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An ELAN consists of the following components:

￿A single LANE service, which itself consists of a LAN Emulation Configuration Server (LECS), a LAN Emulation Server (LES), and a Broadcast and Unknown Server (BUS). Each of these components are discussed in more detail later in this document.

￿A set of LECs.

The LEC communicates with other LECs and with the LANE service using virtual channel connections (VCCs) in an ATM switched virtual circuit (SVC) environment.

An ELAN comprises a group of ATM-attached devices, logically analogous to a group of LAN stations attached to an Ethernet/802.3 LAN segment. Several ELANs can be configured within an ATM network, and membership to an ELAN is independent of where the end station is physically connected. The end station can belong to multiple ELANs.

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LANs use a MAC address to designate the source and destination addresses for sta- tions. For LANE to function transparently, it must be capable of offering similar functionality. In practical terms, this means that each LEC has a MAC address, and when more than one LEC uses the same network interface, each LEC is assigned a different MAC address.

When the LEC needs to send data to another MAC address, it must first resolve that address to an ATM address, thus enabling it to establish a data direct VCC to that LEC. To do so, it sends an LE_ARP_REQUEST to the LES. The LES can either respond to this request, if it can, or it can forward it to other LECs. If the specified MAC address is known anywhere on the ELAN, the originating LEC gets an LE_ARP_RESPONSE frame containing the corresponding ATM address.

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The LEC is part of an ATM end station or a MAC bridge and performs data forwarding as well as address resolution, among other control functions. The LEC supplies higher-level software with an Ethernet/IEEE 802.3 MAC layer interface that enables LAN-based application software to communicate over ATM networks just as they would over a traditional LAN.

LECs communicate with other clients using the LANE Service, and represent users by their MAC addresses. An LEC employs separate VCCs for data and control commu- nication, including LE_ARP requests for address resolution. User data, intended for another end station, is encapsulated in IEEE 802.3 frames.

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The LANE Service, consisting of a LES, BUS, and LECS, can be implemented as part of one or more end systems or as part of the ATM switch. In cases where the service is implemented in a distributed fashion over multiple devices, benefits include parallel operation as well as better error recovery through redundancy.

Dell PowerVault 7x0N Systems — Connecting to ATM and FDDI Networks 3