Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureMedium
A company is experiencing intermittent voice quality issues (jitter and packet loss) on its VoIP calls, especially during peak network usage. The network uses a combination of Cisco Catalyst switches and routers. Which QoS mechanism, when implemented end-to-end, would be most effective in ensuring preferential treatment for voice traffic over other data traffic?
- ARate-limiting on all access ports
- BTraffic shaping on WAN links
- CImplementing a larger MTU size across the network
- DClassification and Marking followed by Congestion Management and Avoidance
Show answer & explanationAnswer & explanation
Correct answer: D. Classification and Marking followed by Congestion Management and Avoidance
Effective QoS for VoIP requires a multi-step approach. Classification and Marking identify and tag voice packets. Congestion Management (e.g., queuing mechanisms like LLQ) prioritizes these marked packets, while Congestion Avoidance (e.g., WRED) drops lower-priority traffic proactively to prevent congestion. This end-to-end strategy ensures voice traffic receives preferential treatment.
Why the other options are wrong
- A. Rate-limiting restricts bandwidth for all traffic, potentially harming voice quality by indiscriminately dropping packets.
- B. Traffic shaping is useful for controlling outbound traffic on WAN links, but without prior classification and marking, it won't specifically prioritize voice over other traffic.
- C. A larger MTU size can reduce fragmentation but doesn't inherently prioritize voice traffic or address congestion management directly.
QoS Pillars
The sequential steps involved in implementing an effective Quality of Service (QoS) policy to manage network traffic.
- Begins with identifying and categorizing different types of traffic.
- Involves marking traffic to indicate its priority level.
- Requires mechanisms to manage and avoid congestion based on these priorities.
Memory trick: VoIP Quality: Classify, Mark, Queue, Drop.