MS Teams PSTN call flow with Direct Routing

Lets try to investigate what happens when user dials a PSTN number from their MS Teams client.

1. User launched dial pad in MS Teams.
2. User dialed a number +1-425-765-6xxx
3. Check for the dial plan (policy) assigned to the user. If any custom dial plan assigned to the user then conversion will happen e.g. Extension number to full E.164 format conversion.
4. Next it will check for the Voice routing policy assigned to the user.
5. Under Voice routing policy it will check for the PSTN-usage.
6. PSTN-usage contain all the available routes for that user. If one among the route matches the dailed number. Then call will be routed. Or else it will be dropped.
7. We can have multiple routes under PSTN usage e.g. we can have one route for US number which points to a specific SBC and other route for Canada numbers which goes via other SBC.
   
   Ok, let’s see the configuration flow. Below is the order you will configure Direct routing.
8. Configure SBC (PSTN gateway)—>Create Voice Route —>Add the previously configured SBC to the voice route—->Add this voice route to PSTN Usage—>Add PSTN usage to Voice routing policy or Calling policy—>Assign it to user.