[PSAMP] PSAMP-INFO IE realtiveError

Hi Benoit and Paul,

here my suggestions for clarification of the error IEs in PSAMP-INFO.

-    I suggest to rename the fixedError to absoluteError

-    I suggest to introduce CI limits and level to also report
estimation errors

-    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.

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>
]. The 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.

Sorry for the late comments, I was quite busy with PSAMP-TECH before...

Kind regards,

Tanja