Explain the concept of multi-protocol encapsulation in ATM networks.

ATM-based networks are of increasing interest for both local and wide area applications. The ATM architecture is different from the standard LAN architectures and, for this reason, changes are required so that traditional LAN products will work in the ATM environment. In the case of TCP/IP, the main change required is in the network interface to provide support for ATM. There are several approaches already available, two of which are important to the transport of TCP/IP traffic.

Multiprotocol Encapsulation over ATM is specified in RFC 2684. It defines two mechanisms for identifying the protocol carried in ATM Adaptation Layer 5 (AAL5) frames. It replaces RFC 1483, a standard data link access protocol supported by DSL modems.

RFC 2684 describes two encapsulation mechanisms for network traffic: Virtual and DSL modems often include a setting for RFC 1483 bridging. This is distinct from other "bridge modes" commonly found in combined DSL modems and routers, which turn off the router portion of the DSL modem.