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ATIS 1000615 2014 Edition, June 1, 2014
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Digital Subscriber Signalling System No. 1 (DSS1) – Layer 3 Overview
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Scope, Purpose, & Application

The Digital Subscriber Signalling System No.1 (DSS1) is a suite of protocols that provides the means for users to invoke the full range of services and capabilities available from an ISDN.

The structure of the interface between a user and an ISDN is described in ITU-T Recommendation I.412. That structure defines an interface which consists of a variable number of discrete channels. The channels are of various types. One type of channel (the DChannel) is used to carry the DSS1 signalling messages between the user and the network.

The structure of the DSS1 protocol suite is based on the seven-layer model described in ITU-T Recommendation I.320. Layer 1 functions are described in American National Standard for Telecommunications - Integrated services digital network - ISDN basic access interface for use on metallic loops for application at the network side of NT - Layer 1 specification1, ATIS-0600601, American National Standard for telecommunications - Integrated services digital network - ISDN basic access interface for S and T reference points - Layer 1 specification, ATIS-0600605; and American National Standard for telecommunications - ISDN primary rate - Customer installation metallic interfaces - Layer 1 specification, ANSI T1.408-1990. Layer 2 functions are described in American National Standard for telecommunications - Integrated services digital network - ISDN signalling specification for application at the user-network interface - Layer 2 specification, ATIS-1000602.

The Layer 3 protocols provide:
  • the means to establish, maintain, and terminate network connections across an ISDN between communicating entities; and
  • procedures that may be used to invoke and control supplementary services.


This standard describes the Layer 3 DSS1 functions and protocol in general terms. Details of the Layer 3 protocols are provided in the standards listed in clause 8. A glossary of Layer 3 terms is provided in clause 3