Understanding MPTCP in Multi-WAN Routers: Measurements and System Design

MPTCP is used in Multi-WAN Routers to aggregate multiple WAN/Internet connections using two architectural variants: proxying and tunneling. The proxy variant creates one MPTCP connection for each TCP connection, resulting in a large number of parallel uncoordinated MPTCP connections, which leads to underutilizating the available capacity, suboptimal scheduling, and increased loss rate. The tunnel variant encapsulates TCP over MPTCP, stacking two reliability layers, which leads to large number of spurious retransmissions, an issue known as TCP meltdown. We propose a new solution, BOOST, that eliminates the problems with both variants by multiplexing TCP connections over a single persistent multi-path connection. BOOST also takes a hybrid approach to multi-path scheduling combining load balancing and scheduling by transmitting short flows across a single path, avoiding HoL blocking, and opportunistically transmitting long flows across multiple path, utilizing left-over capacity. Evaluations show that BOOST provides better throughput, lower losses, and retransmissions compared to MPTCP