TCP-friendly transmission of voice over IP

In the near future, congestion control should be introduced for multimedia UDP-based traffic, in such a way that this traffic becomes "TCP-friendly". To this end, several TCP-friendly algorithms have been proposed in the literature. However, although these algorithms were introduced to support real-time applications on the Internet, the only target in optimizing them, until now, was to achieve fairness with TCP flows in the network. No attention has been paid to the quality of service (QoS) perceived by their users. The target of this paper is to analyze the problem of transmitting voice over IP when voice sources use two of the most promising TCP-friendly algorithms, RAP (rate adaptation protocol) and TFRC (TCP-friendly rate control). With this aim, a VoIP system architecture is introduced and the characteristics of each of its elements are discussed. To optimize the system, a voice multirate encoder, which is able to work over a TCP layer, is used, and a modification of both RAP and TFRC is proposed. Finally, in order to analyze the performance of the proposed system architecture and to compare the modified RAP and TFRC with the original algorithms, the sources have been modeled with an arrival process modulated by a Markov chain, and the model has been used to generate traffic in a simulation study performed with the ns-2 network simulator.