Call Admission Control and Traffic Engineering of VoIP

This paper presents an extension of the Erlang-B model for traffic engineering of voice over IP (VoIP). The Erlang-B model uses traffic intensity and grade of service (GoS) to determine the number of trunks in circuit-switched networks. VoIP traffic, however, is carried over packet-switched networks, and network capacity is measured in bits per second instead of the number of trunks. In this paper, we propose a new measurement scheme to translate network bandwidth into the maximum call load. With this new metric, the Erlang-B model is applicable to VoIP. We conducted experiments to measure the maximum call loads based on various voice codec schemes, including G.711, G.729A, and G.723.1. Our results show that call capacity is most likely constrained by network devices rather than physical connections. Based on this result, we recommend considering both packet throughput (pps) and bit throughput (bps) in determining the max call load. If network capacity is constrained by pps, codec schemes would have almost no effect on the maximum call load, while the sampling rate could easily double or half the call load.