MmWave communications, one of the cornerstones of future 5G mobile networks,are characterized at the same time by a potential multi-gigabit capacity and bya very dynamic channel, sensitive to blockage, wide fluctuations in thereceived signal quality, and possibly also sudden link disruption. While theperformance of physical and MAC layer schemes that address these issues hasbeen thoroughly investigated in the literature, the complex interactionsbetween mmWave links and transport layer protocols such as TCP are stillrelatively unexplored. This paper uses the ns-3 mmWave module, with its channelmodel based on real measurements in New York City, to analyze the performanceof the Linux TCP/IP stack (i) with and without link-layer retransmissions,showing that they are fundamental to reach a high TCP throughput on mmWavelinks and (ii) with Multipath TCP (MP-TCP) over multiple LTE and mmWave links,illustrating which are the throughput-optimal combinations of secondary pathsand congestion control algorithms in different conditions.
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