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5-4
Quality of Service (QoS): Managing Bandwidth More Effectively
Introduction
■ Upgrade or downgrade traffic from various servers.
■ Control the priority of traffic from dedicated VLANs or applications.
■ 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.
Figure 5-1. Example of 802.1p Priority Based on CoS (Class-of-Service) Types and
Use of VLAN Tags
Figure 5-2. Example Application of Differentiated Services Codepoint (DSCP)
Policies
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 down-
stream switches can be configured to honor the new policies.
Honor New Priority
Edge Switch
Classify inbound traffic
on these Class-of-
Service (CoS) types:
• IP-device (address)
• Source-Port
Apply 802.1p priority to
selected outbound
traffic on tagged VLANs.
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.
Downstream
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.
Downstream
Switch
Tagged VLANs on
inbound and outbound
ports.
Traffic arrives with
priority set by edge
switch
Forward with 802.1p
priority.
Set Priority
Honor Priority
Change Priority
Edge Switch
Classify inbound traffic
on IP-device (address).
Apply DSCP markers to
selected traffic.
Downstream
Switch
Classify on ToS DiffServ
and Other CoS
Apply new DSCP markers
to selected traffic.
Downstream
Switch
Classify on ToS Diffserv
Downstream
Switch
Traffic arrives with DSCP
markers set by edge
switch
Classify on ToS DiffServ.
Set Policy
Honor Policy
Change Policy
Honor New Policy