Recommendation ITU-T G.107 gives the algorithm for the so-called E-model as the common ITU T transmission rating model. This computational model can be useful to transmission planners, to help ensure that users will be satisfied with end-to-end transmission performance. The primary output of the model is a scalar rating of transmission quality. A major feature of this model is the use of transmission impairment factors that reflect the effects of modern signal processing devices. In the 2000 version of this Recommendation, an enhanced version of the E-model was provided in order to better take into account the effects of room noise at the send side, and quantizing distortion. With the 2002 version, the impairment due to random packet loss was included in a parametric way for different codecs. Since the 2003 version, an enhanced modelling of quality in case of low talker sidetone levels is provided. The 2005 version enabled more accurate quality predictions for codecs under (short-term) dependent packet loss. The 2009 version included an Appendix II describing a provisional impairment factor framework for wideband speech transmission. In 2011, this Appendix was updated in favour of new Recommendation ITU-T G.107.1. In the current version, the model has been extended to provide an assessment of delay impairments better tailored also to less delay-sensitive use cases. Carrier- or enterprise-grade telephony systems must be assessed with the default delay sensitivity parameters, while communication systems with low or very low interactivity requirements can be assessed with different parameters. A reference implementation is given in Appendix III.