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Question 15/16

Question 15/16 – Voiceband signal discrimination and modem/facsimile terminal protocols

(Continuation of Questions 8/16 and 14/16)


This Question is responsible for all aspects of voiceband modem, facsimile terminal and voiceband signal discrimination standardization. This includes the functionality and performance across different network types.

Voiceband signal discrimination is a means to discriminate speech, music, tones and other voice¬band signals, and is widely used in telecommunication networks for example to save bandwidth and obtain trunking efficiency in codecs, voice gateways, circuit multiplication equipment, voiceband terminal, or to ensure correct operation of echo control and other signal enhancement devices, etc.

Generic voiceband signal discrimination (VSD) is motivated by two problems. Historically, VSD algorithms have been developed separately for individual network elements and applications, and there are currently numerous VSD algorithms. However, they are based on different principles, which make it difficult to provide common performance enhancements across all VSDs.

Therefore it is beneficial to develop a generic voiceband signal discriminator, which can be applied across a range of applications. The benefits from a standardized generic VSD are:

With the emergence of packet-based networks and specifically voice over packet, the GSTN has expanded to include the advantages of these network types. The need to ensure the best performance transmission of voiceband modems and facsimile over both circuit and packet switched networks is a necessary requirement. Packet-based networks that are designed for voice require methods and procedures to allow end-point modems to interoperate with the same performance as expected from circuit switched networks. In this spirit, the Question has developed Recommendations ITU T V.150.1, V.151, V.152, T.37 and T.38, all of which support different aspects of the transport of either voiceband modem signals or facsimile over IP networks.

The Question is also responsible for all aspects of voiceband modem and facsimile terminal (such as specification, performance evaluation and interworking) standardization. This includes the functionality and performance of the terminals and the transport of the signals they generate across different network types.

The Question will attempt to work electronically where possible and to make full use of e-mail and conferencing facilities in an attempt to reduce its carbon footprint.

Study items

Study items to be considered include, but are not limited to:


Tasks include, but are not limited to:

An up-to-date status of work under this Question is found in the SG 16 work programme (