ITU-T G.107 PDF

This Recommendation describes 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 conversational2 quality of 3.1 kHz handset telephony. 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 agreed-upon model recommended by the ITU-T).

This version of this Recommendation now includes a packet loss parameter and enhanced talker sidetone modelling.

The E-model has not been fully verified by field surveys or laboratory tests for the very large number of possible combinations of input parameters. For many combinations of high importance to transmission planners, the E-model can be used with confidence, but for other parameter combinations, E-model predictions have been questioned and are currently under study. Accordingly, caution must be exercised when using the E-model for some conditions; for example, the E-model may give inaccurate results for combinations of certain types of impairments. Annex A provides further information in this regard.