📝 IntServ Integrated Services in QoS (12 MCQs)

📖 From Data Communication and Networks • 30. Quality of Service • 12 questions available

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What is IntServ Integrated Services in QoS?

Integrated Services is a fine-grained QoS architecture that provides end-to-end per-flow guarantees by requiring explicit resource reservation and admission control signaling for every individual stream across all routers in the path.

Easy

Medium

Hard

📝 All IntServ Integrated Services in QoS MCQs

Q1. In weighted fair queuing, the router’s total throughput is $R$ . If the highest‑priority class receives $R/2$ , the lowest‑priority class receives $R/6$ , what throughput does the middle‑priority class obtain?

R/2

R/3

✅

R/4

R/6

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: The three fractions must sum to 1: $1/2 + 1/3 + 1/6 = 1$ . Subtracting the highest and lowest shares ( $R/2 + R/6 = 2R/3$ ) leaves $R - 2R/3 = R/3$ for the middle class, so option B is correct.

Q2. In a leaky‑bucket shaper, the bucket capacity is $B$ bytes and the leak rate is $L$ bytes per second. If an incoming burst of $2B$ bytes arrives instantaneously, what happens to the excess bytes beyond the bucket capacity?

A.They are discarded ✅

B.They are delayed until space frees

C.They are transmitted immediately

D.They increase the leak rate

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The bucket can hold at most $B$ bytes; any additional bytes cannot be stored and are therefore dropped. The leak rate $L$ does not change, so the overflow is lost, making option A correct.

Q3. A token‑bucket regulator has a token generation rate of $T = 1$  Mbps and a bucket depth of $B = 2$  Mbits. A flow sends packets of size $S = 0.5$  Mbit at an average rate of $1.5$  Mbps. Which statement best describes the regulator’s behavior?

A.It will continuously drop packets

B.It will delay packets but never drop ✅

C.It will allow all packets without delay

D.It will alternate between dropping and delaying

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: The token bucket generates tokens at 1 Mbps, providing a long‑term allowance of that rate. The bucket can store up to 2 Mbits, allowing occasional bursts. When the flow’s average rate exceeds 1 Mbps, tokens are exhausted and packets are queued until new tokens arrive, so packets are delayed but not discarded.

Q4. Which of the following correctly contrasts the leaky‑bucket and token‑bucket mechanisms regarding output traffic burstiness?

A.Leaky bucket permits bursts, token bucket smooths traffic

B.Both produce identical burst patterns

C.Leaky bucket smooths traffic while token bucket allows bursts ✅

D.Token bucket discards excess packets while leaky bucket stores them

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: The leaky‑bucket model releases packets at a constant rate, eliminating bursts, whereas the token‑bucket model permits bursts up to the bucket depth by accumulating tokens. Therefore the leaky bucket smooths traffic and the token bucket allows controlled bursts, making option C correct.

Q5. In weighted fair queuing, how does varying packet size among classes affect the intended share of throughput compared with the ideal fractions $R/2, R/3, R/6$ ?

A.Throughput shares remain exactly proportional to the fractions

B.Larger packets cause the class to receive more than its fraction

C.Smaller packets cause the class to receive less than its fraction

D.Both B and C can occur depending on which class has larger packets ✅

💡 Difficulty: hard | ✅ Correct: D

📖 Explanation: Weighted fair queuing assumes equal packet sizes; when sizes differ, a class transmitting larger packets consumes more transmission time per packet, potentially gaining a larger share of the link, while a class with smaller packets may fall below its allocated fraction. Thus both effects are possible, making option D correct.

Q6. Consider a router implementing WFQ where the priority weights are adjusted dynamically based on observed delay. If the highest‑priority class begins to experience increased queuing delay, what is the most likely immediate impact on the throughput distribution?

A.Its throughput will increase to reduce delay

B.Its throughput will decrease, allowing other classes more bandwidth ✅

C.Throughput remains unchanged

D.All classes will be equally throttled

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: When a class suffers higher queuing delay, the scheduler typically reduces its weight to alleviate congestion, thereby lowering its allocated throughput. This reallocation grants additional bandwidth to lower‑priority classes, helping to balance delay across flows. Hence option B reflects the expected immediate impact.

