Re: [PSAMP] PSAMP-INFO IE realtiveError

Hi Tanja,
>
> Hi Benoit and Paul,
>
>  
>
> here my suggestions for clarification of the error IEs in PSAMP-INFO.
>
> -    I suggest to rename the fixedError to absoluteError
>
No problem with that, but [PSAMP-PROTO] must follow otherwise we have a 
problem
Can we still change that in AUTH48 maybe?
>
> -    I suggest to introduce CI limits and level to also report 
> estimation errors
>
I'm wondering whether this is a good idea to add upperCILimit, 
lowerCILimit, and confidenceLevel at this stage.
Because it implies that we need a complete new section in [PSAMP-PROTO] 
(as opposed to just editorial change) similar to "Accuracy Report 
Interpretation" but for the accuracy statement for estimated value. 
Now, the simple solution is to add the information elements in 
PSAMP-INFO and don't discuss the accuracy statement for estimated value 
in [PSAMP-PROTO].
>
> -    If it is still possible I would suggest to make a few small 
> changes in PSAMP-PROTO for consistency.
>
> -    Upper and lower CI limits can be also specified as provided 
> absolute or relative limits. So we could also add 2 more IEs (for the 
> relative CI limits)
>
>  
>
> New description of IEs:
>
>  
>
> absoluteError
>
> This Information Element specifies the maximum possible measurement 
> error of the reported value for a given Information Element. The 
> absoluteError has the same unit as the information element it is 
> associated to. The real value of the metric can differ by 
> absoluteError (positive or negative) from the measured value. This 
> information element provides only the error for measured values. If an 
> information element contains an estimated values (from sampling) the 
> confidence boundaries and confidence level have to be provided instead.
>
>  
>
> relativeError
>
> This Information Element specifies the maximum possible measurement 
> error of the reported value for a given Information Element as 
> percentage of the measured value. The real value of the metric can 
> differ by relativeError percent (positive or negative) from the 
> measured value. This information element provides only the error for 
> measured values. If an information element contains an estimated 
> values (from sampling) the confidence boundaries and confidence level 
> have to be provided instead.
>
I like your suggestions for absoluteError and relativeError because 
something that was not clear (neither from PSAMP-PROTO or PSAMP-INFO) is 
that we wanted to quantify the accuracy of the measurement estimation, 
as opposed to the accuracy of the estimated value
>
>  
>
> upperCILimit
>
> This Information Element specifies the upper limit of a confidence 
> interval. It is used to provide an accuracy statement for an estimated 
> value. The confidence limits define the range in which the real value 
> is assumed to be with a certain probability p. Confidence limits 
> always need to be associated with a confidence level that defines this 
> probability p. Please note that a confidence interval only provides a 
> probability that the real values lies within the limits. That means 
> the real value can lie outside the confidence limits.
>
>  
>
> lowerCILimit
>
> This Information Element specifies the lower limit of a confidence 
> interval. For further information see the description of upperCILimit.
>
>  
>
> confidenceLevel
>
> This Information Element specifies the confidence level. It is used to 
> provide an accuracy statement for estimated values. The confidence 
> level provides the probability p with which the real value lies within 
> a given range. A confidence level always needs to be associated with 
> confidence limits that define the range in which the real value is 
> assumed to be.
>
>  
>
>  
>
> Changes to PSAMP-PROTO if still possible:
>
>  
>
> -    Rename fixedError to absoluteError
>
> -    Slightly modify paragraph 2
>
> OLD:
>
> ...  The accuracy 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>].
>
> 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>]. 
> T
>
To be consistent with my statement above, I would not add the following 
sentence.
>
> he accuracy for an estimated information element (from sampling) 
> SHOULD be reported with confidence limits and confidence 
> level.[PSAMP-INFO]
>
>  
>
> -    Remove the following paragraph (very important! Otherwise it 
> would lead to confusion):
>
> For example, the accuracy of an Information Element to estimate the 
> accuracy of a sampled flow, for which the unit would be specified in 
> octets, can be specified with the relativeError Information Element 
> with the octet units.  In this case, the error interval is the 
> Information Element value +/- the value reported in the relativeError 
> times the reported Information Element value.
>
>  
>
> -    Avoid the term error interval
>
> OLD:
>
> In this case, the error interval is the Information Element value +/- 
> the value reported in the fixedError.
>
> NEW:
>
> In this case, the real values lies within the range of the Information 
> Element value +/- the value reported in the absoluteError.
>
>  
>
>  
>
> -    Remove the following paragraph (since absolute or relative error 
> are just different representations I would not gain something if I 
> report both)
>
> Alternatively to reporting either the fixedError Information Element 
> or the relativeError Information Element in the Accuracy Report 
> Interpretation, both Information Elements MAY be present.  This 
> scenario could help in more complex situations where the system clock 
> drifts, on the top of having its own accuracy, during the duration of 
> a measurement.
>
I would also change "Accuracy Report Interpretation" into "Measurement 
Accuracy Report Interpretation" in  [PSAMP-PROTO]

Regards, Benoit.
>
>  
>
> Sorry for the late comments, I was quite busy with PSAMP-TECH before...
>
>  
>
> Kind regards,
>
> Tanja
>
>  
>
>  
>