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+18 votes
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
asked in Computer Networks by Veteran (346k points) | 2.7k views
any good explanation ?

5 Answers

+30 votes
Best answer

C is the answer .

answered by Boss (5.9k points)
selected by
@Mithlesh Can u plz elaborate on why in the router the protocol stack is visited twice.
Ok thanks :)
As the packet visits the network layer in the routers too, why it is not counted ??
Answer to this needs more explaination.
give more explanation broooo diagram is clear but why didn't u addd network at routers and why did u count two two times at thr router why can't it be once
both side of router may have different ethernet network or different frame mtu so it has 2 -2 layer of datalink and physical while network layer can handle mtu ,frame size so only 1 network layer
+19 votes

In source,

it is $1$ data link and $1$ network .. now as routers are in network layer
So in

$\text{Router1:}$At first, it goes to network layer like physical$\Rightarrow$DLL$\Rightarrow$network
(then again comes to physical like)$\Rightarrow$DLL$\Rightarrow$physical 




In both routers after computation in Network layer, it is coming back to physical again...
the reason is signals can only be transmitted with physical layer.


So, Network Layer$=4 \text{ Visit}.$

DLL$=6\text{ Visit}.$

answered by Veteran (21.4k points)
edited by
+8 votes
(C) Network layer – 4 times and Data link layer – 6 times

Sender Has one network layer and data link layer as receiver but router have 1NL,2DL and 2PL;

So Total NL=1NL(Sender)+2NL*(Router)+1N(Receiver)=4NL

Total DL=1*2DL(Sender+Receiver)+2*2DL(Router=6DL)

Option given as

(C) Network layer – 4 times and Data link layer – 6 times
answered by Boss (8.4k points)
+5 votes
ans c)
answered by Boss (5.1k points)
+4 votes

(C) is the correct option!
For detailed explanation:

answered by Veteran (43.6k points)

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