Call quality after picking up call that has been on hold for a while

We have a issue that has been happening since we went live with our freepbx install.

I used the .iso image to install ( a while back )
Currently, the system reports:


We have 8 SIP trunks.

The system is: Intel® Pentium® Dual CPU E2200 @ 2.20GHz with 3gig of memory.

We have 1 .mp3 track that we play when the user is on old.

We have SNOM phones with the latest SNOM firmware installed.

when a customer is placed on hold and the hold goes on for 10 minutes or more when we pick
the call back up, the call quality on the call has degraded. We’ve been told that our
voices ( when we talk to the customer on the phone ) sounds ‘robotic’. We can here them
just fine… it’s our voices that sound mechanical to them.

I don’t see any errors in the asterisk logs… not sure what to look for on the
SNOM sip logs…

We ONLY have SNOM phone… not sure if this is a SNOM issue or asterisk or hardware or what…

Any idea on how to debug or fix this would be appreciated.


I suggest to try a different phone first. I know you said you only have SNOM but for this test you can use a softphone. This will help you narrow down the cause of the problem.

What type of internet connection do you have?
upload & download speed.

What type of firewall are you using? does it support QOS?

Does your ISP maintain QOS?

I’ve got a 4 bonded T1s ( 6mbs up and down ). I use iptables on a linux firewall to
give my pbx box the higest priority for packets on the firewall. I have 8 SIP Tunks.

I can make 4 outbound calls to my self so that I have all 8 trunks active to my SIP
provider. I start my music on hold so that I can ‘hear’ the music on the 4 speaker phones
that make the call.

I then start a file transfer… to stress the network… I don’t have any quality issues
on the phones doing a test like this so I’m thinking that this setup should be ‘ok’…
maybe not optimal… but ok… the CPU on the pbx linux box stays under 4%. The box
doesn’t do anything but be the PBX.

Now… to reproduce this long hold issue… I called myself from an outside line and answered
using a softphone app. No SNOM phone was involved. I placed my call on hold for 30 minutes.
During that time… the music on hold played through my softphone just fine. I didn’t have a
microphone on my soft phone so I TRANSFERRED the call to my SNOM IP Phone extension. Prior to
makeing the transfer, the phone quality on the music on hold was fine.

One I made the transfer and answered on the SNOM phone, I started having audio quality issues
on the call. The voice coming from the PBX/SNOM part of the conversation was choppy. The 'choppy’
part only started AFTER the transfer/pickup. I placed myself back on hold, and then took my self
off of hold after about 10 seconds and the call quality was fine… what ever the issue was… it
seemd to fix it self.

I will do some more testing using JUST soft phones and maybe just an INTERNAL call that doesn’t
go over the SIP trunks… see if I can figure out what is needed to reproduce this easily.

so… since the quality ( to the caller ) is GOOD after being on hold , I do the ransfer…
and now the the quality is BAD… I put myself on hold for 10 seconds or so… pick back up
and the quality goes back to GOOD… what does that tell me / us?

Thanks - jack

That’s a strange situation. I think your heading in the right direction use what you can ( softphone ) to try to see if it’s possibly related to the snom phones.
I would also consider downgrading a phone one version of firmware in case it’s a newly introduced problem.

If you have to try another phone, I would suggest a Cisco SPA504G, they provision perfectly, have nice features and a reasonable price. I would tell you to come borrow one if you were in Miami.

Are you using G729 or G711?

The last thing is to possibly try, is dropping a different sip trunk in there.
I can put one of my numbers on there and see if that eliminates the problem.
Who is your current trunk carrier? you can pm me if you don’t want to say it here.