Bad lines at times - lost packets- Audio is fine until it reaches 3cx server?

[gafferdan]

Hi,

We have had 3CX installed for over 6 months now and all has been fine up to a point.
We are getting a bad line/connection on some calls (crackly line, bitty conversation etc).
Running Wireshark shows a packet loss on those calls but I cant work out the reason why?

Our SIP provider has sent recordings from their end showing a perfect audio connection so its when the audio comes into the 3cx server that the problem appears.
I have used this forum to check the switches and are 3cx setup and as 8/10 calls work fine i don't think its anything to do with them? The firewall is my suspect.

We are running through a Virgin Broadband and using a smoothwall.

Does anyone have any experience with 3cx and a smoothwall? Got any tips or know what may be causing are issue?

Firewall checker on the 3cx goes through fine and like I said 8/10 calls are perfect.

One other thing to add it its only affecting external calls, all internal calls are perfect.

Thanks

Dan

 

[Alphabetic]

Hi

https://www.3cx.com/community/threads/information-to-provide-when-requesting-help.67558/

Does your firewall use SIP ALG?

 

[gafferdan]

Hi, Its turned off.

Its not affecting every call, 8/10 seem fine and because of that its throwing me.
I would have thought it would be all external calls being bad if I had a network/Switch/Firewall issue?

 

[ChrisC_3CX]

First thing I recommend is trying to narrow this down as much as possible, unless of course you are absolutely sure it is the firewall.

If not, consider the following:

1. Is the audio issue only affecting audio in one direction or both? In other words, is the 3CX user only hearing it or the external caller/callee as well?

2.

Our SIP provider has sent recordings from their end showing a perfect audio connection so its when the audio comes into the 3cx server that the problem appears.

Is the recording of both audio streams (incoming and outgoing) and both are clear?

3. Was the Packet capture performed on the 3CX PBX (via Management Console)?

4.

Running Wireshark shows a packet loss on those calls but I cant work out the reason why?

Just to confirm, how did you determine this, did you analyze the RTP stream and specifically saw RTP packet loss?
If yes, was this the case for both forward and reverse directions?
Also, it depends which RTP stream you analyzed, you should have two call legs for the same call meaning that you should have two RTP streams, one two-way stream between PBX and provider and a two-way RTP stream between pbx and IP Phone/Client. They should have the same audio, it is important that you check both to determine if both or only one of the two is affected. I recommend not only looking at the RTP analysis info but also actually listening to the audio from within wireshark for both streams.

 

[gafferdan]

Hi,
1: its affecting the audio in one direction, (external to internal)
2: Crystal clear both directions
3: Packet capture running on the 3cx server
4: Using the RTP stream i can see "Wrong sequence" pop up on the external to internal side of the call. After double checking both sides of the call its definitely the external to internal having the poor quality. The same call but internal to external is crystal clear.

 

[ChrisC_3CX]

I see, we'll that does narrow it down to at least between the PBX and the SIP Provider. You might also want to consider checking if you can run packet captures both on the LAN and WAN interfaces of the firewall so that you can then determine which of the following three is happening:

1. Issue originates outside of your network.
2. Issue is with the firewall.
3. Issue is within your LAN.

 

[gafferdan]

We are banging are heads on a brick wall at the moment!
We have it nailed down to us hearing the choppy audio when calling or receiving an external call.
The receiver never hears a bad line, for them its crystal clear.

This however does not happen all the time! Sometimes like i said before its perfect.

It cant be an issue with our LAN as internally is always perfect and most of the time so is the external calls!

Any more help would be much appreciated.