Solved No Incoming Calls

[Scott EIT]

Hi,

Had an on premise installation working fine for a week now but since last night, when calling into the site we receive a line busy. Outgoing calls working perfectly well. I'm inclined to think it's an issue with the SIP trunk. Just started using this provider with this install so not sure how reliable they are. Given it was working ok and hasn't had any config changes I'm of the belief it must be something their end but not sure how to prove this.

Any help or troubleshooting on how I can prove it's not an issue with the PBX would be greatly appreciated.

 

[AWS2P]

Hi,
is your trunk Green connected?
Is it a supported SIP provider?
Is firewall checker passed green?
What kind of audio do you hear when line busy? coming from provider or 3CX?

 

[Scott EIT]

Hi,
is your trunk Green connected? Yes
Is it a supported SIP provider? No
Is firewall checker passed green? Yes
What kind of audio do you hear when line busy? coming from provider or 3CX? Line busy tone

is your trunk Green connected? Yes
Is it a supported SIP provider? No
Is firewall checker passed green? Yes
What kind of audio do you hear when line busy? Line busy tone
coming from provider or 3CX? How would I tell, it's a line busy tone.

 

[JohnS_3CX]

You could tell by running a capture on your PBX, then calling it.

The capture should show an invite coming in from your provider's IP towards your PBX IP.

You should also see the PBX replying Busy (if the PBX is the one rejecting the call).

If you see nothing coming in though, then most likely your will have to contact the provider so they can look into it further from their side

 

[AWS2P]

I just wanted to know if it was a voice message said by synthetic voice from 3CX or Just a busy tone from provider, but you answered it's just a tone, so most chances this is provider side.

 

[Scott EIT]

You could tell by running a capture on your PBX, then calling it.

The capture should show an invite coming in from your provider's IP towards your PBX IP.

You should also see the PBX replying Busy (if the PBX is the one rejecting the call).

If you see nothing coming in though, then most likely your will have to contact the provider so they can look into it further from their side

Thanks John. Ran a capture and there looks like there's an invite coming in, no idea what's happening or what I'm supposed to see after that though.

Can I send you the dump?

 

[Scott EIT]

I just wanted to know if it was a voice message said by synthetic voice from 3CX or Just a busy tone from provider, but you answered it's just a tone, so most chances this is provider side.

Thanks for that. By the looks of the capture it appears the call is reaching the trunk ok. I've also spoke to the provider who are adamant the SIP is behaving properly and it's an issue with my PBX. They've recommended I reboot things, which I've done.

 

[JohnS_3CX]

Well after you see the invite, you can open the message header on it, right click the Call ID and then "Apply As Filter > Selected". This will clean up the capture and show the interesting part only.

You will now see the whole conversation for that invite (the IP of the provider contacting the IP of your PBX) and then see what your PBX replies back to the provider's IP

 

[Alphabetic]

When you look at the invite what is your SIP provider sending to 3CX?

Are they sending SIPUSERNAMES@SIPTRUNK or are they sending the DDI?

 

[Scott EIT]

Well after you see the invite, you can open the message header on it, right click the Call ID and then "Apply As Filter > Selected". This will clean up the capture and show the interesting part only.

You will now see the whole conversation for that invite (the IP of the provider contacting the IP of your PBX) and then see what your PBX replies back to the provider's IP

"Selected" is greyed out when I right click and try to apply the filter.

 

[Scott EIT]

When you look at the invite what is your SIP provider sending to 3CX?

Are they sending SIPUSERNAMES@SIPTRUNK or are they sending the DDI?

8 0.550690 SIP IP Address 192.168.185.10 SIP/SDP 951 Request: INVITE sip:0131xxxxxxx@Public IP address:5060 |

 

[Alphabetic]

If you run a capture, make a test call then open it up in Wireshark

In the top go to Telephony > VoIP Calls > Click your call > Flow Sequence

you can follow what's going on

 

[Scott EIT]

Not seeing much here.

 

[Alphabetic]

Ok i've been able to replicate this issue on my 3CX.

Check the blacklisted IP for your SIP provider and remove it then whitelist it and try again.

 

[Scott EIT]

Ok i've been able to replicate this issue on my 3CX.

Check the blacklisted IP for your SIP provider and remove it then whitelist it and try again.

Nailed it mate, thanks very much!!

Can I ask how you managed to fathom that from that log?

Also, how would the IP address from the SIP provider end up blacklisted?

 

[Alphabetic]

In all honestly - I’m no good at voip but don’t like to be defeated. When you send an invite you get a response. I couldn’t figure out why your 3CX wasn’t responding at all but SIP was registered. So, I thought I’d blacklist my own trunk to see if it stayed registered, and it did. I then did a test call whilst running a trace and ended up with what you showed.

now you’re back up and running do a test call whilst running a trace and you’ll see a SIP flow

have you modified your security on the PBX or reduced the threshold? Maybe changed your password for SIP? Or IP?

 

[Scott EIT]

In all honestly - I’m no good at voip but don’t like to be defeated. When you send an invite you get a response. I couldn’t figure out why your 3CX wasn’t responding at all but SIP was registered. So, I thought I’d blacklist my own trunk to see if it stayed registered, and it did. I then did a test call whilst running a trace and ended up with what you showed.

now you’re back up and running do a test call whilst running a trace and you’ll see a SIP flow

have you modified your security on the PBX or reduced the threshold? Maybe changed your password for SIP? Or IP?

Your efforts are very much appreciated Kieferschild, thanks again.

I'm actually beginning to think the problem was with the provider previously. They asked me to remove the trunk and replace it with a new one, which I did. It was only then I ran Wireshark and saw the trunk being reached, I'm not sure that was the case previously. It might've been blacklisted at that point?

Just pleased it's going again. Thanks to everyone for their input.

 

[JohnS_3CX]

Hi Scott, glad to hear it was sorted! It sounds like after the replacement, there were source identification issues. If a capture was running during that phase, you would have seen the PBX challenge the provider invite, and eventually it would of course fail and end up in the blacklist. At least this is what I gather looking back at the whole story.