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OSI reference model

Introduction: network layer 7 Protocol (Open System Interconnection), referred to as OSI, is an open reference model for interconnection of traffic systems, and it is a very well-defined protocol specification. The OSI model has a seven-tier structure, and each layer can have several sublayers. The upper layer, namely layer 7, 6, 5, and 4, defines the function of the application, while the lower layer, that is, layer 3, layer 2, layer 1, is mainly oriented to the end-to-end data flow through the network.

7. Application layer: provides an interface for operating systems and applications to access network services, protocol representatives: FTP HTTP SNMP Telnet, etc.

6. Presentation layer: realize the transformation of upper layer data and information to ensure that the application layer information can be understood by another host application (data transformation includes, compression, encryption, etc.)

5 session layer: to manage the session process between hosts, such as establishing a session, closing a session, etc.

4 Transport layer: implement upper data segmentation and end-to-end reliable or unreliable transmission such as TCP,UDP

3 Network layer: implement packet routing, such as ip protocol, etc.

2 data link layer: to realize the transmission of data frames on physical media, such as ppp, frame Relay, etc.

1 physical layer: the physical media that transmits data, such as RJ45, etc.

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