1. Computer network system
Computer network architecture is divided into three kinds: OSI architecture (seven layers), TCP/IP architecture (four layers), five layers architecture.
OSI architectureThe concept is clear and the theory is complete, but it is complicated and impractical.TCP/IP architectureTCP/IP is a four-tier architecture that has been widely used.A five-tier architectureCompromise for the convenience of learningOSI architectureandTCP/IP architecture, integrated the advantages of both, so simple, and can explain the concept clearly.
The major difference between TCP/IP and OSI is that OSI is a theoretical model for network communication, while TCP/IP is a practical network protocol.
2. Overview of five-layer network architecture
Take a look at the main functions of each layer of a five-tier network architecture:
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Application layer: The application layer is the highest layer of network protocols and is responsible for completing specific network applications through interaction between processes. Application layer protocols define the rules for communication and interaction between applications (processes).
Different application layer protocols are required for different network applications. There are many application layer protocols in the Internet, such as domain name system DNS, HTTP protocol supporting world Wide Web applications, SMTP protocol supporting email, and so on. The data units that the application layer interacts with are called packets.
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Transport layer: sometimes translated as transport layer, it is responsible for providing communication services for processes between two hosts. This layer has the following two protocols:
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Transmission Control Protocol (TCP) : Provides connection-oriented and reliable data Transmission services. The basic unit of data Transmission is segment.
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User Datagram Protocol (UDP) : provides a connectionless, best-effort data transfer service without ensuring the reliability of data transmission. The basic unit of data transmission is the User Datagram.
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Network layer: The network layer is responsible for providing communication services for different hosts in the packet network and transferring data to the target host by selecting appropriate routes. When sending data, the network layer encapsulates the packet segments or user data generated by the transport layer into packets or packets for transmission.
In TCP/IP architecture, packets are also called IP datagrams because the network layer uses the IP protocol.
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Data link layer: The data link layer is often referred to as the link layer for short. When two adjacent nodes transmit data, the data link layer assembles IP datagrams crossed by the network layer into frames, and transmits frames on the link between the two adjacent nodes.
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Physical layer: Ensures that data can be transmitted on various physical media and provides a reliable environment for data transmission.
Here is a simple diagram of how the data of an application process changes as it passes between layers:
3. Overview of TCP/IP architecture
The TCP/IP architecture is relatively simple, with only four layers.
| Hierarchical name | Single bit | Can work | agreements |
|---|---|---|---|
| The network interface | frame | Responsible for the transfer of actual data, corresponding to the next two layers of the OSI reference model | HDLC PPP PPP SLIP serial Line Interface Protocol |
| The network layer | The datagram | Responsible for addressing data transfer between networks, corresponding to layer 3 of the OSI reference model | IP Internet Protocol ICMP Internet Control Message Protocol ARP ADDRESS Resolution Protocol RARP reverse Address Resolution Protocol |
| The transport layer | Message segment | Responsible for providing reliable transport services corresponding to layer 4 of the OSI reference model | TCP (Control Transport Protocol) UDP (User Datagram Protocol) |
| The application layer | Responsible for implementing all application-specific functions corresponding to the upper three layers of the OSI reference model | FTP HTTP DNS SMTP NFS Network File System Protocol |
A schematic diagram of this four-layer protocol data exchange is shown below:
4. Comparison of the three models
Reference:
[1] : Xie Xiren, Computer Network
[2] : Network part I: the so-called four-layer structure and seven-layer structure
[3] : Computer network model (four layers, five layers, seven layers)
[4] : OSI 7 layer model and TCP/IP 4 layer model