Re: comments on draft-ietf-psamp-framework-09.txt

[Jennifer Rexford <jrex@research.att.com>]

>> - page 13-14: Under "content-dependent sampling" or "non-uniform
>> probabilistic sampling," it may be helpful to include "sampling
>> packets in proportion to their length" as an example.
>
> Doesn't "sampling packets in proportion to their length" fall into the
> content _independent_ sampling?  If you sample periodically by time,
> you'll get sampling of packets in proportion to their length.

I was trying to think of a meaningful example to make it more clear
why content dependent sampling would be useful.  The one thing that
came to mind was sampling on the packet-length field in the IP header.
That said, you are right that there are content-independent ways to
sample this way, too, so perhaps it isn't a good choice for an example.
In any case, I think including an example might be helpful here.

> "However, if prior selection not based on routing state has reduced the
> packet stream to below line rate, subselection based on routing state
> may be feasible."

Easier to parse, though still a little confusing.  How could the packet
stream on the line be above line rate?  (Or, are you talking about the
packets before they go into the output queue?  Or, is the "line rate"
the bandwidth allocated for psamp records?  Is the idea that subselecting
routing state [such as the prefix entry that matched the packet?] is
not reasonable unless the sampled stream is low-rate enough to enable
the look-ups to take place?  But, isn't the lookup already done as part
of regular packet handling?  Hmmm, I think I still don't quite understand
what the sentence is driving at.)

Thanks!

-- Jen


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