信号将一系列的方式多频(MF)音调，很像之间互动音频拨号开关。

Signaling took the form of a series of multifrequency (MF) tones, much like touch tone dialing between switches.

youdao

信号将一系列的方式多频(MF)音调，很像之间互动音频拨号开关。

Signaling took the form of a series of multifrequency (MF) tones, much like touch tone dialing between switches.

youdao