📝 Flow control techniques for QoS (10 MCQs)

📖 From Data Communication and Networks • 30. Quality of Service • 10 questions available

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What is Flow control techniques for QoS?

Flow control techniques for QoS are mechanisms that regulate the rate of data transmission between sender and receiver to prevent network congestion and buffer overflow, ensuring that high-priority flows maintain their required performance without starving other traffic.

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📝 All Flow control techniques for QoS MCQs

Q1. If a network implements priority queuing, what is the most likely effect on the average delay of low‑priority traffic compared to FIFO queuing?

A.Average delay decreases

B.Average delay increases ✅

C.Average delay unchanged

D.Delay becomes unpredictable

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Priority queuing serves high‑priority packets first, causing them to bypass the queue while low‑priority packets wait behind them. Consequently, low‑priority traffic experiences longer waiting times than in a FIFO system where all packets are served in order of arrival, leading to an increase in its average delay.

Q2. A token bucket is configured with a token generation rate of $r = 2$  Mbps and a bucket depth of $B = 4$  Mbits. What is the maximum burst size that can be transmitted without violating the token rate?

A.2 Mbits

B.4 Mbits ✅

C.6 Mbits

D.8 Mbits

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The token bucket allows a burst up to the amount of stored tokens, which equals the bucket depth. With $B = 4$  Mbits, the sender can transmit a burst of 4 Mbits instantly; any larger burst would exceed the available tokens and breach the configured rate.

Q3. Suppose a traffic shaper first applies a leaky bucket with a leak rate of $L = 1$  Mbps and then a token bucket with parameters $r = 1.5$  Mbps, $B = 3$  Mbits. How does this two‑stage shaping affect jitter compared to using only a leaky bucket?

A.Jitter is reduced because the token bucket smooths bursts ✅

B.Jitter increases due to added token bucket delay

C.Jitter remains the same

D.Jitter becomes unpredictable

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: The initial leaky bucket limits the average output rate, while the subsequent token bucket permits controlled bursts up to the bucket depth. This combination smooths variations in inter‑arrival times, thereby reducing jitter relative to a single leaky bucket that can produce larger, less predictable spacing.

Q4. Which statement best contrasts FIFO queuing with Weighted Fair Queuing (WFQ) regarding bandwidth allocation?

A.FIFO guarantees equal bandwidth to all flows

B.WFQ allocates bandwidth proportionally to assigned weights ✅

C.FIFO provides priority based on packet size

D.WFQ serves packets strictly in arrival order

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: WFQ assigns each flow a weight that determines its share of the link capacity, ensuring proportional fairness. FIFO, by contrast, treats all packets identically and serves them in arrival order, which can lead to one flow monopolizing bandwidth if it sends more traffic, offering no guaranteed share.

Q5. How does RSVP in Integrated Services differ from the DS field used in Differentiated Services for expressing QoS requirements?

A.RSVP carries per‑flow state while DS field marks packets per class ✅

B.RSVP uses a fixed 6‑bit field, DS uses variable length

C.Both mechanisms rely on end‑to‑end signaling

D.DS field provides tighter delay guarantees than RSVP

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: RSVP sets up a reservation for each individual flow, maintaining state in routers for that flow, whereas DiffServ's DS field is a small header bit pattern that classifies packets into a small number of pre‑defined service classes, eliminating per‑flow state and simplifying scalability.

Q6. During a network overload, why might admission control be more effective than simple resource reservation for maintaining QoS?

A.Admission control dynamically rejects new flows when capacity is insufficient, preventing oversubscription ✅

B.Resource reservation pre‑allocates bandwidth regardless of current load

C.Admission control guarantees zero packet loss for all admitted flows

D.Resource reservation adapts to traffic bursts better than admission control

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Admission control evaluates the current load before accepting a new flow; if the network cannot support the requested resources, the flow is denied, preventing the system from becoming oversubscribed. Simple reservation may allocate bandwidth that cannot be honored during congestion, leading to degraded QoS for all flows.

Q7. For a video‑conference application that is highly sensitive to jitter but tolerant of moderate delay, which QoS mechanism should be prioritized?

A.FIFO queuing

B.Traffic shaping with a leaky bucket

C.Priority queuing giving the flow highest priority ✅

D.Weighted Fair Queuing with equal weights

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: Video conferencing requires consistent packet spacing; assigning the flow the highest priority ensures it experiences minimal queuing delay variability, directly reducing jitter. While some delay is acceptable, priority queuing guarantees that packets are transmitted promptly and uniformly, satisfying the jitter‑sensitive nature of the application.

Q8. If a network must support both VoIP (low delay, low jitter) and bulk file transfer (high bandwidth, tolerant of delay), which combination of QoS techniques best satisfies both requirements?

A.Apply token bucket shaping to VoIP and FIFO for file transfer

B.Use priority queuing for VoIP and weighted fair queuing for file transfer ✅

C.Treat both flows with the same DiffServ class

D.Reserve bandwidth for file transfer using RSVP and shape VoIP with leaky bucket

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Priority queuing gives VoIP packets precedence, guaranteeing the low delay and jitter it needs. Weighted Fair Queuing then allocates the remaining bandwidth fairly among bulk transfers, allowing them to use the leftover capacity without starving other traffic, meeting both service requirements.

Q9. Design a QoS policy for three flows: (1) real‑time video requiring 5 Mbps, < 100 ms delay, jitter < 10 ms; (2) interactive gaming needing 1 Mbps, < 50 ms delay, jitter < 5 ms; (3) email with 0.1 Mbps, no strict delay. Which set of mechanisms best meets these constraints?

A.Reserve bandwidth for all three using RSVP, and use priority queuing for video

B.Mark video and gaming as high‑priority DS classes, apply token bucket shaping to limit their burst, and use WFQ for email

C.Apply leaky bucket shaping to all flows and use FIFO queue

D.Use DiffServ with three DS classes, combine token bucket for video, leaky bucket for gaming, and no shaping for email ✅

💡 Difficulty: hard | ✅ Correct: D

📖 Explanation: DiffServ allows classification into three service classes, matching the distinct needs. Token bucket shaping for video permits controlled bursts while keeping jitter low, leaky bucket for gaming smooths traffic to meet tight delay and jitter constraints, and email can be left unshaped, using the remaining bandwidth efficiently.

Q10. In QoS terminology, what does the term 'reliability' refer to?

A.The ability to guarantee zero packet loss

B.The guarantee of ordered packet delivery

C.The likelihood that packets reach the destination without loss ✅

D.The speed at which packets are transmitted

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: Reliability describes how consistently a flow can deliver its packets to the receiver without being lost or requiring retransmission. It reflects the probability that transmitted data arrives intact, which is crucial for applications such as email or file transfer that depend on accurate delivery.

🔗 Related Topics (MCQs)

📝 Data flow characteristics in QoS MCQs 📝 QoS definitions in computer networks MCQs 📝 Application sensitivity to QoS parameters MCQs 📝 Flow classes in quality of service MCQs 📝 Scheduling algorithms for QoS MCQs

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