[net2-wg] call notes 23/3/06

[Joe Polastre]

>       Basic question: what does 'urgent' mean? Existing protocols from SP
>       paper never use urgent. Vaguely defined, hard to know whether or not to
>       use it.

Urgent is VERY clearly defined (and I use it!).  Urgent is a
single-bit priority.  That is all urgent is, and it is defined as such
in both my thesis and the SP sensys paper.

>       Idea: attach 'send-at-latest' timestamp, so that we have a measurable
>       and clearly-defined metric for urgency.

What is the difference between this and calling cancel() if the
message becomes too stale?

Back when we had the first SP proposals, there was this notion that we
should have deadlines.  Eventually we removed it because nothing in
the system can actually guarantee that a deadline is met.  That's how
priority emerged as a much more useful concept, with cancel() as a
mechanism to remove the message if it couldn't be sent after a long
period of time.

Using explicit times are very difficult because they require knowledge
of the underlying link in detail so that you don't make mistakes at
runtime.  What happens if you continually select a time offset that is
not even possible with the underlying link?  I can see all kinda of
chaos from this parameter.

My proposal is the following: If you want to ADD to SP, you have to
implement that functionality within one of the two SP frameworks and
illustrate its utility before the addition is considered.

-Joe