Effects of Variable Bit Rate Vocoder on VoIP QoS

Transmission of voice over packet switched networks, such as the Internet (VoIP), has been gradually evolving due to the advantages it can provide to the different end-users (private user, integrated networks service providers, business arena, etc). However, in order for VoIP to be commonly used, the Quality of Service (QoS) offered by VoIP needs to be at least as high as the traditional Plain Old Telephone Service (POTS).In this research, we aim to improve the QoS parameters of the developing VoIP technology by substituting the traditional constant bit rate vocoder (CRV) with a new type of vocoder that is based on continuously variable bit rate (CVRV). Comparative studies of these two vocoders are performed in the following 3 independent scenarios: 1. LAN, in which the connected terminals transfer/receive voice only. 2. LAN, in which the terminals exchange mixed traffic classes of both voice and data. 3. WLAN, in which the connected terminals transfer/receive voice only. The results of scenario 3 show a significant improvement in performance with use of CVRV in WLAN when more than 50 terminals are involved, as exhibited in all the QoS parameters that were tested. The results of the WLAN are especially interesting and significant as the WLAN is becoming progressively more common nowadays.