computer networks

Question

Comments

Is it option D?

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Ack is next sequence number sender is expecting so y should be 9501 and x should be 4001, between B and C , S has closed connection but T didn't so

Answer should be A

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But at the end, sender is sending ack only not data then why it should consume a sequence no, it can use 4000.

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what about T it has also sent fin segment now it can not send any data to S

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The communuication channel is Half closed from S side, so in B and C point, the T can only send but not S.

Here the value of X should be 4001 and value of Y should be 9501. So option (a) matches.

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@Ashwani,

seq# 4000 can't be reused again(even if the packet is pure ACK) because 4000 is already used up by previous packet..

but if #4001 is just used by pure ACK packet then #4001 can be reused again by next packet, since pure ACK packets doesn't consume seq#

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@Nitish

At the end we are just giving acknowledgement to T in response to it's FIN request as now it also wants to terminate connection from T side, so from S side we will set the  ACK field of the Available flags as significant and now our other flags PSH or SYN are not significant so whatever is the value present in sequence field doesn't matter as respective field is not significant, our ACK is significant only , so why will be we consume a new sequence number because if our segment cannot contain any data then it cannot use a new sequence number

In your second para you said if it used by ack packet then only we can reuse but I think we can also reuse it if used with FIN packet.

Please see the diagram and  point no 3, seq X is reused again and no new sequence no is consumed

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it means sequence number 4000 and 4001 both can be used here

Answer 1

I think option A.