Performance Evaluation of Fast Startup Congestion Control Schemes

The Transmission Control Protocol (TCP) uses the Slow-Start mechanism at the beginning of a connection and after idle times. The Slow-Start delays the transport of data in particular if the round-trip time is large, which is undesirable for interactive applications. In order to speed up transfers, several alternatives have been proposed recently. This paper evaluates the performance and robustness of new fast startup congestion control schemes. We compare both end-to-end approaches as well as protocols that rely on additional feedback from the routers, using implementations in the Linux stack. Both testbed measurements and simulation studies quantify the potential performance improvement, the risk of packet loss, and the benefits of additional router support. Our results, which are also partly verified analytically, reveal that end-to-end fast startup mechanisms would not cause too much performance degradation if they are selectively used and carefully tuned. Additional router support would improve the fairness at the cost of a higher complexity.