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

[Derek Chiou <dchiou@avici.com>]

Some in-lined comments.

Jennifer Rexford wrote:

> Hi folks,
>
> I just read through the latest draft of "A Framework for Packet
> Selection and Reporting" (draft-ietf-psamp-framework-09.txt) and
> think the document looks great.  I have just a few minor comments,
> and one suggestion for a few sentences of additional text (on the
> subject of congestion-aware transport).  More below...
>
> -- Jen
>
> - page 11, Section 4.1: bullet "*" is missing in "Non-Contingency".
> Also, the term "non-contingency" seems a bit strange.  The text for
The term is strange to me as well.  I'm not sure what would be a good 
replacement.  Perhaps Future-Independent?

> the bullet could add something about why this requirement is included
> (e.g., "in order to limit the complexity of the selection logic").
>
> - page 12, Section 4.3: in the bullet on "Congestion Avoidance," it
> would be good to include a forward pointer to Section 8.2 where this
> issue is discussed further.
>
> - 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.

> - page 15: At the end of Section 5.2, I didn't understand the
> sentence "However, if selection not based on routing state has
> reduced down from line rate...."  I had trouble parsing it.
Is the following more clear?

"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."

> - page 21: Section 8.2 talks about the need for unreliable,
> congestion-aware transport, and shifts in the last paragraph to
> talking about IPFIX rather than PSAMP.  I wasn't sure what the the
> IPFIX paragraph was trying to get at, and if/how it relates to the way
> PSAMP should achieve congestion-aware transport.  Somewhere in the
> document (either in 8.2, 8.5, or in 10.2), it would be worth
> commenting on lighweight ways to achieve the goal of congestion-aware
> transport.  Section 8.2 could end by saying something like
> "Congestion-aware transport of PSAMP records could be achieved in
> various ways.  For example, the PSAMP device could have an export rate
> limit (as discussed in Section 8.5) that is configured by the
> controller based on observations of the packet loss rate in delivering
> PSAMP records.  This would ensure that the transport rate adapts in
> the presence of congestion without requiring the PSAMP device to
> receive acknowledgment packets or implement the adaptation algorithm
> directly."  I think this is important for conveying how the requirement
> of congestion-aware transport can be satisfied without introducing
> a lot of complexity in a PSAMP device that much operate at high speed.
>
> - page 32: My room number is A139.
>
>
>
>
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