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.
This has the advantage of allowing all traffic over the same circuit, but the disadvantage of requiring each packet to contain octets that identify the protocol type, which adds overhead.
Both the sender and receiver must agree on how the circuit will be used, and the agreement may involve manual configuration.
Furthermore, the standards suggest that when hosts choose to include type information in the packet, they should use a standard IEEE 802.2 Logical Link Control (LLC) header, followed by a Subnetwork Access Protocol (SNAP) header if necessary.