PP Presentation

Selective Repeat

• If the line is poor, the pipe line is big (like TFTP) and the timeouts large, you waste bandwidth.
• To save the pipe, we rexmit selective frames. A list of frames is kept by the recvr. New frame are admitted. Dups are discarded. Frames arrive in any order, up to MaxSeq.
• Problem: the sender sends MaxSeq frames, the rcvr acks are all lost...the sender rexmits and the rcvr gets dups.
• Fix: let the window size = (MaxSeq+1)/2.

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