The Internet of Things (IoT) is considered a milestone for the realization of intelligent services through the interaction of smart things. Constrained application protocol (CoAP) was proposed by the Internet engineering task force as a web transfer protocol in the IoT. CoAP inherits the properties of the representational state transfer model to realize communications with low overhead. It is characterized by a small overhead and it uses the stateless UDP protocol in the transport layer. As the IoT has attracted more attention, the demands for various multimedia applications based on the IoT have increased. Video applications and IoT objects communicate through CoAP. CoAP defines a simple congestion control mechanism that can provide reliable communication between IoT endpoints. However, the congestion control mechanism was not proposed considering video streaming applications. In this paper, we evaluate the performance of video streaming applications for reliable CoAP communications between devices over a wireless network. To evaluate the performance, we perform multiple experiments by adjusting the CoAP transmission parameters. Moreover, we analyzed the effect of the segment duration of a video being streamed over CoAP. The results show that the default CoAP parameters do not fulfill the stringent Quality of Experience constraints. The experiments show that the default retransmission RTO is extremely high for the video streaming application. A small increase in the packet loss can significantly affect the video download time which increases the risk of playback interruption. Through experiments, we show that the performance of video streaming applications can be improved by tuning the congestion control parameters according to the network conditions. A smaller RTO value can ensure significant reduction in the segment download time. Similarly, the video can be downloaded quickly by increasing the number of unacknowledged transactions. Furthermore, the experiments show that the risk of playback interruption can be mitigated by downloading longer segments. INDEX TERMS Internet of Things, CoAP, video streaming scheme, congestion control, quality of experience.
Wireless sensor networks collect data from several nodes dispersed at remote sites. Sensor nodes can be installed in harsh environments such as deserts, cities, and indoors, where the link quality changes considerably over time. Particularly, changes in transmission power may be caused by temperature, humidity, and other factors. In order to compensate for link quality changes, existing schemes detect the link quality changes between nodes and control transmission power through a series of feedback processes, but these approaches can cause heavy overhead with the additional control packets needed. In this paper, the change of the link quality according to temperature is examined through empirical experimentation. A new power control scheme combining both temperature-aware link quality compensation and a closed-loop feedback process to adapt to link quality changes is proposed. We prove that the proposed scheme effectively adapts the transmission power to the changing link quality with less control overhead and energy consumption.
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