Cisco Systems RJ-45-to-AUX manual Lane Components, What Are ELANs?, 168

changing the application itself or Layer 3 drivers.

This approach allows backward compatibility with existing LANs, broadcast support, and connectionless delivery. LANE has some drawbacks, however: It prevents the use of ATM−specific benefits such as QoS and doesn’t have the ability to provide flexible bandwidth allocations.

LANE is the primary component that provides connectivity between ATM devices and the devices residing on the Layer 2 LAN. This connectivity extends to devices attached to ATM stations and devices attached to LAN devices spanning the ATM network. This connectivity between ATM devices and other LAN devices is done through ELANs.

What Are ELANs?

ELANs are just like VLANs—one of their functions is to create independent broadcast domains in ATM, the same way that VLANs do in Ethernet and Token Ring networks. ELAN workstations are independent of the physical location, and like VLANs, ELANs must be connected to a Layer 3 device in order to communicate with members of another ELAN.

The Data Link layer’s MAC sublayer allows ELANs to use the Microsoft or Novell upper−level NDIS/ODI driver interfaces. This method allows ELANs to transmit Layer 3 protocols such as TCP/IP, IPX, and AppleTalk.

LANE is a standardized conversion process that allows a connectionless environment in a LAN to connect to a connection−oriented ATM environment. LANE fragments an incoming Layer 3 into a 48−byte payload and places a 5−byte ATM−specific identification header on the front of the packet, yielding a 53−byte cell. It then removes the checksum from the cell and forwards the cell through the ATM network. When the cell has traveled the ATM network, the ATM information is removed and the cell fragments are reassembled and returned to the LAN environment as a packet.

The LANE 1.0 standard can be summed up as a software interface for the Layer 3 protocol environment that encapsulates user data for either Ethernet or Token Ring packets. LANE isn’t actually the media access method for this conversion process—LANE uses three servers, which clients access over the ATM connections. The LANE servers provide address registration and resolution functions, including collecting address and route descriptor types based on the LANE standard. Let’s take a look at the LANE components.

Note FDDI can be used with LANE 1.0; however, it is not accurately defined like Ethernet and Token Ring protocols. ATM uses translational bridging techniques to map FDDI packets into either Ethernet or Token Ring.

LANE Components

LANE uses several components to provide LAN−based network connectivity. The interaction of these components allows address registration, address caching, and searchable databases. LANE uses the following components:

∙LAN Emulation Client (LEC)—Emulates a LAN interface to higher−layer protocols and applications of the OSI Reference Model.

∙LAN Emulation Server (LES)—Provides a database of LANE services, resolves addresses, manages stations that make up an ELAN, and provides registration services to LANE clients for the emulated LAN.

∙LAN Emulation Configuration Server (LECS)—Uses a database to track device memberships in each ELAN.

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