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Re: 95th Percentile = Lame

  • From: James Thomason
  • Date: Sun Jun 03 22:47:10 2001

>   I think the others have made the point regarding the above
> comment. However, let me explain my view of this a bit differently.
>   As pointed out, the providers have to build to provide a certain quality
> of service during peak hours. It's the behavior of their network at those
> peak hours that determines what they need to build/buy and therefore their
> costs, which then determines what they need to charge their customers.

Very true.  Providers have built their network to ensure a certain level
of quality (that they cannot quantify due to packet based delivery), and
the cost of this infrastructure reflects what they must charge customers
to effect delivery of service. 

What I fail to understand is why is this cost not simply passed on equally
to ALL customers?  

Averages of any kind have the effect of removing the structure of the
underlying data. 

Averaging either:  

1. Destroys real bits. 
2. Creates make-believe bits. 

Why not simply quantify the cost of a transimitted bit, either generally,
or based on point of egress, and pass that cost on equally to all

Do bits have value?  

The responses I have seen so far indicate: 

Bits have value sometimes depending on .....
	a. if they are included in the average. 
	b. if they increase or decrease the theoretical cost to the

But do not all bits have value all of the time?  Are there free bits?	

Perhaps it was initially very difficult for a provider to quantify this
cost - perhaps it still is.  I am sure that assuming equal costs among
providers that exchange traffic "freely" only contributes to this problem. 

>   Personally, I think the 95% billing is a rational simplification of a
> more complex problem. If you accept that peak loading occurs for something
> around 3-4 hours/day (sounds about right) and that 95% billing ignores the
> top 1.2 hours of usage each day, it's kind of like drawing a line
> horizontally roughly midway up the usage curve during the few hours of
> peak usage. In a way, it's what others have refered to as "average
> peak" usage.
>   If you don't assume that a customer's usage is a smooth curve, but
> rather has some random variability during the few hours around peak
> loading time, and you assume that you have enough customers with similar
> somewhat random variations that those variations average out over the bulk
> of all customers to be a somewhat smooth loading, then you can only come
> to one conclusion. You can rationally evaluate, provision and bill for,
> that "average peak" usage of your network and have some level of
> confidence that you're being fair not only to yourself, but also your
> customer.
>   As I see it, the only way to be even more fair, would be to truely
> average a customer's peak usage using some kind of "rolling average"
> calculation, then take the peak of that rolling average. That would
> possibly be more fair to customers who have wierd peak usage curves which
> could skew the 95% value to the point where it is NOT a reasonable
> estimation of the customer's average peak usage.

What seems to be truely fair to me, is to have each and every customer pay
a fair and reasonable price for the delivery of the actual bits they
transmit and receive.  I think this applies to carriers too.  

> Chuck Scott

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