This Recommendation defines mechanisms/auxiliary functions for a signal processing network equipment (SPNE) designed for the use in the circuit switched part of a network (mobile@ fixed and hybrid). The SPNE addressed in this Recommendation is a physical entity that contains one or more of the following signal processing functions (SPFs) optimized for speech quality@ acoustic echo control@ electric echo cancellation@ noise reduction and automatic level control. The SPNE can be designed as stand-alone equipment or can be integrated in some other network equipment. The SPNE provides the SPFs permanent associated to the circuits or arranged in a pool. Depending on where in the network the SPNE is going to be provided@ the mechanisms/auxiliary functions identified in this Recommendation include appropriate interfaces to allow external control of the SPFs and the support of in-band signalling such as tandem free operation (TFO) and of services such as high speed circuit switched data (HSCSD).