What is Weighted Random Early Detection (WRED) and how does it contribute to congestion management?

• A. First-In-First-Out (FIFO) queuing drops packets only when the queue is full.
• B. Weighted Random Early Detection drops packets probabilistically before the queue becomes full to prevent global congestion.
• C. Tail drop drops all packets when queue is full.
• D. Explicit Congestion Notification (ECN) replaces the queue with a fixed size.

Answer: (B)

WRED is a congestion-management technique that acts before the queue is full by dropping (or marking) packets with a probability that increases as the queue grows. This early, probabilistic signaling prevents sudden bursts of packet loss and helps avoid global synchronization where many TCP connections back off at once. The weighted part means different traffic classes have different drop probabilities, so higher-priority traffic is spared more while lower-priority traffic may be dropped more often, providing some level of service differentiation. If ECN is enabled, WRED can mark packets instead of dropping them, signaling congestion without actual loss. In short, WRED proactively manages congestion by probabilistically dropping or marking packets as the queue fills, keeping delays lower and throughput steadier.