[PCN] Key results from PCN

[Tom Taylor <tom111.taylor at bell.net>]

This is a small report in advance of the official notes, written from my point 
of view. The key outcomes I noted from the PCN meeting were these:

1) The egress node will always report the measured rates of unmarked, 
excess-traffic-marked, and, if applicable, threshold-marked traffic. This is for 
two reasons: flexibility in the application of policy at the decision point, and 
flexibility in future applications in general.

2) Two remarks apply to the signalling requirements draft. One has to do with 
the current division into ingress vs. centralized control. Fortune has sent 
notes on that topic. Probably more importantly, the draft has to talk about how 
each end knows that the other end is alive, and how long it is permissible for 
the system to proceed without some assurance that the peer is still alive. 
Steven was going to write a note on this, since he raised it.

3) The piggybacking behaviour draft needs fixing to match how RSVP and NSIS 
actually work. I have to do some studying. Francois LeFaucheur gave me a 
reference that should serve as a tutorial.

4) I don't think we came to a conclusion on how much memory/lag is desirable in 
the measurements. Accumulating over an interval introduces some lag. Exponential 
smoothing or moving averages introduce some lag. These are both means to 
reducing very short-term oscillations in system behaviour. I'm personally 
indifferent to the means used, but believe that some damping is desirable.

4) The final point is, I think, the most important one for us to resolve going 
forward. That is the question of when reports are issued. It could be at the end 
of fixed intervals, or it could be when something significant has changed. The 
question is tied up with whether reliable transport is needed and also with the 
liveness question described in 2) above.

Tom Taylor