The design in one paragraph
Teams separates modalities by CLIENT SOURCE PORT (audio 50000-50019, video
50020-50039, sharing 50040-50059 — TeamsMeetingConfiguration, in your scan).
Your network marks by those ranges — audio EF(46), video AF41(34), sharing
AF21(18) by convention — and every queue-capable hop from the access switch to
the WAN edge honours the marks. Microsoft marks nothing FOR you on your LAN;
outside your network the internet ignores DSCP entirely — QoS is a
your-network-only instrument protecting the segments you control (LAN, Wi-Fi
WMM, WAN links, VPN tunnels where applicable).
Two marking mechanisms: network-side (switch/router ACLs by port range — works for every client type incl. mobile and rooms) or endpoint-side (Windows GPO QoS policies marking at source — needs domain/MDM reach and the app path right). Prefer network-side as primary: fewer moving parts, covers unmanaged devices.
Where marks go to die (verify at each)
| Hop | Failure |
|---|---|
| The client's own OS | Endpoint marking policy not applied (wrong app path, non-domain machine) |
| Access switch ingress | Trust boundary resets DSCP to 0 (default on many switches!) |
| Wi-Fi | DSCP-to-WMM mapping absent — marks exist, air interface ignores them |
| Router/WAN edge | Re-marking policy or MPLS provider's class map eats your values |
| VPN tunnel | Inner marks not copied to outer header — tunnel queues blind |
What to watch (proofs)
- Marks at origin: capture on the client — DSCP values on outbound RTP by port range; zero here = endpoint/policy layer, go no further.
- Marks in transit: capture at (or SPAN of) the WAN edge — the same streams' DSCP; the hop where 46 became 0 is between your two captures. Binary-search with two more captures.
- Port config truth:
Get-CsTeamsMeetingConfiguration | fl Client*Port*— ranges on vs off; serv365 versions this nightly (a helpful admin 'simplifying' ranges breaks every ACL downstream — that's a drift alert). - Effect, not just marks: CQD jitter/loss for on-net calls before/after QoS on a congested link — the business case is that delta.