GATE CS 2024 Set 1 — Question 36
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Computer Networks → Data Link Layer → Stop-and-Wait
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Question
Consider a network path P—Q—R between nodes P and R via router Q. Node P sends a file of size bytes to R via this path by splitting the file into chunks of 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 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 .
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?
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?
Correct answer
(B) 8.008
Solution
Given:
Packet size in bits = bitsIn a packet-switched network with pipelining (store-and-forward at router Q), the total time to transfer packets over hops is given by:Here, the number of hops (P-Q and Q-R).Converting to seconds:Alternatively, we can trace the packets:
- File size bytes
- Chunk size bytes
- Bandwidth bits/sec
- Path: P Q R (2 hops)
Packet size in bits = bitsIn a packet-switched network with pipelining (store-and-forward at router Q), the total time to transfer packets over hops is given by:Here, the number of hops (P-Q and Q-R).Converting to seconds:Alternatively, we can trace the packets:
- The first packet arrives at Q at ms. Q immediately starts forwarding it to R. It arrives at R at ms.
- Due to pipelining, subsequent packets arrive at R every ms after the first packet.
- There are remaining packets.
- Total time = Time for 1st packet + Time for remaining 999 packets
- Total time = .
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