Improving TCP Fairness over Latency Controlled 5G mmWave Communication

Abstract

In order to increase the capacity of 5G networks, using mmWave band communication links both for access and backhaul are an interesting alter- native due to the large spectrum portion available at those frequency bands. However, mmWave bands exhibit special propagation characteristics which require the usage of highly directional and beam-steerable antennas in order to cope with significantly higher pathloss. Using such links in urban scenarios may lead to frequent blocking events due to moving pedestrians or cars, which may result in the links dynamically changing their characteristics from Line-of-Sight (LOS) to Non Line-of-Sight (NLOS) or outage (OUT). Due to the sudden significant variation in available capacity when changing the link states, TCP connections may experience sudden spikes in end-to-end latency and severe bufferbloat. Although bufferbloat solutions such as CoDel can be deployed to control the delay, they significantly impact both capacity and fairness between different TCP flows sharing the same mmWave link. In this paper, we study this fairness issue when running multiple TCP connections over fluctuating mmWave links and deploying AQM schemes to control the latency. We study the effect of length and severity of the NLOS episode upon fairness and latency.