01. Computer Network Architecture

Computer Network Architecture

1. Basic Concepts, Components, and Functions of Computer Networks

• Computer Network: A system consisting of multiple computers and their peripherals interconnected via communication lines, enabling resource sharing and information transfer according to network protocols.
• Components: Hosts, communication subnet (transmission media, switching devices), network protocols
• Functions: Data communication, resource sharing, distributed processing, improved reliability

2. Classification of Computer Networks

• By geographic scope: Wide Area Network (WAN), Metropolitan Area Network (MAN), Local Area Network (LAN), Personal Area Network (PAN)
• By topology: Bus, star, ring, mesh
• By users: Public network, private network

3. Main Performance Metrics of Computer Networks

• Rate (Bandwidth): Amount of data transmitted per unit time (bps)
• Throughput: Actual amount of data passing through the network per unit time
• Delay: Time required for data to travel from source to destination
• Delay-bandwidth product, utilization, packet loss rate, bit error rate

4. Network Layered Structure, Protocols, Interfaces, Services

• Layered structure: Divides complex network communication tasks into several layers, each implementing specific functions
• Protocol: Rules for communication between entities at the same layer
• Interface: Rules for connection and interaction between adjacent layers
• Service: Set of functions provided by a lower layer to an upper layer

5. ISO/OSI Reference Model

• Seven-layer structure: Physical layer, Data Link layer, Network layer, Transport layer, Session layer, Presentation layer, Application layer
• Brief functions of each layer:
  • Physical layer: Transmission of bit streams
  • Data Link layer: Framing, error detection, flow control
  • Network layer: Routing, packet forwarding
  • Transport layer: End-to-end reliable transmission, flow control
  • Session layer: Session management, establishing/releasing sessions
  • Presentation layer: Data format conversion, encryption/decryption
  • Application layer: Provides network application services to users

6. TCP/IP Model

• Four-layer structure: Network Interface layer, Internet layer, Transport layer, Application layer
• Brief functions of each layer:
  • Network Interface layer: Functions of physical and data link layers
  • Internet layer: IP addressing and routing
  • Transport layer: TCP/UDP protocols, end-to-end communication
  • Application layer: Application protocols such as HTTP, FTP, SMTP

7. Comparison of OSI and TCP/IP Models

• OSI model is more theoretical and finely layered, but less used in practice
• TCP/IP model is more practical and widely adopted on the Internet
• Layer correspondence: OSI’s Physical + Data Link ≈ TCP/IP’s Network Interface; OSI’s Network ≈ TCP/IP’s Internet; OSI’s Transport ≈ TCP/IP’s Transport; OSI’s Session/Presentation/Application ≈ TCP/IP’s Application

8. Introduction to Typical Network Devices

• Repeater, hub (Physical layer)
• Bridge, switch (Data Link layer)
• Router (Network layer)
• Gateway (Multiple layers)

Exercises

1. Briefly describe the three main functions of computer networks.
2. List the names and main functions of each layer in the OSI seven-layer model.
3. What are the similarities and differences between the TCP/IP model and the OSI model?
4. Explain the differences among network protocol, interface, and service.
5. Give examples of typical network devices and their corresponding OSI layers.