Discover why Direct Routing is the optimal PSTN model for Microsoft Teams deployments requiring existing carriers, Location-Based Routing, and Dynamic 911 compliance.
Table of Contents
Question
You have a Microsoft Teams deployment that has offices in Boston, San Francisco, and Austin.
You plan to deploy Microsoft Teams Phone to all three offices. The solution must meet the following requirements:
- Phone numbers must be registered with an existing carrier.
- The solution must support Location-Based Routing (LBR).
- The solution must support Dynamic 911.
Which PSTN connectivity model should you recommend?
Select only one answer.
A. Calling Plans
B. Direct Routing
C. Operator Connect
D. Teams Phone Mobile
Answer
To meet the requirements of retaining existing carrier-registered phone numbers, supporting Location-Based Routing (LBR), and enabling Dynamic 911, Direct Routing (B) is the correct PSTN connectivity model.
B. Direct Routing
Explanation
The answer is Direct Routing. The only option that supports LBR is Direct Routing.
Key Requirements Analysis
Existing Carrier Registration
Direct Routing allows organizations to retain their current PSTN carrier and phone numbers by connecting a certified Session Border Controller (SBC) to Teams. This avoids dependency on Microsoft’s Calling Plans or Operator Connect providers.
Location-Based Routing (LBR)
Direct Routing uniquely supports LBR, which enforces call routing policies based on a user’s network location (e.g., office IP addresses). For example:
- Calls from Boston users route through Boston’s PSTN gateway.
- Roaming users outside defined sites are restricted from making PSTN calls via unauthorized gateways.
- Operator Connect and Calling Plans lack granular LBR control, as they rely on carrier-managed infrastructure.
Dynamic 911 Compliance
Direct Routing supports Dynamic Emergency Calling in the U.S., enabling:
- Automatic PSAP routing based on the Teams client’s detected location.
- Emergency address validation via network topology (e.g., matching Boston office IPs to a registered address).
- While Operator Connect also supports Dynamic 911, it is limited to carrier-managed SBCs, reducing flexibility for multi-site configurations.
Why Other Options Fail
- Calling Plans (A): Requires porting numbers to Microsoft, violating the existing carrier requirement. LBR is unsupported.
- Operator Connect (C): Restricts carrier choice to Microsoft-approved providers and lacks LBR customization.
- Teams Phone Mobile (D): Designed for mobile-centric users with carrier SIM cards, not office-based PSTN needs.
Implementation Steps with Direct Routing
- Deploy certified SBCs (e.g., Ribbon, Audiocodes) at each office.
- Configure network sites in Teams Admin Center for Boston, San Francisco, and Austin.
- Enable Dynamic Emergency Calling policies and assign emergency addresses.
- Validate LBR rules to enforce local PSTN gateway usage.
By prioritizing carrier flexibility, location-aware routing, and emergency compliance, Direct Routing is the only model satisfying all requirements.
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