Azure Hosting and Skyetel Trunk

[Wilbo]

I've got an issue with a Skyetel trunk for a 3CX host on Azure. I am getting a bunch of "temp failures" on call logs from Skyetel which their support tells me means the call couldn't reach our 3CX host. Inbound callers are reportedly calling multiple times before they can finally get through. Its very intermittent can go a day with only 1 failure or you will have a day with 50% of total calls failing. Outbound calls are all working just fine. So far this is only isolated to the Azure hosts we have and the failures don't correlate with each other. Hosts are sized at Standard B2s. All these hosts were backed up and converted from on-premises debian installs to Azure hosting.

I've gone through all the troubleshooting I can think of at this point:

• Followed the azure hosting setup guide on https://www.3cx.com/docs/pbx-azure-marketplace/ including setting up the swap.
• Confirmed the network rules are setup properly. Firewall test passes.
• Ran packet capture. No packets from the "temp failures" are even reaching the VM. 3CX doesn't report any of the failures in call logs or activity log.
• Re-setup the host from scratch on a new VM.
• Changed from UDP to TCP communication for the trunk.

I am completely out of ideas. Any suggestions for things to try or check? Anything about deploying in Azure that isn't explicitly stated in the setup guide?

I am currently in the process of setting up hosting on Digital Ocean and going migrate a backup of the tenant just as a test to see if its something in the original configuration that still carries over to the new host.

 

[bjeung]

You need to switch to TCP due to UDP packet fragmentation. That means no SIP registration as they only support that over UDP. There's an article on it in their support section

 

[Wilbo]

You need to switch to TCP due to UDP packet fragmentation. That means no SIP registration as they only support that over UDP. There's an article on it in their support section

I assume by they/them you mean Skyetel. I see this troubleshooting article which mentions

"If Azure is your PBX host, their support are aware of a VOIP issue within their routing. Azure recommends changing the transport protocol from UDP to TCP in Skyetel and in PBX settings to workaround their VOIP routing issue at this time."

I've done this with no improvement as stated in my post but, your adding to not use SIP registration w/ TCP. I don't see where they mention anything about SIP registration not working over UDP but, I will give that a try and see where we get. Thanks.

 

[bjeung]

Sorry, I read quickly and didn't see you mention TCP. When you said you switched from UDP to TCP, was this on the Skyetel side or the 3CX side? If on the 3CX side, that only forces 3CX to use TCP outbound. You want TCP inbound which means making an IP authenticated trunk and selecting TCP on the Skyetel side. So IP auth trunk + TCP on both sides.

 

[Wilbo]

No problem. Switched on the Skytel side to TCP. Default trunk settings in 3CX are set to auto-discover. I did leave the SIP auth which seemed to be the suggested configuration but, I will switch to using IP auth w/ TCP and see where that's gets me. Thanks.

 

[Wilbo]

Just to follow-up on this in case anyone else runs into this issue.

It is 100% the trunk settings and I could not find any documentation that addressed this directly in any kind of meaningful way. The 3CX and Skyetel documentation for trunk configuration both use SIP credentials with routing via username as the method. This is not the best way to do it if you are using these services.

The most stable and reliable configuration is using IP authentication with TCP set as the default protocol to 100% avoid communication issues regardless of your hosting configuration.

I feel like 3CX documentation should be updated to reflect this for the Skyetel trunk config guide and should definitely mention this in the azure hosting configuration guide.