Research And Implementation Of The Protocol Conversion Proxy Of HTTP And CoAP In M2M Communication

In the Internet of things,there are the traditional Internet and resource constrained network which is mainly composed of sensor nodes.The nodes which composed in the constrained network are usually characterized as containing low power,weak processing ability and low storage capacity.Therefore,the communication links in the constrained network are generally of low speed and full of multiple errors.Due to the complexity and high overhead of the protocol,the application layer protocol(HTTP)which is widely used in the traditional Internet is considered not to be applicable for the resource constrained network.Therefore,it is necessary to introduce a new type of communication protocol which is targeted to this kind of Internet environment.It is in that context that IETF sets up CoRE working group,who is responsible for designing the application layer communication protocol of the constrained network-CoAP.There are two ways for resource access in the Internet of things.The first one is to access the resources in a CoAP server by a CoAP client.The second one is to access the resources in a CoAP server by a HTTP client.In the second way,HTTP client is the Internet browser.Under this circumstance,it is necessary to do a conversion between HTTP and CoAP for accessing the resources.Through the protocol conversion proxy,the user can directly access the resources in the constrained network from the browser,which will further achieve the data sharing of the Internet of things and meet the application requirements defined in LWM2M OMA.In Addition,the paper conducts further research on the performance of protocol conversion proxy.Based on the in-depth study of the standard COAP and the protocol conversion draft mapping-07,starting from the modular structure of the proxy,this paper conducts a detailed analysis and design to each affiliated function of the core module--mapping module of the protocol conversion proxy in small-scale cluster,namely the URI mapping,code mapping,mapping of media types,mapping and processing of head options and so forth.In addition to this,a discussion of the special circumstances in conversion is carried on and also the solutions are demonstrated.On the basis of the above research and design,this paper has implemented the protocol conversion proxy of HTTP and CoAP.The job of the proxy can be summarized as request mapping,response mapping and cache,among which the request mapping and the response mapping both contain a media type translation and the processing of the header options.Besides,there are the mapping of the URI and the mapping of method code in the request mapping,as well as the mapping of response code in the response mapping.In order to meet the demand of reducing the network bandwidth and response time in the constrained network environment,the proxy uses the ehcache mechanism to manage the safety cache.At last,function and performance evaluations are done to the proxy.In terms of functionality,different test cases are carried out.In terms of performance,the performance data is given.Test results show that the proxy is able to correctly implement the protocol conversion between COAP and HTTP and the performances of system is favorable.Finally,it is proved that the design of the protocol conversion proxy is correct and feasible.