The evolution towards interactive multimedia applications and the implementation of new signal processing devices, both in terminals and communication networks, means that a number of sophisticated signal processing algorithms will be deployed for echo control, noise reduction, level control, voice activity detection, speech coding, speech recognition and voiceband traffic technologies. These may interact with one another and with the imperfections of transmission systems, such as delay and error bursts, to adversely affect the quality of speech and voiceband signals. The purpose of this Recommendation is to describe interaction aspects and to provide requirements for the interoperability of Speech Processing Network Equipment (SPNE), between different SPNE, between SPNE and terminals and between SPNE and the transmission systems in the General Switched Telephone Network, including mobile networks.