Intermittent VoIP call quality issues that occur during peak hours are a classic symptom of network congestion caused by voice and data traffic competing for the same network resources. According to CompTIA Core 1 (220-1201) networking and VoIP objectives, one of the most effective solutions is to configure VLANs to separate voice and data traffic.

By placing VoIP devices on a dedicated voice VLAN, the network can apply Quality of Service (QoS) policies that prioritize voice packets over standard data traffic. This reduces latency, jitter, and packet loss, which are the primary causes of poor call quality. VLAN separation ensures that even during heavy data usage, voice traffic remains clear and reliable.

Routing calls through a gigabit port does not address traffic prioritization and is unlikely to resolve congestion during peak usage. Installing shielded network cables only helps in environments with excessive electromagnetic interference, which would affect performance consistently—not intermittently. Increasing the VoIP bit rate would actually worsen congestion by consuming more bandwidth.

CompTIA emphasizes VLAN implementation and QoS as best practices for VoIP deployments, especially when call quality degrades under high network utilization.