I have just been forwarded a problem from a company that we provided with two Grandstream phones - one GXP1628 and one GXP2160. While GXP2160 works fine, GXP1628 does not seem to send any sound when calling. Problem is that the RTP packet stop (or reach) at the wrong IP. I am attaching a picture of communication: the upper one is GXP1628 and the lower one is GXP2160.
Thank you for your help.