Telephony over IP: theoretical modelling and lab experiments

In 1999-2000 CSELT has started to analyse the feasibility to provision Telephony over IP (ToIP) services. ToIP is different from voice over IP, because it is intended as a carrier-class service, fully featured and with quality guarantees, to be offered to large number of users, either overlapping or substituting classical POTS services. The analysis has been both theoretical and experimental: first a model for quality of service evaluation has been developed, in order to cope with all the aspects that allow to characterise the ToIP service (voice quality, signalling quality, supplementary telephony services, OAM&P aspects); these concepts have then been validated on a prototype system provided by a leading manufacturer. From our theoretical analysis and lab experiment we have seen that the architectures proposed in the standardisation bodies and by the manufacturers seem to be adequate for the provisioning of ToIP services. From a functional point of view, the system experimented, in particular considering its prototype nature, has given good results, in terms both of voice quality and of signalling quality. The big problem that remains to be resolved is the reliability of the systems, that is a fundamental concept for providing carrier-class services. The detailed results of both the theoretical analysis and the lab experiment are presented.