[aninhumer]

It's fairly simple. You let the user set QoS bits in their own packets, and discriminate based on those, with appropriate target neutral constraints to prevent abuse. (e.g. limit the bandwidth available to packets marked low latency.)

This allows people to use whatever services they like, but still get the benefits of QoS.

[derekp7]

You can also use those same constraints without QOS bits. Small amounts of data sent bi-directionally gets lower latency (VOIP). Large amounts of data sent in one direction gets lower priority (large ISO downloads). Combine with protocol detection to set initial values.