Forum Discussion

Sims_Krastev's avatar
Sims_Krastev
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
Sims_Krastev's avatar
Sims_Krastev
Copper Contributor

Lt_Flash I had no luck with changing the voice route, so ended up raising it with MS support.

Apparently if you disable REFER as an allowed method within your SBC's signalling messages, then MS Teams does not use REFER for transfers and just re-INVITEs to the SBC. That way the internal transfers work perfectly fine.

 

Lt_Flash's avatar
Lt_Flash
Brass Contributor
Jul 25, 2019
How did you disable REFER? I mean - does your SBC sends some 4xx code when MS sends a SIP REFER message? Or somehow different? Thanks!
  • Sims_Krastev's avatar
    Sims_Krastev
    Copper Contributor
    Jul 25, 2019

    Lt_Flash 

    No, not by rejecting the REFER with a response code. I basically did a message manipulation rule to re-build the Allow header for calls to MS Teams without including REFER. Which vendor are you using? If you have an AudioCodes as well, I can give you the rule syntax.

     

     

    • Lt_Flash's avatar
      Lt_Flash
      Brass Contributor
      Jul 25, 2019
      No, we're using a custom SBC, but yes, that was my second guess - to strip REFERs from packets. Thanks a lot, I'll give it a go and let you know if it works for me!
    • Lt_Flash's avatar
      Lt_Flash
      Brass Contributor
      Jul 25, 2019

      Sims_Krastev you seem to be correct! I've just edited all messages that were coming from PSTN side of our SBC and stripped 'REFER' on SBC in 'Allow' field - and yes, Microsoft started to transfer calls correctly! Thanks a lot, mate, I've already read that disabling SIP REFER method helped some people, but I was trying to reply with 4xx or 5xx when receiving REFER from MS side, while I should have just removed that REFER method from SIP 'Allow' list! By the way, looking at the packets coming from Microsoft side I can see that they don't send REFER in allowed method list! Here's an example:

      CONTENT-LENGTH: 685
      MIN-SE: 90
      SUPPORTED: timer
      USER-AGENT: Microsoft.PSTNHub.SIPProxy v.2019.7.4.9 i.USWE2.4
      CONTENT-TYPE: application/sdp
      ALLOW: INVITE
      ALLOW: ACK
      ALLOW: OPTIONS
      ALLOW: CANCEL
      ALLOW: BYE
      ALLOW: NOTIFY
      SESSION-EXPIRES: 1800;refresher=uas

      Thanks again for your help and I'm glad everything is working fine for you too now!

      • Matej_Maric's avatar
        Matej_Maric
        Copper Contributor
        Aug 01, 2019

        Lt_Flash 

         

        I can confirm this behavior, just that REFER triggered transfer is most common way for it and only fully standardized one. If your SBC is capable to terminate REFER note that MS still clearly indicates in Refer-To where to send INVITE back: 

        REFER-TO: <sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:fce2158f-0e99-4ff7-a0b3-5b6b87d16689><sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:fce2158f-0e99-4ff7-a0b3-5b6b87d16689>sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:fce2158f-0e99-4ff7-a0b3-5b6b87d16689</sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:fce2158f-0e99-4ff7-a0b3-5b6b87d16689></sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:fce2158f-0e99-4ff7-a0b3-5b6b87d16689><sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:fce2158f-0e99-4ff7-a0b3-5b6b87d16689>
        </sip:sip.pstnhub.microsoft.com:5061;transport=tls;x-m=8:orgid:fce2158f-0e99-4ff7-a0b3-5b6b87d16689>

         

          and making sure you fill RURI with Refer-To and Contact uri-host correctly you will see MS does rest of the job nicely for REFER case too.  

    • Jason Turpin's avatar
      Jason Turpin
      Copper Contributor
      Sep 10, 2019

      Sims_Krastev 

      Can you post how to do message manipulation to re-build the allow header for this on AudioCodes?

      • Sims_Krastev's avatar
        Sims_Krastev
        Copper Contributor
        Sep 11, 2019

        Jason Turpin 

        Sure - here it is:

         

        Action Subject - Header.Allow

        Action Type - Modify

        Action Value - 'PUBLISH,MESSAGE,UPDATE,PRACK,SUBSCRIBE,INFO,NOTIFY,REGISTER,OPTIONS,BYE,INVITE,ACK,CANCEL'

         

        You can strip out any method you like or match what Microsoft send in their messages if you'd like. Its working fine for me with these.

         

        Regards,

        Sim

Resources