Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 978)

Quality of Service (QoS) Introduction
Software Reference for x310 Series Switches
38.6 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Processing pre-marked packets
A logical question to ask at this point is: how does the QoS switch deal with data that
arrives with a pre-existing service level tag such as a DSCP? As previously touched on, the
differentiated services model envisages a network that comprises QoS boundary routers
at its edge and QoS core routers in its core network.
At the network edge the QoS boundary routers filter the incoming data based on specific
packet components. Based on this filtering each packet is assigned a DSCP value. This
value will determine the service level - priority, queueing etc - that will be applied.
Within the network core, the packet filtering required is reduced to simply reading the
DSCP within each incoming packet, and applying the appropriate set of service levels. This
relieves the core routers of the processing overhead of applying complex filtering to its
high speed data streams.