Incoming calls (from external) ring but get immediately hung up when trying to answer (via 3cx softphone and webclient)

[johnranger2]

Hi all,

I have a very strange problem with our on-premises - 16.0.4.493 - 3cx which I detected today (we have rarely calls coming in so I don't know for how long this problem really exists) but I never have seen this with 3cx versions before 16.0.4.493 and this has still worked 2 months ago).

Description of problem:
When a call from external is coming in, the destination 3cx softphone or the web client (we don't have hard phones) rings and shows calling number correctly - but the moment when someone tries to accept the call (either via 3cx softphone or the web client, the call gets instantly hang up - but then reappears within half a second or so and continues to ring. Any further try to accept the call does the same - call disappears and reappears after 0.5-1 second but it is impossible to establish a connection.

Also incoming calls - when they are diverted to voice mail box are immediately hung up to the external caller and he/she gets a "cannot establish connection" or sometimes "network error".

Outgoing calls from internal work absolutely fine.

Hint: The call is coming in via a ring group as every DID is assigned to a ring group and within the ring group there are 1 or more internal phones.

Environment:

• 3CX runs on Windows 2008 R2 Server Hyper-V VM with plenty (16 GB) of Memory and 2 vCPUs - Machine load is max. 20% CPU and 60% RAM), Hyper-V host has 32 GB and currently only the VM with the 3CX running on it
• Firewall is Draytek 2860
• Internet Link: 40 MBit down, 10 Mbit up, only used for e-mail and Voice traffic (currently 4 internal phones), no web surf traffic, very little load
• SIPcall-compatible 3rd party VoiP provider (they are also using 3cx themselves for their business)

What I already have tried:

1. Run the firewall checker --> All ok
2. Re-checked Firewall config according to here: https://www.3cx.com/docs/draytek-firewall-configuration/
3. Re-initialized the trunk connection --> Connects successfully to the VoiP provider
4. Restarted the router
5. Rebooted the 3CX Server VM
6. Restarted Client computer where 3CX softphone and web client are running

Apart from contacting the VoiP provider (which I didn't yet do) - what could I check further / what could possibly be the cause of such behavior?

(Looks to me like a signalling problem between the 3cx and our provider - but I am no expert - in no wise...)

Thanks for any help.

With kind regards,

John

 

[Evolute IT]

Are you trying to have the 3CX Client connected via SIP TLS/SRTP?

And as for your trunk?

Put the logging in verbose and run a few tests. You'll see any errors appear in the Activity Log.

 

[johnranger2]

Hi Frederick,
thanks for your feedback.

The 3CX client (softphone) is connecting via 3CX tunnel - so it is encrypted but I don't know if inside the tunnel it is also using SIP TLS / SRTP or not. .

Trunk is unfortunately not encryptable with this provider (they don't provide TLS/SRTP). I have already requested this 2x but they don't want to provide this.

Have now made a verbose logging (good idea, thanks) and there it is visible that the session is hanged up by the VoiP provider's ip:

----------------------

01/16/2020 3:13:01 PM - SendMsg from ":xxx yyy:xxxx"<sip:[email protected]:5060;nf=e>;tag=23193521 to <sip:[email protected]>;tag=6f701b4b
01/16/2020 3:13:01 PM - [CM503008]: Call(C:17): Call is terminated
01/16/2020 3:13:01 PM - Blocking refers for the Call(C:17)
01/16/2020 3:13:01 PM - Call(C:17) is terminated
01/16/2020 3:13:01 PM - Leg L:17.1[Line:10000<<xxxxxxxxx] is terminated: Cause: BYE from 212.117.203.158:5060
01/16/2020 3:13:01 PM - L:17.1[Line:10000<<xxxxxxxxx] got Terminated Recv Req BYE from 212.117.203.158:5060 tid=blaV20000gv2 Call-ID=blabla~2o:
BYE sip:[email protected]:5060 SIP/2.0
Via: SIP/2.0/UDP 212.117.203.158:5060;branch=bla bla
Max-Forwards: 70
To: <sip:[email protected]>;tag=a66ba14b
From: <sip:[email protected]>;tag=unTSCBaGcYwV.o
Call-ID: blabla~2o
CSeq: 191 BYE
Content-Length: 0

----------------------

(This is while the call from external is still trying to get through and when on the softphone the call is picked up)

I have now opened a ticket with our VoiP provider.

Thanks again for your help.

With kind regards,

John

 

[johnranger2]

Hi all,

a quick update on this issue. As we checked with our VoiP provider, they checked our 3CX logs and told me that the internal phone is ending the call (they pointed at some log entries which suggested this). But as we clearly don't hang up the phones this could not be the error.

I then re-checked the trunk config to the VoiP provider - with no obvious result.

I then just - for a test - activated SRTP on the trunk and re-registered the trunk - and voilà: The problem was gone. Interestingly enough - after I deactivated SRTP and re-registered the trunk again - the problem did not re-appear.

So it seems to be a communication problem between our VoiP provider and our 3CX (or an "under the hood" config problem which occured because of the upgrade to the newest 3CX sub-release).

We probably will never know - but I leave this feedback here so if some of you have the same problem, this could be a fix for it.

With kind regards,

John