QoS Queue
Calculate queue depth and bandwidth allocation for QoS traffic classes.
About QoS Queue
Quality of Service (QoS) queueing allocates a link's finite bandwidth among traffic classes according to priority weights. Weighted Fair Queuing (WFQ) gives each queue a bandwidth share strictly proportional to its weight relative to the total: per_queue_bandwidth = total × (weight / sum_of_weights) — every queue always gets its proportional share, even under congestion. Strict Priority Queuing instead services higher-priority queues first up to their full demand, with lower-priority queues only getting what's left over, which better protects latency-sensitive traffic (like voice) but can starve lower-priority queues entirely under heavy load.
Formula
Weighted Fair Queuing allocation
per_queue_bandwidth = total_bandwidth × (weight / sum_of_all_weights)
- w_i
- Weight assigned to queue i
- B_{total}
- Total link bandwidth
Worked example
With the default values below, QoS Queue returns Allocation Summary of 4 queues sharing 100 Mbps by weight. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Total Link Bandwidthminimum 0.1 Mbps
- 100 Mbps
- Queue Priority Weights
- 40, 30, 20, 10
Results
- Allocation Summary
- 4 queues sharing 100 Mbps by weight
- Queue 1 Bandwidth (WFQ)
- 40.000 Mbps
- Sum of Weights
- 100
Step by step
- 1Values used
- 2Weighted Fair Queuing allocation
- 3Allocation Summary= 4 queues sharing 100 Mbps by weight
- 4Queue 1 Bandwidth (WFQ)= 40.000 Mbps
- 5Sum of Weights= 100
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What's the difference between strict priority and weighted fair queuing?
Strict priority always services the highest-priority queue's traffic first, so lower-priority queues can be completely starved if high-priority traffic saturates the link. WFQ instead guarantees every queue its proportional weighted share regardless of congestion, trading some priority protection for fairness.
Why is voice traffic usually given the highest QoS priority?
Voice (VoIP) traffic is extremely sensitive to latency and jitter — even small delays cause audible quality problems — while consuming relatively little bandwidth overall, making it a natural candidate for strict priority treatment ahead of bulk data transfers.
Can a low-weight queue still get bandwidth if the link isn't congested?
Yes — in both WFQ and strict priority models, weights and priority only determine how bandwidth is divided under contention. If the link has spare capacity beyond what higher-priority/weighted queues are actually using, lower-priority queues can typically use the surplus.
How do I choose queue weights in practice?
Weights are usually set proportional to each traffic class's expected or required bandwidth share — e.g. giving voice a smaller absolute weight but treating it with strict priority, while splitting the remaining weight among video, business-critical data, and best-effort traffic based on business needs.