📝 Flow classes in quality of service (10 MCQs)
📖 From Data Communication and Networks • 30. Quality of Service • 10 questions available
What is Flow classes in quality of service?
Flow classes categorize network traffic into distinct groups based on their performance requirements, allowing routers to treat real-time streams, interactive data, and best-effort traffic differently to ensure each receives the appropriate level of service.
📝 All Flow classes in quality of service MCQs
Q1. A CD can store 1 hour of uncompressed high‑fidelity music. If a lossy codec compresses audio by a factor of 10, approximately how many hours of music could be stored on the same disc?
📖 Explanation: A factor‑10 reduction means the data size becomes one‑tenth of the original. Since the disc originally holds 1 hour, dividing the hour by 0.1 yields 10 hours of compressed audio. However, practical codecs also add overhead, so the realistic estimate is about 8 hours, making option B correct.
Q2. In perceptual coding, a loud tone at 3 kHz masks a softer tone at 3.2 kHz. Which masking principle is illustrated, and what implication does it have for bit allocation in that frequency region?
📖 Explanation: Because the two frequencies are close, the louder 3 kHz tone masks the softer 3.2 kHz tone—this is frequency masking. The encoder can therefore reduce or omit bits for the masked component, concentrating bits on the dominant tone, which matches option C.
Q3. Predictive coding algorithms typically introduce latency under 10 ms, suitable for telephony. If a new algorithm exhibits 25 ms latency, what is the most likely impact on a real‑time voice conversation?
📖 Explanation: Human listeners begin to perceive delays above roughly 20 ms as echo or lag, which interferes with turn‑taking in dialogue. A 25 ms latency exceeds this threshold, causing speakers to experience awkward pauses and reduced naturalness, thus degrading conversational quality, as stated in option D.
Q4. Which statement correctly contrasts lossless and lossy audio compression regarding compression ratio and typical application?
📖 Explanation: Lossless compression keeps the original audio unchanged, yielding modest ratios around 2:1 and is chosen for archival or editing where fidelity matters. Lossy compression sacrifices some fidelity for much higher ratios (5–20:1), making it suitable for consumer devices and streaming, which aligns with option A.
Q5. When choosing a coding method for a streaming service that delivers both speech podcasts and music tracks, which combination best balances latency and quality?
📖 Explanation: Speech communication demands low latency, favoring predictive coding, whereas music benefits from high fidelity achievable through perceptual coding that exploits psychoacoustic masking. Combining predictive coding for speech segments and perceptual coding for music segments therefore satisfies both latency and quality requirements, making option C the optimal choice.
Q6. How do predictive coding and perceptual coding differ in their treatment of the audio signal, particularly regarding domain transformation and masking techniques?
📖 Explanation: Predictive coding methods such as DPCM work directly on time‑domain samples and rely on predicting future values without exploiting masking, resulting in low latency. Perceptual coding first converts the signal to the frequency domain and then uses psychoacoustic masking (both frequency and temporal) to discard inaudible components, which matches option B.
Q7. According to the masking threshold, a 100 Hz tone with power below 20 dB can be omitted without audible loss. If the original signal required 500 kbps, what approximate bitrate can be saved by omitting this component, assuming it occupies 5 % of the spectrum?
📖 Explanation: If the 100 Hz component represents 5 % of the total spectral content, its bitrate contribution is 0.05 × 500 kbps = 25 kbps. Since its power is below the masking threshold, it can be removed without perceptible degradation, yielding a saving of approximately 25 kbps, which corresponds to option D.
Q8. Why does a perceptual coder allocate more bits to frequencies near the peak of the human audibility curve (≈2.5–5 kHz) compared to frequencies far outside this range?
📖 Explanation: The human ear’s sensitivity peaks around 2.5–5 kHz, meaning the masking threshold is elevated; small distortions become audible. Consequently, a perceptual encoder must allocate sufficient bits to preserve fidelity in this region, whereas frequencies with lower sensitivity can be compressed more aggressively, supporting option C.
Q9. Designing a hybrid codec that switches between predictive coding for speech segments and perceptual coding for music segments aims to optimize bandwidth. Which factor is most critical for determining the switch point?
📖 Explanation: The codec must accurately identify whether a segment contains speech or music. This decision is primarily based on analyzing the spectral characteristics and energy distribution, which indicate the segment type. Detecting these features allows the encoder to select the appropriate method, making option B the key factor.
Q10. What defines lossless audio compression?
📖 Explanation: Lossless compression algorithms compress audio without any loss of information, ensuring that decompression reproduces an identical bit‑for‑bit copy of the original signal. Typical ratios are modest (around 2:1), and no psychoacoustic masking is employed, which matches the definition in option B.