You might have already heard about “Direct Routing” with Microsoft Teams and what it does. In case you haven’t;

Direct Routing is there for the people who wants to use their on PSTN Trunks and SBC with Microsoft Teams. You can call it BYOT (Bring Your Own Trunk). The SBC must be a Teams certified SBC for this to work. And you can use it with a SIP Trunk, or an ISDN link (or with FXO lines if you really want). The connectivity will be as shown below;

License Requirement

In order to use Direct Routing, Microsoft Calling Plan license is required. Preferably, Microsoft 365 E5 license with complete set of features. Otherwise, an E3 license with add-on Phone System licenses to enable PSTN calling capability. Below are the license options that can be used;

Required licenses:

• Office 365 Enterprise E3 (including SfB Plan2, Exchange Plan2, and Teams) + Phone System
• Office 365 Enterprise E5 (including SfB Plan2, Exchange Plan2, Teams, and Phone System)

Optional licenses:

• Calling Plan
• Audio Conferencing

SBC Requirement 

As i mentioned above, not all SBCs are capable of supporting Direct Routing. As for now, there’s only Ribbon Communications (former Sonus) and AudioCodes SBCs are in the certified list. Below are the official document from the vendors;

AudioCodes : https://www.audiocodes.com/solutions-products/products/products-for-microsoft-365/direct-routing-for-microsoft-teams

Ribbon Communications : https://ribboncommunications.com/solutions/service-provider-solutions/microsoft-solutions/direct-routing-service-providers 

Will it work with Analogue?

Yes!. It can be integrated with an on-premises Analogue Gateway. However, Teams infrastructure in Microsoft 365 will have nothing to do with the Analogue configuration. The on-premises SBC will need to handle the routing between Teams endpoints and Analogue Gateway.

Will it work with Microsoft Phone System (Skype for Business Online)?

Unfortunately, Direct Routing is not supported for Skype for Business Online. Only possible way to use an on-premises SBC with BYOT is, to use the CCE (Cloud Connector Edition). Both of above mentioned vendors are certified for CCE as well.

I’d strongly recommend not to use this path as the CCE is expensive and soon to be obsolete option. Using Teams with Direct Routing will be the most cost effective and future proof option to consider.

I’m hoping above high level explanation will be sufficient to understand the concept behind how Direct Routing works. I’m planning to write a deployment and configuration guide regarding this in near future, when this becomes GA. Until then, please post any questions or clarifications in comments.