The answer is Low Latency Queuing (LLQ). LLQ provides the lowest latency queuing mechanism for voice traffic because it combines a strict priority queue with Class-Based Weighted Fair Queuing (CBWFQ), ensuring that real-time packets marked with EF or CS5 are always dequeued before any other traffic class, even during congestion on a WAN link. On the ENCOR 350-401 exam, this concept tests your understanding of QoS design for voice and video, often appearing in scenario-based questions where you must select the mechanism that guarantees minimal jitter and delay. A common trap is choosing CBWFQ alone, which lacks the strict priority element, or confusing LLQ with FIFO or WFQ. Remember the memory tip: “LLQ = Priority Lane for Voice” — think of an emergency vehicle bypassing all other traffic to ensure it arrives first, just as the priority queue empties before any other queue.
350-401 Network Assurance Practice Question
This 350-401 practice question tests your understanding of network assurance. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer is implementing QoS on a WAN link to prioritize voice traffic. Which queuing mechanism provides the lowest latency for real-time traffic?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Low Latency Queuing (LLQ)
LLQ is correct because it combines strict priority queuing with CBWFQ, ensuring that voice traffic (marked with EF or CS5) is dequeued before any other traffic class. This strict priority mechanism guarantees the lowest possible latency for real-time traffic, as packets in the priority queue are always transmitted first, regardless of congestion on the WAN link.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Low Latency Queuing (LLQ)
Why this is correct
Option B is correct because LLQ provides a strict priority queue for real-time traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
Weighted Random Early Detection (WRED)
Why it's wrong here
Option D is wrong because WRED is a drop policy, not a queuing mechanism.
✗
Class-Based Weighted Fair Queuing (CBWFQ)
Why it's wrong here
Option A is wrong because CBWFQ treats all classes fairly without strict priority.
✗
First-In, First-Out (FIFO)
Why it's wrong here
Option C is wrong because FIFO does not differentiate traffic types.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse CBWFQ with LLQ, assuming that CBWFQ's bandwidth allocation provides low latency, but CBWFQ lacks a strict priority queue and cannot guarantee the sub-10ms jitter required for real-time voice traffic.
Detailed technical explanation
How to think about this question
Under the hood, LLQ uses a strict priority queue (PQ) that is policed to prevent starvation of other queues; the priority queue is serviced first as long as it does not exceed the configured bandwidth limit (e.g., 'priority 256' in kbps). In real-world deployments, voice traffic is typically marked with DSCP EF (46) and placed into the priority queue, while call signaling (AF31) and other data use CBWFQ classes, ensuring voice latency stays below 150 ms one-way as per ITU-T G.114.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-401 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Network Assurance — This question tests Network Assurance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Low Latency Queuing (LLQ) — LLQ is correct because it combines strict priority queuing with CBWFQ, ensuring that voice traffic (marked with EF or CS5) is dequeued before any other traffic class. This strict priority mechanism guarantees the lowest possible latency for real-time traffic, as packets in the priority queue are always transmitted first, regardless of congestion on the WAN link.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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