The ETSI computation model: a tool for transmission planning of telephone networks

This article deals with the ETSI computation model-the E-model-for evaluating speech communication quality in telephone networks. The reasons why such models are of interest for transmission planning of modern networks and the various subjective tests and customer surveys that must form the basis for the computation algorithms are discussed. Then a survey is given of models that are described in the ITU's documents. The structure of the new E-model and the various considerations taken in its development and verification are also discussed. Results from application of the E-model on typical connections agree well with results from other models and from published subjective tests. In particular, impairments caused by low-bit-rate codecs can be quite well predicted by the model, better than by the hitherto used methodology of "quantizing distortion units." The E-model has also been used in the process of updating some of the ITU-T C-series Recommendations on transmission planning.