TestBook Test Series: Computer Networks - Flow Control Methods

Question

Two station A and B are connected via a point to point Link.A sends a freame to B using Go back-n protocolwith window size 7 and sequence number is of 3 bit.A sends frame one by one but B's ack for frame 3 is not reached to A..before the timer expiers B received frame 4   sent ACK4,but frame 5 is lost and not received by B..so now what will be the buffer frame of current window of A?

Answer 1

GO BACK N  use cummulative  ack. so , though it is not received ACK  for packet 3  , ACK  for packet 4 assures sender A  that packet 3 successfully received by receiver  . but due to some reason ack is lost .  packet 5 itself is lost , so after that,  all out of order packets  are rejected by receiver and no ack is generated . so after timeout , a window of 7 packet is again transferred that starts from sequence no 5 .

Comments

GBN uses cumulative ACKs

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@sudrashana it is mistakenly happenen. i hv edited now  @prabhanjan_1  yes , GBN use cummulative ack , SR  use independent ack

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point 1 – go back N can also use independent acknowledgement

point 2 – if it is using commulative ack. then why it send an independent ack. for 3 then a commulative ack. for 4?