ECF: An MPTCP path scheduler to manage heterogeneous paths
Multi-Path TCP (MPTCP) is a new standardized transport protocol that enables devices to utilize multiple network interfaces. The default MPTCP path scheduler prioritizes paths with the smallest round trip time (RTT).In this work, we examine whether the default MPTCP path scheduler can provide applications the ideal aggregate bandwidth, i.e., the sum of available bandwidths of every paths. Our experimental results show that heterogeneous paths cause underutilization of the fast path, resulting in undesirable application behaviors such as lower streaming quality in a video than can be obtained using the available aggregate bandwidth. To solve this problem, we propose and implement a new MPTCP path scheduler, ECF (Earliest Completion First), that utilizes all relevant information about a path, not just RTT. We compare ECF with both the default and other MPTCP path schedulers, using both an experimental testbed and in-the-wild measurements. Our results show that ECF consistently utilizes all available paths more efficiently than other approaches under path heterogeneity, particularly for streaming video. In Web browsing workloads, ECF also does better in some scenarios and never does worse.