Head Office QoS and Voice

Because IP telephony is included in the Venti Systems design, you must also consider managing the quality of service that the traffic experiences. Recall that although you typically think of applying queuing only to slow WAN links, LAN links can also be congested, so queuing should be deployed on any link that could potentially experience congestion, to provide the needed services to the network traffic. Queuing policiesin other words, how each traffic class is handledshould be consistent across the enterprise.

Venti Systems will use IP phones to digitize and packetize the voice traffic. As illustrated earlier in Figure 12-6, IP phones with a built-in switch will be used; one port will connect to the access switch and another will connect to the user's laptop. Access switches will provide inline power for the IP phones, using power over Ethernet (PoE).

The voice and data traffic will be on separate VLANs to allow easier implementation of QoS tools; the connection to the access switch is an 802.1q trunk, with the laptop on the native VLAN.

Classification and marking of voice traffic will be done by the IP phone. Recall that the point within the network where markings are accepted is known as the trust boundary; any markings made by devices outside the trust boundary can be overwritten at the trust boundary. A Cisco IP phone could be considered to be a trusted device because it marks voice traffic appropriately, while a user's laptop would not usually be trusted because users could change markings (which they might be tempted to do to attempt to increase the priority of their traffic). Therefore, the access switches will mark the laptop traffic appropriately.

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