ITU-T G.107.2 PDF

This Recommendation describes the FB version of a computational model, known as the E-model, that has proven useful as a transmission planning tool for assessing the combined effects of variations in several transmission parameters that affect conversational¹ quality. This computational model can be used, for example, by transmission planners to help ensure that users will be satisfied with end-to-end transmission performance whilst avoiding over-engineering of networks. It must be emphasized that the primary output from the model is the "rating factor" R, but this can be transformed to give estimates of customer opinion. Such estimates are only made for transmission planning purposes and not for actual customer opinion prediction (for which there is no agreedupon model recommended by the ITU-T).

This version is an adapted version of the NB (300-3400 Hz) and WB (50-7000 Hz) E-models, which are described in [ITU-T G.107] and [ITU-T G.107.1]. The FB version addresses scenarios which include FB (20-20000 Hz) transmission. It does not replace the NB or WB E-model. Instead, it describes a separate FB-version of the model that uses, within limits, similar concepts and input parameters as the NB and WB E-models. The current version only captures the effects of FB speech coding, voice-over-IP packet loss, and pure delay. Other degradations such as loudness loss, background noise at the sending side or receiving side, circuit noise, talker echo, listener echo, nonoptimum sidetone levels and quantizing distortions have not yet been covered by the model.

Regarding the interpretation of the FB E-model ratings, note that the current versions of [b-ITU-T G.108], [b-ITU-T G.108.1] and [b-ITU-T G.109] do not refer to the FB version described here, but only to the NB version of the E-model described in [ITU-T G.107].

¹ Conversational quality in this context refers to transmission characteristics, e.g., long transmission times, effects of talker echoes, etc. However, the E-model, as described in this Recommendation, has not yet been developed to an extent which would cover those characteristics in a. realistic way; most of its formulae, except the ones of Section 7.4, have been developed on the basis of subjective listening-only experiments. The model is also not intended to model transmission impairments during double talk situations. These effects are for further study within ITU-T Study Group 12.