QSIG (Q -Interface Signaling Protocol) is a telecommunications based on ISDN signaling protocol for networking PBX systems. The abbreviation means QSIG signaling at the Q reference point. The Q reference point is based on the ISDN reference model, a point of attachment for private switching systems (see ISDN reference points, he would lead out there NT2).


The networking of PBXs is usually with manufacturer or system-specific protocols. These proprietary protocols almost the full extent of the features of the PBX can also across locations, use within the corporate network formed by cross-linking. The networking of PBXs from different manufacturers is possible without a powerful common protocol only at a low level (for example, dialing and speaking). This also systems from different manufacturers with the art performance characteristics can be networked together, was originally developed by the ECMA QSIG and the European Telecommunications Standards Institute (ETSI ) standardized. The QSIG protocol works similar to the DSS1 protocol and is compatible with this principle. However, differences exist in the implementation of features.

The QSIG protocol was applied also by the ATM Forum, in order to define a signaling protocol for ATM switches for voice calls across ATM networks.