Assume that source S and destination D are connected through two intermediate…
20132013
Assume that source S and destination D are connected through two intermediate routers labeled R. Determine how many times each packet has to visit the network layer and the data link layer during a transmission from S to D.
- A.
Network layer – 4 times and Data link layer – 4 times
- B.
Network layer – 4 times and Data link layer – 3 times
- C.
Network layer – 4 times and Data link layer – 6 times
- D.
Network layer – 2 times and Data link layer – 6 times
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Correct answer: C
Key idea: count network-layer processing at each host/router and count data-link processing at both ends of every link.
Network layer: The packet is handled by the network layer at S, at the first router, at the second router, and at D → 4 times.
Data link layer: There are three links (S–first router, first router–second router, second router–D). Each link requires data-link work by the sender and the receiver, so 3 links × 2 ends = 6 visits.
Answer: Network layer – 4 times; Data link layer – 6 times.
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