Microsoft Teams has become essential for business communication, bringing voice, video, and chat together on a single platform. However, many organizations need to extend Teams to support external voice calling.
Direct Routing provides a powerful solution, enabling businesses to connect Microsoft Teams to the Public Switched Telephone Network (PSTN) using SIP trunking. While it offers flexibility and cost savings, it also introduces security risks that must be carefully managed.
What is Direct Routing for Microsoft Teams?
Direct Routing is a Microsoft Teams feature that enables users to make and receive external phone calls through the Public Switched Telephone Network (PSTN). It works by connecting Teams to a certified Session Border Controller (SBC) and a SIP trunk, bypassing Microsoft Calling Plans. This setup gives businesses greater control over their telephony infrastructure while often reducing costs.
Direct Routing consists of three key components:
- Microsoft Teams Phone System – The core platform for managing voice communication.
- Certified SBC – Secures and controls voice traffic between Teams and the PSTN.
- SIP Trunking Provider – Connects calls to external phone networks.
This integration allows organizations to unify their internal and external communications under one platform while maintaining flexibility in carrier selection and routing configurations.
What are the Security Considerations for Direct Routing in Teams?
Connecting Microsoft Teams to external phone networks exposes your environment to various security risks, including:
- Unauthorized access to your telephony infrastructure
- Toll fraud and malicious call rerouting
- Denial of Service (DoS) attacks targeting your SIP services
- Data interception or leakage over unencrypted channels
Given these threats, businesses must prioritize security when planning and deploying Direct Routing. Improper configurations or unsecured connections can lead to financial loss, reputational damage, and compliance violations.
How Do I Secure Direct Routing for Microsoft Teams?
To deploy Direct Routing securely, follow these best practices:
1. Use Certified SBCs
Choose only Microsoft-certified Session Border Controllers that support secure SIP protocols and are tested for Teams compatibility.
2. Enable TLS and SRTP
Encrypt call setup and voice data using Transport Layer Security (TLS) for signaling and Secure Real-Time Transport Protocol (SRTP) for media.
3. Configure IP Whitelisting
Restrict SIP traffic to known IP addresses by setting up whitelists on your firewall and SBC, preventing unauthorized access.
4. Implement Strong Authentication
Use mutual TLS and certificate-based authentication to verify communication between Teams, the SBC, and the SIP provider.
5. Monitor SIP Traffic for Anomalies
Regularly analyze SIP traffic and logs for suspicious patterns, such as repeated failed call attempts or unusual call durations, which may indicate an attack.
6. Apply Rate Limiting
Limit SIP requests per second to mitigate the risk of brute-force and denial-of-service (DoS) attacks.
How Do I Perform a Security Audit of My Team’s Direct Routing Setup?
Conducting regular security audits of your Direct Routing environment helps identify vulnerabilities and ensure ongoing compliance. Here’s how to perform one:
- Review SBC Configurations: Check for outdated firmware, insecure protocols, and unnecessary open ports.
- Validate Encryption Settings: Ensure TLS and SRTP are enforced for all SIP sessions to protect signaling and voice data.
- Inspect Access Logs: Analyze logs for unauthorized access attempts and confirm that audit trails are properly maintained.
- Test Firewall Rules: Verify that only essential ports and IP addresses are permitted to prevent unauthorized connections.
- Verify Compliance: Align your configurations with regulatory requirements such as CMMC, HIPAA, or GDPR, depending on your industry.
How Does Direct Routing Security Relate to CMMC Compliance?
The Cybersecurity Maturity Model Certification (CMMC) is required for contractors working with the U.S. Department of Defense. When implementing Direct Routing in a government or defense environment (e.g., Microsoft Teams GCC High), organizations must meet strict CMMC standards:
- Controlled Access: All endpoints must be verified and restricted to U.S. persons.
- Audit Logging: Call logs and access attempts must be recorded and reviewed.
- Encryption in Transit: All signaling and media must be encrypted to protect sensitive communications.
- Incident Response: Mechanisms must be in place to detect and respond to SIP-related threats.
