Tool Description: P.862 and P.OLQA

P.862 provides a method for measuring call quality. It is an intrusive tool, i.e. it requires a known voice file to be sent over a test connection and then compares the original and impaired files. P.862 will be superceded by a new ITU standard - P.OLQA.

Application

P.862 is one of a number of "analog" signal analysis tools that are used to measure signal distortion levels and identify problems affecting speech quality. P.862 does not measure the effects of echo, signal bandwidth and certain other impairments, and becomes less accurate for packet loss rates in excess of 20%.

The scores from P.862 range from -1 to 4.5 and are hence in a similar range to MOS, which can cause some confusion. A new P.862.1 standard introduced a mapping function that can be used to translate P.862 scores to a MOS-like scale.

Various factors affect the scores obtained by P.862:

(i) It is important to know if the P.862 software you are using is generating P.862 or P.862.1 scores, as these are similar enough to be confusing but different enough that the same score can mean quite different quality levels.

(ii) P.862 is more sensitive to packet loss occurring in talkspurts than in silence periods, hence for the same packet loss rate scores may vary by 0.1-0.2 or so.

(iii) P.862 is sensitive to noise levels that may be imperceptible to people.

(iv) If you are using P.862 on systems that use VAD or silence suppression then background noise is synthesized by the receiving VoIP system, hence is likely to be different to the original (suppressed) noise.

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