Question

During a network audit you review the following QoS policy applied outbound on a WAN interface: a class-map matches voice RTP (DSCP EF), and the policy-map assigns it 'priority 512'. The circuit is congested during peak hours, and users report that after a large batch of new calls connect, some active calls develop choppy audio while others sound fine. Signaling and video classes are unaffected. What is the most likely explanation for this behavior?

Accepted Answer

The priority command includes an implicit policer that drops EF packets exceeding 512 kbps during congestion, starving some voice flows once the aggregate exceeds the guaranteed rate

Answer

LLQ does not support DSCP EF matching, so the packets are being reclassified into the default class and queued behind bulk data

Answer

The priority queue only activates when the interface is uncongested, so during peak hours voice receives no priority servicing at all

Answer

The bandwidth remaining percent value for the class is too low, causing voice packets to be tail-dropped in the CBWFQ scheduler