Subject: RE: comments on draft-ietf-psamp-framework-09.txt

From: <[email-masked]>
Date: Mon, 22 Nov 2004 01:16:33 -0500

> 
> - 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.
> 

This is a good point which has been lost in the recent draft
modifications. 

Lightweight implementations of PSAMP, with e.g.
	- a relatively dumb device
	- supports only 1 in N periodic sampling
	- supports basic packet reports (the first m bytes)
	- export using UDP (now allowed by IPFIX)
do not require all of IPFIX to be implemented for them to function.
(Just insert required sequence numbers and identifiers for observation
point and PSAMP processes in reports and use UDP export).

So we need also to qualify, in Section 8.1. at least, that not all of
IPFIX need be supported by a PSAMP device. The details would be pinned
down in the PSAMP protocol document.

Nick

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