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Question 16/16 – Speech enhancement functions in signal processing network equipment
(Continuation of Question 16/16)


This Question deals with network-based speech enhancement devices, including electrical network echo control, acoustic network echo control, automatic level control devices, and speech enhancement devices.

The application of echo cancellers continues to evolve in existing general switched telephone networks (GSTN), cellular, ATM and emerging IP networks. These applications bring new issues to echo canceller performance, and will require study to ensure that network operators have adequate assurance of transmission quality from echo cancellers complying with G.168. These issues may result in adding and improving the tests within G.168, and studying the issues arising from the deployment of echo cancellers to ATM and IP networks and new services within the GSTN.

With the deployment of automatic level control (ALC) and voice enhancement devices (VEDs), new issues are expected to arise as these devices are applied to existing and emerging networks. As a result, Recommendation G.169 may need to be revised and work on new Recommendation G.160 (VED) needs to continue to ensure adequate transmission quality.

As echo cancellers are embedded into gateways it will become necessary to review the applicability of G.168 to these devices and to develop either a separate Recommendation or Annex to G.168 to ensure that any specific requirements for these embedded echo cancellers are taken into account.

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:

  • Functional characteristics and requirements that are necessary for network-based speech enhancement devices to provide good performance in existing GSTN and emerging ATM/IP and cellular networks
  • Tests and requirements that are necessary to ensure good performance of speech enhancement devices and how can they be enhanced to better correlate with subjective test results
  • Performance of speech enhancement devices in GSTN, ATM/IP, cellular and other wireless environments with speech, facsimile and voiceband data signals, text telephones, signalling tones, call-processing tones, etc
  • Hardware and software tools that are necessary to support the testing of speech enhancement devices
  • Realistic echo paths and test signals that are required for testing speech enhancement devices
  • Design of in-path speech enhancement equipment so as not to interfere with tandem codec avoidance mechanisms (e.g. codec bypass or tandem-free operation)
  • Requirements of speech enhancement devices to minimise any degradations in performance due to tandeming
  • Requirements for speech enhancement devices to operate with wideband signals
  • Impact of testing with voice-over-packet interfaces (e.g. IP) and overcoming of any associated problems
  • To consider any additions to Recommendations that may help to measure and reduce the impact of climate change. Examples include reduced power consumption of hardware and hardware tools, and reduced complexity of algorithms


Tasks include, but are not limited to:

  • Continue the development and enhancement of G.160-series Recommendations on VEDs
  • Develop guidelines for the application of speech enhancement devices to be included in the respective Recommendations above
  • Develop new Recommendation or Annex to G.168 covering the requirements of embedded echo cancellers
  • Maintenance of ITU-T Recommendations G.164, G.165, G.168, G.169

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




  • G.161, G.108.2, P.501, P.502, P.340, Q.115.1, Q.115.2, P.800-series


  • 14, 15 and 18/16 on network signal processing
  • 7, 8 and 10/16 on sound activity detection, software tools and speech coding aspects

Study Groups:

  • ITU-T SG 2 on Telecommunications Management Network (TMN) aspects
  • ITU-T SG 11 on signalling issues
  • ITU-T SG 12 on application guidelines and subjective performance
  • ITU-T SG 13 on ATM and IP issues
  • ITU-R SGs 4 and 5 on voice on mixed terrestrial/satellite networks

Other Bodies:

  • IP/MPLS Forum on ATM, MPLS and frame relay transport
  • IETF working groups AVT and IPTEL on IP transport
  • ETSI 3GPP, 3GPP2 and TIA on mobile networks and tandem-free operation


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Updated : 2008-12-05