LAN Emulation (LANE)

 

 LAN Emulation allows end systems to connect to ATM Networks, without adapting higher layers to interface directly to ATM. It provides an interface equal to existing LAN technology. Existing LAN technology should be read as  Ethernet and  Token-Ring ( IEEE 802.3 and  IEEE 802.5 respectively), and not as the general ``layer 2'' service provider in the way as discussed in Chapter 2. LANE is defined in  ATM Forum's LANE version 1.0 document [AFLE95].

  
Figure: LANE as replacement for Ethernet (simplified protocol stack view)

In Figure  a  protocol stack is shown with LANE as a replacement for Ethernet. The  ATM Bearer Service shown here is the same as shown in Figure . Notice that the IP layer (and higher layers, which are not shown) are unchanged. The LANE layer provides all the services offered by Ethernet, like broadcast and multicast addressing, by the same interface as Ethernet. Of course Ethernet behaviour, like  collisions and the   CSMA-CD protocol, is not emulated.

LANE Architecture

An  Emulated LAN ( ELAN) consists of  LANE Clients (LECs) and a LANE Service. The LECs are typically located in the ATM end-stations and they request services from the LANE Service through the  LANE User-Network Interface (LUNI). The LANE Service consists of a  LAN Emulation Configuration Server (LECS), a  LAN Emulation Server (LES) and a  Broadcast and Unknown Server ( BUS).

LANE Clients

The entity on the ATM end-stations that uses the LANE Service to provide an IEEE 802.3/5-like Network Interface service to higher layers (e.g. the Internet Protocol). Communication with the other LANE components goes through the LUNI.

LANE Configuration Server

The LECS assigns a LANE Server (LES) to any LANE Client (LEC) contacting the LECS. When a LECS is not present in an ELAN, the LES for a LEC must be defined on the LEC by the system administrator.

LANE Server

The LES provides the control coordination functions for the ELAN. Only one LES can be present in an ELAN, the members of an ELAN are defined by the LES they use. LECs register their  MAC addresses (The emulated Medium Access Control addresses) when they join the ELAN, which can later be used for address resolution for direct transmissions. The LES establishes a point to multipoint ATM connection to all LECs in the Emulated LAN of the LES for distributing control information.

Broadcast and Unknown Server

Since ATM has no direct mapping for ``Ethernet'' broadcast and multicast addresses, the BUS handles all traffic sent to these addresses by the LECs. The BUS establishes a point to multipoint connection to all clients of the ELAN the BUS belongs to. A second function of the BUS is to handle traffic for clients that must send to a unicast MAC address that is not yet resolved and no direct connection is available to the host with that MAC address.

More detailed information on LANE can be found in [AFLE95]. The information in this section is largely extracted from Marko Kiiskilä's master's thesis: ``Implementation of LAN Emulation Over ATM in Linux''.

LANE can be used as a  LAN service provider for full IP over ATM including multicasting (from now on referred to as `` mIP/ATM'' for ``multicasting IP over ATM''). Multicast traffic is forwarded to the LECs by the BUS using a point-to-multipoint VCC. Within the ELAN, this is a broadcast, so not optimal in the sense that a   point-to-multipoint VCC from the sender to the host group member would be. Still, the code for the implementation of the BUS may be a good basis for an implementation of a  Multicast Server Implementation (see Section ).