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Must say: Exchange in group

From;    Author:Stand originally

Why to exchange in group

Like all electronic systems, we can regard commutative system as to have many inputs and output " black box " . Nevertheless, an input that exchanges a system and output often very much. We often call these inputs the line, or enter end, call output to output a line, or output end.

The view that the function that exchanges a system can differ with two kinds will describe. A kind of view is, the function that exchanges a system is to be being entered carry and go out link is established between end. Press this kind of view, can think commutative system into one caboodle switch, when mixing to give upright connection to rise into end when need, pull use switch. Another kind of view is, the function that exchanges a system is an information that enters end distribute a line. Press this kind of view, can think commutative system into a big information transfer station, it receives the information on end, next classify ground distributes end.

At first sight, what two kinds of views appear and do not have essence is different. The purpose in the final analysis that establishs link also is for deferent information, and can information from go up into the line serve a line, also was equivalent to rising with join giving a clue into the line. Nevertheless, if we are start with these two kinds of views,try amplify, give two kinds of completely different exchange kind to come with respect to meeting development.

The commutative kind that is a purpose with circuit connection is circuit exchange kind. Circuit is used to exchange means namely in telephone network. We can hit a phone to learn way of this kind of exchange. When calling, it is to pick next word engine to dial above all. Dial end, switching equipment knew to want to communicate with who, establish link for both sides, wait for one party to hang machine hind, switching equipment disconnects bilateral circuitry, begin to communicate newly severally for both sides ready-made. Accordingly, we can be experienced, the movement that circuit exchanges, build when communication namely (namely connection) circuit, when communication ends, demolish (disconnect namely) circuit. As to the content of bilateral in communication process deferent information, with exchange the system has nothing to do.

Telephone switch appears in centenary before, at that time, people still does not have the concept about information, and the circuit link that the phone is exchanged even if wants a both sides rises, this thing is such apparent, so using circuit to exchange means is only alternative of course.

Nevertheless, if we consider carefully, also can discover the defect that a lot of circuit exchange. The most apparent is: Wanted to build a circuit only, so, no matter whether both sides is deferent information (no matter whether both sides is,phonate communicate) , this circuit cannot change him to use, until demolish this circuit till.
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