Which option reduces jitter in a VoIP network?

WRED is a congestion avoidance tool that drops packets probabilistically before queues fill up - it does not directly smooth the variable packet arrival intervals that constitute jitter at the receiver.

Call Admission Control limits active calls to prevent network overload, which may indirectly reduce congestion-induced delay variation but does not directly address jitter experienced at the endpoint.

The playout delay buffer (jitter buffer) at the receiver directly compensates for jitter by holding incoming packets for a configurable interval and releasing them at a uniform rate, smoothing variable arrival times before audio is decoded and played out to the listener.

Increasing link bandwidth reduces congestion and packet loss but does not eliminate jitter, because variable queuing delays can persist even on high-bandwidth links.