Consider a network path P—Q—R between nodes P and R via router Q. Node P sends…
2024
Consider a network path P—Q—R between nodes P and R via router Q. Node P sends a file of size 10^6 bytes to R via this path by splitting the file into chunks of 10^3 bytes each. Node P sends these chunks one after the other without any wait time between the successive chunk transmissions. Assume that the size of extra headers added to these chunks is negligible, and that the chunk size is less than the MTU.
Each of the links P—Q and Q—R has a bandwidth of 10^6 bits/sec, and negligible propagation latency. Router Q immediately transmits every packet it receives from P to R, with negligible processing and queueing delays. Router Q can simultaneously receive on link P—Q and transmit on link Q—R.
Assume P starts transmitting the chunks at time 𝑡 = 0. Which one of the following options gives the time (in seconds, rounded off to 3 decimal places) at which R receives all the chunks of the file?
- A.
8.000
- B.
8.008
- C.
15.992
- D.
16.000
Attempted by 36 students.
Show answer & explanation
Correct answer: B
Key idea: use pipelining because router Q can forward while receiving and both links have the same bandwidth.
Number of chunks = 1,000,000 bytes / 1,000 bytes = 1000.
Transmission time per chunk = (1000 bytes × 8 bits) / 1,000,000 bits/s = 0.008 s.
First chunk finishes arriving at R after two chunk transmission times = 2 × 0.008 s = 0.016 s.
Each subsequent chunk arrives every 0.008 s, so total time = 0.016 + (1000 − 1) × 0.008 = 8.008 s.
Therefore, R receives all the chunks at 8.008 seconds.
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