Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureMedium
A network engineer is troubleshooting a recently deployed application that uses UDP for real-time video streaming. Users are reporting significant quality degradation, including pixelation and freezing. The engineer suspects network congestion is causing packet loss and jitter. Which QoS mechanism should be prioritized to mitigate these issues for UDP-based real-time video?
- AWeighted Random Early Detection (WRED)
- BTraffic Policing
- CLow Latency Queuing (LLQ)
- DTraffic Shaping
Show answer & explanationAnswer & explanation
Correct answer: C. Low Latency Queuing (LLQ)
Low Latency Queuing (LLQ) is designed to provide strict priority to delay-sensitive traffic, such as voice and video, ensuring it is forwarded before other traffic types. This directly addresses jitter and packet loss for real-time applications.
Why the other options are wrong
- A. WRED drops packets proactively to prevent congestion but does not guarantee strict priority for specific traffic types.
- B. Traffic policing drops packets that exceed the configured rate, which can worsen packet loss for real-time applications.
- D. Traffic shaping buffers excess traffic and sends it out in a smoothed rate, which can introduce additional delay for real-time applications.
Low Latency Queuing (LLQ)
A QoS congestion management mechanism that combines Class-Based Weighted Fair Queuing (CBWFQ) with a strict priority queue for delay-sensitive traffic.
- Ensures that delay-sensitive traffic (e.g., voice, video) is forwarded before other traffic.
- Minimizes jitter and delay for critical applications.
- Uses the 'priority' command within a class map.
Memory trick: Queues Ensure Order, Priority Speeds the Critical.