Solved SIP Trunk Doesn't Respond Inbound Unless Dial Out First

[daveking]

Hi All.

I have SIP trunks from 2 providers going into my 3cx. For years they have worked fine, until recently, one of the providers will only accept an inbound call if we make an outbound call first. I have disabled every firewall rule you can think of in terms of IPS and so on, and the link literally goes offline about 3 minutes after the outbound call is made.The calls on the fully working SIP go through the same firewall and is on the same 3cx machine, and is faultless.

Any ideas please?

Thanks

Dave

 

[leejor]

until recently, one of the providers will only accept an inbound call if we make an outbound call first.

Just so I'm clear....A call to your number, will not come through, from your provider, until you place an outgoing call...is that correct?

If that is the case....what does the 3CX Activity Log show when someone calls you in this situation?
Is a call presented to 3CX?

Does the trunk show as registered, in 3CX?
What does the caller hear when this happens?
Have you asked your provider what they see, when they attempt to send a call? It could be either " we are sending an INVITE to you, but get no response", or "we do not see your trunk as registered"

Were any changes made, to anything, about this time this began?

 

[daveking]

Hi

Thanks for the reply.

Yes you are correct on the first point. Every night our SIP goes down, and we have been trying to figure out what it is, and now we have, its when someone makes an outgoing call, inbound works for some time, but as there are lots of outgoing I guess it keeps it awake. But the other SIP does not act like this at all.

Nothing of any use in the log sadly.

Interestingly the SIP trunks that are not working are not shown as registered, but I can dial out and then back in on them. Last week these SIPs took over 200 calls a day once woken up with an outgoing call. When it occurs, it tries to connect and then just does a beep and drops.

No changes from what I remember, it just started happening.

EDIT: I have called the provider, and they say there are no issues there.

 

[leejor]

Interestingly the SIP trunks that are not working are not shown as registered

If the trunk is not being shown as registered in 3CX, then check to see the last time this occurred (successfully), and was attempted (failed). Then check the Activity Log to see if there is an indication as to why the registration failed. DNS error?

Does your provider see the trunk as registered? If not, then that will prevent incoming calls, and they should be able to tell you that, as it is not normal. If they see the trunk as registered always, then they will be sending all calls, and as long as the destination is correct (your IP), then it should show in the Activity Log.

 

[daveking]

Ok thanks, but how is an incoming call working after an outgoing call if not registered?

The last register sent, failed are both blank.

 

[daveking]

Provider has updated my case. However as above the other SIP works flawlessly!

No Response to invites from site

No Response to invites from site

INVITE SDP on port 5060

Issue resolved by making OB call from site

Points to a NAT issue and the PBX making an OB call re-establishes the session allowing IB calls to hit the PBX

EDIT: Also important to note, I have the same SIP added 3 times but with different DIDs on each for different routing and the inbound call to one wakes them all up and they all start working outbound. This has been the config for years and worked, nothing changed.

 

[cobaltit]

I didn't see it posted so I have to ask. Does the firewall checker pass?

 

[daveking]

Well it didn't, as it had the "full cone NAT" error, but it has always had that and always worked. And the other SIP works.

However... I have an Enterprise license, so I just "switched to hosted" and now of course the firewall checks pass, but I still have the same issue.

Do I need to say somewhere in the config I don't have an SBC anymore now I have moved to hosted? We all use the apps now anyway.

EDIT: The SIP provider says the IP is not accepting invites. Yet the other SIP works fine! I have emptied the IP blacklist in case this was causing it.

 

[daveking]

Its fixed, seems the IP just took some time to update at the SIP provider to point to the new hosting.

So certainly a firewall issue at the original host.

Thanks all for your time.

 

[cobaltit]

Thanks for the update. Definitely lots of cases where it works until it doesn't when the firewall check passes. But glad you had the flexibility to move to hosted that it's working out!