OSI is divided into seven layers, its names and functions are as follows:
1. Physical Layer: The main function is to define the physical structure of the network, the transmission of electromagnetic standards, BIT coding and time principles of the network, such as time-repetitive and divided. The network connection type (end-to-end or multi-end connection) and physical topology are determined. Some of the popularity, this layer is primarily responsible for actual signal transmission.
2, according to the Data Link Review: The data link connection is established on both hosts, transmitting the data signal to the physical layer, and processing the signal so as nothing, and reasonable transmission.
3, Network Layer: Mainly responsible for routing, selecting the appropriate path, performing blocking control.
4. Transfer Layer: The most critical layer, providing a reliable end-to-end service to the support, which blocks the underlying data communication details, so that users and applications do not need to consider actual Communication method.
5, session layer: Mainly responsible for communication between two session processes, that is, information exchange between two session layer entities, the exchange of management data.
6. Presentation Layer: Processing a representation of a communication signal, performing translation between different formats, and responsible for encrypted data encryption, compression and recovery of data.
7. Application Layer: Keep the data records required to connect between the application to serve the user. In the work, each layer will give the data from the previous layer to the header, then send it to the lower layer, and then transmitted to the other party by physical media, each layer of the opponent is processed, Remove the information header, and finally restore actual data. In essence, the host's communication is a communication between layers and layers, and is physically transmitted from the upward, and then transmits backward upwards from the lower-by-side host by a physical channel.
In practical applications, the most important thing is the TCP / IP (Transport Control Protocol / Internet Protocol) protocol, which is the most popular commercial agreement, relative to OSI, is current industrial standard or "factual standard", It was made by kahn in 1974. It is divided into four levels: application layer (corresponding to OSI's application layer), transport layer (corresponding to OSI's transport layer), interconnected layer (corresponding to OSI's network layer), host-network layer (with OSI data chain Corresponding to the road floor and physical layer). The TCP / IP protocol is mainly used in the wide area network, and there is also applications in some local area networks, such as use in Windows 9x and NetWare networks, but there is also a gap in terms of functionality and speed. The design goals of TCP / IP are not same. When setting the TCP / IP protocol, there are main IP addresses and subnet masks, gateways (Gateway: Conversion between network protocols in communication, suitable for information exchange between different protocol hosts), domain name resolution server (NDS : Domain name system, that is, converts the URL you entered into digital IP addresses) and NetBIOS, and more. The IPX / SPX (InternetWork Packet Exchange / Sequenced Packet Exchange) protocol is now explained now. This application is a wide range of network protocols. You must have a fast online game in the LAN, you know that this is the credit of IPX / SPX. IPX / SPX is based on Xerox's Xerox's Network System (XNS) protocol, while SPX is based on Xerox's Xerox's SPP (SEQUENCED PACKET Protocol: Sub-Package Protocol) protocol, which is developed by Novell's high-speed protocol to LAN. . It's a significant difference in it and TCP / IP that it does not use the IP address, but the physical address of the NIC, is the (MAC) address. It is also like the TCP / IP protocol to correspond to OSI. Only parts of the transport layer and the network layer are included in the OSI. In actual use, it does not need to set up, it can be used. Since it has played a huge role in the initial in the Internet, many manufacturers have been supported, including Microsoft (but later it has developed their own compatible Novell'ipx / SPX IPX / SPX protocol), etc., now many software and Hardware also supports this protocol.
Compared to the front two routing protocols (routing, it is understood that the selection of two-point path on the network) is in daily applications, and there are two non-routing protocols. They need us to understand, they are: NetBIOS (Network Basic Input / OutputSystem) And NetBEUI (NetBIOS Extended User Interface). NetBIOS is developed by Microsoft and IBM, which is a context-like protocol that establishes a connection session that allows applications on different computers through network transmission. It is designed to design with other computational opportunities to be computational opportunities in the same network. In Win9X & Me, when you select "I hope to enable NetBIOS" in IPX / SPX, you can select "Enable NetBIOS" through TCP / IP. " NetBeui is an IBM designed for its own network product as a network transmission station. It is an expansion version of NetBIOS that defines a low-sized single-network single-wire online. It can be installed directly in Win9X & ME. In some online games, these two protocols may be needed. If you encounter can't play, you can try it two, maybe you can solve your urgent needs.
There are two main network architectures formed in the computer network: OSI reference model and TCP / IP reference model. OSI Open System Interconnence Model is developed by the International Standardization Organization (ISO), divided into 7 layers: physical layer, data link layer, network layer, transport layer, session layer, representation layer, application layer. The TCP / IP reference model is the foundation of the Internet. Compared with the 7-layer protocol of OSI, there is no session layer and representation in the TCP / IP reference model. TCP / IP is a set of protocols, TCP / IP is actually a protocol (or protocol package), including more than 100 interconnected protocols, where IP (Internet Protocol, internet protocol) is the network layer Main protocols; TCP (Transmission Control Protocol, Transmission Control Protocol), and UDP (User DataGram Protocol, User Datasters) are the most important protocols in the transport layer. It is generally considered IP, TCP, and UDP is the most fundamental three protocols, which are the foundation of other protocols. IP defines the format and rules transmitted by Datase (DATAGRAM); TCP is a reliable service, a connection-oriented protocol; UDP is unreliable and unconnected protocol. TCP is built on the IP (this is the origin of TCP / IP), defines the data transfer format and rules on the network on the network, provides the transmission confirmation of the IP packet, and the reclaimed packet, will receive The packet is re-assembled according to their sequence of sequence. The TCP protocol is a connection-oriented protocol, similar to calling, and must first establish a clear connection before starting data. UDP is also built on IP, but it is a connectionless protocol, and the transfer between the two computers is similar to delivery: The message is sent from one computer to another, and there is no clear connection between the two. DataGram in UDP is a data packet that comes from the data source to the end point of the data source independently. UDP does not guarantee the transmission of data, nor does it provide rearrangement or reclaim function, so it is unreliable. Although UDP's unreliability limits its application, it has better transmission efficiency than TCP. TCP / IP uses the protocol stack to work, and the stack is a collection of all protocols for completing a transfer between two machines. The TCP / IP protocol is divided into four layers: Application Layer, Transport Layer, Network Layer, Network Interface Layer (Network Interface Layer)
