Energy-Efficient TCP Operation in Wireless Sensor Networks

Abstract

Many applications of wireless sensor networks require connectivity to external networks to let monitoring and controlling entities communicate with the sensors. By using the TCP/IP protocols inside the sensor network, external connectivity can be achieved anywhere in the sensor network. In such IP-based sensor networks, TCP can be used for remote management and reprogramming of sensor nodes. However, the high bit error rates in multi-hop sensor networks lead to energy-inefficiencies that reduce the lifetime of the sensor network. This paper introduces and compares two approaches to support energy-efficient operation of TCP in sensor networks: Distributed TCP Caching (DTC) and TCP Support for Sensor networks (TSS). Both concepts allow intermediate sensor nodes to cache TCP segments and to perform local retransmissions in case of errors. This allows reducing the total number of packet transmissions in the sensor network when transferring data to or from a sensor node. DTC caches and immediately forwards TCP data segments, whereas TSS does not forward a cached segment until it knows that the previous segment has been successfully received by the next hop node. We show by simulation that both approaches significantly reduce the number of TCP segment and acknowledgement transmissions. Their performance differs slightly depending on the error rate. Both approaches have also slightly different needs in buffer requirements and TCP options to be supported.