Compare the advantages and disadvantages of circuit switching, packet switching, and group Switching

Compare the advantages and disadvantages of circuit switching, packet switching, and group switching. Advantages of circuit switching: both users in a call always occupy end-to-end communication resources. Disadvantages: the transmission efficiency of lines is very low. Most of the communication lines occupied by users are idle, and resources are not used, while consumption group switching advantages: high exchange rate, high data transmission efficiency, high reliability, and High Efficiency, flexible and fast. Disadvantages: delay and overhead Packet Exchange advantages: the user can send packets at any time, reliability, easy to find Code Conversion and rate matching, send multiple destination addresses at the same time, priority packet conversion, high utilization of communication lines. Disadvantage: Long latency. The working principle of CSMA/CD protocol and the Ethernet frame format are briefly described. (1) When the carrier listens to any station to send information, it must first monitor the bus to determine whether there are other station sending signals on the media. if the media is busy, continue detection until it is found that the media is idle. If the detection media is idle, it can be sent immediately. Because of the channel transmission delay, the method of using the carrier listener still cannot avoid conflicts between frames sent by the two sites during the transmission delay. (2) Conflict Detection: each site can detect conflicts during frame sending. Once a conflict is detected, the system immediately stops sending messages and sends a string of blocking signals to the bus, notifying that the bus has conflicted with each other. (3) After multiple access channels detect a conflict and send a blocking signal, the sending site returns and waits. In order to reduce the probability of re-conflict, we need to wait for a random time (different conflicting sites), and then resend it with the CSMA algorithm. It can be summarized as follows: before sending, while sending and listening, conflict stops, delay resend. The Ethernet frame format (MAC frame) consists of five fields. The first two fields are 6-byte Destination Address and source address fields. The third field is a 2-byte type field, the fourth field is the IP datagram, and the fifth field is the frame verification sequence (FCS ).