Solved 3CX not responding to some SIP INVITES

[ausip]

Hi All,

We have a bizarre situation that we are trying to get to the bottom of. We have SIP calls coming in from the Vodafone mobile network that 3CX is not responding to. SIP INVITES come in, but 3CX does not respond. All other carriers seem to be OK. When switching logging onto Verbose we are not seeing the SIP invites in the activity log, but we are seeing the packets hitting the VM's interface when doing a packet capture from the CLI. Below is a screenshot of 2 test calls that 3CX isn't recognizing / responding to. (sorry numbers and IP's redacted for privacy)

I am assuming a 3CX ticket in this case will be a waste of time and money as it's not a supported SIP provider. In saying that, it's a provider we've been using for years with no issues.

I need to try and work out why 3CX isn't accepting / responding to these SIP invites so I can pass information on to the trunk provider for further troubleshooting.

 

[leejor]

We have SIP calls coming in from the Vodafone mobile network that 3CX is not responding to. SIP INVITES come in, but 3CX does not respond. All other carriers seem to be OK.

Just to be clear...callers from only the Vodafone network cannot reach you, but all other callers, mobile and landline can?
Who is your provider (it is, after all, their network the calls are going to), and, have you contacted them for an explanation?
Your provider should be passing on Invites, from all callers in an identical manner, with the only difference being the caller ID (and perhaps, DID information). If you are experiencing differences because of the origin of the caller all the more reason to put this in your providers lap.

 

[ausip]

Yes it only seems to be calls originating from the Vodafone network. I have a prepaid vodafone mobile specifically purchased for testing this that I can replicate the issue on. Looking at INVITE packets from calls that work and incoming calls from the Vodafone mobile, there is nothing out of the ordinary that suggest that 3CX shouldn't respond to the Invites.

I have pushed this back on the upstream provider, but they are pushing back saying that the INVITES are being sent and reaching the 3CX systems, yet 3CX is not responding. They are still happy to assist and investigate, but have requested that I try and find out why 3CX is not responding to these invites.

 

[YiannisH_3CX]

1. Run a capture from the 3CX interface and make a call from the Vodafone network. Check if you see if the Invites hitting the system.
2. Check your blacklist. See if any IPs are blacklisted which should not be.
3. Make another capture of a call coming from a different network and put them side by side. Do you see anything different?

Calls may originate from different networks but they coming to you from the same provider so the general format should be the same. Check for any differences in headers or source IPs etc and see what may be causing the issue.

 

[ausip]

The only differences I could find are in SDP data.

Vodafone SDP from INVITE


Optus SDP from INVITE

 

[lancerichards]

Looking at your capture, it seems your incoming call is Vodafone > Symbio > You

Test your trunk on another system or standalone on a softphone.

If the issue can be replicated, then raise this with your carrier.

I certainly am not seeing any calls from Vodafone failing and we process hundreds of thousands of minutes a day.

Best,
Lance

 

[ausip]

We solved the issue. There was a problem with our Softswitch. Our software provider finally worked out what the issue was. There was a restriction on SIP packet sizes and the Vodafone INVITE packets are longer than the rest due to the additional Media Attributes. It seems the packets must have been getting trimmed and 3CX must have been seeing them as incomplete and ignoring them.

 

[NicholasP_3CX]

Good to hear that you got it sorted, and thanks for reverting back with what the issue was. You're the MVP!