Testseries-doubt

Question

“An SR sender’s window base cannot a have lower sequence number than the receiver window base”

can some one explain this statement ? Why it is false

Comments

I think there is a little grammatical error in the statement. The statement should be “An SR sender’s window base cannot have a lower sequence number than the receiver window base”.

Honestly, the statement “An SR sender’s window base cannot have a lower sequence number than the receiver window base” does not make any sense.” Because let’s say we have packets with sequence numbers 0,1,2,3,4 and somehow the packet with sequence number ‘0’ is lost or corrupted, as per the functioning of SR, it will be re-transmitting the packet with sequence number ‘0’, which is a lower sequence number.

Or

Suppose we have received an ACK for the acknowledged packet, so the thing that happens in SR is that the sender window base is moved forward to the unacknowledged packet with the smallest sequence number. If the window
moves and there are untransmitted packets with sequence numbers that now
fall within the window, these packets are transmitted.

So that’s why the statement is false. If there is any other reason than this, do share.

Ref: Selective-Repeat (Page No. 3 -> Figure No. 3 -> Point No. 3)

Ref: CN – 6^th ed  Kurose & Ross (Page no. 225 & 226)

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@Shubham Sharma 2 What does the base mean here ? is it the index of the smallest packet which is not yet acknowledged ?

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Yes, it is sort of an index for the packets within the window which are sent but not ack'd yet and those on the receiver which are expected but not received yet.
Moreover, the word 'base' is a terminology picked up by a certain authors. we may find a different term ( like "First outstanding") if we refer to some other standard textbook.

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@Shubham Sharma 2 thanks bro got it