This chapter covers Microsoft Teams Calling Administration, a critical part of the Tenant Management domain (Objective 1.3) for the MS-102 exam. Teams Calling enables voice services—PSTN connectivity, call routing, and emergency calling—through Calling Plans, Direct Routing, or Operator Connect. Approximately 15-20% of exam questions touch on Teams Calling configuration, licensing, and troubleshooting. You will learn the architectural components, licensing requirements, configuration steps, and common pitfalls tested on the exam.
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Imagine a large company with a single main phone number and hundreds of employees with internal extensions. Historically, a switchboard operator would receive all incoming calls, ask who the caller wanted, and manually connect the call to the correct extension. When an employee made an external call, the operator would assign an outside line and log which extension used it. This is exactly how Microsoft Teams Calling works with Direct Routing. The Session Border Controller (SBC) acts as the operator — it receives SIP trunks from the carrier, registers with Microsoft Phone System, and routes calls to the correct Teams user based on dialed number. For outbound calls, Teams sends the call to the SBC, which selects an available trunk and places the call on the PSTN. The SBC maintains a mapping of users to internal SIP URIs, just like the operator's extension list. Without the SBC, Teams would have no connection to the public phone network — just like employees with phones but no outside lines. The operator (SBC) enforces rules: which extensions can call internationally, what hours calls are allowed, and how many concurrent calls can be handled. If the operator is misconfigured, calls fail or go to the wrong extension.
What is Teams Calling and Why It Exists
Microsoft Teams Calling provides voice over IP (VoIP) telephony within Teams, replacing traditional PBX systems. It allows users to make, receive, and transfer calls using the PSTN (Public Switched Telephone Network). The primary reason for Teams Calling is to unify communications—voice, video, chat, and collaboration—into a single client, reducing the need for separate phone systems and lowering costs.
How Teams Calling Works Internally
Teams Calling relies on three main deployment options: - Calling Plans: Microsoft provides PSTN connectivity directly. Users get a phone number from Microsoft, and calls are routed through Microsoft's carrier network. - Direct Routing: Organizations connect their own SIP trunking via a certified Session Border Controller (SBC) to Microsoft Phone System. This allows retaining existing carrier contracts and phone numbers. - Operator Connect: Similar to Direct Routing but with Microsoft-managed SBCs and simplified provisioning.
All options use the same core architecture: the Teams client communicates with Microsoft Phone System via SIP over TLS, and media (audio/video) flows over SRTP. For Calling Plans, Microsoft handles the SBC and carrier interconnection. For Direct Routing, the customer’s SBC must be certified and configured with specific FQDNs and certificates.
Key Components and Defaults
SBC (Session Border Controller): Must support Microsoft Teams Direct Routing specifications. Default SIP port: 5061 (TLS). Must present a certificate issued by a public CA.
Phone System License: Required for all users with PSTN calling. Includes voicemail, call queues, and auto attendants. Does NOT include PSTN minutes.
Calling Plan License: Adds PSTN minutes. Available in Domestic (120/300/1200 min) and International (600 min) plans. Domestically only calls within the country/region are counted.
Communication Credits: Pay-as-you-go for overflow minutes beyond the Calling Plan. Must be set up if using Calling Plans.
Emergency Calling: Dynamic emergency calling (E911) requires a registered address for each user. Static emergency calling uses a single address per location.
Configuration and Verification Commands
To configure Direct Routing, you use PowerShell or Teams Admin Center. Key cmdlets:
New-CsOnlinePSTNGateway -Identity "sbc.contoso.com" -Enabled $true -SipSignalingPort 5061 -MaxConcurrentSessions 100To enable a user for Direct Routing:
Set-CsUser -Identity "user@contoso.com" -EnterpriseVoiceEnabled $true -HostedVoiceMail $true -OnPremLineUri "tel:+14255551234"To assign a voice routing policy:
New-CsOnlineVoiceRoutingPolicy -Identity "USOnly" -Description "US calls only" -OnlinePstnUsages @("US")
Grant-CsOnlineVoiceRoutingPolicy -Identity "user@contoso.com" -PolicyName "USOnly"Verification:
Get-CsOnlineUser -Identity "user@contoso.com" | fl EnterpriseVoiceEnabled, HostedVoiceMail, OnPremLineUri
Test-CsOnlinePSTNOutboundCall -TargetPSTNNumber "+14255551234" -CallerId "user@contoso.com"Interaction with Related Technologies
Teams Calling integrates with: - Azure AD: User identities and authentication. Calling features require Azure AD accounts. - Teams Policies: Dial plans (number normalization), voice routing policies, and emergency calling policies control call behavior. - Exchange Online: Voicemail is stored in Exchange Online. Transcription and call answering rules are managed there. - Call Quality Dashboard: Monitors call quality metrics like jitter, packet loss, and round-trip time. - Network Assessment: Teams requires specific network conditions: < 30ms latency, < 10ms jitter, < 1% packet loss for optimal quality.
