Re: problem 4 - simple decision alg
Bob Walton (walton@deas.harvard.edu)
Tue, 18 Apr 2000 06:20:29 -0400 (EDT)
..One last question. As we discussed today, there are no exchanges of ACKs in
..this type of communication, rather the master senses receipt of the message.
..Well, how about the slave? It has to terminate if it gets no messages at all.
..
..So either there is both a sense_received signal that the master uses and a
..sense_lost signal that the slave uses, or there is a timer started by the
..slave, which must tell it when to terminate in the face of no communication.
..
..Which is preferable? I favor the timer, since the sense_lost may not work if
..the sensing medium is severed.
..
Timers and ACKs do not work as a way of telling that a message YOU HAVE SENT
has not been received. Since `sense_lost' = `negation of sense_received' they
are really the same thing, and only they can get the job done. Of
course they are impossible to implement in practice: that's the point.
Timers can be used to tell if you are not going to receive a message
SENT TO YOU.
BW