SBC No RTP session for local destination packet dropped

[jerome_hizkia]

Hi everybody,
I'm trying to connect 3CX + SBC with Cisco spa8800.
SIP sessions are ok, but one way audio (outgoing audio fail)

The schema connexions :
Sip phones -- 3CX -- SBC -- SPA8800 -- boxtel

3CX is hosted by 3cx.com and SBC is on local network with SPA8800

SBC version :16.2.24 on debian 10 buster
SBC Debug :

NOTICE | 20201017-161033.912 | 3CX | SBC | 140663871064000 | BridgeRtp.cpp:134 | No RTP session for local destination 192.168.1.250:16436, packet dropped

All packets from SBC to SP8800 are dropped !! with incoming and outgoing call.

I tried almost all the solutions found on the forum, without success..

Somebody to help me ?

Thanks.
Jerome

I tried with minimal asterisk instead of SBC and it works !

PS: SBC logs join

 

[leejor]

The 8800 support 4 FXO and 4 FXS ports. I'm going to assume you are attempting to use the 4 FXO ports to the provider. This configuration, behind and SBC, is not supported by 3CX (without VPN), and as many have found, has issues. In many attempts, calls will work inbound to 3CX, but calling out through the gateway ends up failing. Much of that is because, unlike an ATA, or VoIP set, 3CX does not rely only on registration information, when sending calls to the gateway.

That said, there have been posts of doing a work-around, but, as far as I can recall, it was only for one specific make.

The text attachment of the logs is a mess, and essentially unreadable without the original formatting.

Here are a few, on the subject...

https://www.3cx.com/community/threads/why-does-not-remote-pstn-gateway-work-with-sbc.58067/

https://www.3cx.com/community/threads/grandstream-gxw-4104-via-sbc-for-cloud-3cx.62120/

https://www.3cx.com/community/threads/patton-4112-fxo-behind-sbc-no-inbound-calls.74859/

I also came across this, which I had not seen before...

https://en.58voip.com/connect-fxo-gateway-3cx-sbc/

 

[eddv123]

This configuration, behind and SBC, is not supported by 3CX (without VPN)

To add a little more, the configuration, brand/model and device type are not supported:
https://www.3cx.com/voip-gateways/

Even supported brand combination units have never been supported by 3CX and probably never will be.

We have recently seen Grandstream and Patton supported FXS types supported behind SBC which is a good step however.

 

[jerome_hizkia]

Thanks for your answers, it's a shame I was very close, just need a rtp connetion between SBC and Gatewway...
I use a asterisk instead of the sbc, it is less elegant but it works.