ISO-Developed OSI profile

OSI is an open access system interconnection Reference model, and he is a well-defined protocol specification. The OSI model has 7 layers of structure, and each layer can have several child layers. Below I briefly introduce these 7 layers and their functions.

The 7 layers of OSI are from top to bottom, respectively.

7 Application Layer
6 Presentation Layer
5 Session Layer
4 Transmission Layer
3 Network Layer
2 Data Link Layer
1 Physical Layer

The high-level, 7, 6, 5, 4 layer defines the function of the application, the following 3 layers, both 3, 2, 1 layers are mainly targeted at End-to-end data flow through the network. Let me give you a description of the 7-tier features:

(1) Application layer: An application that communicates with other computers, which is the communication service of the corresponding application. For example, a word processing program without communication can not execute the code of communication, and programmers engaged in word processing do not care about the 7th layer of OSI. However, if you add an option to transfer files, the word Processor programmer needs to implement the 7th layer of OSI. Example: Telnet,http,ftp,www,nfs,smtp and so on.

(2) Presentation layer: The main function of this layer is to define data format and encryption. For example, FTP allows you to choose to transmit in binary or asii format. If you select Binary, the sender and receiver do not change the contents of the file. If you select the Asii format, the sender converts the text from the sender's character set to the standard Asii and sends the data. Converts the standard asii to the character set of the receiving computer at the receiving party. Example: Encryption, Asii, and so on.

(3) Session Layer: He defines how to start, control, and end a session. Includes control and management of multiple two-way hours so that the application can be notified when only part of a continuous message is completed, so that the data that the presentation layer sees is contiguous, and in some cases the presentation layer is represented by the data if all the data is received. Example: Rpc,sql and so on.

(4) Transport layer: the function of this layer includes whether to select the error recovery protocol or error-Free recovery protocol, and to reuse the input of different application data streams on the same host, and also to reorder the packets that are not received in order. Example: Tcp,udp,spx.

(5) Network layer: This layer defines the End-to-end packet transport, defines the logical address that identifies all nodes, and defines the way in which the route is implemented and how it is learned. To accommodate a transmission medium with a maximum transmission unit length less than the packet length, the network layer also defines a segmented method for breaking a packet into smaller packets. Example: Ip,ipx and so on.

(6) Data Link layer: He defines how data is transmitted on a single link. These protocols are related to the song-type media discussed. Example: Atm,fddi and so on.

(7) Physical layer: The physical layer specification of the OSI is a standard for the characteristics of the transmission medium, which is usually referenced by the standards established by other organizations. The connection head, the needle, the needle use, the current, the current, the coding and the light modulation and so on all belong to each kind of physical layer standard content. The physical layer uses multiple specifications to complete the definition of all the details. Example: rj45,802.3 and so on.