After the win 11 upgrade, teams calling is not working properly

Dear @Sugandh Suvarnan,

Thank you for reaching out to Microsoft Q&A forum.

I’m truly sorry to hear about the issue you're experiencing in Teams. I understand how challenging it is for your user after upgrading to Windows 11, especially when internal and mobile calls work correctly, but landline calls fail in a very specific way. This kind of one‑directional audio loss, affecting only PSTN landline connections, is indeed unusual and highly specific.

As a forum moderator, I genuinely wish I could directly access your account or delve into the backend systems to diagnose and fix this for you. However, our role here is limited to providing general guidance and solutions that can be applied by users.  

From the scenario you described, the issue is likely a complex interaction between the new Windows 11 audio stack, the specific codecs used for PSTN (Public Switched Telephone Network) landline calls, and the settings of your organization's voice infrastructure (Direct Routing or Calling Plan).

The fact that the problem is one-way (the user on the other end cannot hear her) strongly suggests an upstream encoding or routing problem that is triggered only by the landline gateway.

Here are a few steps you can try to resolve this:

1.Check Teams for New Audio Device Selection (Most Common)

Windows 11 introduces subtle changes to device prioritization that can confuse Teams.

• Verify Input Device: Ask the user to start a test call (or a call to a mobile phone that works) and, during the call, go to Teams Settings > Devices.
• Crucially, ensure the Microphone dropdown is set to the physical headset microphone and not a Windows 11 default like "Default Communications Device" or a built-in laptop mic. Sometimes, Windows 11 separates the audio channels in a way that the landline gateway rejects the signal from a default or combined input.

2.Clear Teams cache

2. Clear Teams cache
3. Type settings in the search box, and then select the Settings app from the results.
4. Select Apps > Installed apps, and then type Microsoft Teams in the search box.
5. Locate the New Microsoft Teams app from the results, select the More options button (...) on the right, and then select Advanced options.
6. In the Reset section, select Reset.
7. Restart Teams.

For reference: Clear the Teams client cache - Microsoft Teams | Microsoft Learn

From my research, you may also want to check for NAT or SIP ALG interference on the infrastructure side, because one‑way audio that happens only on PSTN (landline) calls often points to dropped or rewritten RTP traffic at the network edge. When the SBC or firewall alters RTP headers or when SIP ALG is active on a router the landline carrier receives incorrect IP/port information, which results in the far‑end hearing nothing.

An admin can confirm this quickly with a call trace or packet capture on the SBC. If the SIP/SDP portion shows a private IP or mismatched RTP ports being advertised to the carrier, that’s a clear sign of NAT or ALG interference. From there, verifying the SBC topology, firewall rules for the full RTP port range, and ensuring SIP ALG is disabled are the key steps to restoring proper two‑way audio.

It also helps to review the affected calls in Teams Call Analytics via the Teams Admin Center. This provides the cloud‑side view and helps correlate what the SBC saw versus what Teams received.
Notes:
NAT (Network Address Translation)

SIP ALG (Session Initiation Protocol Application Layer Gateway)

SBC (Session Border Controller)

PSTN (Public Switched Telephone Network)

RTP (Real-time Transport Protocol)
For references:
Plan Direct Routing - Microsoft Teams | Microsoft Learn
Microsoft Teams call flows - Microsoft Teams | Microsoft Learn
Microsoft Teams PSTN usage report - Microsoft Teams | Microsoft Learn
Please also follow the steps in this article to rule out Windows-level audio routing issues: Fix sound or audio problems in Windows - Microsoft Support

I hope this information is helpful. If none of the above solutions work, let me know in the comments for further investigation. Please note that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution. Thank you for your patience and understanding. I'm looking forward to your reply.

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