Quality of Service (QoS): Managing Bandwidth More Effectively
Introduction
■Change the priorities of traffic from various segments of your network as your business needs change.
■Set priority policies in edge switches in your network to enable traffic- handling rules across the network.
Edge Switch
Classify inbound traffic on these
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Apply 802.1p priority to selected outbound traffic on tagged VLANs.
Set PriorityDownstream
Switch
Tagged VLANs on inbound and outbound ports.
Traffic arrives with priority set by edge switch
Forward with 802.1p priority.
Downstream
Switch
Tagged VLANs on some or all inbound and outbound ports.
Classify inbound traffic on CoS types.
Change priority on selected CoS type(s).
Forward with 802.1p priority.
Change PriorityDownstream
Switch
Tagged VLANs on at least some inbound ports.
Traffic arrives with the priority set in the VLAN tag. Carry priority downstream on tagged VLANs.
Figure
Edge Switch
Classify inbound traffic on
Apply DSCP markers to selected traffic.
Set PolicyDownstream
Switch
Traffic arrives with DSCP markers set by edge switch
Classify on ToS DiffServ.
Downstream
Switch
Classify on ToS DiffServ and Other CoS
Apply new DSCP markers to selected traffic.
Change PolicyDownstream
Switch
Classify on ToS Diffserv
Figure
At the edge switch, QoS classifies certain traffic types and in some cases applies a DSCP policy. At the next hop (downstream switch) QoS honors the policies established at the edge switch. Further downstream, another switch may reclassify some traffic by applying new policies, and yet other downstream switches can be configured to honor the new policies.
QoS is implemented in the form of rules or policies that are configured on the switch. While you can use QoS to prioritize only the outbound traffic while it is moving through the switch, you derive the maximum benefit by using QoS