01
The Problem
Users need Teams Phone, but the organization still depends on existing carriers, PBXs, numbers and critical voice services.
Use Case • PBX-to-Teams Voice Migration
Move enterprise calling to Microsoft Teams without disrupting your voice operations.
Keep your existing SIP carriers, phone numbers, PBX integrations and critical voice services while moving users to Microsoft Teams Phone through a controlled migration architecture.
PBX-to-Teams Migration
PBX • SIP CARRIER • SENTINEL SBC • EXISTING PBX
TEAMS PHONE
SENTINEL SBC
SIP CARRIERS
TEAMS PHONE
TeamsEnterprise calling
SBCSupported connectivity
SIPPBX and carrier integration
Preserve Carrier ChoiceKeep preferred SIP carriers, numbers and regional routing during the Teams migration.
Reduce Migration RiskMove users in phases while maintaining PBX coexistence and operational continuity.
Retain Existing AssetsContinue using selected PBXs, contact centers, gateways and legacy services.
Control the CutoverValidate routing, failover, emergency calling and interoperability before expansion.
Supported Sentinel SBC models are listed by Microsoft for Teams Direct Routing. Certification applies only to documented Sentinel models and supported software versions; it does not apply to Mediatrix gateways, Audiotrix products or the complete solution architecture. Verify the current Microsoft list.
The customer use case
Your users need Teams, but your existing voice environment cannot simply be switched off.
Organizations adopt Microsoft Teams to unify collaboration, calling and meetings. But enterprise voice is not only a cloud license. It requires secure SIP interconnection, PSTN access, carrier choice, emergency routing, migration planning, resiliency and interoperability with existing systems.
02
The Migration Approach
Deploy a supported Sentinel SBC as the controlled interconnection point and migrate users, sites and call flows in phases.
03
The Business Outcome
Adopt Teams calling while preserving carrier choice, reducing disruption and maintaining visibility over enterprise voice.
Technical schematic
A phased PBX-to-Teams migration architecture.
The SBC is the secure interconnection point between Microsoft Teams and external telephony. It provides SIP security, routing intelligence, interoperability, policy control and visibility.
Existing Voice Environment
PBX users, SIP trunks, phone numbers, contact centers and legacy services.
Sentinel SBC
TLS/SRTP, topology hiding, SIP normalization, routing and policy control.
Microsoft Teams Phone
Teams users, calling policies, cloud collaboration and phased enterprise adoption.
Migration control layer
Why a controlled SBC layer reduces PBX-to-Teams migration risk.
Teams Direct Routing exposes a critical voice boundary. Sentinel SBCs help protect that boundary while enabling interoperability with SIP trunks, carriers and enterprise voice systems.
TLS SignalingSecure SIP signaling between Teams and the SBC to reduce exposure of voice-session control traffic.
SRTP MediaEncrypted media transport for protected voice communications across the Teams voice edge.
Topology HidingConceal internal voice architecture from external networks and carriers.
SIP NormalizationAdapt and normalize SIP behavior between Teams, carriers, PBXs and other voice systems.
Policy ControlApply routing, session and access policies at the voice border.
Diagnostics & VisibilityImprove troubleshooting for registration, routing, media and interoperability issues.
Use case outcome
Move users to Teams while keeping the voice services the business still depends on.
The objective is not simply to deploy an SBC. It is to create a migration path that preserves phone numbers, carrier agreements, PBX functions, contact centers, emergency calling and selected legacy systems until they can be retired safely.
01
Before
Multiple PBXs, carriers, sites and legacy services create complexity and make a one-time cutover risky.
02
During
Sentinel provides the controlled interconnection layer for Teams, carriers, PBXs and phased user migration.
03
After
The organization gains a clearer Teams voice architecture while retaining only the legacy systems that still provide business value.
Certification scope
Certification applies to supported Sentinel SBC models and software versions.
Microsoft certification is specific to documented Sentinel SBC models and supported firmware versions listed for Teams Direct Routing. It does not certify the complete customer architecture, SIP carrier, PBX, Mediatrix gateway or Audiotrix product. Current eligibility should always be verified before deployment.
Migration strategy comparison
Replace everything at once vs migrate in controlled phases.
A phased Direct Routing strategy is often better suited to organizations that must preserve carriers, PBXs, phone numbers, contact centers or regional routing.
| Capability | Full replacement approach | Phased migration with Sentinel SBC | Business Impact |
|---|---|---|---|
| Carrier Choice | Limited to available Microsoft plans and regions | Use preferred SIP carriers and regional providers | More control over cost, routing and telecom strategy |
| SIP Trunk Integration | Limited | Full SIP trunk integration through SBC | Preserve existing carrier contracts and trunking architecture |
| PBX Coexistence | Limited | Supports migration and coexistence with PBX systems | Reduce migration risk and avoid forced rip-and-replace |
| Contact Center Integration | Limited depending on architecture | Can support broader SIP and contact center interconnection | Better fit for complex enterprise voice environments |
| Voice Security Control | Less customer-controlled | Controlled SBC layer with SIP security policies | Greater visibility and demarcation at the voice edge |
| Geographic Flexibility | Region-dependent | Flexible by SIP carrier and SBC deployment strategy | Better alignment with global and multi-site requirements |
Platform selection for this use case
Select the Sentinel platform that fits the migration scale.
