※ 引述《sisay ()》之铭言： : 1 2 3 : 4 5 6 : 7 8 9 : * 0 # : 我记得以前有电影演说可以窃取别人在公共电话拨的号码 : 是因为他 每按一个键有两个tone 只要记住tone的声音就可以反解译出来 : 就是横排有4个音 直排有3个音. 3*4=12 有12个组合 : ...那我要问的是 : 为什麽要有这样的声音存在呢? http://zh.wikipedia.org/wiki/%E5%8F%8C%E9%9F%B3%E5%A4%9A%E9%A2%91 恕我驽钝，不晓得您要问的问题是什麽。 "双音多频信号是贝尔实验室发明的，其目的是为了自动完成长途呼叫。" "DTMF was developed at Bell Labs in order to allow dialing signals to dial long-distance numbers, potentially over nonwire links such as microwave links or satellites. Encoder/decoders were added at the end offices that would convert the standard pulse signals into DTMF tones and play them down the line to the remote end office. At the remote site another encoder/decoder would decode the tones and perform pulse dialing. It was as if you were connected directly to that end office, yet the signaling would work over any sort of link. This idea of using the existing network for signaling as well as the message is known as in-band signaling." --

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