27.0073GPPAT command set for User Equipment (UE)Release 18TS
The "Voice Control Interim Standard for Asynchronous DCE", TIA IS‑101, contains some commands that are useful when passing audio "data" (that is, data which represents audio information) between the computer and the TA.
Some of the following clauses describe commands from IS‑101 which are central to this TA application. However, with the exception of necessary extensions, these descriptions are not intended to replace the definitions found in IS‑101. Other novel commands from the interim standard are not included because they are peripheral to TA operation.
NOTE 1: IS‑101 also uses ITU‑T Recommendation V.250  AT commands, but these are not mentioned here.
The standard specifies the following modes:
‑ command mode, where there is no transfer of audio "data" between the TA and the computer. In command mode, the computer is neither sending audio data to the TA nor receiving audio data from the TA.
‑ transmit mode, where audio "data" is being transferred from the computer to the TA. No audio "data" is transferred from the TA to the computer in this state. A transition back to command mode occurs when an embedded command indicates "end of play" or "flush data", or an inactivity timer times out.
‑ receive mode, where audio "data" is being transferred from the TA to the computer. No audio "data" is transferred from the computer to the TA in this state. A transition back to command mode occurs when any command is sent from the computer, or an inactivity timer times out. During the receive mode, the TA embeds result codes into the audio "data". These result codes indicate pertanent events such as "silence detected", "busy detected", and so on.
Strictly, the standard specifies another mode (translation), but this is not directly of interest here.
NOTE 2: The TA "knows" the type of an incoming call (whether it is voice, data, fax, whatever), and certain POTS events cannot occur. Hence some standard result codes for indication of events and discrimination of call type are unnecessary.
There are three possible levels of service:
‑ a TA supporting level A performs the following operations and detects the following events: audio transmit, audio receive, DTMF detection, DTMF generation and single tone generation. The following indications are supported:
Event Description Handset state
3 ring idle
4 DTMF received idle
5 receive buffer overrun receive
6 unsolicited fax request idle
8 phone on/off hook idle
9 presumed hangup receive
10 presumed end of message receive
18 ringback idle
19 busy idle
23 playback buffer underrun transmit
25 fax or data request acknowledged idle
‑ a TA supporting level B performs the operations and events of level A, and also supports DTMF detection while in the transmit state.
‑ a TA supporting level C performs the operations and events of level B, and also supports double DTMF tone generation.
Since DTMF detection and generation cannot be guaranteed over current digital networks, it follows that none of the three levels of service can be supported.