ITU-T Q.1912.5 PDF

This Recommendation defines the signalling interworking between the Bearer Independent Call Control (BICC) or ISDN User Part (ISUP) protocols and Session Initiation Protocol (SIP) with its associated Session Description Protocol (SDP) at an Interworking Unit (IWU). ISUP is defined in accordance with ITU-T Recs Q.761 to Q.764 and BICC is defined in accordance with ITU-T Recs Q.1902.1 to Q.1902.4. SIP and SDP are defined by the IETF. The capabilities of SIP and SDP that are needed to interwork with BICC or ISUP are defined in Annex C.

An IWU may be stand-alone or may be combined with an ISUP exchange or BICC Interface Serving Node (ISN). It is assumed in this Recommendation that the initial service requests are forwarded and/or delivered via a trusted Adjacent SIP Node (ASN) within a SIP network domain. The ASN is viewed as a trusted network entity rather than untrusted user entity, and thus the interface between the IWU and the ASN is a Network-to-Network interface (NNI). Where Profile C (SIP-I) is used, it is assumed that the remote SIP User Agent is able to process ISUP. Support for SIP interworking at a User Network Interface (UNI) is out of scope of this Recommendation. Interworking with forking in the SIP network is not specified in this Recommendation and is for further study.

The services that can be supported through the use of the signalling interworking are limited to the services that are supported by BICC or ISUP and SIP-based network domains. Services that are common in SIP and BICC or ISUP network domains will interwork by using the function of an Interworking Unit (IWU). The IWU will also handle (through default origination or graceful termination) services or capabilities that do not interwork across domains.