[Freeswitch-users] Transfer fails (does nothing) when receiving REFER message with no user in the Refer-To: URI

[Ben Kaufman]

Setting up Freeswitch to connect to Microsoft Teams' "Direct Routing" (https://docs.microsoft.com/en-us/microsoftteams/direct-routing-plan).  General call setup-teardown is successful, but I'm encountering a problem with call transfers if the transfer target is another Microsoft Teams user.

The most immediate obvious difference between the transfer to an external party and the transfer to another Teams user is in the Refer-To header of the Refer message on the transfer event.

In the case of transfer to an external party, the Refer-To is (phone number redacted to 555-555-1000):

>  REFER-TO: <sip:+15555551000 at sip.pstnhub.microsoft.com:5061;user=phone;transport=tls>

In the case of transfer to another Teams user, the transfer Refer-To: header looks like this:

>  REFER-TO: <sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:13bc82d9-003a-43b8-aad2-8f2f561a9b8d>

When this occurs, the last line in the Freeswitch log for the call is:

>  [DEBUG] sofia.c:8544 Process REFER to [(null)@sip.pstnhub.microsoft.com]


There is nothing else in the log until this times out, no indication it has entered any dialplan, etc.  Even on timeout, it is just the teams client saying that the call has failed, and unless one end hangs up, or reconnects to the failed transfer, there is no action in freeswitch.  I believe this to be a bug, but wanted to get an opinion before opening a formal bug report.

Regards,

Ben Kaufman
AltiGen Communications, Inc.

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