scope:

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). The ISUP is defined in accordance with [ITU-T Q.761] to [ITU-T Q.764] and BICC is defined in accordance with [ITU-T Q.1902.1] to [ITU-T Q.1902.4]. The SIP and SDP are defined by the Internet Engineering Task Force (IETF). The capabilities of SIP and SDP that are needed to interwork with BICC or ISUP are defined in Annex C.

An IWU may 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 an 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 the 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 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.

The scope of this Recommendation is shown in Figures 1 and 2, respectively.

Items relating to security when interworking between two signalling systems in this Recommendation are for further study.

[b-ITU-T Q.Sup.45] specifies the set of common capabilities supported by the interworking between SIP and BICC/ISUP for three different profiles (A, B, and C) in the form of tables. Tables 1 and 2 of [b-ITU-T Q.Sup.45] specify the interworking capabilities for Profile A, tables 3 and 4 specify the interworking capabilities for Profile B, and tables 5 and 6 specify the interworking capabilities for Profile C (SIP-I), respectively. The details on the capabilities supported by the different profiles, and all profiles in common, are shown in clause C.1.1.2.

Administrations may require operators to take into account national requirements in implementing this Recommendation, and in particular, in determining the local trust policy for the IWU.