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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.

1. Network layer – $4$ times and Data link layer – $4$ times
2. Network layer – $4$ times and Data link layer – $3$ times
3. Network layer – $4$ times and Data link layer – $6$ times
4. Network layer – $2$ times and Data link layer – $6$ times

### 2 Comments

any good explanation ?
I think answer is A because even routers have DLL and NL.

NL is used to find the add of next hop or router.

So NL of Source and Destination + NL of 2 routers

## 4 Answers

Best answer

C is the Answer.

### 4 Comments

Thanks man !

great @Ayush Upadhyaya sir!🙌

someone include this comment in answer!!

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

$\text{Router2}:$
Physical$\Rightarrow$DLL$\Rightarrow$network$\Rightarrow$Dll$\Rightarrow$physical

Destination:

Physical$\Rightarrow$DLL$\Rightarrow$Network$\Rightarrow$TCP$\Rightarrow$Application

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$=6\text{ Visit}.$

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

### 1 comment

Good Explanation
(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
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