Signalling System R2 is a signalling protocol for telecommunications that was in use from the 1960s mostly in Europe, and later also in Latin America, Asia, and Australia, to convey exchange information between two telephone switching systems for establishing a telephone call via a telephone trunk.[1] It is suitable for signaling on analog as well as digital circuits.
R2 signaling specifications were first published by the International Telegraph and Telephone Consultative Committee (CCITT) in ITU White Book Volume VI of 1969,[2] and are maintained by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) in Recommendations Q.400 through Q.490. The name R2 is a derived from a designation as Regional System No. 2.
R2 signaling methods may be logically divided into two protocol groups. The line signaling group comprises supervisory signals for call setup and termination, while interregister signaling uses in-band multifrequency signals to transfer calling-party and called-party addressing information.
- ^ ITU-T Recommendation Q.400-Q.490 - Specifications of Signalling System R2
- ^ IVth Plenary Assembly (Mar Del Plata, 23 September-25 October 1968), White Book Volume VI, Telephone Signaling and Switching, Recommendations Series Q, ITU 1969.
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