📝 Traffic shaping and policing in QoS (29 MCQs)

📖 Explanation: When the traffic exceeds the policing threshold, the device applies the configured action—typically marking the packets as non‑conforming and then discarding or deprioritizing them. This ensures the flow does not surpass 800 kbps, while the rest of the traffic continues unaffected.

📖 Explanation: A larger burst size provides more tokens that can be accumulated, allowing a sender to transmit a higher volume of data instantaneously before the bucket empties. The average rate remains unchanged because tokens are refilled at the same constant rate, preserving long‑term bandwidth limits.

📖 Explanation: Traffic shaping buffers packets to smooth out bursts, introducing queuing delay as packets wait for transmission slots. In contrast, policing typically marks or drops excess packets without buffering, so it does not add extra latency. Therefore, shaping increases latency while policing leaves it unchanged.

📖 Explanation: The content specifies a sampling rate of 44,100 samples per second, which is the widely adopted CD‑quality audio standard. This rate, combined with 16‑bit resolution, yields the bitrate calculations discussed and is a fundamental parameter in digital audio processing.

📖 Explanation: When the bucket is full, it contains the maximum number of stored tokens equal to the burst capacity (200 kb). These tokens can be used immediately, allowing a burst of up to 200 kb to be sent. The refill rate governs only the long‑term replenishment, not the instantaneous burst.

📖 Explanation: A leaky bucket enforces a constant outflow rate by draining packets at a fixed speed (2 Mbps) while temporarily storing arrivals in a buffer. This smoothing effect prevents abrupt rate changes, making it suitable for maintaining consistent video quality when the source exceeds the permitted bandwidth.

📖 Explanation: VoIP is sensitive to packet loss; stricter policing discards or marks excess packets, leading to higher loss rates. While the policy enforces bandwidth contracts, the resulting loss or re‑marking can cause audible degradation, increased latency, and reduced call quality.

📖 Explanation: During the burst, the bucket can supply only its stored 100 kb of tokens. The remaining 2 Mbps × 0.05 s = 100 kb exceeds the available tokens, so those packets are considered non‑conforming and are dropped or marked according to the policing policy.

📖 Explanation: Placing shaping functions at the network edge allows traffic to be regulated before it enters the backbone, preventing large bursts from overwhelming core infrastructure. This early control limits congestion spread, improves overall stability, and reduces the need for complex policing within high‑speed core routers.

📖 Explanation: Marking excess packets allows downstream routers to apply lower‑priority handling rather than discarding them outright. TCP can still receive acknowledgments for marked packets, maintaining its congestion‑control mechanisms, whereas dropped packets trigger retransmissions and reduce effective throughput.

📖 Explanation: The buffer can hold up to 300 kb. As the leak rate continuously drains the bucket, the first 300 kb of the burst are transmitted while the buffer fills. Once the buffer reaches capacity, any additional incoming bits cause overflow, so exactly 300 kb are transmitted before overflow occurs.

📖 Explanation: By limiting the sender’s outbound rate through shaping, TCP’s slow‑start still probes the available capacity but cannot exceed the imposed ceiling. This coordination prevents aggressive window growth that would overshoot the link, leading to smoother utilization and fewer packet losses.

📖 Explanation: The token bucket accumulates tokens up to the burst size, enabling short, high‑rate transmissions of up to 100 kb. In contrast, a leaky bucket releases packets at a constant rate, buffering arrivals and effectively smoothing out bursts, so the traffic appears less bursty on the outbound side.

📖 Explanation: In a Differentiated Services (DiffServ) environment, marked packets are assigned a lower‑priority DSCP value. Downstream routers treat these packets with reduced scheduling priority, possibly delaying or dropping them during congestion, which enforces the original policing policy without immediate discard at the source.

📖 Explanation: Burst tolerance describes the token bucket’s capacity to absorb short, high‑rate traffic surges without violating the configured average rate. The stored tokens represent this tolerance, allowing a flow to transmit a burst of data up to the bucket’s size before it must wait for additional tokens to be generated.

