scope:

This European Telecommunication Standard (ETS) specifies how narrowband (Integrated Services Digital Network (ISDN) or Public Switched Telephony Network (PSTN)) videophony terminals without data-facility can access interactive audio-visual retrieval services. To control the retrieval process, the terminal should support some interactive protocol between the end user and the service centre. For ISDN videophony terminals, the solutions using inband signalling via Dual Tone Multi Frequency (DTMF), CCITT Recommendation Q.23 [1] in the audio stream and the use of transmitting Single Byte Extension (SBE) control and indication messages (ETS 300 144 [5]) are specified in this ETS. In the case of the PSTN, use of transmitting UserInputIndication (UII) via ITU-T Recommendation H.245 [23] messages in the control channel is specified. In I-ETS 300 837 [4], this user input is not considered as data capability.