Calculating Network-1 Overview

1 Definition of computer network

2 The difference between a computer network and a distributed system

3 Division of the development stages of computer networks

• The first stage: 50-60s. This stage is mainly represented by the emergence and development of computer terminal systems.
  Data communication technology and packet switching
• The second stage: late 1960s-1970s. This stage is mainly represented by the emergence and development of ARPANET, the predecessor of the Internet, and various network systems.
  TCP/IP protocol, email, ftp...
• The third stage: late 70s-80s. This stage is mainly represented by the emergence of OSI open network interconnection standards and the parallel development of the Internet.
• The fourth stage: late 80s-90s. This stage is mainly represented by the popularization and development of the Internet on a global scale.
  ATM (Asynchronous Transfer Mode) asynchronous transfer mode

4 (Message) packet switching

• It is the foundation of modern computer network technology
  

• The key component of packet switching: the router plays a special role in the core part of the network . The router is the key component for packet switching . Its task is to forward received packets. This is the most important function of the core part of the network.

• The meaning of "switching": The meaning of "switching" here is switching-to transfer one telephone line to another, so that they are connected. From the perspective of communication resource allocation, "switching" is to dynamically allocate transmission line resources in a certain way .

• The main feature of packet switching: At the sending end, the longer message is first divided into shorter, fixed-length data segments.

• step:

  1. Add the header to form a group: add the header before each data segment to form a group.
  2. The transmission unit of packet switching: The packet switching network uses "packet" as the data transmission unit. Send each packet to the receiving end in turn (assuming the receiving end is on the left).
  3. Strip the header after receiving the packet: The receiving end strips the header after receiving the packet and restores it to a message.
  4. Finally restore to the original message: restore the received data to the original message at the receiving end.

• Importance of group header

  1. The header of each packet contains control information such as addresses.
  2. The nodal switch in the packet switching network forwards the packet to the next nodal switch according to the address information in the header of the received packet.
  3. With this store-and-forward method, finally the packet can reach the final destination.

• The packet switching network uses "packets" as the data transmission unit. The header of each packet contains control information such as addresses.
  The nodal switch in the packet switching network forwards the packet to the next nodal switch according to the address information in the header of the received packet. (Temporarily store in the router, look up the forwarding table, and find the forwarded port) Using this store-and-forward method, finally the packet can reach the final destination.

The core part of the Internet

The main contribution of ARPANET

1. Completed the research on the definition and classification of computer networks
2. Put forward the network structure concept of resource subnet and communication subnet;
3. Researched the packet switching method;
4. Adopt a hierarchical network architecture model and protocol system.

Characteristics of computer network

Classification of computer networks

Computer network performance index

109
Rate: bit (bit), namely data rate or bit rate, is the most important performance index of computer network varieties, unit bps or kbps
bandwidth (bandwidth): the "highest data rate" that digital channel can transmit, unit bit Per second or bps (bit/s)
1kbps=10 ³ b/s
1KB=2 ¹⁰ B (storage unit)

C/S and P2P

• the difference
  
  
• Features of C and S in C/S
  
  

Network topology

The information highway can be divided into 5 layers:

Asynchronous transfer mode ATM