On Preventing Unnecessary Retransmission with Optimal Fragmentation Strategy

Abstract—Multi-path transferring provides higher available bandwidth for a session. It also has the ability to provide load balancing and error resilience for end-to-end multiple paths. One major problem of multi-path transferring scheme is that utilizing different paths with diverse delays causes reordering among packets of the same session. Unfortunately, in the case of TCP-like, the reordering intensifies the problem by bringing more timeouts and so unnecessary retransmission which eventually degrades the throughput of connections considerably. To address this issue, we first presented the fragmentation conditions that should be held to avoid retransmission timeouts due to reordering. Then, we enhanced our approach by preventing unnecessary fast retransmission/recovery events in TCP or SCTP. We introduced an analytical framework for the optimal fragmentation strategy of real-time traffic that decreases the probability of triggering 3 or 4 duplicate ACK. Specifically, it formulates optimal traffic fragmentation as a constrained optimization problem using deterministic network calculus and derives its closed-form solution by our proposed progressive water-filling algorithm. Compared with previous work, the proposed scheme is simpler to implement and enforce. Analytical results show that a set of paths can achieve the maximum end-to-end bandwidth with O(N) time complexity, where N is the number of available paths. Keywords—Multihoming, Concurrent multi-path transfer, Reorder, Retransmission.