ITU-T Recommendations

Voice-band data traffic has traditionally been transported by circuit switched systems and equipment. With the advent of the networks optimized for the transport of Internet Protocol (IP), and as a result of its considerable growth and pervasive nature, more and more voice-band data traffic is expected to be carried over IP networks.Given that voice and voice-band data services remain a significant part of telecommunications, there is a need to ensure a high quality of service for voice and voice-band data carried in part, or wholly, via IP. Recommendation ITU-T V.152 defines procedures for equipment that interconnect GSTN networks with IP networks to provide satisfactory, transparent delivery of modulated voice-band data (VBD) as encoded audio content over IP (data modems, facsimile terminals and text telephones).Annex B defines a method that uses data signal detection and silence insertion in voiceband data that adds a means of providing bandwidth savings during transmission. Annex C addresses a problem discovered during the implementation of ITU-T V.152 gateways with the transmission of facsimile terminals. While this issue has been resolved by an amendment to Recommendation ITU-T T.30, due to the extremely large numbers of terminals deployed in the field and the low probability that they would be corrected retroactively, it was considered pre-emptive to include a solution in an ITU-T V.152 media gateway.This Recommendation is complementary to the modem relay and voice-band data Recommendations (Recommendations ITU-T V.150.0 and V.150.1).This revision includes the updating of references, general editing improvements for clarity and many additional examples of call control. It also integrates changes introduced by Corrigendum 1 (2005) for clarification to clauses 7.1 and 7.1.1; by Corrigendum 2 (2006) for clarifications on the use and control of echo cancellers and the application of IETF RFC 2833 with VBD; and by Amendment 1 (2009) for new Annexes B and C.