GATE CS 2015 Set 3 — Question 47
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Computer Networks → Data Link Layer → Go-Back-N
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Question
Consider a network connecting two systems located 8000 kilometers apart. The bandwidth of the network is bits per second. The propagation speed of the media is meters per second. It is needed to design a Go-Back- sliding window protocol for this network. The average packet size is bits. The network is to be used to its full capacity. Assume that processing delays at nodes are negligible. Then, the minimum size in bits of the sequence number field has to be _________.
Correct answer
8 to 8
Solution
Given:
Bandwidth bps
Distance km m
Speed m/s
Packet size bitsPropagation time seconds.
Transmission time seconds.Let .For a sliding window protocol to utilize full capacity (100% efficiency), the sender window size must be at least .
.In the Go-Back- protocol, the relationship between the sequence number space size (where sequence numbers are ) and the sender window size is . If is the number of bits for the sequence number, then .
So, .Substituting :
We need to find the minimum integer satisfying this:
(too small)
(sufficient)Thus, the minimum size in bits of the sequence number field is 8.
Bandwidth bps
Distance km m
Speed m/s
Packet size bitsPropagation time seconds.
Transmission time seconds.Let .For a sliding window protocol to utilize full capacity (100% efficiency), the sender window size must be at least .
.In the Go-Back- protocol, the relationship between the sequence number space size (where sequence numbers are ) and the sender window size is . If is the number of bits for the sequence number, then .
So, .Substituting :
We need to find the minimum integer satisfying this:
(too small)
(sufficient)Thus, the minimum size in bits of the sequence number field is 8.
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