Fast Coupled Retransmission for Multipath TCP in Data Center Networks

Multipath TCP (MPTCP) is emerging as a new potential candidate that replaces the existing single-path TCP (SPTCP). One applicable area of MPTCP is cloud data center networks, where multiple paths are often available between servers. However, it is observed that MPTCP may not fully leverage the multiple paths and sometimes perform even worse than SPTCP, especially for time-sensitive short flows in data center networks. To address this challenge, we propose a fast coupled retransmission mechanism for MPTCP. The key observation is that one of the paths is likely to be congested if an out-of-order packet exists even after all data packets have been transmitted. In this case, we forward the data packets from the congested path onto the noncongested path and quickly retransmit them. This mechanism effectively avoids network congestion and, hence, helps reduce the overall flow completion time. We implement the proposed scheme in the Linux kernel and evaluate it on our real data center testbed, and the results show that our proposal significantly outperforms the existing schemes.