  Wireless Sensor Networks have recently attracted many researchers attentions
due to their wide range of applications. Even though a plethora of studies have
been carried out on characteristics, special conditions, and various aspects of
WSNs, transport protocol which is compatible with conditions of Wireless Sensor
Networks has not been considerably addressed. Wireless Sensor Networks have
limitations such as storage space, energy resources, and wireless communication
issues. Accordingly, widely-used transport protocols like Transmission Control
Protocol (TCP) may not enjoy sufficient efficiency in such networks. In this
paper, we study the characteristics of WSNs leading to design transport layer
protocol for WSNs and aim at evaluating the efficiency of TCP and its dependent
protocols (TCP variables), which are introduced to wireless networks. We
propose to employ proxy nodes near sinks to improve the performance of
transport layer. Our NS-2 simulation results indicate that throughput and
packet delivery ratio are improved from 20 to 50 percent after employing proxy
nodes, while the average message delay is almost increased twice.
