350-801 Question #335: Real Exam Question with Answer & Explanation

Question

What is a description of the DiffServ model used for implementing QoS?

Options

• AAF41 has higher drop precedence than AF42, which has higher drop precedence than AF43.
• BVoice and video calls are marked with different DSCP values and placed in different queues.
• CAF43 has higher drop precedence than AF42 but lower drop precedence than AF41.
• DRTP traffic from voice and video calls is marked EF and placed in the same queue.

Explanation

The DiffServ QoS model distinguishes between different types of traffic, such as voice and video, by assigning them distinct DSCP values and directing them into separate queues for appropriate prioritization.

Common mistakes.

• A. In Assured Forwarding (AF), a higher drop precedence number (e.g., AF43) indicates a higher likelihood of being dropped than a lower drop precedence number (e.g., AF41), meaning AF41 has lower drop precedence than AF43.
• C. AF43 has higher drop precedence (more likely to be dropped) than AF42, and AF42 has higher drop precedence than AF41; therefore, AF43 has higher drop precedence than AF41.
• D. While RTP traffic from voice is marked EF, RTP traffic from video is typically marked with an Assured Forwarding (AF) class (e.g., AF41) or a different DSCP value, not EF, because voice and video have different characteristics and tolerances.

Concept tested. DiffServ QoS model principles

Reference. https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book/QoSDiffServ.html

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