Counterexample:
Receiver will get duplicate copies.
I--Sender sends a frame which the receiver gets successfully.
Receiver sends an ack which is lost.
sender will
assume packet is lost when it does not get an ack and retransmits . Receiver
will accept this frame
without
realising it is a duplicate.
b)No, the receiver does not need to renumber the acks.
This is because an ack received at time n+1 could
only be an ack for the frame sent at time n.
Since we transmit at discrete time intervals
no confusion with old acks is possible.
c) A simlple protocol is as follows
Sender waits for 1 time unit for all
older acks to die out . It then sends a reset message
Receiver initializes number when it
gets reset and sends back a reset ack .