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. Node P sends these chunks one after the other without any wait time between successive chunk transmissions. Assum

Question

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. Node P sends these chunks one after the other without any wait time between successive chunk transmissions. Assume that the size of extra headers added to these chunks is negligible, and that the chunk size is 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?

Accepted Answer

8.008. Each chunk is 10^3 bytes = 8000 bits, so one transmission on a link takes 8000/10^6 = 0.008 s. With store-and-forward and pipelining over two links, the first chunk reaches R at 0.016 s, and each subsequent chunk arrives every 0.008 s; for 1000 chunks, the last arrives at 0.016 + 999×0.008 = 8.008 s.

Solution

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