Specifications

CHAPTER 8
Voice and Video in a Campus Network
n Electrical power for the IP phones: Use either PoE from Catalyst switch or power inline module, or a power brick.
n Bandwidth: Commit no more than 75 percent of bandwidth. Consider all types of traffic: voice, video, and data.
Have more than enough bandwidth if possible. Include both voice and call-control traffic in your planning.
n Network management: Monitor and proactively manage the network so that it is always available. Need voice
VLANs on the switches and DHCP for the phones.
n High availability: Provide redundant hardware links. Need uninterruptible power supply (UPS) with auto-restart,
monitoring, and four-hour response contract. Might need generator backup. Maintain correct operating temperatures.
Network and Bandwidth Considerations
The network requirements for VoIP include:
n Maximum delay of 150–200 ms (one-way)
n No more than 1 percent packet loss
n Maximum average jitter of 30 ms
n Bandwidth of 21–106 kbps per call, plus approximately 150 bps per phone for control traffic
A formula to use when calculating bandwidth needed for voice calls is as follows:
(Packet payload + all headers) * Packet rate per second
Voice VLANs
Cisco switches can be configured to dynamically place IP telephones into a Voice, or auxiliary, VLAN separate from the
data VLANs. They can do this even when the phone and PC are physically connected to the same switch port. Voice
VLANs enable phones to be dynamically placed in a separate IP subnet from hosts, to have QoS (using 802.1Q/p
headers) and security policies applied, and make troubleshooting easier.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue