Music on Hold in Teams & 4 seconds until Hold is in place for caller

There was a time I found out during my tests of our Direct Routing implementation that Microsoft made its promises happened and Music On Hold started to work on regular PSTN calls to Teams users.

It was a time when I got a report of the new "issue". Users complained it takes too long until the call is put on Hold after clicking on the button. I was just curious what happened because I remember from previous tests this was just matter of second but users reported 4 seconds. Hmmm.... 

Then I realized I can hear the music ... wohoooo ...  

So deeper deep dive showed that Microsoft is handling Hold and Music on Hold in very specific way. At least for me.

If you click Hold in Teams during the PSTN call you are basically transferring the call to another Teams "user"/object which is playing music for you. You can even hear the very short ring! 

Very confusing for the caller on PSTN side but I believe it's about way how you want to handle the Ring message on your SBC at the end. Good reason I believe not to change that behavior because of other reasons.

And that's also the explanation why it takes so long time! Imagine with Direct Routing following scenario (below is SIP trace for better understanding)

1/Teams proxy is sending REFER,

if you have your SBC setup in proper and recommended way then

2/ SBC sends invite back to Teams Proxy,

3/ then you have Ringing in place,

4/ all the SDP exchange of media sources (we are also running Mediabypass so imagine all ICE lite story happening) and boom,

5/ your call is on hold aka transferred to something else than your Teams user. 

Obviously the other way around, I mean getting the call back from Hold, is somehow reverted process but without REFER. Teams proxy basically sends new INVITE but now with Teams users media sources. Also takes a while and some users might be confused that they did something wrong or call is gone?!

So at the end it's not 4 seconds but slightly around 3 (users are exaggerating a bit, right)

I believe that this way of handling MoH is also reason why it will take some time until Microsoft will provide also MoH for Transfer function in Teams. Now if you click transfer or consult transfer the Teams Proxy sends Invite with inactive media session so might be another confusion for PSTN caller that there is just silence. 

Looking forward for Microsoft delivering these features for 100% and even more I would be happy to provide our management their own company MoH (not only on queues or AA 😉 but for users)

Hope this article helps some of you