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ECA-CTP: An Enhanced Congestion Avoidance Mechanism for the CTP Protocol in Wireless Sensor Networks
Peizhong Shi, Yun Wang And Alvin T.S. Chan

In wireless sensor networks (WSNs), congestion may lead to a plethora of malfunctions such as packet loss, lower throughput and energy inefficiency, potentially resulting in reduced deployment lifetimes and underperforming applications. In this paper, we comprehensively investigate the drawbacks to the CTP protocol in congestion control and propose an ECA-CTP protocol that is equipped with an enhanced congestion avoidance mechanism. Distinguished from the existing protocols, the ECACTP protocol detects node-level and link-level congestion by queue full degree (FD) and congestion degree (CD) respectively, which are used to drive the selection of the proper parent nodes for rerouting paths as needed under an overall routing metric. We implemented the enhanced congestion avoidance mechanism for the ECA-CTP protocol based on the Forwarding Engine, Routing Engine and Link Estimator in the CTP protocol executing under the TinyOS platform. The experimental results show that ECA-CTP improves the throughput performance, and provides better performance in data yield when the sending interval is small. Moreover, ECA-CTP reduces the average energy consumption for every packet successfully received by the sink, which again validates the effectiveness of ECA-CTP.We believe that the enhanced congestion avoidance mechanism of ECA-CTP is an effective method to improve network performance when congestion is frequent.

Keywords: Wireless sensor networks, link estimation, congestion avoidance, congestion degree, queue full degree.

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