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Circuit switching needs to establish a physical path between the two communicating parties before communicating. |
The message is the unit of data exchange, and the message carries information such as destination address and source address, and the storage and forwarding transmission method is adopted at the switching node |
Based on message exchange, the message is divided into smaller data units: message grouping (also called segment, packet, grouping), using store and forward transmission mode |
| advantage |
① The communication line is dedicated for both users of the communication, and the data is direct, so the transmission delay is small . ② Once the physical path between the two communication parties is established, the two parties can communicate at any time with strong real-time performance . ③When the two parties communicate, the data is transmitted in the sending order, and there is no problem of disorder . ④Circuit switching is not only suitable for transmitting analog signals , but also for transmitting digital signals . ⑤ The switching equipment and control of circuit switching are relatively simple . |
① Message exchange does not need to establish a dedicated communication line for both parties in advance, there is no time delay in connection establishment , and users can send messages at any time . ②Using the storage and forwarding transmission method : a. It is convenient to set up code inspection and data retransmission facilities in the message exchange, and the switching node also has path selection, so that when one transmission path fails, another one can be selected The path transmits data, which improves the reliability of transmission ; b. It is easy to realize code conversion and rate matching in store and forward , and even the sending and receiving parties can not be in the available state at the same time. This facilitates communication between computers of different types, specifications and speeds; c. Provides multi-target services , that is, a message can be sent to multiple destination addresses at the same time, which is difficult to achieve in circuit switching; d. Allowed Establish the priority of data transmission so that the packets with higher priority are converted first. ③The communication parties do not occupy a communication line fixedly, but partly occupy this physical path at different times, thus greatly improving the utilization rate of the communication line . |
① Speed up the transmission of data in the network . Because the packets are transmitted one by one, the storage operation of the next packet can be paralleled with the forwarding operation of the previous packet. This pipeline transmission mode reduces the transmission time of the message. In addition, the buffer required to transmit a packet is much smaller than the buffer needed to transmit a message, so the probability of waiting for transmission and the waiting time due to insufficient buffers are also much less. ② Simplified storage management . Because the length of the packet is fixed, and the size of the corresponding buffer is also fixed, the management of the memory in the switching node is usually simplified to the management of the buffer, which is relatively easy. ③ Reduce the error probability and the amount of retransmission data . Because the packet is shorter, its error probability will inevitably be reduced, and the amount of data retransmitted each time is also greatly reduced. This not only improves the reliability, but also reduces the transmission delay. ④As the grouping is short and small, it is more suitable for adopting the priority strategy to transmit some urgent data in time. Therefore, packet switching is obviously more suitable for the burst data communication between computers. |
| Disadvantage |
① The average connection establishment time of circuit switching is long . ②After the circuit-switched connection is established, the physical path is exclusively occupied by both parties of communication. Even if the communication line is idle, it cannot be used by other users, so the channel utilization is low . ③When the circuit is switched, the data is direct, and it is difficult for terminals of different types, specifications, and speeds to communicate with each other, and it is also difficult to carry out error control . |
① After the data enters the switching node, it has to go through the process of storage and forwarding, which will cause forwarding delay. Moreover, the larger the network traffic, the greater the delay caused. Therefore, the real-time performance of message exchange is poor and it is not suitable for transmission. Real-time or interactive business data. ②The message exchange is only applicable to digital signals . ③Because the message length is not limited, and each intermediate node must receive the entire message completely. When the output line is not idle, it may also store several complete messages waiting to be forwarded. The node has a larger buffer. In order to reduce costs and reduce the capacity of the node's buffer memory, sometimes the messages waiting to be forwarded are stored on the disk, which further increases the transmission delay . |
①Although packet switching has less transmission delay than message switching, there is still storage and forwarding delay , and its node switch must have stronger processing capabilities. ② Packet switching is the same as message switching. Each packet has to add information such as source, destination address and packet number, which increases the amount of information transmitted by about 5% to 10%, which reduces the communication efficiency to a certain extent and increases Processing time, latency increases . ③When packet switching uses datagram services , out-of-sequence, loss or duplication of packets may occur . When the packets arrive at the destination node, the packets must be sorted by number, which increases the trouble. If the virtual circuit service is adopted, although there is no disorder problem, there are three processes of call establishment, data transmission and virtual circuit release. |
