Performance implications of a bounded receive buffer in concurrent multipath transfer

We study the performance of Concurrent Multipath Transfer using SCTP multihoming (CMT) in the presence of a bounded receive buffer (rbuf). We demonstrate using simulation that if two paths are used for CMT, the lower quality (i.e., higher loss rate) path degrades overall throughput of an rbuf-constrained CMT association by blocking the rbuf. We argue that rbuf blocking is not specific to the transport layer, but applies to multipath transfers at other layers as well. We present and discuss CMT performance using several retransmission policies and various constrained rbuf values. We also study the impact of rbuf blocking with different combinations of end-to-end loss rate and delay on the two paths and show that when large differences exist in path delays and loss rates, using only the better path outperforms using two paths concurrently. While rbuf blocking cannot be eliminated, it can be reduced by choice of retransmission policy — a mechanism available to only the transport layer.