What is QoS and how do I configure it on an industrial switch?
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QoS (Quality of Service) prioritizes network traffic to ensure critical applications get bandwidth and low latency even under congestion.
QoS Mechanisms
- Classification: Identify traffic (by port, VLAN, IP, DSCP, 802.1p)
- Marking: Tag frames/packets with priority values
- Queuing: Assign to priority queues (typically 4-8 queues)
- Scheduling: SP (Strict Priority), WRR (Weighted Round Robin), DRR
- Policing/Shaping: Rate-limit traffic
Priority Standards
| 802.1p (L2) | DSCP (L3) | Traffic Type |
|---|---|---|
| 7 | EF (46) | Network control (GOOSE, PTP) |
| 6 | CS6 | Voice (VoIP) |
| 5 | AF41 | Video (surveillance) |
| 3 | AF31 | Critical data |
| 0 | Default | Best-effort |
Industrial Use Case
In IEC 61850 substation networks, GOOSE messages must be delivered within 4ms. Configure GOOSE VLAN with 802.1p priority 4-6 mapped to strict priority queue, ahead of SCADA and video traffic.
Configuration Steps
- Enable QoS globally
- Trust incoming DSCP or 802.1p markings
- Map priorities to queues
- Configure scheduling (SP for critical, WRR for others)
- Verify with traffic tests
2 Other Answers
19
For IEC 61850, always use SP for GOOSE — WRR won't meet the 4ms requirement.
10
Don't forget to enable trust boundary at access ports!
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