Network protocol hierarchy and Division

Hierarchy and hierarchy of network protocols: due to the complexity of the connection between network nodes, complex components are usually divided into simple components during protocol preparation, and then combined. The most common compound technology is the hierarchical method. the hierarchical structure of the network protocol is as follows: (1) each layer of the structure specifies a clear service and interface standard. (2) Use user applications as the highest level (3) In addition to the highest level, each layer in the middle provides services to the next layer, and at the same time, users at the next layer. (4) The physical communication line is used as the lowest layer. parameters transmitted from the highest layer are the basis for providing services. Hierarchy: To enable computers produced by different computer manufacturers to communicate with each other and establish computer networks in a larger scope, the International Organization for Standardization (ISO) in 1978, the "Open System Interconnection Reference Model" was proposed, namely the famous OSI/RM Model (Open System Interconnection/Reference Model ). It divides the communication protocols of the computer Network architecture into seven layers, which are from the bottom up: physical Layer, Data Link Layer, and Network Layer) transport Layer, Session Layer, Presentation Layer, and Application Layer ). The layer-4 data transmission service is complete, and the layer-3 above is intended for users. There are at least two standards for each layer: service definition and protocol specification. The former provides an accurate definition of the services provided by the layer, and the latter describes the actions of the Protocol and various related procedures in detail to ensure the provision of services. Application Layer Session Layer transport layer data link layer Physical Layer