Virtual Gate Test Series: Computer Networks - Sliding Window

Question

What is send as ack in sliding window? The next packet which the sender want to received or the packet right now sender received?

I think the sender send the ack as the packet it has got right now. ?

In sliding window protocol, sender's window size is $'n'.$ Sender sent first $'n$' frames. Then he received first acknowledgment as ACK $'n'$. What frame(s) has receiver accepted$?$

$(A)$ Frame $n$

$(B)$ Frame $n-1$

$(C)$ Frames $0$ to $n$

$(D)$ Frames $0$ to $n-1$

Comments

D is the answer???

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Concept Is what I am looking for?

Answer 1

In sliding window concept the receiver sends the ACK to sender with packet number which it is expecting it from the sender and the sender will assume that before that packet number which he recieved as and ACK from reciever has been succesfully accepted .

EX. if reciever send ACK =4 then upto 0 to 3 reciever has accepted packet from sender. So if ACK =n then from "0 to (n-1)"  reciever has accepted frame from sender and sender has to send frame from frame number "n"

So answer is D

Comments

bro why bot option b becouse if the reciever got only n-1th packet then what will it ackowlwdge n only na

correct me if iam wrong

Answer 2

If this is stop and wait and go back and arq than we can say d is correct.

But if this is selective repeat than B is also correct because out of order packet accepted in selective repeat.

Comments

if we take the  case of SR, then it is not possible then sender will receive ACK=n as its first acknowledgment.

because last sequence number of the first window is n-1.

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In all SWP when window size =n

Than ack=n is not possible

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In case of SR if out of order packet is accpeted then at receiver side sorting is performing and send NACK of missing order packet so ACKN is not possible as first acknowledgment.