For incoming calls, you can use autodetection of the B-channel protocol. The call autodetection procedure detects the call type, uses the right framing and ASYNC/SYNC Conversion Module if necessary in order to present the data to the RAS PPP application like it comes from an analog modem (ASYNC PPP framing). This allows you to use a standard RAS application that serves the incoming calls on the same port, independent from the call type.
In autodetection mode, the TTY proceeds as follows:
It analyzes the BC/LLC if present. If enough information is given in BC/LLC, the appropriate protocol is selected.
If not enough information is given in BC/LLC, the first frame that is received over the B-channel is analyzed and the appropriate protocol is selected.
B-channel data is analyzed and the ASYNC/SYNC PPP conversion module is inserted if necessary.
The following protocols can be autodetected in this way:
HDLC/Transparent/Transparent
HDLC/X.75/Transparent
HDLC/X.75 with V.42bis data compression/Transparent
HDLC/V.120/Transparent
HDLC/V.120 with V.42bis data compression/Transparent
V.110/Transparent/Transparent
Analog Modem with full negotiation (up to V.90 central office)/V.42+V.42bis or V.42 or Transparent - buffered mode/Transparent
PIAFS/PIAFS/Transparent
If the Diva Media Board is operated on broken ISDN links that provide wrong call-type information over the signaling channel, it might be necessary to force the Diva TTY driver to handle the incoming calls in a specific way independent of the signaled call type. This functionality is provided by the AT+iE command that affects the virtual TTY interfaces exposed by the Diva TTY driver and can be changed only by unloading the driver or issuing another AT+IE command. See AT-Command Set for more information on the commands.