The notes come from the video of teacher Han Ligang, thank you very much for this excellent course
1.1 The role of computer networks in the information age
An important function of computer network: information sharing software and hardware sharing connectivity
1.2 Overview of the Internet
(b) It is a router device (a) It is a switch The
network and the network are connected together called the Internet, and the router is connected in the middle
Internet: the largest Internet in the world
Network: Many computers are connected together
Internet: Internet Many networks are connected together
Internet: Internet The world’s largest Internet
Internet Association ISOC
1.3 Internet composition
Edge of the network:
Communication between hosts:
- Client server mode (C/S)
- Peer-to-Peer (P2P)
P2P downloads more machines, the faster it is, which is equivalent to downloading from a computer that has been downloaded by others. Each computer is both a client and a server.
The core of the internet
Data exchange method
- Circuit switching: typical switching applications (phone calls) suitable for real-time communication, circuit switching can be used between core routers
- Packet switching: group the data that needs to be sent, and the contents of the divided groups may not follow the same path
- Message exchange: messages are generally longer than packets, and the delay of message exchange is longer
Internet = edge part + core part
= resource subnet + communication subnet
Time comparison:
packet switching saves time, and message exchange takes the longest time
1.4 The development of computer networks in my country
1994.4.20 my country officially connected to the Internet
1.5 Types of computer networks
The new understanding does not only distinguish between LAN and WAN from the scope of network coverage.
Wide area network technology is
applied. Local area network technology is generally not more than 100 meters.
Local area network self-purchase equipment and maintain broadband fixed 100M 1000M within 100 meters of distance.
WAN pays for services and pays for bandwidth
1.6 Performance of computer network
Performance indicators:
1. Rate: The rate at which the host connected to the network transmits the number of data bits on the digital channel is also called data rate or bit rate
2. In the field of bandwidth data communication, the highest data rate transmitted by the digital channel
3. Throughput : The amount of data that passes through a certain network in a unit of time
4. Delay
5. Delay bandwidth machine: Delay bandwidth machine = propagation delay * bandwidth
6. Round trip time: from the start of the data sender sending the data to the sending Receiving confirmation from the recipient
7. Utilization rate:
non-performance indicators: quality cost management and maintenance, scalability, reliability, upgradeability, standardization
1.7 Computer network architecture
The OSI reference model has seven layers
- Application layer can generate network traffic and user interaction applications
- Issues considered by developers of presentation layer encryption and compression
- The session layer service and the client establish a session to check the Trojan horse netstat -nb (this is the cmd command to check the session)
- Reliable transmission at the transport layer, session establishment, unreliable transmission flow control
- Network layer selects the best path IP addressing selects the best path
- How to encapsulate data at the data link layer and add a physical layer address MAC
- Physical layer voltage interface standard
Network troubleshooting
Investigate from the bottom to the high-level
network security and OSI reference model
- Physical layer security
- Data link layer security ADSL wireless AP password
- Network layer security
- Application layer security SQL injection vulnerability Upload vulnerability
Class practice
1. View the session
2. View the procedure for establishing a session
3. Ping www.baidu.com Return time
ping www.taobao.com Return time
4. View computer network connection