[PCN] CLE vs. admission state

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

The current versions of the edge behaviour drafts have stepped back slightly 
from the extreme of reporting only transitions in admission state. Now admission 
state is reported at regular intervals.

A fair amount of off-list discussion has been happening over the appropriateness 
of the current arrangement. For one, there is a certain amount of opposition to 
specifying exponential smoothing of the CLE. For another, Phil has raised the 
possibility of a CLE-dependent policy at the decision point, where more 
important flows are allowed in at higher CLE values than less important flows. 
That suggests that instead of admission state, the egress node should be 
reporting at least the CLE.

I believe the discussion should be happening on the list -- that's what it is for.

Michael Menth suggested an useful principle to which the present drafts adhere: 
actions at the decision point/ingress node should be exactly the same for CL and 
SM. He argued that the egress node unavoidably knows the difference between CL 
and SM in any case, so it might as well absorb all the differences.

It is true that at least one end has to know the difference, but it doesn't have 
to be the egress node. If the egress node simply reports rates of unmarked, 
threshold-marked, and excess-traffic-marked traffic each interval, the decision 
point/ingress node can apply the CL- or SM-specific algorithms and draw the 
correct conclusions.

It seems reasonable to design the system so one end is the same whether CL or SM 
is deployed. If we accept that, we have one-and-a-half questions really:

1) Which end should know that SM or CL is deployed?

1) a) If it is the egress node, should it report admission state or CLE? Either 
way, the egress node would have to report the estimated edge-to-edge supportable 
traffic rate whenever termination might possibly be required, and the decision 
point/ingress node would have to compare that with the admitted traffic rate to 
see if termination is really needed.

Tom