Plan Phone System with on-premises PSTN connectivity in Skype for Business Server

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Important

Skype for Business Online was retired on July 31, 2021 and PSTN connectivity between your on-premises environment whether, through Skype for Business Server or Cloud Connector Edition and Skype for Business Online, is no longer supported. Learn how to connect your on-premises telephony network to Teams using Direct Routing.

Learn about the planning considerations for Phone System (Cloud PBX) with on-premises PSTN connectivity.

This content is relevant if you already have Skype for Business Server or Lync Server 2013 deployed on-premises. For other scenarios, see Microsoft telephony solutions.

Phone System with on-premises PSTN connectivity enables you to leverage Phone System (Cloud PBX) capabilities for your users. This can help with the following scenarios:

  • You have some of your Skype for Business users homed on-premises and others homed in Skype for Business Online. You can now enable Phone System capabilities and features for your users homed in Skype for Business Online, but continue to use on-premises PSTN connectivity.

  • You have an on-premises deployment and you want to move some or all of your users to Skype for Business Online but continue to use on-premises PSTN connectivity.

    Important

    To successfully enable users for Phone System with on-premises PSTN connectivity, their SIP address must be in your own domain. The use of the default domain for Microsoft 365 or Office 365, onmicrosoft.com, is not supported.

To learn more about Phone System, including licensing and plans, see PSTN Calling plans for Skype for Business.

Feature comparison

Cloud PBX with on-premises PSTN Connectivity does not offer the same feature set as a fully on-premises Enterprise Voice solution. To help you decide whether Cloud PBX with on-premises PSTN Connectivity will provide the right feature set for your organization, see Here's what you get with Cloud PBX.

Benefits and planning considerations

Caution

Lync Phone Edition devices MUST be updated to minimum required firmware in your on premises environment PRIOR to moving to Skype for Business Online. If you move your users from on-premises to online prior to updating the firmware, users will be unable to connect using their phones. To correct this problem, users must be moved back to the on premises environment to have their phones updated to the minimum firmware. DO NOT ATTEMPT TO UPDATE TO MINIMUM FIRMWARE OR HARD RESET THE PHONE PRIOR TO MOVING THE USER BACK TO YOUR ON PREMISES ENVIRONMENT. If a hard reset is performed while the device is not at minimum firmware it will default to using PIN Authentication, which is not supported in Skype for Business Online. For more information, please refer to Getting phones for Skype for Business Online.

By deploying Phone System with on-premises PSTN connectivity, you can move your users to the cloud via Skype for Business Online at your own pace, while retaining their on-premises PSTN connectivity. If you have a PBX, you continue to use it to provide PSTN connectivity for the users you move to the cloud. Once a user is moved to Skype for Business Online and Phone System, their legacy PBX phone will no longer work, but their phone number will route to any of the Skype for Business clients for PCs or Smart phones as well as Skype for Business-compliant desk phones. Once ported, Phone System users and legacy PBX users can call each other normally as well as make/receive PSTN calls using their normal phone number.

You may have a custom feature or a major add-on to your legacy PBX, such as a call center. If the custom feature is not currently available on Phone System, you should leave those users that require that custom feature on-premises with the legacy PBX, and just port the users who do not need to access the custom feature to Phone System with on-premises PSTN connectivity.

For a list of legacy PBXs that interoperate directly with Skype for Business Server 2015 see Infrastructure Qualified for Microsoft Lync. If your PBX is not on this list, you can use a Session Border Controller to connect your PBX with Phone System in Skype for Business Online.

Network considerations for quality and performance

When deploying a cloud-hosted service like Phone System with on-premises PSTN connectivity, you must keep the following in mind. In a purely on-premise Skype for Business Server 2015 Enterprise Voice deployment, all the infrastructure and clients are on the enterprise's own network. The quality and performance of this network, which is critical for high-quality audio and video, are under the direct control of the enterprise staff. With Phone System with on-premises PSTN connectivity, there are three networks involved, two of which the customer is responsible for but only one of which the enterprise staff has direct control over:

  • Microsoft's Global Media Delivery Network Microsoft's global cloud network and infrastructure. Phone System servers and traffic traverse this network.

  • Enterprise/Cloud PSTN Interconnect This is the network that connects your enterprise to the cloud. This is not necessarily the same as your generic Internet connection.

  • Your enterprise's own network The quality of the real-time media is heavily dependent on your own network: especially the WiFi network and the quality of the interconnect used to reach the cloud.

Note

For more information on tuning performance in Skype for Business Online, see Tune Skype for Business Online performance.

Prerequisites for using Phone System with on-premises PSTN connectivity

Before you can configure Phone System with on-premises PSTN connectivity and move users to Skype for Business Online, you must confirm that you have the following prerequisites in place:

On-premises server versions. The versions of the servers in your on-premises deployment must be listed in the following table to support Phone System with on-premises PSTN connectivity.

Server role Supported versions\*
Federation Edge**
Skype for Business Server 2015
Next Hop Federation Route Internal Pool Server
Skype for Business Server 2015, March 2016 Cumulative Update 6.0.9319.235 or higher (Front End or Director)
Front End User Server
Skype for Business Server 2015
Lync Server 2013
Edge Server
Skype for Business Server 2015
Mediation Server
Skype for Business Server 2015
Lync Server 2013

*Minimum supported versions are:

  • Skype for Business Server 2015, March 2016 Cumulative Update 6.0.9319.235

  • Lync Server 2013 July 2015 Cumulative Update 5.0.8308.920

**The federation route for all supported SIP domains must route through the Skype for Business Server 2015 Edge Server running the March 2016 or higher Cumulative Update. If the user pool is on Lync Server 2013, that external pool traffic remains on Lync Server 2013 Edge Server.

In addition you must ensure the following:

For information about deploying Phone System, see Enable users for Phone System with on-premises PSTN connectivity in Skype for Business Server.