Quality of service (QoS) is the correct answer because it allows the administrator to prioritize VoIP traffic over other types of traffic, ensuring sufficient bandwidth and reducing latency or jitter during peak hours. QoS is designed specifically to manage packet scheduling to provide higher priority to certain traffic types like VoIP. Traffic shaping, while useful for controlling bandwidth consumption and preventing network congestion, does not necessarily prioritize one type of traffic over another. Increasing bandwidth will only provision more capacity but won't manage how traffic is prioritized. Encryption does not address the issue of traffic prioritization or improvement of VoIP quality.