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)
This document is an early notification of a behaviour change that will be introduced in IOS XR release 6.5.
IOS XR configuration principles relevant for this article are:
On router platforms all interfaces must be by defaul...
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The Cisco EPN system incorporates a network architecture designed to consolidate multiples services on a single Multiprotocol Label Switching (MPLS) transport network. This network is designed primarily based on Application ...