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Question 8/12

Question 8/12 – E-Model extension in wideband transmission and future telecommunication and application scenarios
(Continuation of Question 8/12)


Study Group 12 has established a concept of impairment factors which aim at predicting the perceptive effects of different types of degradations on overall speech communication quality, for network planning purposes. The core algorithm related to this concept is the so-called E-model, a computational model for use in transmission planning, see Recommendation G.107. This model is now frequently applied to plan traditional, narrow-band and handset-terminated networks, and to an increasing extent also for wideband and packet-based networks. Methodologies have been set up to derive impairment factors for codecs from subjective listening-only tests and from instrumental models (Recommendations P.833, P.833.1, P.834 and P.834.1). In addition, it has been shown that the E-model principle can also be extended to wideband networks, and an extension of the E-model has been recommended in Recommendation G.107.1.

With respect to the application of the E-model to the planning of modern and Next-Generation (Mobile) Networks (NGN, NGMN), however, there are still several open questions, which limit the model's usability. They result from the terminal and transmission characteristics of modern telecommunication scenarios, which could not have been taken into account at the time the model was established. In order to guarantee that the successful concept keeps track with the technological progress, it is highly desirable to maintain and update the model. The validity range of the E-model should be extended so that it cannot only be applied to planning traditional networks, but also to packet-based transmission, NGN, NGMN, wideband systems, non-handset terminal equipment, speech processing equipment. The suitability of the E-model for quality monitoring should also be assessed.

 Today, the current E-model is rarely used to support decisions before changes are implemented in a network. Management is asking how much impact deployment of a new technology will have on user perceived quality. Therefore, it is highly desirable to come up with a proposal of an operational quality estimator which can combine results from field trials with other impairments, such as one-way delay, etc.

The following major Recommendations, in force at the time of approval of this Question, fall under its responsibility:

 G.107, G.107.1, P.833, P.833.1, P.834, P.834.1.


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

  • Which quality issues have to be taken into account when extending the E-model to terminal equipment other than standard handset telephones (e.g. HFTs, headsets)? Which parameters can be used to describe such terminal equipment? 
  • How can the perceptive effects introduced by speech-processing devices included in the network or in the terminal equipment (e.g. (acoustic) echo cancellers, level control devices, voice activity detectors, noise suppression devices) be covered by the E-model?
  • Is the E-model suitable for quality monitoring? How would such a monitoring application take into account strongly time-variant channel characteristics, e.g. due to bursty frame or packet loss, or in a cellular network?
  • Is it possible to derive an operational quality estimator (based on the E-model), which can combine results from field trials with other impairments and which can serve as a decision support tool?
  • How could the E-model reflect the influences of degradations such as pure delay on interactivity in different conversational situations? Impacts might be e.g. those resulting from the system's double-talk performance (see Recommendation G.108.1).
  • How can the E-model be used in mixed-band and beyond-wideband transmission scenarios?
  • In how far is the additivity property of different types of impairments on a perceptual scale a valid underlying assumption of the E-model? Which deviations from this assumption are tolerable for network planning purposes? How can interdependencies be integrated into the E-model algorithm?
  • What are the psychological dimensions commonly handled by the term "expectation"? How will user expectation develop with time and with different types of services (cf. Recommendation G.113)?
  • What are the experiences of the users of the E-model (e.g. the users of the ITU-T web interface to the E-model)?
  • Considerations on how to help measure and mitigate climate change.


Tasks include, but are not limited to:

  • Maintenance and enhancement of the E-model described in Recommendation G.107 and G.107.1 and input to depending Recommendations
  • Maintenance of the Recommendations P.833 and P.834 and corresponding wideband Recommendations for determining equipment impairment factors
  • Development of a new approach to provide a conversational quality predictor (based on the E-model) for decision support
  • Maintenance of the E-model on the ITU website.

An up-to-date status of work under this Question is contained in the SG 12 work programme



  • G.108, G.108.1, G.108.2, G.109, G.113, G.114, G.131, G.1070, P.11, P.562, P.564
  • 7/12, 9/12, 13/12, 15/12
Study Groups
  • ITU-T SG 15, SG 16
Standardization bodies