VoIP Voice and Fax Signal Processing

20.2 E-MODEL-BASED VOICE QUALITY ESTIMATION

The E-model is the equipment impairment model described in G.107 [ITU-T-G.107 (2005)]. This model examines signal and packet transmission characteristics to predict voice quality on a linear scale. The objective of the E-model is to determine a transmission quality rating (R) (i.e., the R-factor or R-value that incorporates the “mouth to ear” characteristics of an end-to-end speech path). In the usage, it is also common practice to reference the E-model as the R-model. This model helps in analyzing and identifying the root causes of voice quality degradation. The R-factor is mapped to subjective MOS and to many other voice quality parameters. The typical useful range for the R-factor is 50 to 94 for narrowband telephony. An R-value below 50 is not suitable for continuing call conversation. Voice quality monitoring (VQmon) [URL (Telchemy)] and RTCP-XR packets [Friedman et al. (2003)] in VoIP makes use of E-model parameters. It is widely used for VoIP service quality measurements.

An E-model-based voice quality estimate for multiple voice compression codecs is given in Section 3.7. More details on this topic are available at [ITU-T-G.107 (2005), ITU-T-G.113 (2007), ITU-T-G.108 (1999), ITU-T-G.175 (2000)]. In this section, an overview and some more extensions from the published literature and recommendations are included. The E-model makes use of several parameters broadly classified under delay, delay variations, echo, noise, and phone ...