Suppose that $x$ bits of user data are to be transmitted over $k-$hop path in a packet-switched network as a series of packets each containing $p$ data bits and $h$ header bits with $x>>(p+h)$. The bit rate of lines is $b$ bps and propagation delay is negligible.What is the time taken by the source to transmit total bits?
Here is asked about the time taken by source to upload the total packets. So, B should be the answer.
Answer is wrong because asking about total time ,,answer is given in bits,,although acc. to me solution will be-
The total number of packets needed is x/p. The total of data+header
works out to (p+h)x/p bits. The source takes (p+h)x/(pb) sec to transmit
this. The forwarding of the last packet by intermediate routers on the way
takes up (k-1)(p+h)/b sec. Adding up the two gives the time to clear the
full pipe (that is, from start at source of the first bit of first packet
to move out till the receipt of the last bit of the last packet at the
Total time = (p+h)x/(pb) + (p+h)(k-1)/b.