SpeedDetect: A Simple TCP Extension for Handling Sudden Capacity Increase

Emerging broadband mobile cellular networks are inherently heterogeneous due to the co-existence of multiple wireless access technologies. In such a network sudden capacity changes are bound to happen due to inter-system handovers, user mobility and flow dynamics. Existing congestion control protocols are shown to deal sufficiently with capacity drops but tend to reach full link utilization slowly after abrupt capacity increases. In this paper we propose SpeedDetect, a simple, sender-side TCP extension for handling sudden capacity increase. The key idea behind our approach is to improve link utilization by explicitly detecting increased link capacity then triggering the underlying congestion control scheme to an aggressive probing regime. We evaluate the performance of SpeedDetect with testbed experiments and simulations. Our findings suggest that the proposed mechanism can significantly improve the reaction time of TCP by detecting sudden capacity increase quickly and consistently. Furthermore, our approach retains the RTT-fairness of the underlying TCP and exhibits favorable inter-protocol fairness towards standard TCP NewReno.