Forum Discussion
MS Teams Direct Routing - Internal call transfer failure
Hi for us it's the other way around. Internal calls transfer perfectly fine and transfer to PSTN only works via the Teams Client. We do use some 3PIP Phones from AudioCodes, Yealink and Poly and if we try to transfer a call to an external Number, our SBC does not receive a refer-to number.
Now i have heard from someone, that their AudioCodes SBC receives this from Number even when it's coming from a 3PIP Phone.
Does anybody have an idea, why 3pip Phones or SfB Client for that matter (i know it's not supported but if 3pip should work, the SfB Client should also work) does not send a Refer to number to our SBC? Or is there anyone around who can test it and tell me if it's working with their SBC?
Thanks,
mozzie
Also, maybe your SBC has a rule to remove Refer-To header and sometimes that rule is applied by incorrectly configured Match policy? Have you tried sniffing traffic and decoding TLS to see the actual SIP packet coming from MS before it's handled by SBC?
Lt_Flash I don't think that the SBC removes the refer, because when I do it via the Teams Client, everything works fine. If I disable Referred-By on the SBC transfers stop working, even internal Teams Transfers. I'm not sure who to do TLS sniffing and decoding. What do I need to do? Run wireshark while i transfer and filter for TLS/TCP packets?
It's not that easy, you will need your SSL certificate and private key in order to decrypt the traffic, you need to google about that. But maybe you just disable REFER support like we did? That's much simpler and works much better and requires less rules on SBC to make calls work. Just strip 'REFER' from any 'Allow:' header coming from SBC on requests and responses.
It turned out, that there was in fact something wrong with how Microsoft / 3PIP SfB Phones sent the refer to our SBC. (Our SBC did not receive a refer-to number) Microsoft has now fixed the issue and we can correctly transfer calls to external numbers via the Teams Desktop Client and 3PIP Modes with users in TeamsOnly mode.