NEC UNIVERGE SV9100 Manual page 13

Once the router has been configured for QoS, it will examine incoming packets and allocate the relevant
priority to the packet. The diagram below shows the effect that Priority Queuing would have on "voice"
and "data" networks. The packets arrive randomly and are processed and output according to the
QoS policy – in this case VoIP traffic is output first.
To enable this type of queuing it is necessary to:
a) Configure the VoIP equipment to mark its packets with a specific value so that the switches/
routers can identify that it is "voice" - known as Marking
b) Configure the network equipment to recognise the difference between the different "Marked"
packets – known as Classification. i.e. Inform the router what a "voice" packet looks like.
c) Configure the network equipment to give priority to the packets that have been classified as "voice"
– known as Priority Queuing
3.2 Layer 2 QoS (802.1pq)
QoS is most commonly implemented at Layer 3 of the OSI model. This layer deals with IP
Part 1: VoIP Reference Manual 13