Circuit Switching packet switching group Switching

The differences between circuit switching and group switching and their advantages and disadvantages are briefly described.
Answer: 1) circuit switching: prior to communication, circuit switching requires the establishment of a physical path exclusively exclusive to both parties (composed of the switching devices and links of both parties). Therefore, it has the following advantages and disadvantages. Advantages: ① because the communication line is dedicated to users of both parties, the data transmission latency is very small because the data is direct. ② Once a physical path is established between the communication parties, the two parties can communicate with each other at any time in real time. ③ When both parties communicate, data is transmitted in the sending order, and there is no out-of-order problem. ④ Circuit switching is applicable to both analog signal transmission and digital signal transmission. ⑤ The switching equipment (switches, etc.) and control of circuit switching are relatively simple. Disadvantages: ① The average connection establishment time of circuit switching is too long for computer communication. ② After the circuit switching connection is established, the physical path is exclusive to both parties. Even if the communication line is idle, it cannot be used by other users. Therefore, the channel utilization is low. ③ When the circuit is switched, the data is directly transmitted. It is difficult for terminals of different types, specifications, and rates to communicate with each other and to control errors during communication.

(2) packet exchange: the Packet Exchange is a unit of data exchange. The packet carries information such as the destination address and source address, and uses the storage and forwarding transmission method at the exchange node, therefore, it has the following advantages and disadvantages: ① Packet Exchange does not need to establish a dedicated communication line for both parties in advance, and there is no connection delay. Users can send packets at any time. ② It has the following advantages because it adopts the storage and forwarding transmission mode:. in Packet Exchange, it is easy to set up code verification and data re-transmission facilities. In addition, the exchange Node also has a path selection, so that when a transmission path fails, you can reselect another path to transmit data, improves the reliability of transmission; B. it is easy to implement Code Conversion and rate matching in storage and forwarding, and even the sending and receiving sides can be available at different times. This facilitates communication between computers with different types, specifications, and speeds. provides multi-target services, that is, a message can be sent to multiple destination addresses at the same time, which is difficult to implement in circuit switching; D. data transmission priority can be set up to enable conversion of packets with higher priority. ③ The communication parties do not possess a fixed communication line, but partially occupy this physical path in different periods of time, thus greatly improving the utilization of the communication line. Disadvantages: ① as the data enters the switching node, it must go through the process of storage and forwarding, resulting in forwarding latency (including receiving packets, checking correctness, queuing, and sending time ), the larger the network traffic, the larger the latency. Therefore, the poor real-time Packet Exchange is not suitable for transmitting real-time or interactive business data. ② Message exchange is only applicable to digital signals. ③ Because there is no limit on the packet length, each intermediate node must completely receive the entire packet. When the output line is not idle, several complete packets may need to be stored for waiting for forwarding, each node in the network must have a large buffer zone. In order to reduce costs and reduce the buffer storage capacity of nodes, packets waiting for forwarding are sometimes stored on disks, further increasing the transmission latency.

(3) group exchange: the group exchange still uses the storage and forwarding mode, but a long packet is first divided into several shorter groups, then, these groups (with source, destination address, and serial number information) are sent one by one. Therefore, Packet Exchange has the following advantages and disadvantages compared with Packet Exchange: ① accelerated data transmission over the network. Because groups are transmitted one by one, the storage operations of the last group can be parallel with the forwarding operations of the previous Group. This pipeline transmission method reduces the transmission time of packets. In addition, the buffer zone required for transmitting a group is much smaller than that required for transmitting a packet. In this way, the probability of waiting for sending due to insufficient buffer zone and the waiting time are also much less. ② Simplified storage management. Because the group length is fixed and the corresponding buffer size is also fixed, memory management in SWAp nodes is usually simplified to buffer management, which is relatively easy. ③ Reduces the error probability and resend the data volume. Because the grouping is short, the error probability is inevitably reduced, and the data size of each re-transmission is greatly reduced, which not only improves the reliability, but also reduces the transmission latency. ④ Because grouping is short, it is more suitable for adopting priority policies to facilitate timely transmission of some urgent data. Therefore, grouping exchange is more appropriate for burst data communication between computers. Disadvantages: ① although Packet Exchange has less transmission latency than Packet Exchange, there is still a storage and forwarding latency, and its node switches must have stronger processing capabilities. ② In the same way as Packet Exchange, each group must add information such as the source, destination address, and group number to increase the amount of information transmitted by about 5% ~ 10%, to a certain extent, reduces the communication efficiency, increases the processing time, makes the control complex, and increases the latency. ③ When the group exchange uses the datagram service, unordered, lost, or duplicate groups may occur. When the group reaches the destination node, sort the groups by number, which increases the trouble. If virtual circuit service is used, although there is no out-of-order problem, there are three processes: Call creation, data transmission, and virtual circuit release. In short, if the data volume to be transferred is large and the transfer time is much higher than the call time, circuit switching is more appropriate. When the end-to-end path consists of many segments of links, it is more appropriate to transmit data through group exchange. In terms of improving the channel utilization of the entire network, packet switching and packet switching are superior to circuit switching. packet switching has lower latency than packet switching, and is especially suitable for burst data communication between computers.