scope:

The present document specifies tunnelling of "QSIG" over the Session Initiation Protocol (SIP) within a corporate telecommunication network (CN).

"QSIG" is a signalling protocol that operates between Private Integrated services Network eXchanges (PINX) within a Private Integrated Services Network (PISN). A PISN provides circuit-switched basic services and supplementary services to its users. QSIG is specified in ECMA Standards, in particular [1] (call control in support of basic services), [2] (generic functional protocol for the support of supplementary services) and a number of Standards specifying individual supplementary services.

NOTE: The name QSIG was derived from the fact that it is used for signalling at the Q reference point. The Q reference point is a point of demarcation between two PINXs.

SIP is an application layer protocol for establishing, terminating and modifying multimedia sessions. It is typically carried over IP [4], [6]. Telephone calls are considered as a type of multimedia session where just audio is exchanged. SIP is defined in [9].

Often a CN comprises both PISNs employing QSIG and IP networks employing SIP. A call can originate at a user connected to a PISN and terminate at a user connected to an IP network or vice versa. In either case, a gateway provides interworking between QSIG and SIP at the boundary between the PISN and the IP network. Basic call interworking at a gateway is specified in [3]. Another case is where a call originates at a user connected to a PISN, traverses an IP network using SIP, and terminates at a user connected to another (or another part of the same) PISN. The present document addresses this last case in a way that preserves all QSIG capabilities across the IP network. It achieves this by tunnelling QSIG messages within SIP requests and responses in the context of a SIP dialog.

The tunnelling of QSIG through a public IP network employing SIP is outside the scope of this specification. However, the functionality specified in this specification is in principle applicable to such a scenario when deployed in conjunction with other relevant functionality (e.g. address translation, security functions, etc.).

This specification is applicable to any interworking unit that can act as a gateway between a PISN employing QSIG and a corporate IP network employing SIP, with QSIG tunnelled within SIP requests and responses.