作者milop ( )
看板ask-why
標題Re: [請益] 按鍵式電話的問題
時間Sat Mar 11 08:06:43 2006
※ 引述《milop ( )》之銘言：
※ 引述《sisay ()》之銘言：
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: 我記得以前有電影演說可以竊取別人在公共電話撥的號碼
: 是因為他 每按一個鍵有兩個tone 只要記住tone的聲音就可以反解譯出來
: 就是橫排有4個音 直排有3個音. 3*4=12 有12個組合
: ...那我要問的是
: 為什麼要有這樣的聲音存在呢?
http://zh.wikipedia.org/wiki/%E5%8F%8C%E9%9F%B3%E5%A4%9A%E9%A2%91
恕我駑鈍，不曉得您要問的問題是什麼。
"雙音多頻信號是貝爾實驗室發明的，其目的是為了自動完成長途呼叫。"
"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:就是按鍵按下去為什麼要有那些聲音 恩的 03/11 01:11
2F：→ sisay:這邊有答案了 ;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.
簡單的說，用DTMF只是一種傳送技術。
至於為什麼要選用這種技術，我就不清楚了。
而我猜你的問題應該就是要問這個。(為什麼要選用這種技術)
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