A short description of my system.
We have a VitalPBX in Google Cloud and connect to it on several location.
On the location where the problem is noticed the most, I have 2x Gigaset N870 IP Dect Basestations + about 7x Gigaset SL750H Handset. Call waiting is enabled on VitalPBX and DECT phones. As router I use a Draytek 2926 with SIP ALG off and QOS on for VOIP.
When I call the loction the quality of the connection is good, however when a second or third call starts ringing, the quality of the call drops during every ring.
So the call is degraded for 0.5 -1 seconds during every ring. This makes it heard to hear the customer when he or she is telling us the article number he/she is looking for.
(I think) when the calls are answered the good quality of already established call returns.
I have set the codec on the incoming trunk on: G722, G729 en Ulaw and Alaw.
Does anyone have some idea what could cause, the active call quality to degrade when the other incomming lines are ringing ?
I did some test calls at night, when no one was at the location.
We use an IVR to choose between 2 departments, after choosing, the caller is put on-hold in a queue and the Music On Hold is played.
I have noticed that when no one is around the playing of the MOH still has some distortions (somewhat ruling out the problem is created by the employees).
Our MOH is a MP3 file.
Could it be that the processing of the MP3 file has glitches (memy use = 40% and cpu <10%) ?
Should I use another format than the MP3 format, if so what format would be best used with VitalPBX use ?