UIT - Secteur de la normalisation des télécommunications ITU - Telecommunication Standardization Sector UIT - Sector de Normalización de las Telecomunicaciones Study Period 1997-2000 Commission d études Study Group Comisión de Estudio 1

双音多频 DTMF（Dual Tone Multi Frequency），双音多频，由高频群和低频群组成，高低频群各包含4个频率。-Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communic

ITU-T Q.931 SERIES Q: SWITCHING AND SIGNALLING Digital subscriber Signalling System No. 1 – Network layer