(Continuation of Question 21/16)

Background and justification

During the 1993-1996 Study Period, ITU-T specified the G.729 speech-coding algorithm, which is capable of encoding speech signals at telephone (or toll) quality at 8 kbit/s. The increasing use of wireless access and circuit- and packet-switched multimedia applications, such as low bit rate video telephony, motivates the standardization of an algorithm with equivalent performance at bit rates around 4 kbit/s.

Successful completion of this effort will permit significant economies in bandwidth utilization to be realized, both within the access network and within the core network, while providing the high quality that a user would expect from the fixed network. The increasing use of packet bearers, such as IP and packet radio, will be an important factor in the selection of a suitable algorithm.

Study items

What algorithm should be specified for the encoding of 3.4 kHz band-limited, telephone-quality speech at transmission rates in the region of 2.4 kbit/s to 6.4 kbit/s?

Items for study include:

a) Study and definition of applications and performance for low-rate speech coding.

b) Definition of performance requirements with consideration to the constraints of key systems and networks.

c) Definition of the test conditions and evaluation procedures to be applied in selecting between candidate algorithms on the basis of subjective performance, as specified by SG 12, and objective performance.

d) What type of Voice Activity Detection/Comfort Noise Generation (VAD/CNG) algorithm should be recommended for this speech-coding algorithm?

e) Study of encoding techniques and evaluation of possibility of selecting a single type of technique capable of operating at a number of selectable transmission rates with an associated improvement in speech quality as the transmission rate is increased.

f) Selection and specification of procedures to be used in verifying the implementation of algorithms implemented in accordance to the recommended procedures.

g) Study of the support of text-telephony (TDD) devices in systems using low bit-rate speech coding.

Specific tasks and deadlines

• Definition of network, algorithm, performance and test requirements (2000).
• Evaluation of algorithm performance against specified requirements (late 2000).
• Definition of 4 kbit/s algorithm and associated verification procedures (mid 2001).
• Definition of bit rate extensions and VAD/CNG (2002).

Relationships

• Other relevant Questions of SG 16.
• ITU-T SG 2 (to identify other potential user applications).
• ITU-T SG 12 (evaluation of performance with respect to voice quality).
• ITU-T SG 13 (for IP matters).
• ITU-R SG 8, ITU-T SG 11 (to ensure compatibility with mobile transmission system constraints).
• 3GPP and 3GPP2.
• IETF (for packetization issues).
• ISO/MPEG.