A Fast-Startup TCP Mechanism for VoIP Services in Long-Distance Networks

In this paper, a fast-startup TCP (fsTCP) mechanism for VoIP services in long-distance networks is proposed. Most VoIP applications usually operate on the top of UDP/IP protocol. However, there are some weaknesses in long-distance connections. For example, UDP offers no congestion control and no adjustment in voice packet rate. Traditional TCP protocol employees sliding windows to solve the problems, but the slow-startup feature of TCP causes a low initial throughput of VoIP connections at startup. The low throughput caused by TCP slow-start operation is not able to meet the bit-rate requirement of VoIP Codec. The quality of voice will degrade seriously during startup period of TCP. To improve the deficiency, the fast-startup TCP is proposed. A feasibility study of TCP-like congestion control applied on VoIP services. The proposed scheme improves throughputs of VoIP connections by adjusting TCP congestion window parameters before transmitting VoIP data. Three popular VoIP codecs, including G.711, G.726 and G. 729, are simulated in the proposed TCP to demonstrate the fast start-up throughput characteristics. Via the sliding window of congestion control, the VoIP services operating on TCP protocol will be able to adjust the bit-rates of codec in response to the time-varying network dynamics.