Similarities and differences between circuit switching, packet switching, and group Switching

Introduction to three exchange technologies

1. Circuit Switching Technology

The network switching technology has gone through four stages: Circuit Switching Technology, packet switching technology, group switching technology and ATM technology. Public Telephone Network (PSTN) and mobile network (including
Both GSM and CDMA networks use circuit switching technology. The basic feature of this technology is connection-oriented.
For a fixed-bandwidth communication circuit, the communication parties will occupy the allocated resources until the communication ends, and the related resources must be used during the establishment and release of the circuit.
Signaling protocol. The advantage of this method is that in the communication process, the user can be guaranteed to provide sufficient bandwidth, and the real-time performance is strong, the latency is small, and the switching device costs are low.
The bandwidth utilization of the network is not high. Once the circuit is established, the allocated circuit is occupied no matter whether the communication parties are in the call status.

2. Packet Exchange Technology

The packet exchange technology is similar to the group exchange technology. It also uses the storage and forwarding mechanism, but the Packet Exchange uses the packet as the transmission unit. Due to the large difference in the message length, long packets may cause
Large latency, and it is also difficult for each node to allocate a buffer. To meet the needs of various length packets and achieve high efficiency, nodes need to allocate different sizes of delay.
Or data transmission may fail. In practical applications, Packet Exchange is mainly used for communication services with short message transmission and low real-time requirements, such as public telegraph networks. Packets
The exchange of group-to-group switching occurs earlier. Group-to-group switching is based on Packet Exchange. packets are divided into groups for transmission, which balances the transmission latency and efficiency.
It is widely used.

3. Group Exchange Technology

Circuit Switching technology is mainly applicable to speech-related services. This network switching method has great limitations for data services. First, data communication is very sudden,
The peak bit rate differs greatly from the average bit rate. If circuit switching technology is used, allocating circuit bandwidth based on the Peak bit rate will cause a great waste of resources.
Allocating bandwidth will cause a large amount of data loss. Second, compared with the voice service, the data service has no strict requirements on latency, but it requires error-free transmission, while the voice signal
It can be distorted to a certain extent, but the real-time performance must be high. The group exchange technology is a kind of exchange method based on the characteristics of data communication services. Its basic characteristic is that it is oriented towards connectionless
The storage and forwarding method is used to divide the data to be transmitted into many small pieces of data according to a certain length, and add the corresponding functions for data selection and verification before the data.
The header field, which is the basic unit of data transmission. With the group exchange technology, no connection is required before communication. Each node first accepts the Group sent by the previous node and
Save it in the buffer zone, and then select an appropriate link based on the address information in the group header to send it to the next node. In this way, you can set the network performance
To dynamically allocate bandwidth. Group switching is more efficient than circuit switching, but has a high latency.

Services provided by group exchange
Switching a virtual circuit refers to a temporary logical connection established between two users.
Permanent virtual circuit-a permanent logical connection established between two users. A permanent virtual circuit is automatically established when the user starts the machine.

Group Switching Network

A datagram network is a connectionless network.

A virtual circuit network is a connection-oriented network that provides connection maintenance information for each connection.

Features and comparison of route, packet, and group exchange

(1) circuit switching: Before communication, a physical channel exclusive to both parties must be established between the two parties.
.
Advantages:
① Because the communication line is dedicated to users of both parties, the data transmission latency is very small.
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.
Advantages and disadvantages:
Advantages:
① For message exchange, no special communication line needs to be established for both parties in advance, and no delay is established for the connection. You can send messages at any time.
② Because the storage and forwarding transmission method is used, it has the following advantages: A. It is easy to set up code verification and data re-transmission facilities in message exchange. In addition, the exchange Node also has the path selection.
When a transmission path fails, you can reselect another path to transfer data, improving transmission reliability. B. It is easy to implement Code Conversion and rate matching in storage and forwarding,
Even the receiving and receiving sides can be in the available status at the same time. 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 data enters the switching node, it must go through the process of storage and forwarding, resulting in forwarding latency (including receiving packets, verifying correctness, queuing, and sending time), and the network
The larger the traffic, the larger the latency. Therefore, the poor real-time message 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 receive the entire packet completely. When the output line is not idle, several complete packets may need to be stored for waiting for forwarding.
Find that each node in the network has a large buffer zone. In order to reduce costs and reduce the buffer memory capacity of the node, sometimes the packets waiting for forwarding must be stored on the disk, 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, group (with the source, destination address, and number)
Messages are sent one by one. Therefore, Packet Exchange has the following advantages and disadvantages compared with Packet Exchange:
Advantages:
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 streamlined transmission mode reduces
The transmission time of the message is reduced. In addition, the buffer zone required for transmitting a group is much smaller than that required for transmitting a packet, so that the probability of waiting for sending due to insufficient buffer zone and waiting
There must be much less time.
② Simplified storage management. Because the group length is fixed and the corresponding buffer size is also fixed, memory management in the SWAp node is usually simplified to the management of the buffer, relatively compared
Easy.
③ Reduces the error probability and resend the data volume. Because the grouping is short, the probability of errors will inevitably decrease, and the amount of data re-sent each time will be greatly reduced, which not only improves the reliability, but also reduces
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 obviously more appropriate for burst data communication between computers.
Some.
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.
It 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
Although there is no out-of-order problem with the use of virtual circuit services, there are three processes: Call creation, data transmission, and virtual circuit release.
In short, if you want to transmit a large amount of data, and the transfer time is much larger than the call time, circuit switching is more appropriate. When the end-to-end path consists of many segments of links, grouping is used.
Exchange