The fact is that IoT devices will be found everywhere and will enable circulatory intelligence in the future. So, the communication models used in IoT, have a great value. The follows people and things to be connected anytime, in any space, with anything and anyone. using any network and any service. From an operational, it is useful to think about how IoT devices connect and communicate in terms of their technical communication models, before making decisions:

Request-Response Model

The Request response model is stateless and each request is independently handled. The client is the IoT device that sends a request to the server. The request may be for the transfer of data or upload of data. The server may be remote or local and can handle requests of multiple clients. The server can receive the request, decide its response and fetch the data.

Request-Response Communication Model - Iot communication models
Fig. Request-Response Communication Model 

Publish-Subscribe Model

There are three entities publisher, broker, and consumers. Publishers send the data to the brokers on topics managed by the brokers. Consumers subscribe to topics and brokers send the data on the topics to the consumers. Hence, brokers' responsibility is to accept data from publishers and send it to the appropriate consumer. 

Publish subscriber model - IoT communication models
Fig. Publish subscriber model 

Push-pull Model

This is a communication model. In this model data producers push data to queues and consumers pull data from queues Producers and consumers are not aware of each other. Queues act as buffers and are useful when there is a mismatch between the rate at which the producer push data and the rate at which the consumers pull data.

Push-pull Model - iot communication models
Fig. Push-pull Model 

Exclusive Pair Model

This model is a full-duplex communication model that uses a cond connection between client and server, The connection is constant and remains on till the client sends a request to close the connection. This is a stateful connection not and the server is aware of all open connections.

Exclusive Pair Model - IoT communication models
Fig. Exclusive Pair Model