Forum Discussion

Copper Contributor

Jul 15, 2019

MS Teams Direct Routing - Internal call transfer failure

Hi all, My organisation is planning a move to direct routing. We have an AudioCodes VE SBC. I've been working on this for awhile and got everything to a pretty decent state. I've come across ...

microsoft teams

Lt_Flash

Brass Contributor

May 21, 2020

davidmcgrath Well, in first place, why is it sending REFER if you're putting call on hold? It should just send a SIP re-INVITE with SDP a=inactive. SIP REFER is used for blind and/or attended transfers as per RFC5589. If you're getting an INVITE and then REFER - probably INVITE has SDP with a=inactive thus putting call on hold, but REFER is definitely for transferring calls somewhere else, can you post a tcpdump of these two packets you're seeing? And what happens after you press un-hold in Teams client - do you get any packets coming from MS side to your SBC?

davidmcgrath

Copper Contributor

May 21, 2020

Hi Lt_Flash

I can share a fill PCAP for a call, but don't want to share it publicly. Is there a way I can share it directly with Lt_Flash.?

I have attached a screen shot of the sip flows from wire-shark. I have also added the refer and invite packets as well.

We don't understand why MS Sends a REFER after the re-invite. If you look at the attached png ,I click the hold button in teams at 12.205 secs, we respond to the re-invite, then MS sends us a REFER, which we respond to in the same way as we respond to a teams transfer request,

Any attempts to un-hold the call do not work after this. The call drops and a popup appears in the top left corner of teams client showing the call is on hold. MOH plays on the pstn leg. No more packets are sent from MS to my SBC.

Regards

David

DaveChomi
Iron Contributor
Nov 28, 2020
Lt_Flash
I don't see any issue with REFER over the last year on our infrastructure and we are using almost every type of DR configuration even with Local Media Optimization and proxy SBC. The only issue I had with REFER was that our firewall was setup all the time wrongly for mediabypass (first version) when SBC wanted to reach it's own public IP for media flow and crazy hairpin was needed over the FW.
Lt_Flash
Brass Contributor
Oct 03, 2020
davidmcgrath
Sorry, somehow I have missed your reply and didn't receive a notification about your answer. You need to block 'REFER' method in both initial requests coming from PBX or MS side and in replies too, in that case MS will be sending just Re-INVITES as per my SIP dump above. But currently, in October 2020, it looks like they've fixed REFERs, we're actually testing if they're working fine now, but haven't come to conclusion yet. Looks like REFERs are working, but we haven't finished full testing procedure in our company.