Circuit, packet and message exchange

1. Circuit switching

1. Development background
   People realize that if you need to connect two phones , You need to n*(n-1)/2 Links , It's huge , So you can use a telephone exchange
   

2. The way a telephone exchange connects telephone lines becomes circuit switching

3. From the perspective of communication resource allocation , Switching is the dynamic allocation of line resources in a certain way

4. Three steps of circuit switching

• Establishing a connection （ Allocate communication resources ）
• conversation （ Always occupy communication resources ）
• Release Links （ Return of communication resources ）

5. When circuit switching is used to transmit computer data , The transmission efficiency of its line is very low , Because of exclusive communication resources

2. Packet switching

1. In the Internet , The most important packet switch is the router , It is responsible for connecting various networks , And forward the received packet

3. Message switching

A little , Since the size of the message is not limited , Each node switch needs a large cache space

4. Three ways to compare