TCP/IP

TCP/IP defines the standards for how electronic devices connect to the Internet and how data is transmitted between them. The protocol adopts a four-layer layer structure, each layer calling the next layer of the protocol provided to fulfill its needs. Generally speaking, TCP is responsible for detecting the transmission problem, when there is a problem, sending a signal and requesting the re-transmission until all data is safely transmitted to the destination.

To reduce the complexity of network design, most networks use layered structures. For different networks, the number of layers, names, contents and functions are different. In the same network, the N layer on one machine and the N layer on another machine can communicate using the N layer protocol, which is basically a consensus between the two parties on how to communicate.

The entity of the corresponding layer contained in the different machines is called the peer process. When the peer process uses the protocol to communicate, it is not actually directly transferring data from the N layer of a machine to the N layer of another machine, but each layer delivers data together with the control information package of the layer to its next layer, its next layer sees this content as data, plus its control information together to the next layer, thus pushing to the lowest layer. The lowest layer is the physical medium, it conducts actual communication. There is an interface between the neighboring layers, the interface defines the original operation and service of the lower to the upper layer. To exchange information between the neighboring layers, the peer interface must have a consistent rules layer and a set of protocols is called the network architecture

The active elements in each layer are commonly referred to as entities, and entities can be both software entities and hardware entities. The services implemented by the N+1 layer entities are used by the N+1 layer. In this case, the N+1 layer is referred to as service providers and the N+1 layer as service users.

The service is used to provide the upper layer of the service access point. The service can be divided into connected-oriented services and non-connected-oriented services, which are formally described by a set of native languages. These native languages can be used by users and other entities accessing the service.