Re: psamp vocabulary

[Maurizio Molina <molina@ccrle.nec.de>]

Rae McLellan wrote:

> > I wonder whether this "invariance" in the selected packet stream when swappig
> > the order of selectors can be considered a generally "desirable" property.
> > while it is for some application (e.g trajectory sampling), for some other
> > (e.g. traffic profiling) what matters is only that, independently of selector
> > ordereing,
> > 1) the amount of selected packets doesn't (significantly) change
> > 2) the selected sample has a distribution of the metric of interest similar
> > to that of the parent population, so that it can be correctly inferred
> > analyzing the sample.
>
> Invariance frees psamp from specifying the order and allows different vendors
> to implement the selectors in different way w/o affecting the results.

Rae,
that's exactly the point: it seems that "the results" for you means "the resulting
selected sample".
With my comment above, I was saying that "the results" should be on the contrary
"1) the size of the selected sample" and "2) the results you derive from the
analysis of the selected sample".
Note that it's not only a terminology issue. If we require that varying the
selector ordering (which is something that we may desire to ease implementations)
we get the same selected sample, then we have to exclude the whole "third group" of
samplers you outlined in your previous e-mail, i.e. random samplers and samplers
based on packet position. To this last category belongs e.g. the simple 1 out of N
sampler implemented by decrementing a counter, which is the simplest we can think
of. Do we want to exclude it?
Maurizio

>  When it comes to high speed interfaces, its much easier to implement the
> selectors
> in the order that the packet arrives, than having to provide random access to
> the packet header.

>
>
>         Rae McLellan
>
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