This Recommendation defines the operation of the Digital subscriber Signalling System No. 1 (DSS 1) for the frame mode basic call and on-demand frame mode switched virtual connections at the TB or at the coincident SB and TB reference point of the user-to-network Interface of the Integrated Services Digital Network (ISDN).

It provides as Annex A signalling procedures for frame mode permanent virtual connection status monitoring, which have been enhanced in this revised version together with the corresponding Protocol Implementation Conformance Statements (PICS) proforma, as a new Annex D.

It also includes a description of means to provide OSI connection oriented network services over Switched Virtual Connections in Annex C and provides a multiprotocol encapsulation scheme for use over frame mode virtual connections, in a new Annex E.