An insurance contact center runs voice, interactive video, call signaling, and bulk backup over a congested WAN, and agents complain of choppy audio during nightly backups. The design must protect voice latency, prioritize video, and relegate backups to leftover best-effort bandwidth. Which traffic-class to PHB mapping should the designer select to meet the QoS requirements?

The correct mapping works because EF uses strict-priority with low latency, jitter and policing to protect voice, AF41 gives interactive video assured yet prioritized forwarding with low drop probability, CS3 preserves call signaling in its own precedence without consuming the voice priority queue, and default with policing forces bulk backup to use only leftover bandwidth so nightly transfers cannot starve real-time queues on the congested WAN. The signaling to AF31 variant fails because AF31 is a data-oriented assured-forwarding class with active drop behavior rather than the precedence treatment expected for signaling, so call setup can be delayed or dropped under congestion even when voice and video are correct. The video to AF31 variant fails because AF31 is commonly assigned to streaming or on-demand video with lower priority than conferencing, so it does not provide the prioritized treatment required for interactive video and choppiness can persist. The backup to AF11 with assured bandwidth variant fails because AF11 explicitly guarantees minimum bandwidth and drop protection to bulk traffic, which preserves backups instead of relegating them and lets them continue to contend with voice. As an exam caveat, distinguish AF41 for interactive video from AF31 for streaming and CS3 for signaling from EF for voice rather than treating all high markings as equivalent. As a practical check, inspect queuing, policing and drop counters during a backup window to verify EF latency stays low, video is preferred, and backup is dropped first.