1. The physical layer is just a process and mechanism, which is used to place signals on the transmission medium and receive signals from the media. Its lower layer boundary is a physical connector of a transport medium. The physical layer does not have any specification for the performance of the medium. The performance characteristics of the medium are required for the process and mechanism defined by the physical layer and assume that it exists. Therefore, the transmission medium is in addition to the physical layer, sometimes referred to as a 0th layer of the OSI reference model. 2, DLL function: transmission and reception. It also provides end-end (end-to-end) connections for data effective transmission. In the sender, D L1 needs to be responsible for packaging instructions, data, etc. into the frame, frame (f R a m e) is a structure generated by D L layer, which contains sufficient information to ensure that data can safely reach the destination through the local local area network. Successful transmission means that the data frame is completely free to reach the destination. That is, the frame must contain a mechanism for ensuring the integrity of the content during the transfer. To ensure that the data transfer is completely secure, two points must be done: 1) When each frame is completely free, the source node must receive a response. 2) You must verify the integrity of the frame before the target node issues a response from the frame. There are many situations that can result in the transmission of the frames that cannot be reached or in the transmission process or cannot be used. D L1 has a responsibility to detect and correct all these errors. Another responsibility of D L1 is to reorganize the data bitstream received from the physical layer. However, if the structure and content of the frame are issued, D L1 does not reconstruct a frame. Instead, it caches the bits arriving until these bit streams constitute a complete frame. 3. The network layer is responsible for establishing the routes used between the source machine and the target machine. This layer itself does not have any error detection and correction mechanism, so the network layer must depend on the reliable transmission service provided by the DLL between the ends. The network layer is used to establish a communication on the computer system above the local LAN network. So it can be done because it has its own routing address structure. 4, the responsibility of the transport layer is also to ensure that the data is completely transmitted between the terminals, but the DLL is different, the function of the transport layer is provided on the local LAN network segment. This feature, it can detect the router discarded package, and then automatically generate a re-transmit request. Another important feature of the transport layer is to reorder the packets received by the sequence, and there are many reasons for the data package. For example, these packages may be different from the path of the network, or some are destroyed during transmission. Regardless of the situation, the transport layer should be able to identify the original package order, and return them to the sequence of sequence before transmitting the contents of these packets to the session layer. 5, the fifth layer of the session layer O S i is a session layer. Relatively, this layer is not too large, and many protocols are bundled with the function of this layer with the transport layer. The function of the O S i session layer is mainly used to manage communication flow between two computer system connections. The communication stream is called a session, which determines that communication is single work or duplex. It also guarantees that a new request must be done after another request. 6. The representation layer is responsible for managing data coding, not all computer systems use the same data coding mode, indicating that the duty is to translate, for example, between A S C I I and E B C D i C, providing translation. Indicates that the layer can be used in floating point formats and provides encrypted decryption services. 7, the application layer only provides an interface between those applications and network services. This layer can be seen as the cause of initializing the communication session. For example, mail customers may generate a request from the mail server to retrieve new messages, and the client application automatically issues a request to the seven-layer protocol associated with it, and generates a communication session to obtain the required files.
Welcome, I will write a model detailed model in TCP IP next time, including the optimization scheme of TCP IP in the wireless network! ! ! Http://www.cnblogs.com/zhongxing http://www.cnblogs.com/zhongxing
