Investigate reordering in Linux TCP

Abstract

When you re using your mobile device, you can connect to several wireless networks at the same time, such as 3G (HSPA) / 4G (LTE) and WiFi. These links could be used at the same time to increase the download speed or make streaming of video more reliable. These links introduce differences in delay and TCP should fail if you simply try to aggregate them at the network layer because this will also introduce network reordering in relation to the difference in network delay. There are several existing solutions out there that tries to fix this, but if you simply use Linux and transparently send packets over two different network links which has a large difference in network delay, you will notice that the TCP connection can maintain a high throughput which corresponds to the sum of possible throughput for both links. A patch from August 2013 has made the situation even better, but how does it work? In this thesis, we have investigated how Linux TCP is robust against network reordering. We have also done extensive testing of Linux TCP s performance where we have transparently sent packets from a TCP connection over two different network paths which differs in both latency and delay.