Re: [PSAMP] PSAMP-INFO IE realtiveError

Tanja,

>>> absoluteError
>>>
>>> This Information Element specifies the maximum possible measurement
>>> error of the reported value for a given Information Element. The
>>
>> We should indicate how to connect the *Error values to specific fields,
>> eg by using an option with the specific field as scope. Else, someone
>> may put the *Error elements adjacent to the relative fields in the data
>> record - which could work, but is open to misinterpretation.
> 
> Maybe I don't understand the comment correctly. Isnt the usage explained
> in the example in PSAMP-PROTO? The error can also be applied to relative
> values.

Either in the description for these fields, or at least in the title for 
the section, we should indicate that they should be used for the 
"Accuracy Report Interpretation" in PSAMP-PROTO.

>>> absoluteError has the same unit as the information element it is
>>> associated to. The real value of the metric can differ by
>>> absoluteError
>> "with" ------^^
> 
> ? Where to put the with?

Before the wrapping, the ^^ originally pointed to "to" - ie "to" -> "with".

>> We should specify that upperCILimit, lowerCILimit and confidenceLevel
>> are all required, and what to do if too few of them are provided.
>>
> 
> Maybe just a sentence: "All three values (upperCILimit, lowerCILimit and
> confidenceLevel) are necessary to provide an complete accuracy
> statement."
> 
> I think the checking for the complete accuracy statement as out of scope
> for IPFIX/PSAMP. I think this is something that the applications that
> requires the statement should check. So I would consider no mandatory
> action by collector.

If the *Error elements are provided in an option (eg, the Accuracy 
Report Interpretation) then the collector can obviously ignore them.

But that's not the only way to use them. What if they appeared right in 
a data record - and there weren't enough of them? Should the collector 
ignore the entire data record?

>>> NEW:
>>>
>>> ... The accuracy for a measured information elelment SHOULD be reported
>>> either with the fixedError Information Element [PSAMP-INFO
>>> <http://tools.ietf.org/html/draft-ietf-psamp-protocol-09#ref-PSAMP-INFO>],
>>> or with the relativeError Information Element [PSAMP-INFO
>>> <http://tools.ietf.org/html/draft-ietf-psamp-protocol-09#ref-PSAMP-INFO>].
>>> The accuracy for an estimated information element (from sampling) SHOULD
>>> be reported with confidence limits and confidence level.[PSAMP-INFO]
>>
> > Agreed. I'd also like to add something indicating how this can be done,
>> eg by using an option with the correct scope.
> 
> o.k. Maybe you can add a sentence for this?

It should be per the "Accuracy Report Interpretation" in PSAMP-PROTO - 
which should be updated to include these new IEs.

>> The intention was to say that the clock is 5 minutes slow, +/- 10
>> seconds - so there's both an absolute error and a relative error.
>>
> 
> NOW I finally understand what you meant by fixedError initially !!
> This I would not consider as error. Any fixed deviation I would rather
> name "offset"...
> If it is known couldn't you add it to the value and report the correct
> time?

In that case there would be no need to ever report "absoluteError" - 
because all the original measurements can be corrected before being 
exported.

However, it may be we want to export the actual observed value, rather 
than a corrected value.

> Or maybe check whether the NTP and TICTOC have a term for this...

We need a generic solution that works for all different kinds of IEs, 
not just for time.

Thanks.
-- 
Paul Aitken
Cisco Systems Ltd, Edinburgh, Scotland.
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