Discussion
Which provision can resolve/overcome the shortcomings associated with duplication or failure condition of Stop-and-Wait Automatic Repeat Request protocol especially due to loss of data frames or non-reception of acknowledgement ?
Answer: A
The provision is a sequence number in the header of the message.
In Stop-and-Wait ARQ, if an acknowledgement is lost, the sender times out and retransmits the frame, and the receiver would accept the same frame twice. Numbering frames, modulo 2 being enough (0 and 1), lets the receiver recognise a duplicate and discard it while still acknowledging it. Acknowledgements are numbered too, so the sender knows which frame they refer to.
A checksum detects corrupted frames, but it cannot tell a correct duplicate from a new frame. So the duplication problem is solved by sequence numbers, not by the checksum, and the options including or relying on the checksum are wrong.
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