Incoming calls not connecting the first time

[maurice]

Hello ,

I have an issue.
Also an 4 channel sip
4 snom DECT extensions ( STUN)
Version 16.0.4
different sip ports
When there is an incomming call the first picks up the phone, no connection, the 3 others phone's are stil ringing.
the second one picks up and he has picked up the call.
The symptoms are random, so will it be ok for weeks , and so they have it every day.

We have switched the phone's for other phone's
We reset the pbx
Build a whole new Pbx

requested info:

3Cx version 16.0493 Profesional
server: Debian 9

ip Phone model: Snom m25 DECT with the latest firmware
( But we tried Yealink DECT / gigaset DECT all with the same problem)
Provisioning method: STUN
Firewall schecker has passed.
No Custom templates on the DECT phones.

the problems are still there.

This is also the only customer that has this problem.

 

[Evolute IT]

Have you done port forwarding for the Snom base?

Also, 4 extensions means 4 STUN connections. Have you tried an SBC? It might fix your issue.

 

[maurice]

Yes we tried that specific ports and a SBC.
This worked for a few weeks and than the problem was back.

 

[JohnS_3CX]

Hi @maurice

I imagine this is a queue or ring group where the following happens normally:

1. The phones should receive a message to start ringing
2. One picks up and must reply to the PBX that the call is answered
3. If the call still exists, the PBX will attempt to connect this one extension
4. The other extensions will be informed that the call was answered elsewhere and will stop ringing

Steps 2 and 4 seem to fail, which would indicate (at least initially) that the connection between the phones and the PBX is either broken, or impeded by the firewall. This would be the first place to look (especially if the SBC is also affected).

Sometimes it's something silly like the internet connection being fully loaded because someone was uploading an attachment or downloading a large file.

The network is the most important part to ensure the two sides communicate properly so pay special attention to this and try to at least find a way to replicate the issue.

 

[maurice]

Hi John,

The firewall is set just as all the other customers.
We have a separate internet connection thats only used for the phonesystem.
Also the internal network and hardware is separate for data and voice.

 

[maurice]

is there a possibility that you configure a stun extension and test it at your site on the pbx of our costumer ?

 

[JohnS_3CX]

What Snom base are you using, and are all 4x M25 phones on the same base?
How many RTP ports were assigned?

 

[maurice]

the snom base is a snom M700 and all the m25 phones are on this base.
the ports are now basic again, because changing them didn't solved it.

 

[JohnS_3CX]

Ok here is what I would suggest to help with the investigation:

1) Install your SBC again at the customer's site
2) Ensure the SBC has TLS, we don't want their firewall to be able to inspect the traffic
3) Once the SBC is up, enable Email notification on the PBX for "When the status of a trunk / SBC changes"

This way we can monitor the network conditions (at a rudimentary level) as well as the stability of the connection and firewall. If the SBC has frequent disconnections, we can at least isolate the issue for being on the network. This will also bypass SIP-ALG and port forwarding issue from the mix.

Of course you will also need to reset and reprovision the M700 to SBC after changing the settings in your PBX DECT section.

 

[maurice]

the internet connection is in our monitoring and we didn't get any notification that the connection is down or interrupted.

 

[maurice]

Sip alg is off.

 

[maurice]

does any one know what more we can do?
We are wiresharking the phone calls, but as i said earlier this problem is not always and the customer had last week no problems.

 

[JohnS_3CX]

Hi @maurice

I would still suggest to follow my recommendation on post #9

 

[maurice]

We are gone install an 3cx on site and place a pc with wireshark.
This so we can monitor everything

 

[maurice]

Hello ,

We installed everything on a local pc, 3cx and wireshark.
I have been testing , and the problem is still there.
When a call is incomming and i will answer, the 3cx sees it as rejected on the first phone.
(488 Not accepted here)
The second can answer the call.
See attachment .

 

[JohnS_3CX]

Is this only for calls coming from the trunk?

 

[maurice]

no often when i call to the ringgroup i have the same problem

 

[JohnS_3CX]

why do we see anonymous in the caller?

 

[JohnS_3CX]

or rather, what are you making the call from?

3CX Client?
Deskphone?
3rd party VoIP client?

 

[maurice]

Because i am callig whit my private gsm