Smartphones have highly functional operating systems similar to PCs. Their communication throughput depends on behavior of Transmission Control Protocol (TCP). Modern loss-based TCP algorithms take aggressive congestion window (CWND) control strategies in order to gain better throughput, but such strategies may cause a large number of packets to be backlogged and eventually dropped at the entry point to the wireless access network. This problem applies not only to the downstream TCP sessions but also to the upstream TCP sessions when the terminal is connected via a wireless network, such as Wireless Local Area Network (WLAN) and Long Term Evaluation (LTE) network, which disregards the size of packets in its scheduling. This paper focuses on the ACK packet backlog problem with the upstream TCP sessions, and proposes a CUBIC based CWND control mechanism as part of the middleware for the Android terminals. It utilizes the Round Trip Time (RTT) as an indication for the TCP ACK backlog condition at the WLAN AP and LTE base station, and controls the upper and lower bounds of its CWND size to suppress excessive transmissions of own TCP DATA packets. Our experimental study with up to seven Android terminals shows that the proposed mechanism can improve both aggregate throughput and fairness of the WLAN. In addition, our evaluation on LTE network demonstrates that the method suitably controls congestion and communication delay also on LTE network.
['Ayumi Shimada', 'Masato Oguchi', 'Saneyasu Yamaguchi', 'Heidi Kaartinen', 'Marjo Heikkila', 'Joni Jamsa']
Performance Improvement in WLAN and LTE Based on Backlog Control Middleware