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Chapter 3 QoS in an AVVID-Enabled Campus Network
Selecting an Access-Layer Switch
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The switch must be able trust the CoS or DSCP marking that the IP phones provide. This is currently
supported via the mls QoS trust CoS and mls QoS trust DSCP commands for IOS-based switches
and the trust-CoS and trust-DSCP commands for Catalyst OS-based switches.
As mentioned before (in the
the devices attached to an AVVID network do not classify their traffic with the appropriate Layer 2 and
Layer 3 markings. When considering your choices for access-layer devices, consider the switch's ability
to classify and mark traffic at the edge of the network via ACLs and service policies. This will allow
QoS to be offered as a service throughout the network and administered at the edge of the network where
CPU resources are plentiful, rather than at the distribution and core aggregation points where
enforcement of QoS classification and marking could adversely affect network performance.
Catalyst 6500 as an Access-Layer Switch
One of the most popular campus configurations for Cisco AVVID solutions is to use Catalyst 6500
switches in both the wiring closet and the distribution and core layers. There are several compelling
reasons for this:
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The Catalyst 6500 supports dual supervisor engines providing the highest availability of access
solutions.
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The Catalyst 6500 can provide in-line power to the IP phones. The current 10/100 boards for the
Catalyst 6500 support integrated inline power and are standard.
·
The Catalyst 6500 offers the highest growth potential.
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The Catalyst 6500 supports advanced Layer 2/3 campus QoS tools.
shows a general model for the Catalyst 6500 as an access device (as illustrated in the QoS
configurations discussed in this chapter).