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Media Relay fallback and "Satin" codec degradation over TCP/443

Trillas 140 Reputation points
2026-04-03T03:13:53.03+00:00

We’ve noticed a significant drop in meeting quality for our remote users, with the Call Quality Dashboard (CQD) flagging a high percentage of "Poor" calls. Even though these users have high-speed fiber, their audio sounds robotic and video frequently freezes. It turns out their local environments are blocking outbound UDP on ports 3478–3481, forcing the Teams media stack to tunnel through HTTPS (TCP/443). This is a disaster for real-time traffic because TCP’s retransmission logic causes delays that completely overwhelm the jitter buffer, rendering the "Satin" audio codec’s error-correction features useless.

Moved from Microsoft Teams | Development

Microsoft Teams | Microsoft Teams for business | Meetings and calls | Other
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  1. Jade Ng 10,495 Reputation points Microsoft External Staff Moderator
    2026-04-03T04:25:51.27+00:00

    Dear @Trillas,

    Thank you for reaching out!

    I understand how disruptive poor audio and video quality can be, especially when users have reliable, high‑speed internet connections.

    After reviewing the call data, the behavior you are experiencing is consistent with a network transport limitation rather than an issue with Microsoft Teams itself. Microsoft Teams is designed to carry real‑time audio and video over UDP, which prioritizes timeliness over guaranteed delivery. When outbound UDP ports (3478-3481) are blocked in a user’s local environment, Teams must fall back to sending media over TCP/443.

    While TCP allows connectivity, it is intended only as a last‑resort fallback for real‑time media. Its retransmission and flow‑control behavior introduce latency and jitter that real‑time audio and video cannot tolerate. As a result, users may experience robotic or distorted audio, frozen video, and calls marked as “Poor” in the Call Quality Dashboard. This can occur even on high‑bandwidth connections such as fiber, because real‑time quality depends on low latency and jitter not raw speed.

    To restore optimal call and meeting quality, Microsoft recommends allowing outbound UDP traffic on ports 3478-3481 to the Microsoft Teams media endpoints and ensuring this traffic is not routed through HTTP proxies or SSL inspection devices. Once UDP connectivity is restored, Teams will resume using its optimized media path and call quality should improve significantly.

    For more reference:

    I hope this information is helpful. If you need any further assistance, please feel free to reach out. I am here to help. Thank you very much for your understanding and cooperation.

    I am looking forward to your response!

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