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
Answer : (C)
Explanation :
As you can see in the above diagram, The packet goes to Network Layer 4 times and Data Link layer 6 times.
Why network layer is considered as only once and data link layer is considered twice ?
Once the message comes to Network layer, it tries to connect to R's network level. Network level sends message via Data link layer.
Pseudo Code for network layer at the Source (S)
Find R
Send Message to R
Send Message via Datalink layer.
Pseudo Code for network layer at the Receiver (R)
Ready to receive messages.
Receive Message from Source
Message is received via Datalink layer.
Find next R
Send Message to next R
Send Message via Datalink layer.
As you can see datalink layer gets called twice for the message transfer (or pass through), but message gets processed only once at the network layer.
Concepts to Cover :
TCP/IP Stack
Datalink layer
Transport layer
Physical layer
References :
(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
Answer : (C)
Explanation :
As you can see in the above diagram, The packet goes to Network Layer 4 times and Data Link layer 6 times.
Why network layer is considered as only once and data link layer is considered twice ?
Once the message comes to Network layer, it tries to connect to R's network level. Network level sends message via Data link layer.
Pseudo Code for network layer at the Source (S)
Find R
Send Message to R
Send Message via Datalink layer.
Pseudo Code for network layer at the Receiver (R)
Ready to receive messages.
Receive Message from Source
Message is received via Datalink layer.
Find next R
Send Message to next R
Send Message via Datalink layer.
As you can see datalink layer gets called twice for the message transfer (or pass through), but message gets processed only once at the network layer.
Concepts to Cover :
TCP/IP Stack
Datalink layer
Transport layer
Physical layer
References :
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