3CX Delay On External Calls

[plumyeti]

Hi all,

 

Looking for some advice on a strange VoIP issue at our school.

We recently had a new 3CX system installed by a contractor (hosted instance on AWS Lightsail, v20 Update 8A). Yealink T85W handsets are being used as SBCs.

We’re seeing a consistent 0.5–1 second delay on outbound audio only when calling external numbers.

In simple terms:

• Internal extension-to-extension calls are fine

• Inbound external calls are fine

• Audio from our users/LAN out to external callers is delayed

• Audio coming back in is fine

• Delay affects handsets and Windows app

• No delay when using the browser web client

Checks completed

• Tested across multiple phones / locations

• Core/access switching checked with no obvious faults

• Required ports confirmed open

• Direct test with a handset connected at the firewall still showed delay

• Firewall is externally managed and no obvious issues have been reported

• Browser web client works normally

Question

Has anyone seen a case where native clients / handsets have outbound delay, but the web client is fine?

Wondering if this could relate to SBC tunnel traffic, client type, or WebRTC vs native handling.

Any thoughts appreciated.

[mbedford]

We implemented 3CX in the last 6 months.  We had similar issues, mostly with call audio quality, but also a bit of delay issues.  I put the cause down to some part of the call chain (caller to callee) having to transcode between different codecs.  So where the two ends of the call cant negotiate a supported codec, the system has to convert which may cause delay (I am just applying a bit of common sense thinking here, i could be completely wrong!)

 

After playing around for a bit, ended up with the following codec lists and ordering that seems to be working well for us

 

I would contact your SIP provider (we are Gamma) and see which codec's they recommend.  Check which one's your handsets can support and if there is a match, put that near the top of the lists.  My thinking with the above setup that we have was this (again, I could be talking complete BS!)

 

LAN codecs - Primarily desk phone to desk phone, high bandwidth connections, so i chose supported codecs by our handsets (Fanvil) and ordered them based on higher bandwidth and voice clarity first.

 

WAN codes - External calls?  People on a WAN link with lower bandwidth availablity, I went for codec's supported by our SIP provider and also ones which prioritised better compression and lower bandwidth, but still a suitable level of voice clarity.

Edited April 14 by mbedford

[plumyeti]

I passed on your suggestion to our phone company and they made the changes but with no differance. I beleive we are also using Gamma.

 

3CX still think it's network related and suggested putting a priority in for UDP 5090 which I have done with no differance.

 

As i have no control over the firewall there is no way to see if that is the issue or bypass to prove it is not our switches.