Subject: [Tsvwg] How does multiplexing effect draft-briscoe-tsvwg-cl-phb-01.txt?

From: "Geib, Ruediger" <[email-masked]>
Date: Thu, 1 Jun 2006 09:29:08 +0200

Dear Bob,

measurement based admission control using PCN based 
on RED is a simple and effective idea. The 
simulations published by the draft authors demonstrate 
the efficency of measurement based admission control. 
While reading the draft, the following questions 
related to multiplexing effects came to my mind. 
Consider the figure of your simulations:

       A  
        \ 
    B  - D - F 
        / 
       C 

You've simulated traffic (A,B,C) to F with congestion on 
D-F. The PCN mechanism should work also if only one of 
the feeding links is congested, e.g. A-D. It must do 
so also if the overall proportion of traffic A-F is 
small as compared to the total traffic (A,B,C) to F. 

"Thinning" of marked traffic due to multiplexing or 
de-multiplexing may arise in many different 
configurations. 

I excuse if I have missed a draft where this is 
discussed already. 

Regards,

Rüdiger

---

From: Bob Briscoe <[email-masked]>
Date: Thu, 01 Jun 2006 11:55:55 +0100

Ruediger,

Aside from the simulations, the /design/ intends to optimise the packing of 
traffic into a network given multiple bottlenecks. So yes, certainly the 
/design/ ensures admission control will thin traffic correctly on one link 
if only (say) link A-D is congested. Indeed, it should also deal optimally 
with multi-bottleneck scenarios, whereas other algorithms have problems in 
that respect.

However, you are right to point out that the published simulations haven't 
(yet) covered anything more than a single bottleneck with fan-in. I hope we 
made it very clear (in text and presentations) that the simulation was not 
the last word - it was just the only simulations we had time for prior to 
publication.

Before coming to the IETF in the first place, we (in BT) simulated a 
different topology with cross traffic from different traffic matrices,... 
But since then, we have converged on a new marking algorithm with our 
co-authors, which is what you see in the draft (also we point out that its 
not necessarily our last word on algorithms).

In respect of multiplexing, the current marking algorithm is unchanged from 
the early one we simulated, but, we didn't want to confuse the Internet 
Draft by including our old simulations, because they weren't a test of the 
precise marking algorithm we are now describing.

Bob

>I excuse if I have missed a draft where this is

____________________________________________________________________________
Bob Briscoe, <[email-masked]>      Networks Research Centre, BT Research
B54/77 Adastral Park,Martlesham Heath,Ipswich,IP5 3RE,UK.    +44 1473 645196