Enterprise QoS deep dive: classification, queueing and shaping

QoS only matters under congestion. Designed well, voice and video stay clean even when WAN saturates.

Trust boundary

• Trust DSCP at access edge for trusted endpoints (phones).
• Re-mark untrusted at the edge.

Queues

• Voice in priority queue (LLQ).
• Real-time apps in second queue, bulk last.

Shaping vs policing

• Shape on egress to provider rate.
• Police only when shaping isn't possible.

End-to-end

• WAN edge needs deepest queues.
• Inside DC, ECN beats tail drop for TCP.

Validation

• Generate congestion in lab; observe drops by class.
• Real-world test: saturate uplink, measure jitter.

Train QoS reasoning in a TechLeague tournament.