Selective Repeat (SR)
Selective repeats is a connection oriented protocols in which transmitter and receiver have a window of sequence numbers. SR scheme avoids the unnecessary retransmission of the GBN scheme. In this scheme those suspicious packets which were packets received with errors. This individual as needed then the retransmission wil require for packets which the receiver individually acknowledge correctly. A window size of N will again be used to limit the number of outstanding unacknowledged packets in the pipeline. However unlike GBN the sender will have already received ACKs for some of the packet in the window figure e3.23 show the SR sender view of the sequence number space.
figure selective repeat sender and receiver views of sequence number space.