The correct platform depends on site count, deployment model, expected call capacity and whether physical telephony interfaces are required.
| Platform | Deployment Type | Best Fit | Typical Teams Use Case | Key Advantage |
|---|---|---|---|---|
| Sentinel Mini | Compact hardware appliance | Small offices and focused deployments | Branch Direct Routing, small user groups, remote sites | Compact footprint with secure Teams voice edge |
| Sentinel 100 | Hardware appliance | SMB and branch environments | Distributed enterprise voice and regional offices | Balanced capacity, control and deployment simplicity |
| Sentinel 400 | Higher-capacity appliance | Enterprise headquarters and larger sites | Multi-site aggregation, higher-density Teams voice | Greater scale for enterprise Direct Routing |
| Sentinel CS / DGW50 | Virtual SBC software | Virtualized, cloud-aligned and service provider deployments | Large-scale Teams voice, managed services and virtual SBC architecture | Software-driven scalability and deployment flexibility |
Where this use case applies
Organizations that benefit most from a phased Teams voice migration.
Teams Direct Routing is valuable wherever organizations need secure, controlled and flexible voice architecture across users, sites, carriers and operational environments.
Migration roadmap
How to migrate enterprise voice to Teams without unnecessary disruption.
A successful deployment aligns cloud collaboration goals with real-world voice, routing, security, carrier and migration requirements.
1. AssessReview users, carriers, PBX dependencies, sites, numbering and migration goals.
2. ArchitectDesign Teams, SBC, SIP trunk, routing, security and resiliency architecture.
3. SelectChoose Sentinel Mini, 100, 400 or Sentinel CS based on scale and topology.
4. ValidateTest call flows, carrier behavior, emergency routing, failover and interoperability.
5. ScaleRoll out across users, regions, sites and managed voice environments.
Why a direct cutover can create unnecessary business risk.
A successful Teams migration requires more than enabling cloud calling.
A Direct Routing architecture without a controlled SBC layer can create operational blind spots, security exposure and migration complexity.
Without a proper SBC layer
- Limited SIP normalization and interoperability control.
- Reduced visibility into call failures and signaling behavior.
- Carrier lock-in or fragmented regional routing strategy.
- Weaker voice-edge demarcation and security policy enforcement.
- Harder migration from PBX, contact center and legacy voice systems.
With Sentinel SBC architecture
- Secure Teams voice edge using TLS, SRTP and topology hiding.
- Controlled SIP routing, normalization and policy management.
- Carrier flexibility and multi-provider architecture support.
- Better troubleshooting, visibility and operational discipline.
- Cleaner enterprise migration from legacy voice to Teams.
FAQ
PBX-to-Teams migration questions.
What is Microsoft Teams Direct Routing?
Direct Routing connects Microsoft Teams Phone to SIP trunks, PSTN services and enterprise telephony infrastructure through a Session Border Controller.
Why is a Session Border Controller required?
The SBC secures the voice edge, normalizes SIP, controls routing, protects topology and enables interoperability between Teams and external networks.
Can Sentinel SBCs support carrier flexibility?
Yes. Sentinel SBCs help organizations connect Teams to preferred SIP carriers and preserve regional routing and telecom strategy.
Can Direct Routing help migrate from a PBX?
Yes. Direct Routing can support coexistence and phased migration from PBX environments into Teams voice.
Which Sentinel SBC should I choose?
The right model depends on scale, user count, sites, topology, virtual or hardware preference, and service provider requirements.
What exactly is Microsoft-certified?
Certification applies only to supported Sentinel SBC models and software versions documented by Microsoft for Teams Direct Routing. It does not apply to the complete solution architecture, Mediatrix gateways or Audiotrix products.
Can M5 help design the architecture?
Yes. M5 Technologies can help evaluate voice infrastructure, model selection, SIP integration, security and deployment strategy.
PBX-to-Teams migration review
Get a phased Teams voice migration plan for your environment.
Share your current PBX, carriers, sites, phone numbers and migration objectives. M5 Technologies can help identify the right Sentinel architecture and the safest path to Teams Phone.
- Sentinel SBC platform selection
- Microsoft Teams Direct Routing architecture
- SIP trunk, carrier and PSTN integration
- PBX migration and hybrid voice planning
- Teams voice security and interoperability review