Return to the upper level list: Chapter One Overview of Computer Network
Article Directory
1. Concept
OSI/RM (Open System Interconnection Reference Model): The basic reference model for open system interconnection. Initially developed by ISO (National Organization for Standardization)
The most widely used is not the legal nationality standard OSI, but the non-international standard TCP/IP. In this way, TCP/IP is often referred to as the de facto international standard
Today's largest, global coverage, TCP/IP-based Internet does not use OSI standards. OSI has only obtained some theoretical research results, but it has backfired and failed in terms of marketization.
The collection of the various layers and protocols of the computer network is the network architecture
1.2 The benefits of layering and the main functions to be completed by each layer
benefit:
- The layers are independent
- Good flexibility
- Structurally separable
- Easy to implement and maintain
- Can promote standardization
The main function:
- Error control
- flow control
- Segmentation and reassembly
- Multiplexing and demultiplexing
- Connection establishment and release
2. Five-layer protocol architecture (TCP/IP + OSI)
The OSI seven-layer protocol has a clear concept and complete theory, but it is complex and impractical.
TCP/IP four-layer protocol is widely used, but the network interface layer has no specific content.
Therefore, the principle of the school computer network is often to adopt a compromise approach, that is, to integrate the advantages of OSI and TCP/IP, and to adopt an architecture with only five layers of protocol, which is both concise and clear.
- Application layer : Protocol (
域名系统DNS,万维网HTTP,电子邮件SMTP). The application layer protocol defines the rules for communication and interaction between application processes. We call the data unit interacted by the application layer a message (message) - Transport layer (transport layer) : The task of the transport layer is to provide general data transmission services for the communication between processes in two hosts. Multiplexing means that multiple application layer processes can use the services of the lower transport layer at the same time, and sharing means that the transport layer delivers the received information to the corresponding processes in the upper application layer. Transmission Control Protocol
TCP（Transmission Control Protocol）------ Provides a connection-oriented, reliable data transmission service. The unit of data transmission is a segment (segment). User Datagram Protocol-UDP(User Datagram Protocol)Provides a connectionless, best-effort data transmission service (the reliability of data transmission is not guaranteed), and the unit of data transmission is user datagram - Network layer : The network layer is responsible for providing communication services for different hosts on the packet switching network. Another task of the network layer is to select an appropriate route so that the packet transmitted by the source host's transport layer can find the destination host through the router in the network. Network layer protocol is connectionless
网际协议IP（Internet Protocol）和许多种路由选择协议 - Data link layer : When transmitting data between two adjacent nodes, the data link layer assembles the IP datagrams handed over from the network layer into frames, and the link between two adjacent nodes上transfer frame. Each frame includes data and necessary control information (synchronization, address information, error control, etc.). Error detection
- Physical layer (physical layer) : The unit of data transmitted in the physical layer is bits. The physical layer should consider how much voltage is used to represent "1" or "0", and how the receiver recognizes the bits sent by the sender. It is not the task of the physical layer to explain what the bits represent. The physical media (such as cables, optical cables) are below the physical layer, and some people regard it as layer 0
