Loss-tolerant TCP (LT-TCP) : adapting TCP to modern wireless networks

Abstract

The transport protocol most widely adopted for reliable network communication, TCP, does not fully utilize wireless networks where packet losses and topological changes are prevalent. To address this issue, Loss-Tolerant TCP (LT-TCP) has been implemented to provide robust and efficient communications over potentially lossy networks without assuming the presence of a static network structure.

Experiments have shown LT-TCP to yield throughput speedups of greater than 262 over TCP on high bandwidth networks which experience packet loss bursts of average length 5, causing 10% of total packets to be lost.

Finally, this thesis explores some architectural problems with the current LT-TCP implementation, which limit its portability to modern operating systems, and proposes a new architecture which will facilitate integration of LT-TCP into modern Linux-based operating systems as well as simplify the development and testing of new algorithms to support LT-TCP functionality.

This testing identified some weaknesses in the current LT-TCP implementation, and this thesis describes the subsequent revisions to the protocol to address these weaknesses and provides experimental data demonstrating the effects of these improvements.

Demand for widespread, robust wireless computer networking is increasing rapidly, and unlike wired networks, wireless networks frequently drop packets due to interference or signal attenuation. To compound this issue, mobile, ad-hoc networks have no reliable structure, and routes or adjacent nodes may change without notice.

This thesis examines the current implementation of LT-TCP and compares it with other transport layer solutions on network profiles with tunable loss and delay properties. In particular, tests were conducted with correlated losses, where contiguous groups of packets are dropped, and high latencies. Results show that LT-TCP performance is significantly higher than that of TCP on networks with correlated losses or networks with losses and high latency.