Choosing a provider experienced with GCC High and CMMC compliance ensures your Direct Routing infrastructure meets these critical requirements.
What Firewall Configurations Are Required for Direct Routing in Teams?
A properly configured firewall is essential for securing SIP traffic. Follow these best practices:
- Allow SIP Signaling on TCP/UDP Port 5061 – Ensure TLS-secured SIP traffic is permitted.
- Allow RTP Media on Dynamic Ports – Open media traffic ports as specified by your SBC vendor.
- Block SIP Requests from Unknown IPs – Prevent unauthorized access attempts.
- Enable Deep Packet Inspection (DPI) for SIP Sessions – Detect and mitigate potential threats.
- Apply NAT and Port Forwarding Rules – Protect internal network addresses from exposure.
Always refer to your SBC provider’s documentation for a full list of required ports and IP configurations specific to your setup.
What is SIP Trunking, and How Does it Relate to Direct Routing?
SIP Trunking is a method of transmitting voice communication over the internet using the Session Initiation Protocol (SIP), replacing traditional phone lines with a virtual connection.
In Direct Routing, SIP trunks act as the bridge between Microsoft Teams and the PSTN (Public Switched Telephone Network) by routing calls between your Teams environment and external networks.
How Do I Improve Voice Quality in Teams Direct Routing?
Voice quality is just as important as security. Here are several ways to optimize performance:
- Prioritize Voice Traffic with QoS: Use Quality of Service (QoS) tagging to prioritize SIP traffic over the network.
- Use High-Bandwidth, Low-Latency Internet: Ensure your ISP can handle the volume of voice traffic.
- Reduce Jitter and Packet Loss: Use jitter buffers and error correction tools.
- Deploy Redundant Network Paths: Use multiple internet links or SD-WAN to ensure reliability.
- Monitor with Real-Time Tools: Use analytics platforms to track call quality metrics like MOS (Mean Opinion Score).
How Do I Choose a Secure Direct Routing Provider for Teams?
When selecting a Direct Routing provider, prioritize these key security and reliability features:
- Microsoft-Certified SBCs – Ensure seamless integration and compliance with Teams.
- End-to-End Encryption (TLS/SRTP) – Protect voice traffic from interception.
- Geo-Redundant Infrastructure – Maintain service continuity with failover.
- 24/7 Monitoring and Support – Ensure rapid response to issues.
- Proven Compliance Record – Look for adherence to CMMC, HIPAA, FedRAMP, and other relevant standards.
- Clear SLAs for Uptime and Support – Guarantee performance and reliability commitments.
Providers like Intuity specialize in secure Direct Routing tailored for regulated industries, including government, healthcare, and finance.
Common Questions About Direct Routing
What Are the Common Challenges When Implementing Secure Direct Routing in Teams?
- SBC Configuration Complexity: Incorrect SBC setup can lead to dropped calls or security vulnerabilities.
- Interoperability Issues: Not all SIP trunk providers are compatible with Teams.
- Compliance Gaps: Failing to meet industry-specific requirements can result in penalties.
- Lack of Monitoring: Without proactive monitoring, threats may go unnoticed.
How Do I Monitor Direct Routing Security in Teams?
- Use SIEM Tools: Integrate Session Initiation logs into your Security Information and Event Management (SIEM) system.
- Set Alerts for Anomalies: Create thresholds for call volume, duration, and failed attempts.
- Conduct Regular Penetration Testing: Simulate attacks to test your defenses.
- Maintain Up-to-Date Documentation: Keep a record of configurations, updates, and changes for auditing purposes.
Direct Routing is a powerful tool for enabling voice communication within Microsoft Teams, but with great power comes great responsibility. Ensuring the security of your Direct Routing setup requires more than just basic configuration—it involves rigorous planning, continuous monitoring, and ongoing compliance efforts.
By understanding the risks, implementing best practices, and choosing a qualified provider, you can create a secure, reliable, and high-performing Teams voice environment that meets the needs of modern business communication and regulatory compliance. To discuss in more detail, please contact Intuity today at (800) 811-1086. Please feel free to also follow us on Twitter.