The scope of this standard covers the user signalling bearer service procedures at the S or T reference points. The user signalling bearer service is a packet mode bearer service. This standard defines the use of the procedures of ANSI T1.602-1989@ Telecommunications ?C Integrated services digital network (ISDN) ?C Data-link layer signalling specification for application at the user-network interface@ and ANSI T1.607-1990@ Telecommunications ?C Integrated services digital network (ISDN) ?C Layer 3 signalling specification for circuit-switched bearer service for digital subscriber signalling system number 1 (DSS1)@ on basic rate interfaces and primary rate interfaces for the establishment and release of user signalling bearer service through an ISDN. The user signalling bearer service allows users to communicate by means of user-to-user signalling without setting up a circuit-switched connection (no B-channel). The user signalling bearer service is established and cleared in a manner similar to the control of a circuit-switched connection. Structure Clause 1 describes the purpose@ scope@ and structure of this document. Clause 2 lists normative references. Clause 3 references definitions helpful in interpreting the specifications. Clause 4 provides an overview of call control and defines the control states for the user signalling bearer service. Clause 5 specifies the message functional definitions. Clause 6 specifies the message structure and information element coding. Clause 7 specifies the procedures for the user signalling bearer service. Clause 8 specifies the system parameters. Annex A (informative) lists the departures from the provisions of CCITT Recommendation Q.931 (I.451)@ ISDN usernetwork interface layer 3 specification. Annex B (informative) lists standards for information only and is not essential for the completion of the requirements of this standard