📖 Explanation: RSVP (Resource Reservation Protocol) is frequently employed in MPLS environments to reserve resources and enforce bandwidth guarantees. Policing mechanisms can be applied to RSVP‑TE LSPs to ensure that traffic adheres to the agreed‑upon bandwidth, dropping or marking non‑conforming packets.

📖 Explanation: Inbound policing examines arriving packets and immediately marks or discards those that exceed the contracted rate, preventing excess traffic from filling the router’s input buffers. This protects the device from congestion‑induced buffer overrun, whereas shaping would require buffering, which could exacerbate overflow on the inbound side.

📖 Explanation: During one second the bucket generates 2 Mbps × 1 s = 2000 kb of tokens, plus the initial 500 kb burst capacity, totaling 2500 kb. The flow transmits exactly 2.5 Mbps × 1 s = 2500 kb, matching the token supply, so no tokens are exhausted and no packets are dropped or marked.

📖 Explanation: When a subscriber surpasses the allotted rate, the network’s policing function identifies the non‑conforming traffic and either marks it for lower priority or discards it outright. This enforcement maintains fairness among users and ensures that the over‑subscriber does not degrade service for others.

📖 Explanation: Shaping buffers packets to smooth out bursts, delivering them at a steady rate, which lowers variation in inter‑arrival times and thus reduces jitter. Policing, by marking or dropping excess packets without buffering, can cause irregular delivery and increased jitter, especially for real‑time streams.

📖 Explanation: The leak rate defines the constant outflow speed of the leaky bucket; therefore, the shaper cannot transmit faster than this rate. Regardless of buffer size, the sustained throughput is capped at the leak rate, which in this case is 1 Mbps.

📖 Explanation: A shaping system can allocate separate token buckets to each flow, granting each a rate proportional to its intended fair share. As tokens are consumed, the shaper smooths traffic, ensuring that no single flow dominates the bottleneck, thereby enforcing fairness through rate‑based control.

📖 Explanation: A smaller bucket limits the amount of traffic that can be sent in a burst, forcing applications to transmit more evenly and thus reducing queuing delay for time‑critical packets. Conversely, a larger bucket permits bigger bursts, which can introduce additional latency and jitter for latency‑sensitive traffic.

📖 Explanation: The bitrate is calculated by multiplying the sampling rate (44.1 kHz) by the bit depth (16 bits) resulting in 44,100 × 16 = 705,600 bits per second, which equals 705.6 kbps for a single (monaural) audio channel.

📖 Explanation: Policing enforces a strict ceiling by immediately discarding or marking packets that exceed the configured rate, making the limit immutable. Shaping, however, temporarily stores excess packets in a buffer and releases them later, allowing temporary overshoot of the rate without violating the overall bandwidth contract.

📖 Explanation: The outer bucket first limits the flow to its configured rate of 10 Mbps, dropping any excess. The inner bucket then applies its stricter rate of 5 Mbps, further reducing the flow. Consequently, the flow’s sustained throughput after both stages cannot exceed the inner bucket’s 5 Mbps limit.

📖 Explanation: When the shaping buffer reaches capacity, additional incoming packets have nowhere to be stored. The shaper must then discard the excess packets (or, in some implementations, mark them) to prevent overflow, which defeats the smoothing purpose and may lead to packet loss.

📖 Explanation: Burstiness refers to irregular traffic patterns where data is transmitted in short, intense spikes followed by quieter intervals. This characteristic contrasts with steady, uniform traffic and can cause temporary congestion if the network cannot absorb the rapid influx of packets.

📖 Explanation: For real‑time games, low latency is critical, so a smaller buffer is preferred to minimize queuing delay. However, a smaller buffer limits the ability to absorb traffic bursts, potentially causing packet loss. Conversely, a larger buffer can handle bigger bursts but adds queuing delay, raising overall latency and harming gameplay responsiveness.