Hi Saquib,

I am assuming that you are on an SP environment.

The links posted by Laurent is very useful indeed. I see that he has very kindly included Santiago Alvarez's presentation. The same author has a book which I have found useful in the past :

"QoS for IP/MPLS Networks" By Santiago Alvarez.

In regards to your specific query about VoIP, very often voice traffic is given an Expedited Forwarding ( EF or DSCP decinal 46 ) in PHB to guarantee minimum latency . According to RFC 2598 packets marked as EF should be given queuing

preference so that they experience minimal latency, but "the packets should be policed to prevent

them from taking over a link and preventing any other types of traffic from exiting an interface

during periods when this high-priority traffic reaches or exceeds the interface bandwidth." ( quote from Cisco Press)

Let us know how it goes for you :-)

Cheers

santanu