Improving TCP Performance over Wireless Networks with Collaborative Multi-homed Mobile Hosts

Multi-homed mobile hosts situated in physical proximity may spontaneously team up to run high-bandwidth applications by pooling their low wireless wide-area network (WWAN) bandwidths together for communication with a remote application server and utilizing their high-bandwidth wireless local-area network (WLAN) in ad-hoc mode for aggregation and distribution of application contents among the participating mobile hosts.

In this paper, we first describe the need for such a mobile collaborative community, or a community, in which multi-homed mobile hosts exploit the diversity of WWAN connections to improve a user-perceived bandwidth and network utilization. Then, we show that existing one-to-one communication protocols like TCP suffer significant performance degradation due to frequent packet reordering and heterogeneity of WWAN links in the community.

To address the above TCP problem, we propose a proxy-based inverse multiplexer, called PRISM, that enables TCP to efficiently utilize the community members' WWAN connections. PRISM runs at a proxy's network layer as a routing component and stripes each TCP flow over multiple WWAN links by exploiting the transport-layer feedback information. Moreover, it masks variety of adverse effects specific to each WWAN link via intelligent ACK-control mechanism. Finally, PRISM includes a sender-side enhancement of congestion control, enabling TCP to respond correctly to dynamically-changing network states.

We have evaluated the PRISM protocol using both experimentation and ns-2-based simulation. Our experimental evaluation has shown PRISM to improve TCP's performance by up to 310% even with two collaborative mobile hosts. Our in-depth simulation study also shows that PRISM delivers a near-optimal aggregated bandwidth in the community formed by heterogeneous mobile hosts, and improves network utilization significantly.