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.