物聯網裝置的連線通常是以高封包遺失率及不穩定延遲時間的無線通訊界面作連結。掛載了感測器及致動器的這些裝置通常硬體資源有限，並且以電池供應電源。現今的物聯網應用層協定，為了達到輕量化目的，皆運作在UDP之上。為了要確保可靠性，這些協定需要提供重傳機制，也就是當訊息傳出去後，若重傳計時器(RTO)逾時，則將訊息重傳。RTO值的設定可分為固定式及動態式，固定式RTO很簡單，但可能會造成低劣的訊息傳送率及訊息傳送延遲時間。動態式RTO雖可提升封包傳送率及縮短延遲時間，但會在計算RTO值花費較多的電力。在本論文中，我們提出一種可將原本在裝置上動態RTO值的計算移至閘道器之方法。實驗結果顯示，在單一閘道器服務超過30個物聯網裝置時，在平均延遲時間會有些許增加，但平均重傳次數及封包傳送率則會有明顯的提升。實驗結果也顯示，我們的方法只要在單一匣道器服務6個以上的物聯網裝置，即可有效減低平均重傳次數。再者，減少重傳次數可以有效地降低電力的消耗，換句話說，我們的方法可為資源有限的物網網裝置提供節能的RTO設定值。

Internet of Things (IoT) devices are usually wireless connected with high data loss rate and unstable latency. The devices installed with sensors and actuators are usually battery-operated and resource-limited. Current protocols for IoT application generally operate on top of UDP for lightweight purpose. To ensure reliability, these protocols need to provide retransmission mechanism, where a message is retransmitted when a retransmission timeout (RTO) timer expires. The RTO value can be configured as fixed or dynamic. Fixed RTO is simple, but may cause terrible message delivery ratio (MDR) and latency. Dynamic RTO improves MDR and latency, but consumes more energy in computation. In this thesis, we propose a method which calculates dynamic RTO values in gateway instead of calculating in devices. Simulation experiment results show that the average latency increases slightly, but the number of retransmission and the MDR improves significantly when the number of IoT devices is greater than 30. Our results also show that our method can decrease the number of retransmissions as long as the number of IoT devices is greater than 6. Furthermore, the power consumption can be effectively reduced as the number of retransmissions decreases. In other words, our proposal provides energy-efficient RTO values for resource-constrained IoT devices.

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