Section 6.1. refers to systems that are space-coupled but time- uncoupled – that is, messages are directed towards a given receiver (or receivers), but that receiver can have a lifetime independent from the sender’s. Can you construct a communication paradigm with these properties? For example, does email fall into this category?

Question

What will be an ideal response?

Answer 1

This is a subtle point and we invite the reader to dwell on this themselves. Is there a communication paradigm
whereby a message is directed towards a given named receiver with known identity and hence bound in space,
but where the sender and recipient have different lifetimes? This partially depends on the interpretation of
different lifetimes, that is whether this implies the receiver may not exist yet or whether the receiver does exist
but is not available at a given time to receive a message. If we take the first interpretation, we can think of a
non-computer example, that is a letter addressed to a yet unborn great-grandchild. We can also think about
time capsules addressed to a given recipient. If we take the second interpretation, then email does fit this
category, that is a mail message is directed towards a known receiver who may or may not be around at a given
time but who will receive the message when next connected (see also Exercise 6.4. below). Note that this
assumes that we are focusing on the delivery of the message to the intended person rather than their mailbox.