circuit switching, packet switching, message switching

circuit switching, packet switching, message switching

circuit switching

At the beginning, the two devices are connected by two lines. Although it is very convenient to build when there are few devices, once the number of devices increases, the required lines are extremely large.

Therefore, in order to reduce the waste of resources, a telephone exchange is used, so that each user only needs to connect to the telephone exchange to communicate with other users

When the distance between two users is too far, they need to be connected through a multi-layer telephone exchange

Circuit Switching Steps

1. Establish a connection (allocate communication resources, that is, various trunk lines)

2. Talking (always occupying communication resources)

3. Release the connection (return communication resources)

Summarize

Although circuit switching can theoretically be used to transmit network information, it takes too long to occupy resources and is a waste of resources.

packet switching

The data to be transmitted is converted into a binary file (message) in the computer, and then divided into small blocks of equal length, each block has header information, and the target address is stored in the header information, and the transmission During the process, each router forwards through the destination address stored in the header, and the receiver removes the header information after receiving the packet and splices it to get the sent data

sender

Construct group, send group

router

Cache packets, forward packets

receiver

Receive packets, restore messages

message exchange

Packet switching is actually packet switching without direct transmission of packets, which has been eliminated and replaced by more advanced packet switching

Three kinds of exchange comparison

Advantages of Circuit Switching

• 1) Communication delay is small
• 2) orderly transmission
• 3) No conflicts
• 4) Wide range of application
• 5) Strong real-time performance
• 6) Simple control

Circuit Switching Disadvantages

• 1) It takes a long time to establish a connection
• 2) The line is monopolized and the usage efficiency is low
• 3) poor flexibility
• 4) Difficult to normalize

Advantages of message switching

• 1) No need to establish a connection
• 2) Dynamic allocation of lines
• 3) Improve line reliability
• 4) Improve line utilization
• 5) Provide multi-target services

Message Switching Disadvantages

• 1) Caused forwarding delay
• 2) Large storage cache space is required
• 3) Need to transmit additional amount of information

Advantages of Packet Switching

• 1) No need to establish a connection

• 2) High line utilization

• 3) Simplified storage management

• 4) Speed ​​up transmission

  Accelerated transmission is because the size of each block after grouping is small, so data storage and data forwarding can be performed separately in the router

• 5) Reduce the probability of error and the amount of retransmitted data

Packet Switching Disadvantages

• 1) Caused forwarding delay
• 2) Need to transmit additional amount of information
• 3) For datagram services, there are problems of out-of-order, lost or repeated packets; for virtual circuit services, there are three processes of call establishment, data transmission and virtual circuit release