Motivation

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 Rec. G.107. This model is now frequently applied to plan traditional, narrow-band and handset-terminated networks, and to an increasing extent also for packet-based networks. Methodologies have been set up to derive impairment factors for codecs from subjective listening-only tests and from instrumental models (Recs P.833 and P.834). 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 transmission rating scale as well as wideband impairment factors have been defined.

With respect to the application of the E-model to the planning of modern and Next Generation Networks (NGN), however, there are still several open Questions, which strongly 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 can not only be applied to planning traditional networks, but e to packet-based transmission, NGN, wide-band systems, non-handset terminal equipment, speech processing equipment, and to quality monitoring.

The following major Recommendations, in force at the time of approval of this Question, fall under its responsibility: G.107, P.833, P.834.

Question

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. echo cancellers, level control devices, voice activity detectors, noise suppression devices) be covered by the E-model?
• How can the principle underlying the E-model be used for quality monitoring? How would such a separate monitoring model take into account strongly time-variant channel characteristics, e.g. due to bursty frame or packet loss, or in a cellular network,? How could it reflect the influences of pure delay on interactivity in different conversational situations?
• How can perceptive quality dimensions other than “impairment” being covered by the E-model, e.g.
  • speech sound quality”, e.g. due to terminal equipment other than handsets, due to transmission bandwidth other than the normal 3.1 kHz band, e.g. wide-band transmission, or due to frequency distortion or non-linear codecs,
  • conversational quality features not covered by the current E-model version, e.g. those resulting from the system’s double-talk performance (see Rec. G.108.1).
• How can the E-model be extended from narrow-band to wideband and mixed-band transmission scenarios, leaving the narrow-band usage of the model unchanged? How can the extended transmission rating scale and the wideband equipment impairment factors be reflected by the new mixed-band E-model?
• 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 is the influence of user expectation on the overall quality, e.g. for terminal equipment other than handsets, or for computer-operated VoIP services?
• What are the psychological dimensions commonly handled by the term “expectation”?
• How will user expectation develop with time (cf. Rec. 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

Tasks include, but are not limited to:

• Maintenance and enhancement of the E-model described in Rec. G.107 and input to depending Recommendations
• Maintenance of the Recommendations P.833 and P.834 and corresponding wideband Recommendations for determining equipment impairment factors
• It is anticipated that a new Recommendation on a wideband transmission planning model can be produced in the 2009-2012 Study Period.

An up-to-date status of work under this Question is contained in the SG 12 Work Programme http://www.itu.int/ITU-T/workprog/wp_search.aspx?isn_sp=545&isn_sg=551

Relationships

Recommendations: G.108, G.108.1, G.108.2, G.109, G.113, G.114, G.131, G.175, P.11, P.562, P.564

Questions: 7/12, 9/12, 10/12, 14/12

Study Groups: ITU-T SG 15, SG 16

Standardization bodies: ETSI TC STQ, TIA TR-41, T1A1