Suwannapong Chanwit, Khunboa Chatchai
Department of Computer Engineering, Faculty of Engineering, Khon Kaen University, 40002 Khon Kaen, Thailand.
Sensors (Basel). 2019 Aug 5;19(15):3433. doi: 10.3390/s19153433.
The Constrained Application Protocol (CoAP) is a simple and lightweight machine-to-machine (M2M) protocol for constrained devices for use in lossy networks which offers a small memory capacity and limited processing. Designed and developed by the Internet Engineering Task Force (IETF), it functions as an application layer protocol and benefits from reliable delivery and simple congestion control. It is implemented for request/response message exchanges over the User Datagram Protocol (UDP) to support the Internet of Things (IoT). CoAP also provides a basic congestion control mechanism. In dealing with its own congestion, it relies on a fixed interval retransmission timeout (RTO) and binary exponential backoff (BEB). However, the default CoAP congestion control is considered to be unable to effectively perform group communication and observe resources, and it cannot handle rapid, frequent requests. This results in buffer overflow and packet loss. To overcome these problems, we proposed a new congestion control mechanism for CoAP Observe Group Communication, namely Congestion Control Random Early Detection (CoCo-RED), consisting of (1) determining and calculating an RTO timer, (2) a Revised Random Early Detection (RevRED) algorithm which has recently been developed and primarily based on the buffer management of TCP congestion control, and (3) a Fibonacci Pre-Increment Backoff (FPB) algorithm which waits for backoff time prior to retransmission. All the aforementioned algorithms were therefore implemented instead of the default CoAP mechanism. In this study, evaluations were carried out regarding the efficiency of the developed CoCo-RED using a Cooja simulator. The congestion control mechanism can quickly handle the changing behaviors of network communication, and thus it prevents the buffer overflow that leads to congestions. The results of our experiments indicate that CoCo-RED can control congestion more effectively than the default CoAP in every condition.
受限应用协议（CoAP）是一种用于资源受限设备的简单轻量级机器对机器（M2M）协议，适用于内存容量小且处理能力有限的有损网络。它由互联网工程任务组（IETF）设计和开发，作为应用层协议运行，并受益于可靠传输和简单的拥塞控制。它通过用户数据报协议（UDP）实现请求/响应消息交换，以支持物联网（IoT）。CoAP还提供了一种基本的拥塞控制机制。在处理自身拥塞时，它依赖于固定间隔重传超时（RTO）和二进制指数退避（BEB）。然而，默认的CoAP拥塞控制被认为无法有效地进行组通信和资源观察，并且无法处理快速、频繁的请求。这会导致缓冲区溢出和数据包丢失。为了克服这些问题，我们提出了一种用于CoAP观察组通信的新拥塞控制机制，即拥塞控制随机早期检测（CoCo-RED），它由（1）确定和计算RTO定时器、（2）一种最近开发的主要基于TCP拥塞控制的缓冲区管理的改进随机早期检测（RevRED）算法以及（3）一种在重传前等待退避时间的斐波那契预增量退避（FPB）算法组成。因此，所有上述算法都被实现以替代默认的CoAP机制。在本研究中，使用Cooja模拟器对开发的CoCo-RED的效率进行了评估。该拥塞控制机制可以快速处理网络通信的变化行为，从而防止导致拥塞的缓冲区溢出。我们的实验结果表明，在每种情况下CoCo-RED都能比默认的CoAP更有效地控制拥塞。
