There are three main types of data switching technology: circuit switching, message switching and packet switching. The advantage of circuit switching technology is that data transmission is reliable and rapid, the data will not be lost and the original sequence is maintained; the message switching method is suitable for non-real-time communication services, such as telegrams. Packet switching can effectively improve the delay phenomenon during message transmission, and the network channel utilization rate is high.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
There are three main types of data switching technologies: circuit switching, message switching and packet switching.
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A communication subnet is a network interconnected by several network nodes and links according to a certain topology. These switching nodes in the middle are sometimes called switching devices. These switching devices do not process the data flowing through them, but simply transmit the data from one switching device to another until it reaches the destination. A subnet is a path that provides a complete transmission path for all data entering the subnet. The technology that implements this data path is called "data switching technology."
Generally, according to the different forwarding methods implemented by network nodes in the communication subnet for data entering the subnet, data switching methods can be divided into two categories: circuit switching and store-and-forward switching. Commonly used switching technologies include circuit switching, message switching and packet switching.
Circuit Switching
The circuit switching (Circuit Switching) method is very similar to the working process of the telephone switching method. Before two computers exchange data through the communication subnet, they must first establish an actual dedicated physical path through the line connection between switching devices in the communication subnet.
The switching network using this method can provide a temporary dedicated physical path for any incoming data. It is composed of each node on the path completing channel transfer in space or time. It is the source host (output end). ) and the host (receiving end) to establish a direct, exclusive physical line. Therefore, during the path connection, no matter how long the line is, the switching network provides data communication on a point-to-point link for a pair of hosts, that is, the devices at both ends of the connection establish an exclusive use of this line for data transmission. until the connection is released. The switching method of the public telephone network uses circuit switching. Once the call is established, the two parties can occupy the line exclusively until the call ends and the connection is released. At this time, other users can use the line.
The advantage of circuit switching technology is that data transmission is reliable and rapid, the data will not be lost and the original sequence is maintained; its disadvantage is that the channel utilization is low, even during the intermittent period of data transmission between two sites, the circuit Nor is it allowed to be used by other sites. Circuit switching is suitable for real-time large amounts of continuous data transmission.
The most important feature of circuit switching is the establishment of a dedicated data path between a pair of hosts. The communication process includes three processes: line establishment, data transmission and line release. A certain amount of call setup time is required when establishing a path. Once the path is established, there is almost no delay at each node, so it is suitable for real-time or interactive conversational communications, such as digital voice, fax and other communication services. However, since the line is dedicated when the path is established, other users cannot use it even if it is idle, so the line utilization rate is not high. Since each node (switching device) in the communication subnet cannot store data or change data content, and does not have error control capabilities, the entire system does not have the ability to store data and cannot detect and correct data errors that occur during the transmission process. , the system efficiency is low. Based on the circuit switching method, people proposed the store-and-forward switching method.
Message switching
Message switching (Message Switching) means that each node (switching device) of the network first receives the entire message (Message) completely And store it, and then select the appropriate link to forward to the next node. Each node stores and forwards the message and finally reaches the destination.
In message exchange, the intermediate device must have enough memory to completely store the entire received message, and then find out the next step of forwarding the message based on the header control information of the message. A switching node. If there is no idle link at the moment, the message will have to be temporarily stored and wait to be sent. Therefore, the delay caused by a node to a message is often uncertain.
Message data is transmitted entirely in a relay manner in the switching network. The communicating parties do not know in advance the transmission path that the message will pass through, but each message does pass through a logically existing path. Because it works in a relay mode, a message only occupies the resources of one link at any time, and does not need to occupy all the link resources on the path, which improves the sharing of network resources. Although the message switching method does not require the process of establishing a line and releasing the line, the storage and forwarding of message data by each node takes a relatively long time. The message exchange method is suitable for non-real-time communication services, such as telegrams; it is not suitable for transmitting real-time or interactive services, such as voice, fax, etc. In addition, since message exchange uses the entire message as a storage and forwarding unit, when an error occurs in message transmission and needs to be retransmitted, the entire message must be retransmitted.
Packet switching
Packet switching is also called packet switching (Packet Switching), which is a store-and-forward switching together with message switching. The difference between the two is that the length of the data units involved in the exchange is different. In a packet-switched network, the data to be exchanged between computers is not transmitted as a whole, but is divided into many data packets of the same size for transmission. These data packets are called "Packets". In addition to a certain length of data that needs to be transmitted, each packet also includes some control information, including the destination address to which the packet will be sent. The maximum length of a packet is usually limited to 1 000 to 2 000 bits. These data packets can arrive at the same destination address through different routers. After the data packets arrive at the destination, they are merged and restored to ensure that the received data is completely consistent with the sent data.
This communication method is similar to the "single page post office" model. Assuming that the single-page post office stipulates that each letter can only use one page, the person who writes a long letter must number each page of stationery and put it in a different envelope; after receiving the letter, the recipient must sort and merge it in the order of the stationery. , to read the complete letter.
In packet switching, according to the different transmission control protocols and transmission paths in the network, it can be divided into two methods: datagram (Datagram) packet switching and virtual circuit (Virtual Circuit) packet switching.
(1) Datagram packet switching. In datagram mode, each message grouping is also called a datagram. Each datagram must choose a path during transmission, and each datagram can reach its destination according to different paths. On the sender side, the order in which each datagram is grouped is different from the order in which each datagram arrives at the destination. At the receiver, these datagrams are combined into a complete message in the order of the groups.
(2) Virtual circuit packet switching. The virtual circuit method attempts to combine the datagram method with the circuit switching method, taking advantage of the two methods to achieve the best data exchange effect. Before a datagram is sent as a packet, there is no need to establish a connection between the sender and the receiver in advance; in the virtual circuit mode, before sending the packet, a path must first be established between the sender and the receiver. At this point, the virtual circuit approach is the same as the circuit switching approach. The entire communication process is divided into three stages: virtual circuit establishment, data transmission, and virtual circuit teardown. However, unlike circuit switching, the path established during the virtual circuit establishment phase is not a dedicated physical line, but just a path. In the process of forwarding each packet along this path, it still needs to be stored and waited for when passing through each node. Queue output. After the path is established, each packet reaches its destination through this path. Therefore, in virtual circuit switching, each packet arrives at the destination in sequence according to the sender's packet order, which is different from datagram packet switching.
Compared with message switching, packet switching divides the entire data to be transmitted into several groups, and each group contains a large amount of transmission control information. Therefore, the communication method of group switching will significantly reduce the data communication s efficiency. However, packet switching has the following three advantages.
① The communication line is public, and each group will not occupy too long of the communication line time, which is conducive to the reasonable distribution of communication lines and takes into account the communication requirements of each host on the network.
② Errors will inevitably occur in data transmission. If there are transmission errors in some packets, you only need to retransmit the packet instead of retransmitting the entire data, which is conducive to rapid data error correction.
③ It can effectively improve the delay phenomenon during message transmission, and the network channel utilization rate is high.
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