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In the long-distance data transmission, in addition to the direct connection between the transmitter and receiver, a large amount of data transmission margin must pass through the connection and forwarding of several intermediate nodes. Data exchange technology is the technology of how to exchange data when it passes through intermediate nodes. In the data communication of computer network, a large amount of data transmission needs to go through multiple "data exchanges" Website Design Services.

There are three common data exchange modes: line exchange, message exchange and packet exchange.

1. Line switching

Line switching, also known as "circuit switching", is a connection oriented service. That is, before communication, both communication parties should establish a temporary special physical connection channel to achieve data transmission between both parties. After data transmission, the occupied channel is released. The most common line switching application is the telephone system.

As shown in Figure 2-10, the input end of the request communication calls the requested output end; After the line is connected, the middle switches are responsible for establishing a physical path between the two; The communication between the two sides is completely transparent transmission, and its communication content and format are not restricted by the switch, nor do they need intermediate transformation, storage and other processing.

The advantage of line switching is that the data transmission is reliable, rapid, real-time, and maintains the original data sequence. However, once the communication parties occupy a channel, other users can no longer use it, resulting in waste of resources and increased communication costs. Therefore, line switching is suitable for real-time data transmission systems with long connection time and large batch, such as digital voice, fax Marketing website construction And other services. In addition, in the line switching mode, it is difficult for different types of devices with different speeds to work together, so this switching mode is not suitable for data communication in computer networks.

2. Message exchange

Message exchange belongs to the exchange mode of store and forward. The communication parties do not need to establish a special data channel in advance. It is to send the sent data to the intermediate switching equipment as a whole message (with variable length) with the target address, source address and other information attached; The intermediate switching equipment uses the store and forward transmission mode to cache the message first, then select an appropriate idle line according to the target address of the message to forward the message to the next switching equipment, and then forward the message one by one until the data is sent to the destination, as shown in Figure 2-11.

3. Packet switching

Packet switching improves on the message switching technology. It divides the message data transmitted by the user into a certain length (with a length convention), which is called a packet. A packet header is attached in front of each packet to indicate the address information such as where the packet data comes from and where it is sent, and then the packet switch forwards it to the destination according to the address mark of each packet data.

Features of packet switching:

1) The maximum length of data transmission is limited, thus reducing the storage space required by packet switching equipment.

2) Packet is a smaller transmission unit. Only the wrong packet will be retransmitted instead of the whole message, which greatly reduces the retransmission ratio and improves the switching speed.

3) After sending the first packet, the sender can continuously send the subsequent packets. These packets may choose different paths to be received, processed and forwarded by the intermediate packet switching equipment, greatly improving the transmission rate. Now the data communication technology of computer network adopts this data exchange mode.

The three exchange modes are compared as follows:

As shown in Figure 2-12, the longest channel connection time is line switching, while packet switching is the shortest; The maximum delay of information transmission is message exchange, the delay of packet exchange is much smaller, and the minimum delay should be line exchange. Therefore, if the transmitted data carrier is large and the message transmission time is much longer than the call time, line switching is more appropriate; On the contrary, packet switching should be adopted. From the perspective of channel utilization of the whole line, packet switching and packet switching are better than line switching. Because packet switching has less delay than message switching, it is more suitable for burst data communication between computers. Message switching has a large delay, so it is not suitable for real-time data transmission.

The three exchange modes are compared as follows

Data exchange technology

Date：2015-06-23 Source: Shangpin China Type: website encyclopedia
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