GXV3370 person who calls cannot hear us



we use GXV3370. Our ISP installed a new router. Now we have the problem that people who call us cannot hear us, although we can hear them. When we are calling outbound there is no problem both ways, only if someone calls us.

ISP tells us, he was never supporting Grandstream telephones for his routers, so it’s our problem - they cannot do anything for us. Welcome to Germany :slight_smile:

We updated the firmware (both router and telephones). We also looked in this forum for some ideas, but everything seems to be correct. As Codec we use PCMA/PCMU because these are the codecs our provider (Deutsche Telekom) uses. NAT is also at “keep alive”.

Is there anybody who has an idea what we could do inside phone or router configuration to solve this problem?

Thanks a lot!


I could find a solution on my own. You have to activate checkbox “Use First Matching Vocoder in 200OK SDP” in menu “Account>Codec Settings”.


Were you experiencing the 10 to 15 second delay on an incoming call? I hope this will help me out. I’ve been pulling out my hair on this issue…well…if I had hair I’d pull it. Thanks In Advance!