Cisco Certified Support Technician (CCST) NetworkingIP ServicesHard
A company is experiencing intermittent voice over IP (VoIP) call quality issues, including choppy audio and delays, especially during peak network usage. Data traffic (web browsing, email) seems unaffected. Which QoS mechanism is most likely failing to prioritize the VoIP traffic correctly?
- ABandwidth Limiting
- BTraffic Policing
- CTraffic Classification and Marking
- DTraffic Shaping
Show answer & explanationAnswer & explanation
Correct answer: C. Traffic Classification and Marking
VoIP traffic requires proper classification and marking (e.g., using DSCP EF) to be recognized and prioritized by subsequent QoS mechanisms (queuing, congestion management). If classification and marking are incorrect or absent, the network devices won't know to treat VoIP traffic differently, leading to quality issues even if other QoS policies are in place.
Why the other options are wrong
- A. Bandwidth Limiting restricts total bandwidth, which might hurt VoIP if not targeted.
- B. Traffic Policing drops or re-marks packets that exceed configured rates, but depends on initial classification.
- D. Traffic Shaping buffers and delays packets to smooth out bursts, also depends on initial classification.
QoS Classification & Marking
The initial steps in QoS where network traffic is identified and categorized, then tagged with a specific value (e.g., DSCP) to indicate its priority or required treatment.
- First step in QoS implementation.
- Identifies different types of traffic (e.g., VoIP, video, data).
- Uses fields like Differentiated Services Code Point (DSCP) for marking.
Memory trick: Classify Carefully, Mark Meaningfully, or Calls Crash.