TCPlp: System Design and Analysis of Full-Scale TCP in Low-Power Networks

Low power and lossy networks (LLNs) enable diverse applications integrating many embedded devices, often requiring interconnectivity between LLNs and existing TCP/IP networks. However, the sensor network community has been reluctant to adopt TCP, providing only highly simplified TCP implementations on sensor platforms and, instead, developing LLN-specific protocols to provide connectivity. We present a full-scale TCP implementation, based on the TCP protocol logic in FreeBSD, capable of operating over IEEE 802.15.4 within the memory constraints of Cortex-M0+ based platforms. We systematically investigate the behavior of a full-featured TCP implementation in the LLN setting. It provides a 5x to 40x improvement in throughput compared to prior studies. Moreover, we find that TCP is more robust in LLNs than studies of TCP over traditional WLANs would suggest. We empirically demonstrate that, in a lossy environment typical of LLNs, TCP can achieve power consumption comparable to CoAP, a representative LLN-specific reliability protocol. We discuss the potential role of TCP in sensor networks, observing that gateway-free, retransmission-based reliable transport would be an asset to sensor network applications. We conclude that TCP should have a place in the LLN architecture moving forward.