Echo Control (e.g.@ echo cancellation) and Voice Quality Enhancement (e.g.@ voice enhancement device) have become a necessity not only in Circuit Switched Networks (wired and wireless) but also in Next Generation Networks. Signal processing network elements and functions are provided on a per-call basis to guarantee QoS for voice calls. This Recommendation describes the protocols to control on a per-call basis the signal processing functions. The protocols described in this Recommendation include TDM-based as well as IP-based protocol versions for TDM networks and IP networks. The signal processing function specific logic@ i.e. the logic that decides on the need for a signal processing function and the number of signal processing functions to be provided for a call@ is defined in ITU-T Recs Q.115.x.