Mark Multimedia Conferencing with DSCP AF4 (Avoid WRED)

300-420 By islever Editorial Last updated

Design end-to-end QoS policies

Short answer

D Mark branch multimedia conferencing with DSCP AF4 in a bandwidth queue; WRED is congestion-avoidance dropping, not marking, and can hurt delay-sensitive flows.

Question

A customer requires QoS to support multimedia conferencing over MPLS. The network architect chooses to use per-hop behavior. Which solution must the architect use to classify and mark traffic traveling between branch sites?
  1. BW Queue with DSCP AF3
  2. BW Queue and DSCP WRED with DSCP AF4
  3. BW Queue and DSCP WRED with DSCP AF3
  4. BW Queue with DSCP AF4 Correct Answer

Key Takeaways

The task is classify-and-mark -> that is DSCP (AF4 for video conferencing). WRED drops packets; it does not mark, and it is generally avoided for jitter/loss-sensitive real-time media.

For multimedia conferencing over MPLS, the architect classifies and marks the traffic with DSCP AF4 (video) carried in a bandwidth (allocated) queue. WRED is a congestion-avoidance drop mechanism, not a classification/marking action, and its early drops can degrade delay-sensitive real-time traffic.

Common mistake: Picking B (adds WRED): WRED is for congestion avoidance on elastic traffic, not for marking, and can introduce drop variability that hurts conferencing. The marking answer is DSCP AF4 without WRED (D).

Expert Analysis

Why the Answer Is Correct

D is correct. Multimedia conferencing is marked with DSCP AF4 (video) in a bandwidth/allocated queue. The question asks to classify and mark, which is the DSCP action; WRED is a drop/congestion-avoidance feature, not marking.

Why the Other Options Are Wrong

B adds WRED, which is not a classification/marking step and can hurt delay-sensitive conferencing with early drops. A and C use AF3 (more associated with voice) and either omit or add WRED; the conferencing marking is AF4 without WRED.

Community Comment Notes

The vote is split B (50) vs D (33) vs C (17). Commenters note WRED's early drops can degrade real-time media, supporting marking with AF4 and no WRED (D).

Community Votes

B
50%
D
33%
C
17%

50% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 3 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 3

  1. PicoOstrava 👍 2 Answered D
    I think that for multimedia conferencing, which is sensitive to delay and requires low packet loss, applying WRED might introduce variability in packet drops that could negatively impact the user experience.
  2. Aandreyy1 👍 1 Answered C
    SCP AF3 (Assured Forwarding class 3) is part of the Assured Forwarding (AF) PHB group, which is commonly used for multimedia applications like voice and video.
  3. 08511d4 👍 3 Answered B
    Surely WRED is best practice

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