PSTN considerations for upgrading to Teams from Skype for Business on-premises

This article describes Public Switched Telephone Network (PSTN) considerations when upgrading to Teams.

Important

Skype for Business Online will be retired on July 31, 2021. If you haven't upgraded your Skype for Business Online users to Microsoft Teams before that date, they will will be automatically scheduled for an assisted upgrade. If you want to upgrade your organization to Teams yourself, we strongly recommend that you begin planning your upgrade path today. Remember that a successful upgrade aligns technical and user readiness, so be sure to leverage our upgrade guidance as you navigate your journey to Teams.

In addition, the following articles describe important upgrade concepts and coexistence behaviors:

Note

  • Using Phone System with Teams is only supported when the user's account is assigned a Teams upgrade policy with Teams Only mode.
  • Using Phone System with Skype for Business is only supported when the user's account is assigned a Teams upgrade policy with an SfB mode.
  • Phone System is not supported when the user's account is assigned a Teams upgrade policy with Islands mode.
  • Any call forwarding, team-call group, and delegation settings from Skype for Business are not migrated and will need to be re-recreated for Teams.
  • For a general overview of Microsoft Teams cloud voice features, and help deciding which Microsoft voice solution is right for your organization, see Plan your Teams voice solution.

PSTN calling scenarios

There are four possible calling scenarios when moving to TeamsOnly mode:

This article provides a high-level overview only. For more information, see Phone System Direct Routing and Calling Plans.

From Skype for Business Online with Microsoft Calling Plans

This is the simplest upgrade scenario involving voice.

  1. Make sure users have been assigned a Teams license. By default, when you assign a Microsoft 365 or Office 365 license, Teams is enabled, so unless you previously disabled the Teams license, no action should be necessary.

  2. If users already have a Microsoft Calling Plan with a phone number, the only required change is to assign the user TeamsOnly mode in TeamsUpgradePolicy. Prior to assigning TeamsOnly mode, incoming PSTN calls will land in the user’s Skype for Business client. After the upgrade to TeamsOnly mode, incoming PSTN calls will land in the user’s Teams client.

From Skype for Business Online with on-premises voice

In this scenario, the user is already in Skype for Business Online, but their PSTN connectivity is on-premises, either using Skype for Business Server in hybrid mode or Cloud Connector Edition. Migrating these users to TeamsOnly mode with PSTN functionality means enabling them for Direct Routing, in which PSTN trunks connect directly to the Direct Routing service in the cloud, via your on-premises Session Border Controller (SBC).

The basic steps are listed below. Steps 1-4 are listed in the suggested sequence, but they can be done in any order. The key is that all of these should be completed before Step 5.

  1. If you are setting the tenant-wide policy to one of the Skype for Business modes, be sure to grandfather any existing Islands users by explicitly assigning them Islands mode, as previously described.

  2. Configure your tenant for Direct Routing. See Summary of per-tenant configuration of Direct Routing.

  3. If desired, configure various Teams policies for these users (for example, TeamsMessagingPolicy, TeamsMeetingPolicy, etc.). This can be done at any time, but if you want to ensure that users have the correct configuration when they are upgraded, it’s best to do this before the user is upgraded to TeamsOnly mode.

  4. Prepare select users for voice migration:

    • If necessary, assign the Teams license. Assuming the user is already functional in Skype for Business Online on-premises voice, the user already has Skype for Business Plan 2 as well as Microsoft Phone System. Leave both those plans enabled, including the Skype for Business Online Plan 2 license.
    • Assign the desired OnlineVoiceRoutingPolicy.
  5. Upgrade the user: These steps should be coordinated.

    • In Microsoft 365 or Office 365, upgrade the user to TeamsOnly mode (Grant-CsTeamsUpgradePolicy).
    • On the SBC, configure voice routing to enable incoming calls by sending calls to Direct Routing instead of to the on-premises Mediation Server.

From Skype for Business Server on-premises, with Enterprise Voice, to Direct Routing

In this scenario, the user is still homed in Skype for Business on-premises, and their PSTN connectivity is also on-premises. Migrating these users to TeamsOnly mode with PSTN functionality means enabling them for Direct Routing and then moving the user to the cloud.

The basic steps are listed below. Steps 1-5 are listed in the suggested sequence, but they can be done in any order. The key is that all of these should be completed before Step 6.

  1. If you will be setting the tenant-wide policy to one of the Skype for Business modes, be sure to grandfather existing Islands users by explicitly assigning them Islands mode, as previously described.

  2. If you haven’t already done so, configure the organization for Skype for Business hybrid.

  3. Configure your tenant for Direct Routing. See Summary of per-tenant configuration of Direct Routing.

  4. If desired, configure various Teams policies for these users (e.g. TeamsMessagingPolicy, TeamsMeetingPolicy, etc.). This can be done at any time, but if you want to ensure that users have the correct configuration when they are upgraded, it’s best to do this before the user is upgraded to TeamsOnly.

