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QSIG is an internationally standardised signalling protocol for use in corporate or enterprise voice or integrated services networks, typically between Private Automatic Branch eXchanges (PABX). QSIG is used for the establishment and release of calls (basic services) and for the control of a large number of features (supplementary services). Formally QSIG operates within a Private Integrated Services Network (PISN) between nodal entities known as Private Integrated Network eXchanges (PINX). A PABX is an example of a PINX. The name QSIG is derived from the fact that QSIG accomplishes signalling at the Q reference point. The Q reference point is a formal demarcation point between two PINXs.
QSIG is designed to be independent of its own transport and independent of the means of transporting speech or other media in calls established by QSIG. Although a typical deployment of QSIG is on primary rate leased lines (QSIG occupying one of the 24 or 30 64 kbit/s channels, the rest acting as 64 kbit/s bearers for media), many other deployments are possible. In particular, QSIG can be deployed in Internet Protocol (IP networks, tunnelled directly over a transport protocol or over some other signalling protocol such as H.323 or SIP.
Ecma has developed the entire set of QSIG standards in Technical Committee TC32, chiefly in Task Group 14 (TC32-TG14). QSIG is published as a series of Ecma and corresponding ISO/IEC and ETSI Standards.
Ecma TC32-TG17 is presently involved in interoperability between QSIG and IP networks, including interworking between QSIG and SIP or H.323 and tunnelling of QSIG over IP networks.
QSIG is sometimes referred to by other names, including "PSS1" (Private Signalling System no. 1) and "Q.SIG".