Improving XCP to achieve max–min fair bandwidth allocation

TCP is prone to be inefficient and unstable in high-speed and long-latency networks [1]. The eXplicit Control Protocol (XCP) is a new and promising protocol that outperforms TCP in terms of efficiency, stability, queue size, and convergence speed. However, Low et al. recently discovered a weakness of XCP. In a multi-bottleneck environment, XCP may achieve as low as 80% utilization at a bottleneck link and consequently some flows may only receive a small fraction of their max–min fair rates.This paper proposes iXCP, an improved version of XCP. Extensive simulations show that iXCP overcomes the weakness of XCP, and achieves efficient and fair bandwidth utilization in both single- and multi-bottleneck environments. In addition, we prove that iXCP is max–min fair in steady state. This result implies that iXCP is able to fully utilize bottleneck bandwidth. Simulations show that iXCP preserves the good properties of XCP, including negligible queue lengths, near-zero packet loss rates, scalability, and fast convergence. Simulations also show that iXCP overcomes the under-utilization and instability problem of P-XCP [2], and outperforms JetMax [3] in terms of link utilization in the presence of highly dynamic traffic.