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Question 9/16 – Embedded variable bit rate coding of speech signals
(Continuation of Question 9/16. Deleted on 6 Oct 2010, see TSB Circ. 130 and 143)


During the last study period, ITU-T developed Recommendation G.718, which specifies an embedded variable bit-rate speech codec comprising five layers where higher layer bitstreams can be discarded without affecting the decoding of the lower layers. The codec has been designed with the primary objective of delivering high-performance wideband speech coding for error prone telecommunication channels, without compromising the quality for narrowband speech signals or wideband music signals. G.718 incorporates additional optional features such as lower delay operation for its first two bit rates, DTX/CNG functionality, and an interoperability mode with the 12.65 kbit/s mode of AMR-WB in ITU T G.722.2 (3GPP TS 26.190).

In the 2009-2012 study period, standardisation of extensions to this recommendation are expected to provide interoperability with other ITU-T speech and audio coding standards and/or with 2G and 3G mobile radio systems coding standards, to increase the flexibility of these other codecs by enabling them to fulfil the application areas identified for the upper layers of G.718.

This Question will also complete the second phase of the work to characterise the performance of the narrowband and wideband operation of G.718.

Study items

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

  • Study and define additional modes for G.718, with specific attention being paid to the applications, and the consequent constraints imposed jointly by the networks and applications
  • Study and define interoperable enhancements to other codecs by applying the upper layers of the EV-VBR codec
  • Study and define the floating point functionality for G.718
  • Packetization definition for new G.718 coding algorithm
  • Considerations on how to help measure and mitigate climate changes


Tasks include, but are not limited to:

  • Definition of applications, performance requirements and objectives for new modes of G.718
  • Solicit proposals and conduct tests to recommend the best candidate algorithms to meet these Terms of Reference
  • Study and define test conditions and evaluation procedures to be applied to recommend the best solution(s) in conjunction with SG 12
  • Develop new Annexes to ITU-T Rec. G.718 to describe modifications to G.718 necessary to support the new modes of G.718
  • Completion of the second phase of the Characterisation phase of G.718 in conjunction with SG 12
  • Maintenance of the G.718 Recommendation (to be moved to Q10/16 once all tasks are complete)

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




  • H.300-series system Recommendations
  • G.76X-series circuit multiplication Recommendations
  • G.799.X-series voice over IP gateway Recommendations
  • G.16X-series speech enhancement Recommendations


  • 7, 8, 10/16 on speech and audio coding
  • 1, 2, 14, 22/16 on interaction with conferencing systems
  • 15, 16, 18/16 on network signal processing

Study Groups:

  • ITU-T SG 2 to identify other potential user applications
  • ITU-T SG 11 on signalling requirements and protocols
  • ITU-T SG 12 on speech and audio quality evaluation of specified algorithms
  • ITU-T SG 13 on NGN and on speech and audio coding in IMT
  • ITU-R SG 5 to ensure compatibility with mobile transmission system constraints

Other Bodies:

  • 3GPP, 3GPP2
  • IETF for G.718 packetization issues
  • IMTC
  • IP/MPLS Forum
  • ISO/IEC SC 29 WG11 (MPEG)
  • TIA


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Updated : 2010-10-19