Interregister Signalling - Pulse Transmission of Backward Signals A-3, A-4, A-6 or A-15. Multifrequency Signalling Equipment - Specifications of Signalling Systems R1 and R2 (Study Group XI) 2 pp
Since System R2 can provide, in international working, end-to-end signalling from the outgoing international R2 register to an incoming R2 register at the called subscriber’s local exchange (see Recommendation Q.440), the specifications for multifrequency