Licensing Details
Phone System: Included in E5 or as an add-on for E1/E3. Required for all PSTN calling.
Domestic Calling Plan: Included in E5 (limited) or add-on. Provides minutes within the country.
International Calling Plan: Add-on for international calls.
Communication Credits: Needed for Calling Plans when minutes exceed the plan, or for toll-free numbers. Set up as a subscription.
Direct Routing: No per-user PSTN minute license required, but you must have Phone System license and pay for your own carrier.
Emergency Calling
Teams supports dynamic emergency calling (E911) where the user's registered location is sent to emergency services. This requires:
An emergency calling policy that defines how to handle calls.
A network location (wireless or wired) that maps IP addresses to physical locations.
For Calling Plans, emergency addresses must be registered per user or per number.
For Direct Routing, emergency calls can be routed to a specific trunk or to the carrier.
Number Porting
To port existing phone numbers to Teams:
For Calling Plans: Submit a port order in Teams Admin Center. Takes 5-10 business days.
For Direct Routing: Numbers remain with the carrier; you just route calls through Teams.
For Operator Connect: Carrier manages porting.
Troubleshooting Common Issues
No dial tone: Check licensing (Phone System + Calling Plan). Ensure user is Enterprise Voice enabled.
Calls fail: Verify SBC certificate, DNS resolution of SBC FQDN, firewall rules (TCP 5061, UDP 3478-3481, 50-59, 500, 4500).
One-way audio: Check media bypass configuration. Ensure both client and SBC can reach each other's media IPs.
Emergency call routing: Validate emergency calling policy and network location.
Direct Routing Specifics
Direct Routing requires a certified SBC. Microsoft publishes a list of certified SBC vendors (AudioCodes, Ribbon, Oracle, etc.). The SBC must:
Support TLS 1.2.
Present a certificate from a public CA (not self-signed).
Be accessible from Microsoft Teams IP ranges.
Support SIP and SRTP.
Configuration steps: 1. Register the SBC in Teams Admin Center or PowerShell. 2. Configure voice routing policies and PSTN usages. 3. Assign policies to users. 4. Enable users for Enterprise Voice. 5. Test calls.
Operator Connect
Operator Connect simplifies Direct Routing by having Microsoft manage the SBC. The carrier provides the trunk, and provisioning is automated. Benefits: no SBC management, faster deployment, and carrier-grade SLAs. Licensing: same as Direct Routing (Phone System license).
Calling Plans vs Direct Routing vs Operator Connect
Calling Plans: Best for small to medium organizations without existing carrier contracts. Simple but limited minutes and no control over carrier.
Direct Routing: Best for large enterprises with existing carrier relationships, complex routing needs, or compliance requirements. Full control but requires SBC expertise.
Operator Connect: Best for organizations wanting simplicity of Calling Plans with the flexibility of Direct Routing. Microsoft handles SBC, carrier handles PSTN.
Exam Focus
The MS-102 exam tests:
Licensing requirements: Phone System is mandatory for all PSTN calling. Calling Plan is separate.
Direct Routing configuration steps: Register SBC, configure voice routing, enable users.
Emergency calling: dynamic vs static, required components.
Number porting: only applicable for Calling Plans and Operator Connect, not Direct Routing (numbers stay with carrier).
Communication Credits: needed when Calling Plan minutes are exceeded.
Common traps: Confusing Phone System with Calling Plan; thinking Direct Routing doesn't require Phone System; assuming all users need a Calling Plan with Direct Routing (they don't).
License Users for Phone System
Every user who needs PSTN calling must have a Phone System license. This license is included in Microsoft 365 E5 or available as an add-on for E1/E3. Without it, the user cannot be enabled for Enterprise Voice. In the Teams Admin Center, navigate to Users > Manage users, select the user, and assign the Phone System license. Alternatively, use PowerShell: Set-MsolUserLicense -UserPrincipalName user@contoso.com -AddLicenses "contoso:PHONESYSTEM". Verify with Get-MsolUser -UserPrincipalName user@contoso.com | Select-Object Licenses.
Assign Calling Plan or Configure Direct Routing
If using Calling Plans, assign a Calling Plan license (Domestic or International) to each user. If using Direct Routing, register the SBC with Microsoft Phone System. Use PowerShell: New-CsOnlinePSTNGateway -Identity sbc.contoso.com -Enabled $true -SipSignalingPort 5061. Then configure voice routing policies and PSTN usages. For Operator Connect, enable the operator in Teams Admin Center and assign numbers to users.
