Introduction This Recommendation contains principles and examples of signalling between the International Switching Centre (ISC) (exchanges) (see Note) and their associated circuit multiplication equipments. Circuit multiplication equipments may have integral echo control and A/??law converter functions. The information in this Recommendation is compatible with the control procedures for such devices. NOTE ?C As Circuit Multiplication Equipment may also be used in national networks@ the signalling described here could not only be used in International Switching Centres but also in national exchanges.