In Internet of Things (IoT), the simple IPv6 capable electronic devices with limited hardware resources like memory and power resources are called constrained devices. Congestion is a major issue in network communications of these devices. To solve congestion in networks of constrained devices, Internet Engineering Task Force (IETF) had designed Constrained Application Protocol (CoAP). CoAP deals congestion with a basic Congestion Control (CC) mechanism called Default CoAP. Afterward, CoCoA and CoCoA+, an Internet-draft-recommendations, has been introduced as the elective CC mechanisms for CoAP. However, limited evaluations had done on these CC mechanisms of CoAP. In this paper, the performance evaluation of Default CoAP, CoCoA, and CoCoA+ Congestion control mechanisms are evaluated through Simulations in different network topologies and varied in different Link Delivery Ratios (LDR) of sensor nodes in constant traffic scenario by using Cooja Simulator. The simulation results are generated and CoCoA+ shows a better performance in constant traffic scenario comparing to Default CoAP and CoCoA.

翻译：在物联网（IoT）中，具备简单IPv6能力但硬件资源（如内存和电源）有限的电子设备被称为受限设备。拥塞是这些设备网络通信中的一个主要问题。为解决受限设备网络中的拥塞问题，互联网工程任务组（IETF）设计了受限应用协议（CoAP）。CoAP通过一种称为Default CoAP的基础拥塞控制（CC）机制来处理拥塞。随后，互联网草案推荐的CoCoA和CoCoA+被引入作为CoAP的可选CC机制。然而，针对CoAP的这些CC机制进行的评估十分有限。本文通过Cooja模拟器，在不同网络拓扑和传感器节点不同链路交付率（LDR）的恒定流量场景下，对Default CoAP、CoCoA和CoCoA+拥塞控制机制进行了性能评估。模拟结果显示，在恒定流量场景中，CoCoA+相比Default CoAP和CoCoA表现出更优的性能。