Efficient and stateless deployment of VoIP services

A critical issue for the convergence of telephone networks towards an all IP environment is the provisioning of an adequate QoS level to the telephone traffic. Following the guidelines detailed in RFC 2990, we recently proposed an admission control function, named Gauge & Gate Reservation with Independent Probing (GRIP), through which we are able to provide QoS guarantees by means of stateless procedures compliant within the Differentiated Service (DiffServ) paradigm, which is the de facto standard for QoS provisioning in Internet. The main goal of this paper is to present a specific implementation of GRIP optimized for supporting voice over IP (VoIP) services within a DiffServ cloud. In particular, we propose and analyze a simple measurement-based call admission control procedure for carrying VoIP traffic in a DiffServ environment. We assume voice sources are leaky bucket controlled with known leaky bucket parameters. We analyze the leaky bucket to derive the distribution of the times over which voice sources generate traffic at peak and regulated rates. We use the results of that analysis, which provides complete knowledge of the traffic generation characteristics of a single source, to derive a Markov chain model that characterizes the voice packet generation process of a single voice source. We then derive a simple stateless threshold policy for admission control; that is, our policy is of the form if, at admission request time, x <= x_threshold, admit the call; else reject the call. Finally, we show, via simulation, that the QoS achieved using the threshold-based admission control policy is very close to that achieved by a stateful admission control policy even at very high traffic utilization.