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Calls dropped after 30 seconds with SBC

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William Hall

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I have a 3CX PBX in the amazon cloud and 11 phones behind a firewall. This worked reasonably well after I learnt to have the phones on different ports. I recently learnt that a SBC was a good idea in this situation so I installed a Pi3+

Now my Snom phones (710 and 300) drop the connection if they originate a call after 30-32 Sec
This happens if the call is internal, external or to the echo test service.

Incoming calls are ok

Yealink SIP-W52P, IOS app and Windows phone work fine.
 
If you make an external call, is there a reason shown in the 3CX Activity log, for the call dropping? Something such as no ACK?
 
Yes, I get "ACK is not received from ...."
Does the ack go from the phone to SBC to PBX?
 
I believe that it is the end that originates an Invite waiting for an ACK. Most cases that crop in the Forum up are dealing with SIP trunks to a provider. In that case, 3CX sends an Invite to the provider, but never gets an ACK, so the call is dropped, In your case, it is 3CX again, awaiting an ACK from ??? (you didn't include that part), but it never comes, so the call is dropped after about 32 seconds.
So... you need to figure out, what is preventing the far end from responding. Is it a port issue (forwarding?), or is the far end not responding to the correct IP , or port, perhaps based on the Invite.
 
It's pbxexpress in the amazon EC2 cloud with the following ports allowed:
Ports Protocol Source
All icmp 0.0.0.0/0, ::/0
5015 tcp 0.0.0.0/0, ::/0
22 tcp 0.0.0.0/0, ::/0
9000-9500 udp 0.0.0.0/0, ::/0
5090 udp 0.0.0.0/0, ::/0
10600-10998 udp 0.0.0.0/0, ::/0
5060 udp 0.0.0.0/0, ::/0
5061 tcp 0.0.0.0/0, ::/0
5090 tcp 0.0.0.0/0, ::/0
443 tcp 0.0.0.0/0, ::/0
5001 tcp 0.0.0.0/0, ::/0
5060 tcp 0.0.0.0/0, ::/0

It passes the firewall checker
 
You seem to have a gap in your udp ports. 9501 to 10599
https://www.3cx.com/docs/ports/
Don't suspect that as the issue, but still...

Given that it is only the SNOM phones having the issue, I would concentrate on their settings.
Perhaps a complete reset and re-provision.
 
Further to @leejor 's comment, did you edit the phone provisioning tab for each extension to ensure that they are pointing to the SBC's LAN address?

Also, is your SIP provider on the 3CX Approved list?
 
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What sort of firewall is the SBC behind?
AWS security. There is no restriction on outbound traffic

You seem to have a gap in your udp ports. 9501 to 10599

Fixed, as you suspected, no improvement.

did you edit the phone provisioning tab for each extension to ensure that they are pointing to the SBC's LAN address?
Yes, in 3CX phones tab it says typically 10.x.x.x:32768 via SBC 10.x.x.x:5060
Though I did not see this mentioned in the SBC documentation

One thing I note is that when I look at the phone SIP trace I see that some packets are sent to the SBC lan address as expected but some are sent to Udp:169.254.75.198:5060
As I understand it this 169.254.x.x is the address range assumed if a DHCP interface can't find a DHCP server. As far as I'm aware this does not happen on my network. ???
 
I thought I saw someone else having problems with snom phones and SP6. Probably not going to the office this weekend but i'll dig up a snom phone on Monday and test.
 
I thought I saw someone else having problems with snom phones and SP6. Probably not going to the office this weekend but i'll dig up a snom phone on Monday and test.

That would be very helpful - thanks

FWIW I tried wiping a phone and re-provisioning from scratch - no improvement.
 
Ok so I dug up a Snom 821, provisioned via SBC, updated the firmware to the latest 3CX supported and I just did two calls over 30 seconds with no issues. One was external to my e911 test number and one was to the echo test number so I'm unable to replicate here.
 
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Thanks for looking. I will investigate further
 
Thanks for looking. I will investigate further
To be sure, I'd try factory resetting the snom phones. If you had them initially as STUN, then just reprovisioned them over to SBC, they might still have some config from their STUN days.

Just my 2 penny worth on the matter.... :)
 
Thanks, I did try resetting a phone and re-provisioning from scratch via the SBC. No improvement.

I have ordered a Yealink T19P, I'll try that when it arrives to establish if its the phone or the PBX / firewalls / network

My users currently making outgoing calls via Iphone app ......
 
Correction to previous answer:
The SBC is behind a pfsense firewall
(The PBX is the one behind AWS security)
 
Further info:
I have purchased a Yealink T19P E2 which works fine
I have to assume its specific to Snom 300, 710, D710
 
Hmm.. SP6 and stock templates? Just wanted to confirm so I could generate a config on my box and look it over. I'll see if I have one of those models as well since i couldn't replicate with my 821.
 
Ok did some more digging in my pile of phones and found a 760. Testing that now once I upgrade/provision.
 
Yes, standard templates
 
.... My version is Professional Annual 15.5.15502.6
Says it's latest version
 
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