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VoIP Voice and Fax Signal Processing by Sivannarayana Nagireddi

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20.5 VOICE QUALITY MONITORING AND RTCP-XR

On front-end operations, telephone interfaces are monitored using GR-909 diagnostic methods. VQmon is mainly used for monitoring the voice quality from signal and packet transmissions. VQmon, which was popularized by Telchemy, is voice quality monitoring based on the E-model algorithm discussed in previous sections. VQmon and the RTCP-XR framework provide a set of metrics for VoIP performance monitoring and diagnosis. They are used in addition to GR-909 and other proprietary diagnostic methods. It supports both real-time monitoring and postanalysis.

VQmon mainly derives parameters from packet transmission characteristics that include packet impediments on the network and end-to-end delays jitter buffer dynamics as well as signal transmission characteristics that include signal level, noise level, gain, echo rejections, R-factor, and MOS derived from the R-model. The VQmon parameter's role in the RTCP-XR [Friedman et al. (2003)] packet is shown in Fig. 20.6. These parameters are typically updated once every 256 packets. Use of these parameters and applying feedback for improving the voice quality helps the VoIP system to deliver the highest quality under severe conditions.

RTCP-XR sends about 20 parameters categorized as packet loss, discarded metrics, delay metrics, signal-related metrics, call quality or transmission quality metrics, configuration metrics, and jitter buffer parameters. Complete details on these parameters are in RFC3611 ...

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