Data Switching

Data in multiple Data Switching refers to a DTE for between any two terminal equipment, building Data communication temporary interconnect pathways process called Data exchange.

classification

Data exchange can be divided into: circuit-switched; Packet switching and packet switching. Circuit switching principle and basic same telephone exchange principle. Circuit switching drawback is circuit, the parties in communications utilization rate is low in the process of idle time, circuit cannot be used fully. Packet switching principle is when the sender information reached a message switching of computer, at first, to stay in external storage, determine the central processor analysis header, and choose to forwarding routing with corresponding output electricity by turning on line, waiting on the output. Once the circuit spare, immediately be removed from external storage after message out, it improves the utilization rate of this circuit. A message switching although improves the utilization rate of circuit, but a message via store-and-forward will generate large delay. Packet switching is also a store-and-forward exchange with a message switching approach, but the message is different, it is divided into certain length, the group by group as a single unit store-and-forward. This will not only have a message switching mode the advantages of improving circuit utilization, and overcome delay big shortcoming.

Circuit switching

When the user data transfer between, between users exchange center in establishing a temporary data circuit. Circuit after connect, user data transfer, both sides will occupy to transmission, and have been finished dismantling circuit so far. Circuit switching into delay are small and without processing of data switches, and suitable for transmission good real-time performance and batch large data.

Packet switching

Are generally using a computer to realize. Mail end users first put to-be-sent data encoded message, along with receiving mail address and other auxiliary data all sent to local exchange center, where they store intact and appropriate treatment. When local exchange center, when the jammer are free to the next message transmitted to exchange center of received signal, finally by the exchange center will message transfer to the user. Message switching advantage is: (1) transmission high reliability, it can effectively using error calibration and retransmission technology; (2) the line is high efficiency, it can take multiple low-speed circuit is concentrated into high-speed circuits transmission, and can make multiple users sharing a channel; (3) use flexible, it can undertake code transformation, rate transformation, and it work such as pretreatment in type, rate, procedures between different terminals data transmission. But, message exchange is not suitable for conversational and real-time demand higher business. According to general message exchange the data transfer important and urgent degree, divided into different preferences to transmission.

Packet switching

introduction

The data segmentation into several shorter length (usually less than 128 characters) in group, each packet data and information within outside also includes except in switch control information, they exchanged within as a whole. Each packet switching transmission path in the different within. Packet switching also USES store-and-forward technology, and error inspection, retransmission, return to send response operation, finally receiving mail all the grouping the receiving the mix in sequence data.

advantages

Compared with message exchange, packet switching advantage is:

(1), generally in exchange in message transmission delay is every node receiving and forwarding on the sum of the whole message, while in delay, a grouping of packet switching to send a node, can then send the next packet, so total delay is decreased;

(2) each node need buffer capacity reduced, it is helpful to improve the utilization rate of storage resources node;

(3) directs a mistake, as long as transmission resend one or several group, need not reissue the whole message, so that it can improve the transmission efficiency. Packet switching shortcoming is each packet to add some control information, it makes transmission efficiency decreases, especially in long message for them. General packet switching provides a virtual circuit and data reported two basic operations.

Basic classification

(1) a virtual circuit: in data exchange, by sending end before the Internet address sure path and logical channel, and will be connected each logical channel constitute a virtual circuit. A virtual circuit is different from entity circuit. Once established shall occupy entity circuit this circuit, and whether data transmission. But a virtual circuit only in the transmission of data to occupy, namely is only dynamically using entity circuit, data packet along a virtual circuit transmission, its reception sequence and sending sequence is the same. Data transmission is dismantled after this the virtual circuits. This kind of a virtual circuit called exchange virtual circuits (SVC). If in particular between users permanently establish a virtual circuit, there's no establishment and demolished a virtual circuit process, and the only data transmission process. This kind of a virtual circuit called permanent virtual circuits (PVC). A virtual circuit method is suitable for communication time longer interactive session handling. CCITT (CCITT) suggest it as packet-switched public data networks. The basic business way

(2) data report: requirements for each data packet have mail the letter and receive all the network address of each grouping nodes switches to determine each packet transmission path, in net along a different path transmission, such groups receiving order and sending sequence might be different. Sending end to receive the grouping of to sequential change, can return to the original message. Data submitted suitable for transmission method is to contain only a single packet of short message, such as status information, control information, etc.