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CCNA® Cisco Certified Network Associate: Study Guide, Seventh Edition by Todd Lammle

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Telephony: Configuring Voice VLANs

If you do yoga, meditate, chain smoke, or consume mass quantities of comfort food when stressed, take a little break and do that now because, and I’m going to be honest, this isn’t the easiest part of the chapter—or even the book, for that matter. But I promise that I’ll do my best to make this as painless for you as possible.

The voice VLAN feature enables access ports to carry IP voice traffic from an IP phone. When a switch is connected to a Cisco IP phone, the IP phone sends voice traffic with layer 3 IP precedence and layer 2 class of service (CoS) values, which are both set to 5 for voice traffic; all other traffic defaults to 0.

Because the sound quality of an IP phone call can deteriorate if the data ...

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