  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.
