作者milop ( )
看板ask-why
标题Re: [请益] 按键式电话的问题
时间Sat Mar 11 08:06:43 2006
※ 引述《milop ( )》之铭言：
※ 引述《sisay ()》之铭言：
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: 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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1F：推 sisay:就是按键按下去为什麽要有那些声音 恩的 03/11 01:11
2F：→ sisay:这边有答案了 ;d 03/11 01:12
http://en.wikipedia.org/wiki/Dual-tone_multi-frequency
DTMF is an example of a multifrequency shift keying (MFSK) system.
简单的说，用DTMF只是一种传送技术。
至於为什麽要选用这种技术，我就不清楚了。
而我猜你的问题应该就是要问这个。(为什麽要选用这种技术)
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