Inbound Calls Not Working for Mobile / Remote Extensions Registered Through Outbound Proxy

[Carbonara]

Due to certain network requirements, all of our remote and mobile extensions need to have SIP conversations with 3cx via a Proxy server, like so:

              SIP                    SIP
Client <--------------> Proxy <--------------> 3CX
  ^                                             ^
  |                                             |
  -----------------------------------------------
                         RTP

This works fine for outbound calls (to PSTN via SIP Trunk) from the mobile extensions -- with each softphone/app pointing to the Proxy as an "Outbound Proxy" --, but inbound DID calls routed to these mobile extensions are not working.

Can mobile extensions be made to work bi-directionally in this scenario, where SIP traffic must make a hop through a proxy between the client and the PBX?

A bit of detail: The Proxy is (correctly, I believe) adding a Path header to the REGISTERs it sends to 3CX, per RFC 3327. But 3CX does not seem to be respecting this Path header, and does not send INVITEs to the client via the proxy -- in fact, 3CX does not appear to be sending an INVITE at all to the client extension, even though 3CX correctly identifies (per Inbound Rule) the right extension to send to (per verbose 3CX Activity Log). In fact, 3CX does not send an INVITE at all! It just eats the INVITE from the SIP Trunk, and silently fails (again, per 3CX Activity Log).

Does 3CX support such a network configuration? Or, even if not "supported", can it be made to work? Is there some other way to "force" 3CX to make/handle that proxy hop?

Thanks,
Carbonara

 

[leejor]

Is it all calls (I'm assuming it is), including calls from other extensions, that fail, or just incoming calls from DIDs?

You may want to examine how a 3CX SBC "handles" a call, as it will act as a proxy for the extensions behind it.

 

[Carbonara]

Thanks, leejor, yes all calls whether inbound from DIDs or from other extensions, fail.

I'll check out how the SBC makes this work. Though meanwhile if anyone has ideas around this -- either workarounds or the specific ask around RFC 3327 support -- would love to hear!

-Carbonara