A TCP sender transmits a burst of data at twice its contracted rate for 500ms, then returns to normal. Under traffic shaping, what does the receiver observe?
APackets are delayed but eventually all arrive; TCP sees increased latency but no loss
BAll packets exceeding the rate limit are immediately dropped; TCP retransmits them
CThe burst passes through unaffected because TCP handles rate control end-to-end
DThe sender is disconnected from the network for violating the rate limit
Traffic shaping buffers excess packets rather than discarding them. The burst is absorbed into the shaper's queue and released at the configured rate, so all packets arrive — but later than they would have without shaping. TCP sees higher latency and possible jitter, but not packet loss. Under policing, the excess packets would instead be dropped, forcing TCP retransmission.
Question 2 Multiple Choice
In the token bucket algorithm, what does a larger bucket (burst size) allow compared to a smaller one?
ALarger bursts of traffic to pass at full rate before rate limiting kicks in
BA higher sustained average rate over time
CFaster token generation, effectively increasing the configured rate
DMore packets to be dropped before alerting the network operator
The token bucket's burst size determines how many tokens can accumulate. A larger bucket lets more packets pass in a sudden burst (while tokens are plentiful) before the rate limit is enforced. The average sustained rate is still determined by the token generation rate, not the bucket size. A smaller bucket enforces a stricter, more uniform flow.
Question 3 True / False
Traffic shaping adds latency to excess packets but does not discard them.
TTrue
FFalse
Answer: True
Shaping holds excess packets in a queue until enough tokens are available for transmission — packets are delayed, not dropped. This is its defining characteristic and the key difference from policing. The tradeoff is that buffers add latency and jitter, which matters for real-time applications but is generally acceptable for bulk transfers like file downloads or TCP streams.
Question 4 True / False
Policing is generally preferable to shaping because it seldom adds latency to network traffic.
TTrue
FFalse
Answer: False
While policing avoids adding latency (excess packets are dropped immediately, not queued), it causes packet loss, which is often worse. Lost packets force TCP retransmission, wasting bandwidth and adding overall delay. For applications where packet loss is costly (file transfers, video streaming), shaping's added latency is usually preferable. Policing is appropriate at network boundaries where the operator has no buffer obligation — not as a universal improvement.
Question 5 Short Answer
Why would an ISP deploy policing at its network edge rather than shaping, even though policing causes packet loss for customers who exceed their contracted rate?
Think about your answer, then reveal below.
Model answer: The ISP's role at its edge is enforcement, not accommodation. The ISP has no obligation to buffer a customer's excess traffic — doing so would consume ISP resources (memory, latency) on behalf of a customer who has exceeded their service agreement. Policing places the cost of rate violation on the offending party: excess packets are dropped, TCP detects loss, and the sender must retransmit. The customer's own edge router should shape outbound traffic to stay within limits; the ISP polices as a backstop to ensure contracted rates are respected regardless.
The placement of shaping vs. policing reflects who owns the buffer. Shapers are deployed where the sender accepts responsibility for smooth delivery; policers are deployed where the network operator enforces a hard contractual limit and bears no obligation for non-conforming traffic.