TAiM: TCP assistant-in-the-middle for multihop low-power and lossy networks in IoT

We investigate the performance of TCP over multihop many-to-one wireless low-power and lossy networks (LLNs), and present TCP assistant-in-the-middle (TAiM) to improve TCP fairness among LLN endpoints without sacrificing aggregate throughput nor end-to-end backward compatibility. TAiM exploits the fact that RTT over LLN is significantly higher, and more variable, than wired or WiFi networks due to unique characteristics of LLN. TAiM intervenes in the middle of TCP communication only at the LLN border router (LBR), and delicately manipulates the RTT of the passing flows to achieve its goal, but does not infringe anything of packet nor operation of existing protocols. TAiM is adaptive and flexible to network status, and does not require any modifications to the TCP/IPv6 stack at the endpoints. We implement TAiM solely in a Linux-based LBR, and perform experiments on two 30-nodes TelosB testbeds running BLIP/TinyRPL stack in TinyOS. Our experiment results show that TAiM helps TCP to operate fairly and efficiently while maintaining total throughput and end-to-end compatibility.