Extensions of VCP to Enhance the Performance in High BDP and Wireless Networks

While Transmission Control Protocol (TCP) is the most popular transport protocol used in terrestrial networks, its performance is not adequate in wireless networks with long delay, e.g., satellite networks. Though some improvements of TCP and new transport protocols have been proposed, we focus on Variable-structure congestion Control Protocol (VCP) designed for high Bandwidth Delay Product (BDP) networks. In VCP, Explicit Congestion Notification (ECN) is used to generate the feedback signal from routers to sources in order to notify the utilization ratio of a bottleneck link. By adjusting its congestion window according to the network traffic conditions, VCP is able to achieve high link utilization even in high BDP networks. However, VCP requires a long time to fill the link capacity due to its more conservative window control mechanism than the slow start phase in TCP. In addition, throughput is unnecessarily degraded in VCP due to packet losses in wireless environments. In this paper, to address these issues, we propose two extensions of VCP, namely Bandwidth-Independent Start-up Extension (BISE) and Wireless Loss Tolerant Extension (WLTE). BISE can quickly increase its congestion window in the start-up phase. WLTE can maintain high throughput in wireless environments. The performance of the proposed schemes is evaluated through computer simulations. The results demonstrate that the proposed schemes dramatically improve the performance of VCP in the initial phase and also in wireless environments.