SNOM Phones registered via ProSBC to 3CX Cannot Receive Calls

[Guest]

Hello,

I have deployed my ProSBC and applied a preliminary configuration.  The role of the SBC is to handle NAT transversal and eventual routing of remote users to various client PBX’s.  So far, my configuration works well with Fanvil and Yealink phones however I cannot get SNOM phones to work properly. The SNOM’s can make outbound calls just fine but cannot receive inbound calls (get 404 “Not Found”).  I have attached my configuration along with packet captures of calls with the Fanvil (working) and SNOM (not working) devices.  The captures were acquired from the SBC, which is hosted on AWS.   The IP addresses you will see in the captures are as follows:

3CX PBX:  xyz.ccc.aaa.yy
SBC AWS Private NAT:  ccc.bb.aa.yy
SBC AWS Public:  xy.xyz.cc.aa
Endpoints Public:  ab.abc.bbb.cbc
Fanvil Private:  zab.aaa.bb.ccc
Snom Private:  zzz.yyy.aa.bbb

The SBC Serial Number is:  VTB-RIKU-99FA

This is not yet a production system and I am happy to provide you access to the SBC to assist with support, just let me know.

Kindly let me know what additional details you may require.

Thanks in advance!

[Guest]

Hello,

Would you check our wiki for remote registration please?

FreeSBC:Remote Workers - TBwiki (telcobridges.com)

[Guest]

Thanks for the prompt response.

I used the referenced guide to aid in my configuration.

As I stated previously everything works great with Fanvil and Yealink phones. They can place and receive calls is the SBC to 3CX without issue.

There is something unique with the SNOM phones that I have not been able to identify yet that is preventing them from receiving calls, they CAN place calls however.

[Guest]

Hello,

You can use tbsigtrace to capture signaling traces from the SBC. Please check the following link for how to use tbsigtrace and check the signalling differences between SNOM and other brands.

tbsigtrace: Signaling trace capture tool - TBwiki (telcobridges.com)

[Guest]

Issue resolved…

After analyzing the SIP headers in greater detail, I found the SNOM phones were seeing the Private IP of the SBC in the INVITE TO field, where the Fanvil and Yealink phones were seeing the FQDN of the PBX. Upon further investigation and a brief call with SNOM support, we discovered a setting in the phone that resolved this issue.

Under the SIP settings tab of the Identity, “Support Broken Register” needs to be set to “On”. Here is a link to that setting on SNOMS WiKi for your own documentation.
user_sipusername_as_line (snom.com)

Thanks for your help on this!