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Re: PROTO-11: Accuracy Report Interpretation



One comment inline:

Benoit Claise wrote:
Dear all,

We need a way of specifying the accuracy of our reported information, as PSAMP frameworks specifies: "the Report Stream must include information that enables the accuracy of measurements to be determined.". Here is some proposed text.

_Section 7.4.4 Accuracy Report Interpretation_

In order for the Collecting Process to determine the inherent accuracy of the reported quantities (for example timestamps), the PSAMP Device SHOULD send an Accuracy Report Interpretation. The Accuracy Report Interpretation MUST be exported by an Option Template Record with a double scope that contains the TemplateId [PSAMP-INFO] and the Information Element for which the accuracy is required.

If we make the templateId optional then you can have a mechanism for
setting the accuracy for all uses of an element.  Is this useful /
desirable?  It seems to me it is, since the measuring accuracy on
a router (or measurement device) will generally be fixed.

Andrew


The accuracy SHOULD be reported either with the fixedAccuracy Information Element [PSAMP-INFO], or with the proportionalAccuracy Information Element [PSAMP-INFO].

Accuracy Report Interpretation using the fixedAccuracy Information Element
 Scope:            TemplateId
                        InformationElementId
 Non-scope:     fixedAccuracy

Accuracy Report Interpretation using the proportionalAccuracy Information Element
 Scope:            TemplateId
                        InformationElementId
 Non-scope:     proportionalAccuracy

For example, the accuracy of an Information Element whose Abstract Data Type is dateTimeMilliSeconds [IPFIX-INFO], for which the unit is specified as milliseconds, can be specified with the fixedAccuracy Information Element with the milliseconds units. In this case, the accuracy is the Information Element value +/- the value reported in the fixedAccuracy.

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 proportionalAccuracy Information Element with the octet units. In this case, the accuracy is the Information Element value +/- the value reported in the proportionalAccuracy time Information Element value.

Alternatively to reporting either the fixedAccuracy Information Element or the proportionalAccuracy 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.

If the accuracy of a reported quantity changes on the Metering Process, a new Accuracy Report Interpretation MUST be generated. The Collecting Process MUST keep the accuracy of the latest Accuracy Report Interpretation.

Example 1 (to be developed)
Records (using template 12):
1. Scope: TemplateId = 5, InformationElementId = 152
Non-scope: fixedAccuracy = 2
=> we have a accuracy of +/- 2ms)

Example 2 (to be developed):
1. Scope: TemplateId = 5, InformationElementId = 152
Non-scope: proportionalAccuracy = 0.005
=> we had an accuracy of  +/- 0.5%


---------------------
For the PSAMP information model:

fixedAccuracy

       Description:
          Describes the accuracy of an Information Element, as a negative
          and positive relative error in absolute value.
       Abstract Data Type: float64
       ElementId: 320
       Status: current
       Units: The units of the Information Element for which is accuracy is
          specified.


proportionalAccuracy

    Description:
          Describes the accuracy of an Information Element as a negative
          and positive relative error, expressed as a value between 0 and 1.
       Abstract Data Type: float64
       ElementId: 321
       Status: current
       Units: None

 informationElementID

     Description:
          Contains the ID of another Information Element.
       Abstract Data Type: unsigned16
       Data Type Semantics: identifier
       ElementId: 303
       Status: current
       Units: None

Regards, Benoit.

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