End-to-end voice over IP testing and the effect of QoS on signaling

Voice over IP (VoIP) uses IP networks that were never designed to provide any kind of built-in quality of service (QoS) in the first place. And since no specific QoS can be thought of as a set of minimum parameters a network must maintain in order for acceptable voice quality to be attained, it is imperative that there exist tools that can cheaply and effectively measure voice quality over this type of network. The network must be tested with a system that uses speech, and can provide an objective and repeatable analysis of the speech as it is received. The answer lies in the new generation of objective measurement metrics such as PSQM and PAMS that directly relate to perceived subjective quality. Voice quality testing of networks is almost always performed end-to-end, and it divulges important essentials about components like QoS that contribute to the overall performance or system behavior. The challenge to voice quality-testing equipment is to model the very human expectation of quality with mathematical equations, and more importantly, predict the user's experience in terms of objective and measurable criteria. The results are testing methodologies that produce a number that corresponds to how a vast majority of users will perceive the conversation. This paper discusses the effects of different QoS mechanisms on the performance of two signaling protocols in VOIP, namely, SIP and H.323.