Packet Scheduling Calculator
Turn scheduler weights into a real bandwidth share and estimate serialisation and queueing delay per class.
Inputs
Bandwidth for This Class
300.00Mbps
Scheduler Share
30.00%
Serialisation Delay per Packet
8.000µs
Delay at Full Queue
1.707ms
Scheduler Round Time
26.667µs
Step by step
Values used
Link rate = 1,000 Mbps; Weight of this class = 30 weight; Sum of all other weights = 70 weight; Average packet size = 1,000 bytes; Queue depth = 64 packets
Packet Scheduling
class share = weight ÷ sum of weights; queueing delay = queue depth × packet bits ÷ class bandwidth.
Bandwidth for This Class
= 300.00 Mbps
Scheduler Share
= 30.00
Serialisation Delay per Packet
= 8.000 µs
Delay at Full Queue
= 1.707 ms
Scheduler Round Time
= 26.667 µs
How it works
A weighted scheduler hands out service in proportion to weight, so the bandwidth a class receives is its weight divided by the total. Serialisation is how long one packet takes to clock onto the wire, and the worst-case delay a packet sees is the whole queue ahead of it draining at the class rate. Weights are dimensionless in the CLI, so the only way to know whether a class will meet a 30 ms budget is to convert weight into Mbps and multiply by the configured queue depth.
Formula
Packet Scheduling
class share = weight ÷ sum of weights; queueing delay = queue depth × packet bits ÷ class bandwidth.
- weight
- Relative scheduler credit assigned to the class
- queue depth
- Packets the class can hold before tail drop
Frequently Asked Questions
How is Packet Scheduling calculated?
class share = weight ÷ sum of weights; queueing delay = queue depth × packet bits ÷ class bandwidth. A weighted scheduler hands out service in proportion to weight, so the bandwidth a class receives is its weight divided by the total. Serialisation is how long one packet takes to clock onto the wire, and the worst-case delay a packet sees is the whole queue ahead of it draining at the class rate.
Why does Packet Scheduling matter?
Weights are dimensionless in the CLI, so the only way to know whether a class will meet a 30 ms budget is to convert weight into Mbps and multiply by the configured queue depth.
What values do I need to enter?
This calculator takes 5 inputs: Link rate, Weight of this class, Sum of all other weights, Average packet size, Queue depth. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.