VoIP

VIOP Protocol

PESQ

At the time PSQM was standardized as P.861, the scope of the standard was to assess speech codecs, used primarily for mobile transmission, like GSM. VoIP was not yet a topic. The requirements for measurement equipment have changed dramatically since then. As a consequence, the ITU set up a working group to revise the P.861 standard and to cope with the new demands arising from next generation networks like VIOP. Within these networks, the measurement algorithm has to deal with much higher distortions than with GSM codecs, but perhaps the most eminent factor is that the delay between the reference and the test signal is no longer constant. > From P.861 over PSQM+ and PSQM/IP to PESQ A first approach to overcome such problems was the development of PSQM+. It handled well the larger distortions as caused by burst errors, but still had significant problems with the compensation of the varying delay. An advanced Delay Tracking Feature has been added by OPTICOM in OPERA™, called "PSQM/IP" that implemented an easy way to solve the varying delay issue in most cases, without loosing the option of real-time operation. Although this feature may fail for some signals, it still allows to achieve PSQM results for the speech quality of VoIP networks.

With the new ITU standard P.862 (PESQ) this problem is finally eliminated. PESQ combines the excellent psycho-acoustic and cognitive model of PSQM+ with a time alignment algorithm adopted from PAMS, that handles varying delays perfectly. PESQ is not designed for streaming applications, which is it’s only drawback. This is why it cannot fully replace PSQM+. With PSQM and PESQ there are now two standards that cover the entire problem of measuring speech quality. An overview of the structure of the PESQ algorithm is shown in the block diagram, also indicating the new blocks that have been added to the PSQM algorithm.