QoS is not magic.
- QoS cannot offer cures for a poorly performing network.
- QoS does not create nonexistent bandwidth.
- Elevating the amount of resources available to one class of traffic decreases the amount available for other classes of traffic.
- QoS will not alter the speed of light.
- On an unloaded network, QoS mechanisms will not make the network any faster.
- Indeed, it could make it slightly worse!