British Telecommunications Public Limited Company

British Telecommunications Corporation

Richard J B Reynolds

Michael Peter Hollier

Antony William Rix

Philip Gray

Eleanor J Beamond

Gray Philip

The perceptual quality of voice signals used for Voice over IP (VoIP) systems is assessed. The content of the voice data packets may be altered in order to increase the perceived quality of the VoIP system.

Method to reduce the distortion in a voice transmission over data networks

The present invention provides a test method which can determine whether a user terminal is capable of supporting a real time connection, such as a computer telephony link, with a network terminal while simultaneously supporting a connection with a WWW server.

Method to assess the quality of a voice communication over packet networks

The perceptibility of degradations caused to signals transmitted over a transmission medium is measured by generating one or more predetermined transmission degradation conditions (e) and subjecting a test signal (S) to the transmission degradation conditions (e) in a network simulation device. The degree M(e) to which the or each transmission degradation condition (e) is perceptible to the human perceptual system is measured and a data set is generated and stored for converting one or more transmission degradation conditions (e) to respective values of perceptibility M(e). The data set may be a look-up table or an empirically determined formula. The data set may then be used on live traffic (S'), by identifying objectively measured transmission degradation conditions (e) in the received signal (S&#x2032;) and retrieving from the data set in the data storage means (7) a value of perceptibility (M) associated with the transmission degradation conditions (e) so identified. In this way a measure of the subjective significance of degradation in the signal (S&#x2032;) can be derived from objective measures of degradation.

Test signalling

Apparatus for assessing the performance of telecommunications systems by comparison of a reference signal with the same signal as degraded by the system under test tends to give unreliable results when used to test connectionless packet-switching equipment. This is because variable delay in delivery of the individual packets can result in the test signal and reference signal becoming unsynchronised. This may lead to the apparatus recording a poorer performance than a human tester would have recorded. To overcome this problem, the invention separates the test signal into a series of individual sections, which are synchgronised and analysed separately, and a quality value, aggregated over all the sections, is derived.

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Ipswich, United Kingdom

Richard J B Reynolds