Implementation of a Test-Bed for Telephony over IP: Architectural, Theoretical and Performance Issue

CSELT is evaluating the feasibility of provisioning 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 of service guarantees, to be offered to a large number of users, either overlapping or substituting classical Plain Old Telephone Services. CSELT is performing both theoretical and experimental analysis; in particular we are focusing our work on the mechanisms and protocols developed in the standardisation bodies in order to verify how the telephony services can be supported by means of an IP network. In the first half of 2000 we have performed a laboratory trial in order to demonstrate the "proof-of-concept" of ToIP capabilities, performance and interoperability with TDM-based switching technology. In the solution tested in CSELT, provided by a leading manufacturer, the IP technology is deployed in the transit network, so it is necessary to have an interworking function between a traditional circuit network and the IP network. It must be underlined that the solution provided by the manufacturer, as requested by CSELT, was still at an early stage of development, hence it has not been possible to perform a full test campaign. From our theoretical analysis and laboratory experiment we observed the suitability of architectures proposed in the standardisation bodies and by the manufacturers for the provisioning of ToIP services. The experimented system, in particular considering its prototype nature, has shown high performance in terms both of voice and signalling quality. The main problem that arises in ToIP systems is the reliability of the system, that is a fundamental concept for providing carrier-class services. The detailed results of both the theoretical analysis and the laboratory experiment are presented in this paper.