Layer-7 OSI network protocol and its Functions

OSI network layer-7 protocol and its functions OSI is an open reference model for communication between systems. It is a well-defined protocol specification. The OSI model has a layer-7 structure, and each layer can have several child layers. Next I will briefly introduce these 7 layers and their functions. Layer 7 of OSI is Layer 7, layer 6, presentation layer 5, Session Layer 4, Transmission Layer 3, Network Layer 2, data link layer 1, physical layer, layer 7, layer 6, layer 5, and Layer 4 define the functions of the application. Layer 3, Layer 3, and Layer 1 are mainly oriented to end-to-end data streams through the network. Next, I will introduce the functions of these 7 layers: www.2cto.com (1) Application Layer: an application that communicates with other computers. It corresponds to the communication service of applications. For example, a word processing program without communication functions cannot execute communication code, and programmers engaged in word processing do not care about OSI Layer 7th. However, if a file transfer option is added, the programmer of the word processor needs to implement the OSI Layer 7th. Example: telnet, HTTP, FTP, WWW, NFS, SMTP, etc. (2) Presentation Layer: The main function of this layer is to define the data format and encryption. For example, FTP allows you to transfer data in binary or ASII format. If binary is selected, the sender and receiver do not change the file content. If the ASII format is selected, the sender converts the text from the sender's character set to the standard ASII and then sends the data. The receiver converts the standard ASII to the character set of the receiver's computer. Example: encryption, ASII, etc. (3) Session Layer: it defines how to start, control, and end a session, including control and management of multiple two-way hours, so that the application can be notified when only part of the continuous message is completed, so that the data seen in the presentation layer is continuous. In some cases, if the presentation layer receives all the data, data is used to represent the presentation layer. Example: RPC and SQL.
(4) Transport Layer: This layer features whether to select the error recovery protocol or error-free recovery protocol, and reuse the input of data streams of different applications on the same host, it also includes the re-sorting function for packets that are not in the correct order. Example: TCP, UDP, and SPX. Www.2cto.com (5) network layer: This layer defines the end-to-end packet transmission. It defines the logical addresses that can identify all nodes, and also defines the routing implementation and learning methods. To adapt to the transmission medium whose maximum transmission unit length is smaller than the packet length, the network layer also defines how to break a packet into smaller packets. Example: IP, IPX, etc.
(6) data link layer: it defines how data is transmitted on a single link. These protocols are related to the song media discussed. Example: ATM, FDDI, etc. (7) Physical Layer: OSI physical layer specifications are characteristic standards for transmission media. These specifications are generally referred to standards developed by other organizations. Connector, needle, needle usage, current, current, encoding and optical modulation all belong to the content of various physical layer specifications. Multiple specifications are commonly used in the physical layer to define all details. Example: Rj45, 802.3, etc. Advantages of the OSI hierarchy at www.2cto.com: (1) it is easy for people to discuss and learn the specification details of protocols. (2) The standard interface between layers facilitates modular engineering. (3) creating a better interconnection environment. (4) Reduced Complexity, made the program easier to modify, and made product development faster. (5) Each layer makes it easier to remember the functions of each layer by taking advantage of the adjacent lower-layer services. Most computer networks adopt hierarchical structures. A computer network is divided into several layers. A system at a high level only uses interfaces and functions provided by systems at a lower level, you do not need to know the algorithms and protocols used to implement this function at the lower layer. The lower layer only uses parameters transmitted from the higher level system. This is the independence between layers.

With this independence, each module in the hierarchy can be replaced by a new module, as long as the new module and the old module have the same functions and interfaces, even if they use different algorithms and protocols. To transmit information and data correctly between computers and terminals in the network, there must be an agreement or rule on the order of data transmission, data format and content, such an agreement or rule is called an agreement. The network protocol consists of three main components: 1. Semantics: the meaning of the Protocol element is interpreted, and the semantics specified by different types of protocol elements are different. For example, what control information should be sent, what actions should be completed, and the response should be obtained. 2. Syntax: www.2cto.com combines several protocol elements and data to express a complete format that should be followed, that is, to define the data structure of information. For example, the structure and format of user data and control information. 3. Time Sequence: describes the sequence of events. For example, when both parties communicate, a data packet is sent from the sending point. If the target point is correctly received, the source point is correctly received. If an error message is received, the source point must be resold once.