TCP and web browsing performance in case of bi-directional packet loss

Performance modeling of the transport control protocol (TCP) has received a lot of attention over the past few years. The most commonly quoted results are approximate formulas for TCP throughput (Padhye et al. (2000) [1]) and document download times (Cardwell et al. (2000) [2]) which are used for dimensioning of IP networks. However, the existing modeling approaches unanimously assume that packet loss only occurs for packets from the server to the client, whereas in reality the packets in the direction from the client to the server may also be dropped. Our simulations with NS-2 show that this bi-directional packet loss indeed may have a strong impact on TCP performance. Motivated by this, we refine the models in Padhye et al. (2000) [1] and Cardwell et al. (2000) [2] by including bi-directional packet loss, also including correlations between packet loss occurrences. Simulations show that the proposed model leads to strong improvements of the accuracy of the TCP performance predictions. In addition we show how our model can be used to predict quality of experience for web browsing sessions.