Comparing the cost-efficiency of CoAP and HTTP in Web of Things applications

摘要

Constrained Application Protocol (CoAP) has been introduced as a simpler alternative to the Hypertext Transfer Protocol (HTTP) for connecting constrained smart objects to the Web. The adoption of the protocol depends on its relative advantage, and the cost–benefit associated with the use of the protocol is a significant factor affecting a protocol adoption decision. This paper aims at deepening the understanding of the cost–benefits of CoAP and identifies the application scenarios where its use is likely to be economically justifiable. The paper analyzes the costs of using CoAP and HTTP in the Web of Things (WoT) applications, by identifying the components of the total cost of ownership (TCO) model for these applications and by studying the factors affecting individual costs. The use of the model is then demonstrated by means of comparing the TCO of CoAP and HTTP in an environment monitoring application scenario. The results of the analysis suggest that the simpler hardware requirements of CoAP smart objects, as well as the lower communication overhead of the protocol and the resulting reduced power consumption lead to cost advantages in the application scenarios where the smart objects i) are large in volume and/or are deployed in the field, ii) engage in frequent communications with the Web that are charged for on the basis of the volume of the data being transferred, and iii) are sleeping between the communication sessions. The obtained results may be utilized both by the decision-makers considering the adoption of CoAP in specific solutions, as well as by the academics and practitioners involved in the protocol development.