Enable User for Enterprise Voice
For Direct Routing, you must enable the user for Enterprise Voice. This is done via PowerShell: Set-CsUser -Identity user@contoso.com -EnterpriseVoiceEnabled $true -HostedVoiceMail $true -OnPremLineUri "tel:+14255551234". The OnPremLineUri is the user's PSTN number in E.164 format. For Calling Plans, this step is automatic when you assign a phone number. Verify with Get-CsOnlineUser -Identity user@contoso.com.
Assign Voice Routing Policy
Direct Routing requires a voice routing policy that defines which PSTN usages (e.g., 'US', 'International') are allowed. Create a policy with New-CsOnlineVoiceRoutingPolicy, then grant it to the user with Grant-CsOnlineVoiceRoutingPolicy. The PSTN usage must be associated with a route that points to the SBC. For Calling Plans, no voice routing policy is needed—Microsoft routes calls automatically.
Test and Verify Call Functionality
After configuration, test outbound and inbound calls. Use Test-CsOnlinePSTNOutboundCall in PowerShell to simulate a call. Check the Call History in Teams Admin Center for any failures. Verify that the SBC is reachable from Microsoft Teams IP ranges. For emergency calling, test that the correct emergency address is transmitted. Monitor call quality in Call Quality Dashboard.
Scenario 1: Large Enterprise Migrating from On-Premises PBX
A multinational corporation with 10,000 employees and existing SIP trunks from a carrier wants to migrate to Teams Calling. They choose Direct Routing to retain their carrier contracts and phone numbers. The deployment involves:
Deploying two AudioCodes Mediant SBCs in a geo-redundant configuration across two data centers.
Configuring each SBC with a public certificate from DigiCert and FQDN (sbc1.contoso.com, sbc2.contoso.com).
Registering both SBCs in Teams Admin Center.
Creating voice routing policies for different countries (US, UK, India) with corresponding PSTN usages.
Assigning phone numbers to users via OnPremLineUri.
Enabling 911 emergency calling with dynamic locations based on IP subnets.
Common issues: SBC certificate expiration causes call failures; firewall rules blocking SIP traffic; misconfigured voice routing policies causing calls to route to the wrong SBC. Performance considerations: each SBC handles up to 2,000 concurrent calls; need for media bypass to reduce latency.
Scenario 2: Small Business with Calling Plans
A 50-person law firm wants a simple phone system without managing SBCs. They choose Microsoft Calling Plans. Steps:
Purchase Phone System licenses for all users (included in E3 with add-on).
Purchase Domestic Calling Plan licenses (120 minutes per user per month) plus Communication Credits for overflow.
Port their existing 50 numbers from the local carrier to Microsoft (takes 7 days).
Assign numbers to users in Teams Admin Center.
Configure auto attendant and call queues for reception.
Problems: Users run out of minutes and calls are blocked because Communication Credits weren't set up. Solution: Enable auto-recharge for Communication Credits. Also, porting delays due to incorrect letter of authorization (LOA).
Scenario 3: Healthcare Provider with Compliance Requirements
A hospital network with 5,000 users needs to record all calls for compliance. They use Direct Routing with a certified SBC that supports call recording. Configuration:
SBC configured to fork all calls to a recording server using SIPREC.
Emergency calls must bypass the recording to ensure immediate routing.
Users have different dial plans for internal extensions (4-digit) and external numbers.
Network assessment shows high jitter in some locations, requiring QoS DSCP marking (EF for voice).
Misconfiguration: Call recording breaks if the SBC does not support SIPREC or if the recording server is unreachable. Emergency calls might be delayed if the recording fails. Performance: Media bypass is disabled to allow recording, increasing latency.
Exactly What MS-102 Tests
The MS-102 exam (Objective 1.3: Manage tenant configuration) includes Teams Calling. Key subtopics: - Licensing: Know that Phone System is required for any PSTN calling; Calling Plan is separate. Direct Routing does NOT require a Calling Plan license. - Direct Routing: Steps to register SBC, configure voice routing policies, enable users. Be able to identify correct PowerShell cmdlets. - Emergency Calling: Dynamic vs static emergency calling. Requirements: emergency calling policy, network location, registered address. - Number Porting: Only for Calling Plans and Operator Connect. Direct Routing numbers stay with carrier. - Communication Credits: Needed when Calling Plan minutes are exceeded or for toll-free numbers.
Most Common Wrong Answers
Confusing Phone System with Calling Plan: Many candidates think a Calling Plan license is sufficient for PSTN calling. Reality: Phone System is mandatory; Calling Plan adds minutes.
