[PCN] PCN edge behaviour experiment

[Tom Taylor <[e-mail]>]

I am making what I trust will be the final revisions to the edge 
behaviour documents in response to IESG comments. Amongst other things, 
this is the text I propose to add in the introduction to justify the 
Experimental status of the documents. The text will be the same for CL 
and for SM, following on Ruediger's observation that both behaviours are 
valid in different contexts. Comments are welcomed.

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This document describes an experimental edge node behaviour to implement 
PCN in a network. The experiment may be run in a network in which a 
substantial proportion of the traffic carried is in the form of 
inelastic flows and where admission control of micro-flows is applied at 
the edge. For the effects of PCN to be observable, at least some links 
of the network should be running near or at capacity. The amount of 
effort required to prepare the network for the experiment (see Section 
5.1) may constrain the size of network to which it is applied. The 
purposes of the experiment are:

- to validate the specification of the CL [SM] edge behaviour;

- to evaluate the effectiveness of the CL [SM] edge behaviour in
   preserving quality of service for admitted flows; and

- to evaluate PCN's potential for reducing the amount of capital and
   operational costs in comparison to alternative methods of assuring
   quality of service.

For the first two objectives, the experiment should run long enough for 
the network to experience sharp peaks of traffic in at least some 
directions. It would also be desirable to observe PCN performance in the 
face of failures in the network. A period in the order of a month or two 
in busy season may be enough. The third objective is more difficult, and 
could require observation over a period long enough for traffic demand 
to grow to the point where additional capacity must be provisioned at 
some points in the network.