

ˆ	ˆ	ˆ	ˆ
ˆ	ˆ	ˆ	ˆ
ˆ	ˆ	ˆ	ˆ
ˆ	ˆ	ˆ	ˆ

•‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡„‡‡‡‡‡‡‡‡‡‡‡￿‡‡‡‡‡‡„‡‡•

The ®rst 13 octets of an ATM address are the Network Pre®x. Each switch in your ATM network must have a unique Network Pre®x. ATM switches use the Network Pre®x to route VCC setup requests the destination ATM switch. End systems, like this router, retrieve their Network Pre®x from their ATM switch when they activate.

Octets 14±19 of an ATM address are the End System Identi®er (ESI). Each end system attached to the same switch must use a disjoint set of ESIs. When an end system activates, it attempts to register its ESIs with its ATM switch using the Interim Local Management Interface (ILMI).

The ILMI de®nes a set of SNMP-based procedures used to manage the interface between an end system and an ATM switch. End systems use ILMI to:

vObtain the network pre®x from the switch

vRegister their ESIs with the switch

vDynamically determine the UNI version of the ATM switch

vLECs may get a list of LECS addresses from the switch

The switch forces all of its registered ESIs to be unique.

Octet 20 of an ATM address is the selector.

Chapter 20. Overview of LAN Emulation 257