Scheduling over dissimilar paths using CMT-SCTP

Concurrent Multipath Transfer (CMT-SCTP) using the Stream Control Transmission Protocol (SCTP) over multiple paths can achieve an aggregated transmission throughput much greater than a single path. A problem arises when the fair round robin scheduling (RRS) in CMT-SCTP allows the slow paths to affect the overall throughput due to out-of-sequence data at the receiver. Data along the slow and fast paths occupy the shared receiver buffer while waiting for the out-of-sequence data, which can easily lead to performance degradation. Therefore, intelligent scheduling of data transmissions is necessary for efficient data transfer, particularly in realistic situations where the paths are dissimilar and the buffer size is limited. We propose an algorithm for scheduling data transmissions based mainly on the outstanding bytes (CMT-OUT). The algorithm updates the path quality after a successful transmission, which is a measure of how preferable the current destination would be when selection happens in the next round. The experiments on a realistic testbed show that CMT-OUT improved the throughput of CMT-SCTP on average by 21% when the maximum bandwidth dissimilarity is applied over a two-path network. The mechanism in CMT-SCTP to handle the delay dissimilarity in a simple two-path scenario is very efficient due to the rare timer based retransmissions. In the experiments for the more complex four-path scenario, CMT-OUT improved the throughput by 54%.