Voice over IP (VoIP) traffic is highly sensitive to latency, jitter, and packet loss, especially in large environments such as a 200-person call center. Although the technician confirms that VoIP prioritization (QoS) is configured correctly and speed tests show 50 Mbps upload and download speeds, overall available bandwidth can still be insufficient during peak usage.

Speed tests measure raw throughput at a point in time and do not reflect real-world congestion caused by hundreds of simultaneous calls, application usage, and data transfers. On busy days, the cumulative bandwidth demand likely exceeds the available capacity, leading to degraded call quality despite correct VLAN and QoS settings.

If QoS were misconfigured or the VLAN did not allow voice traffic, call issues would be consistent at all times, not only during peak periods. Flapping switchports would cause intermittent connectivity drops rather than predictable performance degradation correlated with high usage.

CompTIA highlights that bandwidth limitations are a common root cause of VoIP performance problems in high-density environments, even when prioritization is properly implemented.