@Abjineet Singh It will be Tt for remaining 999 packets as long as transmission time is same for all the Links because second packet will be transmitted after Tt of first packet got transmitted .Rest of journey from Source to destination is same for every packet. so
At t=0 start
At t=Tt 1st packet got transmitted…...then rest of journey whatever tp it is
At t=2Tt 2nd packet transmitted ..then .rest of journey...so it all depends on Tt ...
At t=3Tt 3rd packet and so on…
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But note that unlike this question if
suppose there are two links and Transmission for Link1=15 and transmission time for Link2= 30 and tp=10
Then
At t=15 first packet transmitted over Link1 At t=30 second packet transmitted over Link1
At t=25 first packet reached at R1 At t=40 second packet reached at R1
At t=55 first packet transmitted over Link2 …………..note (second packet reached at t=40 but waiting for its turn hence data getting accumulated at second router )
At t=65 first packet reached at destination
At t=55+30=85 second packet transmitted over Link2
At t=95 second packet reached at destination …..which is (time taken to reached first packet +slowest link) i.e. 65+30=95 .……….so here bottleneck is slowest link L2 which is 30
to understand this concept
refer this question
https://gateoverflow.in/43572/gate2004-57
and make sure you understand @arjun sir’s comment on this question
For data rate, we need to consider only the slowest part of the network as data will be getting accumulated at that sender (data rate till that slowest part, we need to add time if a faster part follows a slower part).