ProSBC for Microsoft Teams Direct Routing

What a Microsoft Teams SBC does and why your network needs one

Microsoft Teams handles internal chat, meetings, and screen sharing natively, but connecting Teams users to external phone numbers requires a Session Border Controller. A Microsoft Teams SBC serves as the gateway between the Teams cloud environment and the public switched telephone network (PSTN), translating between Microsoft’s protocols and the standard SIP signaling used by carriers worldwide.

The role of an SBC in Teams Direct Routing

Teams Direct Routing is Microsoft’s architecture for PSTN connectivity that gives service providers and enterprises full control over their voice infrastructure. Instead of purchasing Microsoft Calling Plans, organizations connect their own SIP trunks through a compatible SBC. The Teams Direct Routing SBC handles several functions simultaneously:

• SIP signaling normalization — Teams sends and receives SIP messages in a specific format. The SBC translates between Teams’ SIP dialect and whatever format each carrier or PBX expects, handling differences in SIP headers, session timers, and DTMF signaling.
• Media handling and codec transcoding — When a Teams user calls an external number, the SBC bridges the media stream between the two endpoints, managing codec negotiation and, when necessary, transcoding between formats.
• Encryption enforcement — Microsoft requires TLS for signaling and SRTP for media on all Direct Routing connections. The SBC terminates these encrypted connections and can bridge to carriers that use unencrypted RTP, protecting every call without requiring every carrier to support SRTP.
• Topology hiding — The SBC conceals internal network addresses from external parties, preventing reconnaissance of your infrastructure and isolating the Teams environment from the public internet.

Multi-tenant SBC architecture for service providers

For MSPs and ISPs delivering Teams calling to multiple customers, a multi-tenant SBC architecture is essential. ProSBC supports up to 1,024 trunk groups (NAPs), allowing service providers to maintain separate call routing rules, security policies, and SIP trunk configurations for each customer from a single Microsoft Teams SBC instance. One SBC deployment can serve dozens or hundreds of end customers, each with their own carrier connections and call handling rules.

Per-tenant monitoring gives providers visibility into call quality metrics (MOS scores, jitter, packet loss) for each customer independently, supporting SLA commitments without dedicated hardware per tenant. ProSBC exposes these metrics through CDRs, SNMP, and a REST API, making it straightforward to integrate with existing monitoring platforms.

Deploy on the infrastructure you already manage

ProSBC runs as a software SBC on VMware, KVM, or Proxmox in your own data center, on AWS or Microsoft Azure for cloud-native architectures, or on bare-metal servers for maximum performance. An active/standby high availability configuration ensures that if the primary Teams Direct Routing SBC goes down, the standby takes over with minimal interruption. For service providers who prefer not to manage the SBC themselves, TelcoBridges offers a fully managed SBC service covering deployment, monitoring, and ongoing maintenance.

Regulatory compliance built into the call path

Organizations deploying an SBC for Microsoft Teams also need to address regulatory requirements. In North America, the FCC mandates STIR/SHAKEN caller ID authentication for voice calls. ProSBC integrates with STIR/SHAKEN signing and verification services at the SBC layer, applying the correct attestation level (A, B, or C) per call based on the traffic type. This is particularly important for MSPs handling mixed traffic: retail customers may require full attestation, while wholesale or gateway traffic receives partial attestation, all managed through a single SBC for Teams deployment.

Subscription pricing designed for service providers

Unlike traditional SBC appliances that require large upfront hardware investments, ProSBC uses a session-based subscription model rather than per-seat or per-user licensing. This OPEX approach lets MSPs scale their Microsoft Teams SBC capacity up or down as their customer base grows, without the capital risk of traditional hardware SBC purchases.

Test your Teams Direct Routing configuration before going live

ProSBC Lab provides a free, permanent 3-session license that includes full Teams Direct Routing capability. Service providers can validate their SIP trunk configuration, test call routing rules, and confirm interoperability with their carrier’s infrastructure before committing to a production license. The lab runs the same firmware as the production SBC, so configurations tested in the lab transfer directly to production without rework. This is particularly valuable for MSPs evaluating whether to add Microsoft Teams calling to their service portfolio: you can build and test the complete call flow, from Teams client through the SBC to the PSTN carrier, at no cost.

Common Teams SBC deployment scenarios

Service providers deploy a Microsoft Teams SBC to address several common scenarios. An MSP managing voice services for small and mid-size businesses typically connects a single multi-tenant ProSBC instance to one or more SIP trunk providers, then configures separate NAPs for each customer’s Teams tenant. Each customer gets their own phone numbers, call routing rules, and quality monitoring, while the MSP manages everything from one platform. An ISP bundling Teams calling with internet service uses the same architecture to add voice as a value-added service, differentiating their offering from competitors who provide connectivity alone.

Enterprises with existing on-premises PBX infrastructure use ProSBC to bridge their legacy phone systems with Teams. The SBC handles the SIP call flow translation between the PBX and Teams, allowing organizations to migrate to Teams calling at their own pace rather than replacing their entire telephony stack at once. In contact center environments, ProSBC connects Teams with CCaaS platforms and carrier SIP trunks simultaneously, routing customer calls to the right destination based on rules defined in the SBC’s routing engine.