Boost: Transport-layer multi-connectivity solution for multi-wan routers

In this paper, we discuss the challenges faced by MPTCP when used to aggregate multiple WAN/Internet connections in Multi-WAN Routers (MWR). We observe that the two architectural variants, proxying and tunneling, used to deploy MPTCP in MWR suffer from key performance problems. First, the proxy variant creates one MPTCP connection for each TCP connection, which results in a large number of parallel uncoordinated MPTCP connections, which we explain leads to underutilization of the available capacity, suboptimal multi-path scheduling, and increased loss rate. Second, the tunnel variant, which relies on encapsulating TCP over MPTCP, stacks two reliability layers and leads to a large number of spurious retransmissions, an issue known as TCP meltdown. Instead, we propose a new multi-path solution more suited to MWR, called BOOST. This solution eliminates the problems with both the proxy and tunnel approaches by multiplexing TCP connections over a single persistent multi-path connection. BOOST also takes a novel approach to multi-path scheduling that combines multi-path load balancing and scheduling. In particular, short flows are transmitted across a single link to avoid HoL blocking while longer flows are opportunistically transmitted across multiple paths, utilizing left-over capacity. Evaluations show that BOOST provides better throughput, lower losses, and retransmissions while requiring less memory compared to both MPTCP variants.