I need to do a firmware update for some products based on HL7692.
Today, our system is working only on 2G, and we would like that it works in 4G with a 2G fallback.
So , we changed AT+KSRAT=1 (GSM only) to AT+KSRAT=9 (Searching LTE first then GSM).
In this setup, I’m able to do a voice call from my modem to any public phone, and after a longer time than in 2G, the communication is established: I can speak in both ways. I think that the modem at this moment is shifting from 4G to 2G to do the voice call, that it’s normal because it doesn’t have the VoLTE, that should explain the additional delay.
BUT, in this configuration, when I try to do a voice call from any public phone to my modem:
- it’s ring twice in the phone loudspeaker, and the call is automatically ended after 2 rings.
- nothing append on the AT serial port: there are no any event
So, that it’s normal, or do you have an idea that waht I have to do to be able to have some incoming voice call in 4G fallback 2G ?
Thanks to you