Research And Implementation Of Pub/Sub System In IoT Environment

With the rapid development of mobile networks and cloud computing,the number of IoT devices has also exploded.In the concept of the Internet of Things,items and objects are connected through a network connection,and this connection is extended to the user's life.Therefore,the key to the Internet of Things is to use mobile networks to deliver messages between things.Compared with the traditional Internet,IoT terminal devices are mostly embedded devices or sensors with limited computing and storage resources,and the “wireless”characteristics of mobile networks have also led to its instability and low bandwidth defects.The key is to use a lightweight messaging protocol to provide secure and reliable messaging in low bandwidth and unstable network environments.The most common message communication protocol of the traditional Internet is the HTTP protocol used by the Web,and the protocol is customized for various data formats existing in the Internet environment.Therefore,the message transmission amount is small,and a large part of the protocol header overhead is required.The HTTP protocol uses a short-connection connection.Each time a message communication is performed,a TCP connection needs to be re-established,which is not conducive to saving traffic.Finally,the HTTP protocol does not provide the semantics of the server actively pushing messages to the client.The client is required keep polling for the latest news from the server.Therefore,in order to solve the above problems,it is necessary to consider a communication protocol that is truly adapted to the Internet of Things environment.Firstly,this thesis considers the protocols of IoT,and compares their protocol overhead,bandwidth requirement,delay,power consumption and other parameters to select the MQTT protocol as the protocol of the IoT message push system.Through in-depth study of the MQTT protocol,including packet structure,semantics,etc.,and combined with the actual application environment,some defects of the MQTT protocol in message access control and security are discovered.Secondly,the MQTT protocol is extended for the problems in the above two aspects.Under the premise of compatibility with the standard protocol,the protocol extension for secure communication in the mobile network environment is proposed.And in order to prevent the client from stealing message,the occurrence of the message uses a topic-based access control list to solve the security risks of the MQTT protocol.Finally,the message proxy server supporting the extension protocol is implemented,and a reasonable concurrency model selection is made according to the high concurrency requirements in the actual application scenario,and the concurrency and scalability of the entire system are improved again by using the cluster.In order to make the server more portable to various operating systems,it is implemented in the Java language.Then,in order to verify the function and performance of the message push system,it is tested and analyzed.The results show that the message push server designed in this thesis basically meets the requirements of the actual application scenario.