Signalling System R2
FAMILY OF TELEPHONY PROTOCOLS FOR LINE AND REGISTER SIGNALLING
R2 signaling; Multi Frequency Compelled; R2 signalling
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.ITU-T Recommendation Q.