Two Families of Optimal Multipath Congestion Control Protocols

Multiple Path Transmission Control Protocols (MPTCPs) allow flows to explore path diversity of datacenter networks and multihoming to improve throughput, reliability, and network resource utilization. However, the existing MPTCPs are largely empirical by design and fall short of achieving satisfactory tradeoffs among responsiveness, TCP fairness and throughput. By leveraging the TCP utility and a network-utility-maximization (NUM) solution for concave utilities, in this paper, we derive and implement in Linux kernels two distinct families of NUM-optimal MPTCP protocols, EUTCP ( $\gamma$ ), a function of a rate-scaling vector of the sub-flow rate-scaling coefficients, $\gamma$ , and WUTCP ( $\omega$ ), a function of a utility weight vector of the sub-flow weights, $\omega$ , respectively. While the former allows resource pooling, the latter does not. We then show that the Semicoupled algorithm and EWTCP are in fact EUTCP(1) and WUTCP $(1/m^{2})$ , where $m$ is the number of sub-flow paths, and hence, are NUM-optimal. The performance of the two families with equal weight and equal rate-scaling coefficient for all sub-flows when coexisting with TCP is also analyzed based on experiments in a testbed. In particular, the test results demonstrate that the family members of EUTCP ( $\gamma$ ) with rate-scaling coefficient in the range of [1, 1.1] outperform three well-known MPTCPs with resource pooling capability, including LIA, OLIA and Balia, in terms of achieving satisfactory tradeoffs among responsiveness, fairness and throughput. Finally, the effectiveness of the proposed algorithms compared to the existing ones is further confirmed by simulation in a fat-tree datacenter network topology running both long and short flows.