ABSTRACT: Asynchronous Transfer Mode (ATM) is a connection-oriented packet-like switching and multiplexing principle. ATM has been chosen by the ITU-T and Committee T1 as the information transfer mode for Broadband Integrated Services Digital Network (B-ISDN), and is also being implemented for Local Area Network applications.

This Generic Requirements (GR) document provides the Telcordia view of generic requirements for the ATM layer and ATM Adaptation Layer (AAL) protocols to be used in ATM equipment. The document concentrates on the generic requirements for the protocols of the ATM Layer and AAL as they operate across the User Network Interface (UNI) and the Network Node Interface (NNI).

Five AAL protocols to support the following services are presented:

• Unstructured Constant Bit Rate (CBR) service (the AAL1 protocol)
• Variable Bit Rate (VBR) service (the AAL3/4 Common Part protocol)
• Variable Bit Rate (VBR) service (the AAL5 Common Part protocol)
• Frame Relay Service (the Frame Relaying Service Specific AAL protocol, which utilizes the AAL Common Part)
• User Network Interface (UNI) signaling service (the UNI Signaling AAL protocol, which utilizes the AAL Common Part)