General

Signalling System R2 is used as an international signalling system within international regions (world numbering zones). Moreover, System R2 can be used for integrated international/national signalling if it is employed, in conformity with the present specifications, as a signalling system in the national networks of the region concerned. Suitable for both automatic and semi-automatic working it offers a high reliability in transmission of the information necessary for setting up a call. It allows for rapid call set-up and provides sufficient signals in both directions to permit the transmission of numerical and other information relating to the called and calling subscribers' lines and to increase routing facilities.

System R2 is specified for one-way operation on analogue and digital transmission systems and for both-way operation on digital transmission systems. Distinction is made between line signalling (supervisory signals) and interregister signalling (call set-up control signals). Versions of line signalling are specified for use on 4-wire carrier or PCM circuits. Nevertheless, the interregister signalling specified can also be used on 2-wire circuits. System R2 is suitable for use on satellite links and 3 kHz spaced carrier circuits. It is not designed for use on transmission systems with speech interpolation but it may be used on digital transmission systems with speech interpolation as long as transparency for pulsed interregister signals is guaranteed.

The interregister signalling is a compelled multifrequency code system. This offers the possibility of end-to-end signalling and to take advantage of modern switching systems by providing a sufficient number of signals in both directions.

System R2 is capable of normal interworking with other CCITT signalling systems.