GSM CALL not getting through while ppp dial up is progress

IoT Modules Legacy HL Series
1

I have facing this issue ,

Setup:
-> I running gsmmuxd to create two virtual port
-> one Port (say HL0) for gsm -At command
-> Another Port (say HL1) for pppd

when i make gsm call on one part and other port call the pppd , it result gsm getting drop & received NO CARRIER.

2

And this is what unit…

3

This is HL8548 module