Specifications

CHAPTER 8
Voice and Video in a Campus Network
Voice bearer traffic uses an Expedited Forwarding value of DSCP 46 to give it higher priority within the network.
Trust Boundaries
When IP traffic comes in already marked, the switch has some options about how to handle it. It can:
n Trust the DSCP value in the incoming packet, if present.
n Trust the IP Precedence value in the incoming packet, if present.
n Trust the CoS value in the incoming frame, if present.
n Classify the traffic based on an IP access control list or a MAC address access control list.
Mark traffic for QoS as close to the source as possible. If the source is an IP telephone, it can mark its own traffic. If not,
the building access module switch can do the marking. If those are not under your control, you might need to mark at the
distribution layer. Classifying and marking slows traffic flow, so do not do it at the core. All devices along the path should
then be configured to trust the marking and provide a level of service based on it. The place where trusted marking is
done is called the trust boundary.
Configuring VoIP Support on a Switch
Before implementing VoIP, plan the following:
1. PoE: Ensure that enough power is available for all phones, with a UPS backup.
2. Voice VLAN: Determine the number of VLANs needed and the associated IP subnets. Add DHCP scopes for the
phones, and add the phone networks to the routing protocol.
3. QoS: Decide which marking and queues will be used. Implement AutoQoS and then tune as needed.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue