Teams Phone Direct Routing deep dive

Direct Routing is the connectivity option for Microsoft Teams Phone that lets you use any SIP-capable carrier for public-telephone-network (PSTN) connectivity, rather than buying Microsoft Calling Plans or going through Operator Connect. It's the most flexible option, and the right answer for many enterprises with existing carrier contracts or complex telephony requirements.

The architecture

Direct Routing introduces one component you don't have in the simpler options: a Session Border Controller (SBC). The SBC sits between Microsoft Teams and your SIP carrier, translating signalling and media between the two sides.

[Teams clients]
      │
      ▼
[Microsoft Teams Phone service]  (Azure-hosted)
      │  SIP/TLS, SRTP
      ▼
[Your SBC]   (on-prem or in Azure)
      │  SIP, RTP (or SIP/TLS, SRTP — varies by carrier)
      ▼
[SIP carrier]
      │
      ▼
[Public phone network]

The SBC is the only piece in this chain that doesn't come from Microsoft or your carrier. You buy it from one of Microsoft's certified vendors — AudioCodes, Ribbon, Oracle / Acme Packet, Anynode, Cisco, others — and configure it to talk to both Microsoft and your carrier.

Why use Direct Routing

• Existing carrier contracts — your enterprise has negotiated SIP-trunk rates with a specific carrier, and you'd like to keep them.
• Geographic coverage — Microsoft Calling Plans are available in some countries; in others (or for specific regulatory regimes), you need a local carrier.
• Contact-centre integration — Direct Routing can integrate with on-prem contact-centre platforms more flexibly than Calling Plans.
• Compliance recording — recording vendors plug into the SBC for call recording at the network level.
• Emergency-service integration — country-specific 911/112 routing often requires local carrier configuration.

Operational components

• The SBC itself — sized for peak concurrent call capacity, often deployed in pairs for HA.
• Certificates — public TLS certificates trusted by both Microsoft and the carrier.
• Network connectivity — direct paths between the SBC and Microsoft, with appropriate firewall rules and QoS.
• SIP trunk(s) to your carrier — sized for outbound concurrent calls.
• Voice routing policies in Teams admin center — decide which users use which SBC and which carrier paths.

Configuration on the Teams side

In the Teams admin center, Direct Routing involves:

• PSTN gateways — the SBCs registered with Teams.
• Voice routes — patterns that determine which calls route to which gateway.
• PSTN usages — named groupings of voice routes.
• Voice routing policies — assignments of users to PSTN usages.
• Dial plans — local number translations per region.

PowerShell is essential — much of this is more efficiently configured via Teams PowerShell than the GUI.

Common gotchas

• Certificate expiration on the SBC silently breaks signalling. Monitor.
• Media bypass (clients send media directly to the SBC rather than via Microsoft) reduces latency but requires careful network configuration.
• Local Media Optimization (LMO) for international deployments keeps media within regions.
• Emergency calling — every country has specific rules; Microsoft's documentation is essential reading per country.
• Survivability — if your SBC or trunk goes down, calls fail. Plan for HA.

When to pick Operator Connect instead

If you'd take Direct Routing's flexibility but want to skip the SBC operational burden, Operator Connect is the middle ground. Microsoft certifies specific operators who run the SBC for you, manage the trunk, and integrate via the Teams admin center directly. Less flexible, far less operational overhead.

For enterprises with telecoms ops teams that already manage SBCs and SIP carriers, Direct Routing is the natural choice. For enterprises without, Operator Connect is usually a better fit.