What QoS trust boundary is preferred in a typical CUCM deployment?

• A. End device
• B. Distribution switch
• C. Access switch
• D. Core router

Answer: (C)

The main idea is where the network begins to trust the DSCP markings coming from endpoints. In a typical CUCM deployment, IP phones mark their voice traffic with DSCP EF. You want the switch port that the phone plugs into to trust those markings and pass them through without re-marking. That boundary at the access switch ensures voice traffic retains its priority as it moves toward the core, giving consistent QoS for calls across the network.

If the trust boundary were at the end device, the network would have to trust whatever markings the device generates—which can vary or be misconfigured, risking misclassification. Pushing trust further into the core or onto distribution devices increases the chance that non-voice traffic could interfere or that voice markings could be altered before reaching the edge of the network. Placing the boundary at the access layer aligns with how IP phones attach to the network and is the most reliable way to preserve voice QoS end-to-end.