osi模型（OSI模型）

osi模型（OSI模型） osi模型(OSI模型) The seventh layer: the application layer data, user interface, providing the user program interface". Sixth layers: the presentation layer data form data, the realization of specific functions, such as data encryption. Fifth layer: session layer data is allowed to establish a session between users on different machines, such as WINDOWS The fourth layer: data communication between the transmission layer network different host user process, reliable With the unreliable transmission error detection, transmission layer, flow control etc.. Third layers: the network layer provides the logical address (IP), routing, data from source to destination transmission The second layer: data link layer frame of the upper frame data package, the media access by MAC address, error detection And correction. The first layer: physical layer transmission, bit stream bit stream equipment between the physical interface, electrical characteristics etc.. The following is a detailed explanation of the OSI seven layer model of each layer function: Seven layer model of OSI OSI seven layer model called the open system interconnection reference model OSI seven layer model is a framework design method. OSI seven layer model through the hierarchical structure model of seven different systems to realize the reliable communication between different networks, so the most main The function is to help to make different types of hosts to achieve data transmission Physical layer: O S I model of the lowest layer or the first layer, the layer including physical networking media, such as cable connection connector. The physical layer protocol to generate and detect voltage to send and receive data carrying signals. Insert the network interface card on your desktop P C, you can set the foundation of computer networking. In other words, you provide a physical layer. Although the physical layer does not provide error correction services, but it can set the speed of data transmission and monitoring data error rate. The network physical problems, such as wire disconnection, will affect the physical layer. The data link layer: second layer O S I model, it controls the communication between the network layer and the physical layer. Its main function is how to carry out the reliable transmission of data in the physical line is not reliable on. In order to guarantee the transmission of the data received from the network layer can be divided into specific physical layer transmission frame. Frame structure is used for mobile data package, which includes not only the original data, including the sending and receiving of the network address and the error correction and control information. The frame will be sent to the address to determine where the error correction and control information to ensure error free frame arrival. The data link layer function independent of the network and its nodes and the physical layer type, it does not care whether they are running Wo R D, E x C E L I n t e r or n e t. There are some connected devices such as switches, because they want to frame decoding and use frame information to send the data to the correct recipient, so they are working on the data link layer. The network layer: third layer O S I model, its main function is to be translated into a physical address corresponding to the network address, and decide how to transfer data from the sender to the receiver routing. The network layer by considering the transmission priority, network congestion, service quality and cost to determine the optional routing node A best path to another node in B network from a network. Because the network layer routing, But because that router connected to the network segment, and intelligent guidance for data transmission, which belongs to the network layer. In the network, "routing" is based on the addressing scheme, usage patterns and accessibility to direct data transmission. Transport layer: the most important O S I model in a layer. At the same time transmission protocol is based on the speed of the flow control and the receiver can receive data transmission rate of the appropriate provisions. In addition, the transport layer according to the maximum size network can handle longer packets for forced split. For example, Ethernet can not receive more than 1500 bytes of data packet. The transport layer nodes to partition the data into a small piece of data, at the same time to arrange a serial number for each piece of data, so that data arrives at the receiving node of the transport layer, in order to correct the reorganization. This process is called sorting. Work is T C P / I P protocol in T C P set in a service TCP (transmission control protocol), another is I P service transport layer X / S P X S P X protocol set (sequence packet exchange). The session layer: responsible for between two nodes in the network to establish and maintain communication. The session layer includes: establishing a communication link, keep the session communication unimpeded, synchronization between the two nodes of the dialogue, communication is interrupted and decided whether communication is interrupted to decide where to send. You often hear someone called the session layer of network communication "traffic police". When dialing through to your I S P (Internet service provider) request to connect to the Internet, the session layer session layer of I S on the P server to you and your P C client negotiate connection. If your phone line came from the wall jack off, your terminal session layer will detect disconnect and re initiate connections. The session layer by determining priority node communication and communication time to set the communication period The presentation layer between the application and the network translator, in the presentation layer, the data will be formatted according to the network can understand the formatting scheme; because the type of Internet use is different. Said the decryption and encryption layer management data processing, such as system password. For example: check your bank account on Internet, the use of which is a secure connection. Your account data is encrypted before it is sent, on the other side of the network, the presentation layer translates the received data decryption. In addition, the presentation layer protocol for encoding and decoding of images and file format information. Application layer: responsible for providing interface of software so that the program can use the network service. The term "application layer" does not refer to a particular application running on the network, the application layer provides services such as file transfer, file management and e-mail information processing.