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Author(s): Suman Kumar Shriramoju | Jagadeeshwar Madiraju | Adloori Ramesh Babu

Journal: International Journal of Computer & Electronics Research
ISSN 2320-9348

Volume: 2;
Issue: 4;
Start page: 502;
Date: 2013;
Original page

Keywords: Wireless Sensor Networks | MQTT-S Protocol | Constrained Application Protocol (CoAP) | Retransmission Timeout | Packet Delivery Ratio | Smooth Round Trip

Wireless sensor networks (WSNs) have been organized to determine or detect physical and environmental events or any significant parameters of a given situation. Applications usually send queries to sensor nodes to get back the values periodically from the measurements or detections. In Wireless Sensor Networks (WSNs), Message Queuing Telemetry Transport (MQTT-S) and Constrained Application Protocol (CoAP) are two protocols which are capable to use the publish/subscribe model. The elevated scalability provided by the publish/subscribe model may acquire a high packet loss and therefore requires a proficient consistency mechanism to handle with this situation. The consistency mechanism of MQTT-S and CoAP employs a method which defines a permanent value for the retransmission timeout (RTO). This article argues that this method is not resourceful for deploying publish/subscribe in WSN, because it may be not capable to improve a packet, therefore resulting in a lower packet delivery ratio (PDR) at the subscriber nodes. An adaptive RTO method is proposed and which consists in using a Smooth Round-trip Time and multiplying it by a constant parameter (K). The consistency mechanism of MQTT-S and CoAP would be able to respond properly to packet loss and would also be trivial for sensor nodes where these resources are critical. A comprehensive evaluation of the effects of the K value on the calculation of the adaptive RTO method is proposed here. We also set up the setting for obtaining the uppermost PDR on the subscriber nodes for single-hop and multi-hop scenarios.
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