Once MS Teams has processed a user's dialing through their associated dial plan and voice routing policy, MS Teams checks the resulting number for matches in the MS Teams Voice Route entries. The match defines the SBC connection used for the call.
Each voice route has three settings MS Teams uses for matching: a usage label, a dial pattern, and a priority. Direct routing uses these as follows:
MS Teams groups routes by usage. It checks them in the order that the usages appear in the user's assigned voice routing policy.
MS Teams checks the first set of usage voice routes for a dial pattern match.
If MS Teams does not find a match, it checks the next set of usage voice routes.
When MS Teams finds a dial pattern match, MS Teams attempts to connection to the SBC (or SBCs) listed in the matched usage route with the highest priority.
MS Teams first attempts to use an SBC which has recently had a successful handshake. It does this in random order. MS Teams refers to these as 'healthy' SBCs.
If connection to a 'healthy' SBC is not successful, MS Teams attempts to use any other SBC. Again, it does this in random order. MS Teams refers to these as 'demoted' SBCs.
After successful SBC connection, the call follows the SBCs routing settings.
If SBC connection fails, MS Teams checks the SBC settings of the next highest priority dial pattern match in the usage routes. Note, this means that after a dial pattern match has occurred in a set of usage routes, MS Teams will not use another set of usage routes if SBC connection fails.
If MS Teams does not find a successfully route match, MS Teams re-routes the call to Microsoft calling plans if enabled for the user. Otherwise, MS Teams drops the call.
