HTMT: High-Throughput Multipath Tunnelling for Asymmetric Paths

Abstract

Multipath Tunnelling (MT) is an effective approach to increase the reliability and performance of network connections. In contrast to Multipath TCP (MPTCP) or SCTP, it also works for UDP traffic and its deployment is easy. It requires neither full access to all uplink endpoints nor a multipath protocol implementation in every involved host. Despite its potential, research on MT is sparse. Most known prototypes use either round robin or MPTCP schedulers that are not able to fully utilise the potential of MT. This paper proposes HTMT, a novel packet scheduling algorithm designated for MT that achieves high throughput for reliable traffic on asymmetric paths. Using the tunnel transport protocol s path estimation, it is able to dynamically adapt to changing subtunnel characteristics. Additionally flow awareness allows HTMT to associate packets to a flow and only send it on subtunnels where it won t overtake any of its predecessors. This avoids packet reordering and its detrimental effect on TCP throughput, without the latency and performance costs of a re-reordering buffer at the tunnel exit. In multiple testbed experiments, we compare HTMT with several schedulers for MT and MPTCP, including LowRTT (current MPTCP default), OTIAS and AFMT. In terms of throughput, HTMT offers similar performance for symmetric paths but outperforms all competitors on asymmetric paths.