350-501 Networking Practice Question
Which TWO queuing mechanisms best meet the requirements for voice traffic (low latency and jitter) in a service provider network?
⚠ Common exam trap
Cisco often tests the misconception that WRED or CBWFQ alone can handle voice traffic, but the trap here is that only LLQ (or strict priority queuing) provides the necessary low latency and jitter by guaranteeing immediate service for voice packets, while other mechanisms introduce delay or drop packets.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
LLQ (Low Latency Queuing)
LLQ is correct because it combines a strict priority queue with CBWFQ, ensuring voice traffic (which is delay-sensitive) is always serviced first, thereby minimizing latency and jitter. The priority queue is policed to prevent starvation of other traffic, making it ideal for real-time applications like VoIP in service provider networks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
LLQ (Low Latency Queuing)
Why this is correct
LLQ provides a strict priority queue for real-time traffic.
- ✗
WRED (Weighted Random Early Detection)
Why it's wrong here
WRED is a congestion avoidance mechanism that drops packets probabilistically before buffers fill, but it does not provide strict priority or guaranteed low latency for voice traffic. Voice requires a queuing method like LLQ or PQ that can dequeue packets ahead of other traffic, which WRED cannot enforce. It is tempting because WRED is often used to manage congestion for TCP-based data traffic, where dropping packets signals senders to slow down, making it suitable for bulk data but not for real-time voice.
- ✓
Priority queuing
Why this is correct
Priority queuing provides strict priority, ensuring low latency and jitter.
- ✗
CBWFQ without LLQ
Why it's wrong here
CBWFQ provides bandwidth guarantees but no strict priority for jitter-sensitive traffic.
- ✗
FIFO (First In First Out)
Why it's wrong here
FIFO does not prioritize traffic and can cause jitter.
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