ACA Quality of Service & Traffic Management 1 — Questions and Answers
Question 1: What is the primary purpose of Quality of Service (QoS) in a network?
- To encrypt traffic between endpoints
- To prioritize certain types of traffic to ensure performance (Correct answer)
- To increase the total available bandwidth
- To block unauthorized network access
Correct answer: To prioritize certain types of traffic to ensure performance
QoS prioritizes certain traffic types (such as voice and video) to guarantee the performance levels they require, rather than increasing raw bandwidth.
Question 2: Which QoS marking method operates at Layer 2 of the OSI model?
- DSCP
- IP Precedence
- 802.1p CoS (Correct answer)
- MPLS EXP
Correct answer: 802.1p CoS
802.1p CoS (Class of Service) uses a 3-bit field in the 802.1Q VLAN tag to mark traffic at Layer 2.
Question 3: What does DSCP stand for in the context of QoS?
- Dynamic Service Control Protocol
- Differentiated Services Code Point (Correct answer)
- Data Stream Classification Policy
- Distributed Security Control Plane
Correct answer: Differentiated Services Code Point
DSCP stands for Differentiated Services Code Point, a 6-bit field in the IP header used to classify and prioritize network traffic.
Question 4: Which queuing mechanism gives absolute priority to delay-sensitive traffic, ensuring it is always dequeued first?
- Weighted Fair Queuing (WFQ)
- Class-Based Weighted Fair Queuing (CBWFQ)
- Strict Priority Queuing (PQ) (Correct answer)
- First In First Out (FIFO)
Correct answer: Strict Priority Queuing (PQ)
Strict Priority Queuing always services the highest-priority queue first before any other queue, guaranteeing minimal delay for sensitive traffic like VoIP.
Question 5: What is the valid range of DSCP values that can be assigned to IP packets?
- 0–7
- 0–15
- 0–63 (Correct answer)
- 0–255
Correct answer: 0–63
DSCP uses a 6-bit field in the IP header's ToS byte, giving a range of 0 to 63.
Question 6: Which QoS mechanism enforces a traffic rate limit by dropping packets that exceed the defined rate?
- Traffic shaping
- Traffic policing (Correct answer)
- Weighted Random Early Detection (WRED)
- Weighted Fair Queuing (WFQ)
Correct answer: Traffic policing
Traffic policing drops or re-marks packets that exceed the configured rate limit, providing hard enforcement of the policy.
Question 7: What does Wi-Fi Multimedia (WMM) bring to wireless networks?
- Higher encryption standards for multimedia streams
- QoS prioritization of voice, video, best-effort, and background traffic (Correct answer)
- Increased channel bandwidth for HD video
- Automatic frequency selection for multimedia devices
Correct answer: QoS prioritization of voice, video, best-effort, and background traffic
WMM is a Wi-Fi Alliance certification that implements QoS by defining four access categories — voice, video, best effort, and background — to prioritize traffic over wireless links.
ACA Quality of Service & Traffic Management 1
What is the primary purpose of Quality of Service (QoS) in a network?