Because of the explosive growth of multimedia applications, a large number of networks are now required to carry voice, video, and data. While Fast Ethernet networks have allowed network designers to provide high-speed networks, ATM is still the best choice for high-speed, interactive communications.

ATM uses 53 byte fixed-length cells to transport voice, video, and data efficiently through an internetwork. Since ATM uses fixed-length cells, switching can occur in the network hardware, thus reducing delay. To take advantage of ATM’s high speed and low-latency capabilities, many network designers have begun using LAN emulation (LANE) to integrate ATM into their existing Ethernet and Token Ring networks.

What is LANE?
LANE is an ATM forum standard used to connect ATM to existing Token Ring and Ethernet networks. Essentially, LANE hides the ATM network from the upper-layer protocols and allows the network to operate like a Token-Ring or Ethernet network. LANE does this by resolving MAC (Media Access Control) addresses to ATM addresses. Basically, LANE emulates a MAC network.

LANE components
LANE is made up of four components:

  • LAN Emulation Client (LEC)
  • LAN Emulation Server (LES)
  • Broadcast and Unknown Server (BUS)
  • LAN Emulation Configuration Server (LECS)

The LES, BUS, and LECS are collectively referred to as “LAN Emulation Services.”

The LEC and the LAN Emulation Services can run on separate devices, or they can be combined on a single device. Each LANE component performs a specialized function.

The LAN Emulation Client is software that operates at the Logical Link Control layer (LLC) of the OSI model and provides a communication path to upper-layer protocols. Every end station must have LEC software in order to participate in the LANE network. The LEC’s primary responsibilities include:

  • Address resolution
  • Address caching
  • Data forwarding
  • MAC network emulation to upper-layer protocols

The LAN Emulation Server (LES) provides configuration information for connecting LECs. All of the LECs connected to a LES make up the Emulated LAN or ELAN. Each ELAN has a LES. The LES typically runs on an ATM integrated router or switch. The LES provides traffic control, as well as the following functions:

  • LEC Configuration
  • MAC address registration for each LEC
  • ATM address registration and storage

The Broadcast and Unknown Server (BUS) provides broadcast and multicast services on the LANE network. ATM is a point-to-point and multipoint-to-multipoint connection-oriented protocol. As such, broadcast and multicast are not natively supported. LANE implements the BUS to provide these services. The BUS forwards broadcast and multicast data to LECs using a point-to-multipoint virtual channel connection. Like the LES, the BUS usually operates on an ATM integrated router or switch.

The LAN Emulation Configuration server is an optional component of a LANE network and is used to manage ELANs within an administrative domain. LECS store configuration information for multiple ELANs and provide this information to LAN Emulation Clients (LEC). The LECS runs on an ATM integrated router or switch and can greatly simplify ELAN management.

Just the beginning
This brief introduction to ATM and LANE networks offers a glimpse of the complexities of designing ATM networks. Volumes of information have been written about ATM networks. In the coming months, I will explain the basics of ATM networking and provide you with tools to implement your ATM network.

Warren Heaton, CCDA, CCNA, MCSE+I, is the Cisco Program Manager for A Technological Advantage in Louisville, KY.

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