Echo Cancellation and Voice Quality Enhancement 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.