Page 199 43. Look at oldProtocol3.c . This improves on the scheme of the preceding problem by putting one-bit sequence numbers on the frames sent. Give a failure scenario for this version in the case that the time-out interval is too short. Your friend has been reading an article where it is suggested that a one-word checksum might be generated by XORing up all the other words in the frame.
Logical ANDs are easier to do in hardware than XORs.
If we want a really fast checksum generator, we should just AND up all the words. Critique your friend's idea. Thus for most frames, the checksum will be all zeros. Such a checksum would give virtually no information about the possibility of error in the frame. There are checksum schemes that provide much more thorough protection at fairly low cost.