[IPFIX] timestamps, exporters, and other animals

Hi all;

So I wanted to start a discussion around timestamps when exporting flows 
or OID values (qv. http://www.ietf.org/proceedings/81/slides/ipfix-6.pdf).

I think it'd be good thing to specify an association between a timestamp, 
and an exported OID, flow, etc. When exporting an OID, for example, I 
would like a way to know within some limit of certainty when that OID 
value was actually sampled.

A problem I find with SNMP is that the client can only use its own 
timestamp of the server's reply to guess when the requested variable was 
sampled. If there is uncertainty in the server implementation that adds 
some delay between sampling and sending the response (without even 
addressing variable network delay), there's no way to know when the object
was sampled with any certainty.

I have also seen this problem in various sFlow implementations. There, 
often the timestamp is added by the control plane an unknown amount of 
time after the sample was taken.

Has there been any prior work or discussion around this issue? I had a few 
of my own thoughts about how to approach it, but I thought it would be 
useful to start here.

PS. For background - I am looking at NMS/protocol implementation for 
OpenFlow devices, which might have very many distributed individual 
devices with very many ports and variables per port. Therefore I'd very 
much like to implement an efficient NMS "counter" protocol.

Thanks,

--
Josh Bailey
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