Enhancements and Challenges in CoAP—A Survey

Abstract

The Internet of Engineering Task (IETF) developed a lighter application protocol (Constrained Application Protocol (CoAP)) for the constrained IoT devices operating in lossy environments. Based on UDP, CoAP is a lightweight and efficient protocol compared to other IoT protocols such as HTTP, MQTT, etc. CoAP also provides reliable communication among nodes in wireless sensor networks in addition to features such as resource observation, resource discovery, congestion control, etc. These capabilities of CoAP have enabled the implementation of CoAP in various domains ranging from home automation to health management systems. The use of CoAP has highlighted its shortcomings over the time. To overcome shortcomings of CoAP, numerous enhancements have been made in basic CoAP architecture. This survey highlights the shortcomings of basic CoAP architecture and enhancements made in it throughout the time. Furthermore, existing challenges and issue in the current CoAP architecture are also discussed. Finally, some applications with CoAP implementation are mentioned in order to realize the viability of CoAP in real world use cases.

RCOAP: A Rate Control Scheme for Reliable Bursty Data Transfer in IoT Networks

“…However, this calculation is limited to only the first transmission and first retransmission. CoCoA+ is unable to select the correct RTO value for bursty traffic [10].…”

“…Inaccurate measurements of RTTs can lead to spurious retransmissions. The authors in [9], [10], [11], [12] indicated that CoCoA+ performed significantly worse than the basic CoAP in various network conditions, especially for bursty traffic.…”

“…A comprehensive survey of CoAP congestion control mechanisms is presented in [10]. The survey highlighted the shortcomings of basic CoAP and its enhancements.…”

“…The authors in [36] proposed using spikes in relative one-way trip time (ROTT) to distinguish between wireless losses and congestion losses. As indicated in [10], [37], existing end-toend CC schemes mainly focus on the measurement of RTTs and RTOs according to the network conditions.…”

“…In fact, CoCoA+ is similar to CoCoA except for two key differences: 1) a modification of the RTO calculation using a smaller factor that helps to reduce the impact of high fluctuations of RTT on the RTO estimators, and 2) a new aging policy for the RTO values. Although CoCoA+ resolves the problem of weak RTO estimation in CoCoA and can provide better performance than the basic CoAP and CoCoA, recent studies such as [7], [8], [9], [10] highlighted the drawbacks of CoCoA+, including constant RTO settings and poor performance in the case of small RTTs.…”