  5. Assign the Microsoft 365 or Office 365 licenses if necessary. The user should have both Teams and Skype for Business Online Plan 2, as well as Phone System. If the Skype for Business Online Plan 2 is disabled, re-enable it.

  6. Upgrade the user: These steps should be coordinated.

    • Using the on-premises Skype for Business tools, run Move-CsUser with -MoveToTeams switch. If you are using a version of Skype for Business Server that does not support the -MoveToTeams switch, first run Move-CsUser and then assign TeamsOnly mode in tenant remote PowerShell or Teams Admin Console.

    • On the SBC, configure voice routing to enable incoming calls by sending calls to Direct Routing instead of to the on-premises Mediation Server.

    • In Microsoft 365 or Office 365: Assign the relevant OnlineVoiceRoutingPolicy to enable outgoing calls.

From Skype for Business Server on-premises, with Enterprise Voice, to Microsoft Calling Plan

In this scenario, the user is still homed in Skype for Business on-premises, and their PSTN connectivity is also on-premises. Migrating these users to TeamsOnly mode with PSTN functionality means moving the user to the cloud and either porting their number from the old carrier to a Microsoft Calling plan or assigning the user a new number.

The basic steps are listed below.  Steps 1-5 are listed in the suggested sequence, but they can be done in any order. The key is that all of these should be completed before Step 6.

  1. If you will be setting the tenant-wide policy to one of the Skype for Business modes, be sure to grandfather existing Islands users by explicitly assigning them Islands mode, as previously described.

  2. If you haven’t already done so, configure the organization for Skype for Business hybrid.

  3. If desired, configure various Teams policies for these users (for example, TeamsMessagingPolicy, TeamsMeetingPolicy, etc.). This can be done at any time, but if you want to ensure that users have the correct configuration when they are upgraded, it’s best to do this before the user is upgraded to TeamsOnly.

  4. Assign the Microsoft 365 or Office 365 licenses if necessary.  The user should have both Teams and Skype for Business Online Plan 2, as well as Phone System. If the Skype for Business Online Plan 2 is disabled, re-enable it.

  5. Get phone numbers for your users. (For details see Manage phone numbers for your organization.)

    • If you will be re-using the numbers, submit a porting request to your carrier.
    • Alternatively, you can acquire new numbers directly from Microsoft.
  6. Upgrade the user and if needed assign LineUri. Using the on-premises Skype for Business tools, run Move-CsUser with the -MoveToTeams switch.

    • If you are porting numbers to Microsoft, you should coordinate the timing of this operation to occur when the port occurs.

    • If you are using new numbers from Microsoft, you’ll need to change the LineUri for the user. This must be done after the user is moved online using Set-CsOnlineVoiceUser. 

Summary of per-tenant configuration of Direct Routing

  1. Ensure that your Session Border Controller (SBC) is supported with Direct Routing by reviewing this list. You must also ensure that you have correct version of firmware.

  2. Pair your on-premises SBC with the Teams Direct Routing service. For details, see Pair the SBC to the Direct Routing service of Phone System.

  3. This configuration is essentially a mirror of the on-premises configuration. The online configuration consists of:

    • OnlineVoiceRoutingPolicy (based on the on-premises VoiceRoutingPolicy if migrating users from Skype for Business Online, and based on VoicePolicy if migrating users from on-premises with Enterprise Voice).
    • OnlinePSTNUsage objects (based on on-premises PSTN usage).
    • OnlineVoiceRoute objects (based on-premises VoiceRoute).

For more information, see Configure Direct Routing.

Manage EnterpriseVoiceEnabled property during migration

Whether using Direct Routing or a Microsoft Calling plan, a user must have EnterpriseVoiceEnabled=true in Azure AD for the user to have PSTN functionality. EnterpriseVoiceEnabled (“EV-enabled”) is a property (not a policy) that exists in both an on-premises directory and in the cloud. The value in the cloud is what matters for Teams. The exact logic for how EV-enabled gets set to true depends on the following scenario:

  • If the user is EV-enabled in on-premises Skype for Business Server and a Phone System license is assigned to the user prior to moving the user to the cloud with Move-CsUser, the online user will be provisioned with EV-enabled=true.

  • If an existing TeamsOnly or Skype for Business Online user is assigned a Phone System license, EV-enabled is not set to true by default. This also is the case if an on-premises user is moved to the cloud prior to assigning the Phone System license. In either case, the admin must specify the following cmdlet:

    Set-CsUser -EnterpriseVoiceEnabled $True 
    

Plan your Teams voice solution

Migration and interoperability guidance for organizations using Teams together with Skype for Business

Configure hybrid connectivity between Skype for Business Server and Microsoft 365 or Office 365

Move users between on-premises and cloud

Setting your coexistence and upgrade settings

Grant-CsTeamsUpgradePolicy

Using the Meeting Migration Service (MMS)