Improving XCP to Achieve Efficient and Fair Bandwidth Allocation

The explicit control protocol (XCP) is a novel and promising congestion control protocol that outperforms TCP in terms of efficiency, fairness, queue length, packet loss rate and convergence speed. However, the latest research found a weakness of XCP, in a multi-bottleneck environment, a bottleneck link may have a significantly decline in utilization, and some flows may not receive their fair bandwidth allocation. In this paper, according to the classical control theory, we propose an XCP bandwidth compensation algorithm based on the PII controller (PII-XCP). Extensive simulations have shown that PII-XCP achieves efficient and fair bandwidth allocation in a multi-bottleneck environment. Simulations also have shown that PII-XCP preserves the good properties of XCP, including fast convergence, negligible queue length and zero packet loss rate. Compared with improved XCP (iXCP), (1) PII-XCP have the same packet header overhead of XCP; (2) computing complexity significantly declines; (3) convergence time is far smaller; (4) and more effective control in highly dynamic situations.