This Recommendation describes a signalling interface between an International Switching Centre (ISC) and a Digital Circuit Multiplication Equipment (DCME) that has the additional (compared to ITU-T Rec. Q.50) capability to control the compression/decompression function of the DCME. This signalling interface provides for the call by call control of a DCME in real time. The difference between this Recommendation and ITU-T Rec. Q.50.1 is that the DCME control protocol is supported over an IP network.