Improving Multi-homed SCTP Mobile Communication Performance

The growing availability of different wireless access technologies like WiFi 802.11, cellular broadband EV-DO, and the soon to be deployed WiMax 802.16, provide the opportunity for users to carry multiple radio types and potentially benefit from better connectivity and reliability. The multi-homing features of the Stream Control Transmission Protocol (SCTP) appear to be key enablers for improving mobile communications for such multi-radio equipped users. However, satisfactory performance of SCTP in a mobile wireless environment depends heavily on the settings of configurable protocol parameters and questions remain whether multi-homing may actually perform worse than single-homing in some circumstances. This paper examines the complex interactions between various configurable protocol parameters and their effect on performance with the goal of making recommendations for how to set these "knobs" in an informed way. Using simulation, we investigate SCTP's throughput performance between a pair of users in three scenarios: each user equipped with a single radio type, each user equipped with a pair of radios that provide identical data rates, and each user equipped with a pair of radios where one radio's data rate is 10x less than the other. For the last scenario, we find that SCTP's default recovery performance is lacking to such an extent that better throughput is actually achieved when users are equipped with only a single radio. To mitigate this problem, we propose a change to the protocol's heartbeat mechanism and present simulation data showing the resulting improvement.