Difference between LLQ and CBWFQ?

• A. LLQ provides best-effort; CBWFQ provides real-time only.
• B. LLQ provides strict priority; CBWFQ provides weighted queues.
• C. LLQ is for data; CBWFQ is for voice.
• D. LLQ uses fixed queues; CBWFQ uses dynamic queues.

Answer: (B)

The key idea is how QoS queueing handles different types of traffic. CBWFQ (Class-Based Weighted Fair Queuing) creates traffic classes and assigns bandwidth (weights) so each class gets a fair share of the link and some minimum guaranteed bandwidth. It distributes leftover bandwidth based on those weights, but it doesn’t inherently give any class absolute priority over all others.

LLQ (Low-Latency Queuing) builds on CBWFQ by adding a strict priority queue for delay-sensitive traffic (commonly voice). This means the highest-priority traffic is served first, reaching the destination with minimal delay and jitter, while the remaining traffic uses the CBWFQ-driven fair queues.

So the statement that LLQ provides strict priority and CBWFQ provides weighted queues captures the essence: LLQ adds a real-time, strict-priority path on top of the weighted, class-based sharing of CBWFQ.

The other options don’t fit because LLQ is not just best-effort or data-only; voice (real-time) benefits from LLQ, and CBWFQ handles multiple classes with weights rather than implying fixed vs dynamic queues in this distinction.