FreePBX behind SBC Registar phones


I am installing freePBX behind SBC.
The goal is to connect phones from the internet to freePbx via SBC.
phone → SBC → FreePBX
The SBC transfer the registration to FreePBX.
SBC TLS connection.

I have created a registration trunk, and created extensions.
How can I make it work? is there documentation for this flow?

on DEBUG log:
Phone public ip:
SBC internet ip:
SBC internal SIP:
freePBX internal SIP:

[2023-06-26 14:44:45] VERBOSE[2004] res_pjsip_logger.c: <— Received SIP request (848 bytes) from TCP: —>
REGISTER sip:;transport=TLS SIP/2.0
Via: SIP/2.0/TCP;branch=z9hG4bK-1f9bacf37f3e4d78d74ac609c67017f1
Via: SIP/2.0/TLS;branch=z9hG4bK-524287-1—44e5b621e110665b;received=;rport
From: <sip:185@;transport=TLS>;tag=e3cb412f
To: <sip:185 @;transport=TLS>
Call-ID: 77Bd9EbRQaNx-_eXO2R7vg…
Contact: <sip:185 -185-AlIaS-42C96A8C0D77E–@;transport=TCP;rinstance=5e4251b87f580a06>;expires=3600
Max-Forwards: 69
Supported: replaces, norefersub, extended-refer, timer, sec-agree, outbound, path, X-cisco-serviceuri
Allow-Events: presence, kpml, talk, as-feature-event
Content-Length: 0

[2023-06-26 14:44:45] DEBUG[2004] res_pjsip/pjsip_distributor.c: Could not find matching transaction for Request msg REGISTER/cseq=1 (rdata0x7fde88011a18)
[2023-06-26 14:44:45] DEBUG[2004] res_pjsip/pjsip_distributor.c: Calculated serializer pjsip/distributor-00000028 to use for Request msg REGISTER/cseq=1 (rdata0x7fde88011a18)
[2023-06-26 14:44:45] DEBUG[19076] netsock2.c: Splitting ‘’ into…
[2023-06-26 14:44:45] DEBUG[19076] netsock2.c: …host ‘’ and port ‘’.
[2023-06-26 14:44:45] DEBUG[19076] res_pjsip_endpoint_identifier_ip.c: Source address matches identify ‘ProSBC60_Registar’
[2023-06-26 14:44:45] DEBUG[19076] res_pjsip_endpoint_identifier_ip.c: Identify ‘ProSBC60_Registar’ SIP message matched to endpoint ProSBC60_Registar
[2023-06-26 14:44:45] VERBOSE[19076] res_pjsip_logger.c: <— Transmitting SIP response (481 bytes) to TCP: —>
SIP/2.0 404 Not Found
Via: SIP/2.0/TCP;rport=34856;received=;branch=z9hG4bK-1f9bacf37f3e4d78d74ac609c67017f1
Via: SIP/2.0/TLS;rport;received=;branch=z9hG4bK-524287-1—44e5b621e110665b
Call-ID: 77Bd9EbRQaNx-_eXO2R7vg…
From: <sip:185 @>;tag=e3cb412f
To: <sip:185 @>;tag=z9hG4bK-1f9bacf37f3e4d78d74ac609c67017f1
Server: FPBX-15.0.37(16.30.0)
Content-Length: 0

[2023-06-26 14:44:45] DEBUG[19076] netsock2.c: Splitting ‘’ into…
[2023-06-26 14:44:45] DEBUG[19076] netsock2.c: …host ‘’ and port ‘’.
[2023-06-26 14:44:45] DEBUG[19076] netsock2.c: Splitting ‘’ into…
[2023-06-26 14:44:45] DEBUG[19076] netsock2.c: …host ‘’ and port ‘’.
[2023-06-26 14:44:45] WARNING[19076] res_pjsip_registrar.c: AOR ‘’ not found for endpoint ‘ProSBC60_Registar’ (


Are you using Sangoma’s SBC? If so Sangoma has a series of videos on their training page that walks you through the basic setup/configuration of the SBC.


We are using an SBC of another vendor.

I am looking for the right configuration on the FreePBX side.


Don’t have much experience with SBCs but what I have typically involves simply creating a trunk that talks to your SBC. It’ll be up to your SBC how it wants to see that trunk coming in. You might have better luck with your vendor providing you specific configuration instructions.

is the SBC an ingate?

If it is I can give you lot of info.


Actually, the SBC configuration is not problematic.
I already have integrated it with Kamailio for sip registration.

My questions are more relating the pjsip trunk setting on the freePBX.
How do I tell it to process the incoming registration events against configured extensions?


By providing the correct user name and password. Anything else is going to be a work around for what you are claiming doesn’t need a work around.

Hello David,

freePBX can’t support remote registration (internet clients) passthrough SBC?
didn’t understand you answer.


Not sure I follow. FreePBX works great behind almost any SBC. (I am not aware of any SBC that it is not working with)

Please define what a passthrough SBC is?

Providing the SBC is SIP compliant, there should be nothing special about the registration, as far as Asterisk is concerned. The SBC may modify the contact address, to refer to itself, but that isn’t a problem for Asterisk.


Issue solved.

I am using TelcoBiridges SBC.
I used this manual to confirm my setting:

On PBX, when I disabled the inbound trunk for incoming calls from outside, registration started to work.
I realized that the 2nd trunk (which is also connected to SBC) was trying to process the registration requests. I set the Match for it and that solved the issue.


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