Q7. Using a token‑bucket with token rate $T$ and bucket depth $B$ , what is the maximum sustained data rate that can be transmitted without incurring delay?

T

✅

B

T + B

D.Unlimited

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The token rate $T$ defines the long‑term average rate at which tokens become available. As long as the transmission rate does not exceed $T$ , tokens are replenished continuously, preventing any queuing delay. The bucket depth only allows temporary bursts, not sustained higher rates, so option A is correct.

Q8. Which design best combines a leaky‑bucket shaper and a token‑bucket policer to manage a traffic flow that must conform to an average rate of $5$  Mbps with occasional bursts up to $10$  Mbps lasting no more than $200$  ms?

A.Token bucket with rate 5 Mbps, depth 2 Mbits, followed by leaky bucket at 5 Mbps ✅

B.Leaky bucket at 5 Mbps then token bucket at 10 Mbps

C.Two token buckets in series

D.Single leaky bucket at 10 Mbps

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The token bucket permits bursts up to 10 Mbps for up to $10 \text{Mbps} \times 0.2 \text{s}=2 \text{Mbits}$ , matching the burst requirement. After the burst, the leaky bucket enforces the average 5 Mbps rate, smoothing traffic. This combination satisfies both average and burst constraints, making option A correct.

Q9. How does Integrated Services (IntServ) guarantee end‑to‑end QoS when packet sizes differ across hops, and what role do token‑bucket parameters play in maintaining those guarantees?

A.IntServ ignores packet size, relying solely on reservation; token buckets are unrelated

B.IntServ uses per‑flow reservations that account for worst‑case packet size; token‑bucket limits ensure compliance ✅

C.Token‑bucket parameters dynamically adjust reservations at each hop

D.Packet size variability invalidates IntServ guarantees

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: IntServ establishes a reservation specifying the maximum bandwidth and latency, typically based on the largest packet a flow may send, ensuring that even in the worst case the network can meet the QoS contract. Token‑bucket parameters at the source enforce the flow’s rate and burstiness so that it conforms to the reserved profile, preserving the guarantee across hops. Hence option B is correct.

Q10. In the token‑bucket algorithm, what does the bucket depth $B$ represent?

A.Maximum number of tokens that can be stored ✅

B.Rate at which tokens are generated

C.Minimum packet size

D.Time interval for token replenishment

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The bucket depth $B$ defines the upper limit on the number of tokens that may accumulate in the bucket. It determines the maximum burst size a flow can emit, as each token typically corresponds to one byte or packet. The other choices describe different aspects of the algorithm, making option A the correct definition.

Q11. If a leaky‑bucket shaper has a leak rate of $L = 2$  Mbps and the incoming traffic alternates between idle periods and bursts of $4$  Mbps lasting $0.5$  s, what is the average output rate over a long interval?

A.2 Mbps ✅

B.3 Mbps

C.4 Mbps

D.1 Mbps

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The leaky bucket emits at a constant rate $L = 2$  Mbps regardless of input bursts, as long as the bucket is not empty. Over a long period, the average output equals the leak rate, because any excess arriving during bursts is buffered and released at $L$ . Therefore the average output is 2 Mbps, option A.

Q12. Compare the impact on latency for a flow when using (i) a token‑bucket policer at the ingress and (ii) a leaky‑bucket shaper at the egress. Which statement is true?

A.Policer increases latency, shaper decreases it

B.Policer adds no latency, shaper adds latency ✅

C.Both add equal latency

D.Neither affect latency

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: A policer operates at the network edge by dropping non‑conforming packets without queuing them, so it does not introduce additional delay. In contrast, a shaper (leaky bucket) stores packets that exceed the leak rate and releases them later, thereby adding queuing delay. Consequently, only the shaper contributes to latency, making option B correct.

🔗 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 📝 Flow control techniques for QoS MCQs

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