IPtraf is nice, but it does not give you interesting details about each QOS queue lenght on the router.
This information is very usefull to fastly find a bootleneck.
Another interesting parameter is the induced jitter for each class of traffic.
As soon as a queue has too many paquets in it, you know that you should do something to solve the problem.
Queue statistics is the key to set a good QOS system.
IPtraf or all other external monitoring system will not give you an inside view of the router QOS queues.
That’s why it is important to monitor those parameters through SNMP or similar protocols.