7-Layer Network model

OSI is an open access System Interconnect Reference Model, which is a well defined protocol specification. The OSI model has 7 layers of structure, each of which can have several sub-tiers. OSI layer 7 from top to bottom is 7 Application layer 6 represents Layer 5 session Layer 4 transport

Layer 3 Network Layer 2 data Link Layer 1 physical layer where the upper layer, that is, 7, 6, 5, 4 layers defines the functionality of the application, the following 3 layers, 3, 2, 1, are mainly for end-to-end data flow through the network

1 An application layer communicates with other computers, and it is the communication service of the corresponding application. For example, a word processor without a communication function would not be able to execute the code of communication, and the programmer working on the word processing did not care about the 7th layer of the OSI. But

If you add an option to transfer files, a word processor programmer needs to implement the 7th layer of the OSI. Example: Telnet,http,ftp,nfs,smtp and so on.

2 The primary function of the layer is to define the data format and encryption. For example, FTP allows you to choose to transfer in either binary or ASCII format. If binary is selected, the sender and receiver do not change the contents of the file. If you select the ASCII format, the sender will

The data is sent from the sender's character set to the standard ASCII. Converts standard ASCII to the receiver computer's character set on the receiver side. Example: Encryption, ASCII, and so on.

3 Session Layer It defines how to start, control, and end a session, including control and management of multiple bidirectional messages, so that the app can be notified when only part of a continuous message is complete, so that the data that the presentation layer sees is continuous, and in some cases, if the table

The presentation layer receives all the data, the data is represented by the representation layer. Example: Rpc,sql and so on.

4 Transport Layer This layer of functionality includes whether to select the error recovery protocol or the error-free recovery protocol, and to reuse the input of data streams from different applications on the same host, including reordering of packets that are not received in the wrong order. Example: Tcp,udp,spx.

5 Network layer This layer defines end-to-end packet transport, which defines the logical addresses that identify all nodes, and defines the way in which routing is implemented and how it will be learned. To accommodate transmission media with a maximum transmission unit length less than the packet length, the network layer also defines how to

A segmented method that decomposes a package into smaller packages. Example: IP,IPX, etc.

The 6 data Link layer defines how data is transferred on a single link. These protocols are related to the various media being discussed. Example: Atm,fddi, etc.

The physical layer specification of the 7 physical layer OSI is a characteristic standard for transmission media, which is often referenced by other organizations ' standards. Connection head, frame, frame use, current, encoding and light modulation are all the contents of various physical layer specifications. The physical layer is often used for multiple

The specification completes the definition of all the details. Example: rj45,802.3 and so on.

7-Layer Network model