[ History can be used when bragging ]
1. The earliest wide area network
Between two or more parties in communication, a circuit-connected network is established through circuit switching.
Circuit switching network characteristics
1. Establish link -> use link -> release link
2. The physical channel is exclusively occupied by both parties
Computer data appears on the data link in bursts, and the three processes of establishing a link, using a link, and releasing a link in a circuit switching network make the transmission efficiency too low, so circuit switching is not suitable for transmitting computer data.
2. Computer network requirements
On October 4, 1957, the Soviet Union launched the world's first artificial earth satellite, Sputnik, in response to the threat posed by Sputnik. On January 7, 1958, the U.S. Congress allocated funds to establish ARPA (the Advanced Research Projects Agency). Planning Agency)
Requirements for computer networks
1. Not for calling
2. Simple structure and reliable data transmission
3. Ability to connect to different types of computers
4. All network nodes are equally important
5. There must be redundant routing
Packet switching
An exchange method in which data is routed and transmitted through packets marked with addresses, so that the communication channel is occupied only during transmission
The composition of the group:
Each packet consists of a header and a data segment; why?
Exchange method
Exchange mode-store and forward
When the node receives the packet, temporarily store it, and then check its header, press
According to the destination address in the header, find a suitable node and forward it
Features:
- Use packet as transmission unit
- Independent selection of forwarding routes
- Occupy segment by segment, dynamically allocate transmission bandwidth
Think about it: Are the packets received by the node in order?
History of the Internet
The development process from a single ARPANET to the Internet
In 1983, the TCP/IP protocol became the standard protocol of APRANET
Three-tier structure of the Internet (NSFNET National Science Foundation Network)
A computer network built around six large computer centers
Backbone network, regional network, campus network
Multi-level structure Internet
NSFNET is gradually being replaced by commercial Internet backbone
