osi 七层模型（osi 七层模型）

osi 七层模型（osi 七层模型） osi 七层模型(osi 七层模型) OSI seven layer model.Txt OSI seven layer model The definition and function of seven layer model of open system interconnection defined by ISO international standard organization. It's the web Astepping-stone to success technology for beginners, but also analyze and judge all kinds of network technology based on Network - since it is no longer mysterious. It is rational and can be followed. The seven layer model is mainly designed to solve the compatibility problems encountered in heterogeneous network interconnection. It's biggest advantage The three concepts of service, interface and protocol are separated from each other, and the function modules of the network are not shared Same duties. One of the most important milestones in network development is ISO (Internet Standard Organization, International) Standard Organization) determination of seven layer network model of OSI (Open System Interconnect, open system interconnection) Yi. It not only becomes the basis for judging and analyzing all kinds of network technology before and following, but also becomes the design of network protocol Unified reference model. The main purpose of building the seven layer model is to solve the compatibility problems encountered in heterogeneous network interconnection. It's the most The great advantage is that the three concepts of services, interfaces, and protocols are clearly separated from each other: a layer of service description is raised to the next level What functions provide interfaces to explain how the underlying layer uses the underlying services, and protocols involve how to implement the services of this layer Therefore, there is no strong restriction between the layers and what protocols are adopted by entities in the interconnection network Providing the same service up and without changing the interface of the adjacent layer. The partition of the seven layer of the network is also In order to share the different responsibilities of different functional modules (different levels), the following benefits are obtained: Reduce the complexity of the problem, once the network failure, can quickly locate the fault level, easy Search and error correction; The standard interfaces are defined at each layer, so that different network devices with the same peer layer can realize interoperability As a result, each layer is relatively independent, and a high-level protocol can be run on various low level protocols; It can effectively stimulate the network technology innovation, because each update can be carried out in a small range, without the need for integration A network of big operations; Convenient for research and teaching. ---------------------------------------------------------------------------------------------------------------------- OSI seven layer model is called open system interconnection reference model, OSI seven layer model is a kind of frame design method OSI seven layer model enables reliable communication between different systems and different networks through seven hierarchical structure models, so the most important part of the model is its main structure The function is to help different types of hosts to achieve data transmission Physical layer: the lowest layer or the first layer of O S I model, which includes physical networking media, such as cable connector. A physical layer protocol generates and detects voltage to transmit and receive signals carrying data. Plug in the network interface card on your desktop P C, and you build the foundation for computer networking. In other words, you provide a physical layer. Although the physical layer does not provide error correction services, it can set the data transmission rate and monitor the data error rate. Network physics problems, such as disconnection of wires, will affect the physical layer. Data link layer: the second layer of the O S I model, which controls the communication between the network layer and the physical layer. Its main function is how to reliably transfer data on unreliable physical lines. In order to ensure the transmission, the data received from the network layer is divided into specific frames that can be transmitted by the physical layer. A frame is a structured packet for moving data, which includes not only raw data, but also network addresses of the sender and receiver, and error correction and control information. The address determines where the frame will be sent, and the error correction and control information ensures that the frame arrives without error. The function of the data link layer is independent of the network and its nodes and the physical layer type adopted, and it does not care whether the Wo R D, E x C E L or I n t e r n e t are running. There are some connection devices, such as switches, which work at the data link layer because they want to decode frames and use frame information to send data to the correct receiver. Network layer: the third layer of O S I model. Its main function is to translate network address into corresponding physical address, and decide how to route data from sender to receiver. The network layer determines the best path of the node A from one node to another in the network by comprehensively considering the transmission priority, network congestion degree, service quality and the cost of alternative routing. B. Because the network layer processes the router, the router belongs to the network layer because it connects each segment of the network and intelligently guides the data transmission. In the network, routing is based on addressing schemes, usage patterns, and reachability to guide data transmission. Transport layer: the most important layer in O S I model. The transport protocol controls the flow at the same time, or specifies the appropriate transmission rate based on the speed of the receiver's received data. In addition, the transport layer forcibly divides the longer packets according to the maximum size that the network can process. For example, Ethernet cannot receive packets greater than 1500 bytes. The transport layer of the sender node divides the data into smaller data pieces, and arranges a serial number for each data sheet so that the data can be recombined in the correct order when the data reaches the transport layer of the receiver node. The process is called sorting. One service that works in the transport layer is the T C P (Transport Control Protocol) in the T C P / I P protocol set, and the other transport layer service is the S P X (X S X protocol set) I P P (sequence packet switching). Session layer: responsible for establishing and maintaining communication between two nodes in the network. 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 may often hear the traffic cop who calls the conversation layer "cyber communication"". When dialing to your I S P (Internet service provider) request to connect to the Internet, the session layer on the I S P server connects to the session layer on your P C client. If your phone line accidentally drops off from the wall jack, the session layer on your terminal detects a connection break and restarts the connection. The session layer establishes the communication deadline by determining the priority of the node communication and the length of the communication time Presentation layer: the translator between the application and the network, in the presentation layer, the data will be formatted according to the network can understand the format; this format is also different because of the type of network used. The presentation layer manages the decryption and encryption of data, such as the processing of system passwords. For example, querying your bank account on Internet is a secure connection. Your account data is encrypted before sending, and at the other end of the network, the presentation layer decrypts the received data. In addition, the presentation layer protocol also decodes and encodes the picture and file format information. Application layer: responsible for providing interfaces to the software so that the program can use the network services. The term "application layer" does not refer to a particular application running on the network. The services provided by the application layer include file transfer, file management, and e-mail information processing