Assuming Direct Routing doesn't need Phone System: Direct Routing still requires Phone System license for each user.
Thinking number porting applies to Direct Routing: Porting is not needed because numbers remain with the carrier.
Believing all users need a Calling Plan with Direct Routing: Direct Routing uses your own carrier, so no Calling Plan needed.
Specific Numbers and Values
Default SIP port: 5061 (TLS).
Max concurrent sessions per SBC: depends on SBC capacity, but default 100 in Teams config.
Calling Plan minutes: 120, 300, 1200 domestic; 600 international.
Emergency calling: dynamic uses IP location; static uses fixed address.
Communication Credits: auto-recharge threshold default $50.
Edge Cases
Hybrid deployments: If you have Skype for Business Server on-premises, you must use Direct Routing or hybrid voice.
Media bypass: For Direct Routing, you can enable media bypass to reduce latency, but it requires SBC to be in same network as users.
Toll-free numbers: Require Communication Credits and a Calling Plan.
Call park and retrieve: Requires a call park policy.
How to Eliminate Wrong Answers
If the question mentions 'retain existing carrier' -> Direct Routing or Operator Connect.
If the question mentions 'simplest setup for small business' -> Calling Plans.
If the question mentions 'no SBC management' -> Calling Plans or Operator Connect.
If the question mentions 'per-user minute license' -> Calling Plans.
If the question mentions 'custom routing' -> Direct Routing.
Phone System license is mandatory for all Teams PSTN calling.
Calling Plans provide per-user minutes; Direct Routing uses your own carrier.
Direct Routing requires a certified SBC with TLS on port 5061.
Emergency calling requires a registered address (static or dynamic).
Communication Credits are needed for overflow minutes and toll-free numbers.
Number porting applies only to Calling Plans and Operator Connect.
Voice routing policies are only used in Direct Routing.
Operator Connect is a managed version of Direct Routing with carrier-provided SBC.
These come up on the exam all the time. Here's how to tell them apart.
Calling Plans
Microsoft provides PSTN connectivity and carrier.
Simple setup; no SBC required.
Per-user minute licensing (120/300/1200 domestic).
Number porting required to bring existing numbers.
Limited control over call routing and emergency services.
Direct Routing
Organization provides own carrier via certified SBC.
Requires SBC deployment and management.
No per-user minute license; pay your carrier.
Numbers stay with carrier; no porting needed.
Full control over routing, emergency calling, and compliance.
Mistake
Phone System license is optional if you have a Calling Plan.
Correct
Phone System license is mandatory for all PSTN calling, regardless of whether you use Calling Plans, Direct Routing, or Operator Connect. Calling Plan only adds minutes.
Mistake
Direct Routing users need a Calling Plan license.
Correct
Direct Routing uses your own carrier, so no Calling Plan license is needed. Only Phone System license is required.
Mistake
Number porting is required for Direct Routing.
Correct
With Direct Routing, numbers remain with your carrier. Porting is only needed for Calling Plans and Operator Connect.
Mistake
All users automatically get a phone number when assigned a Calling Plan.
Correct
You must manually assign a phone number to each user from the available pool. Calling Plan license alone does not provide a number.
Mistake
Communication Credits are optional and never needed.
Correct
Communication Credits are required when Calling Plan minutes are exceeded or for toll-free numbers. Without them, calls may be blocked.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
At minimum, each user needs a Phone System license. For Calling Plans, you also need a Calling Plan license (Domestic or International). For Direct Routing or Operator Connect, only Phone System is required. Communication Credits are optional but recommended for overflow.
Yes, but the method depends on the deployment. For Calling Plans, you must port numbers to Microsoft. For Direct Routing, numbers remain with your carrier. For Operator Connect, the carrier manages numbers.
Direct Routing requires you to deploy and manage your own SBC. Operator Connect uses a carrier-provided SBC managed by Microsoft, simplifying setup. Both provide the same functionality, but Operator Connect offers faster provisioning and carrier SLAs.
You need an emergency calling policy and, for dynamic E911, a network location that maps IP subnets to physical addresses. For static emergency calling, assign a fixed address per user. Ensure emergency calls are routed to the correct PSTN trunk.
If Communication Credits are enabled, calls continue and are billed per minute. If Communication Credits are not set up, calls are blocked. You can set auto-recharge to avoid disruption.
No. Phone System license is required for any PSTN calling feature, including inbound/outbound calls, voicemail, call queues, and auto attendants.
Latency < 30ms, jitter < 10ms, packet loss < 1%. For media bypass, the SBC must be in the same network segment as users. Firewalls must allow TCP 5061 (SIP), UDP 3478-3481 (media), and UDP 50-59, 500, 4500 (VPN).
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