The Constrained Application Protocol (CoAP) is a new Web protocol for the 
Internet of Things that allows to connect IoT devices directly to services 
hosted in the cloud. CoAP is based on UDP to better fit the requirements of 
constrained environments with resource-constrained nodes and low-power 
communication links. Being an Internet protocol, CoAP must still adhere to 
congestion control, primarily to keep the backbone network stable. Thus, the 
base specification uses conservative parameter values for the number of open 
requests, the retransmission timers, and the overall message rate. More 
powerful CoAP nodes, however, can use metrics to optimize these parameters to 
achieve a better quality of service. For this, the IETF CoRE working group is 
designing an advanced congestion control mechanism for CoAP called CoCoA. This 
paper presents first evaluation results for a mechanism that improves the 
communication between cloud services and resource-constrained IoT devices. We 
implement CoCoA for the Californium (Cf) CoAP framework and evaluate its 
performance on a wireless sensor network testbed that runs IPv6. Our results 
show that CoCoA can better utilize the available network capacity and can 
increase throughput by 19-112%.