Subject: Re: [Geopriv] [geopriv] rfc3825bis #39 (new): AD review

From: "geopriv issue tracker" <[email-masked]>
Date: Fri, 29 Oct 2010 05:07:38 -0000

#39: AD review

Comment(by bernard_aboba@…):

 Hey Bernard,

 Don't think this ever got a follow-up.  Do you recall the discussion that
 Robert is talking about here? It goes back to some intensive discussion
 (around the Philadelphia IETF, IIRC) about how the resolution
 representation is unsuitable for privacy in part because it represents
 some regions so poorly, e.g., those near the equator.

 Would you mind drafting some text, or at least proposing some
 clarifications to Section 1.2?  These don't necessarily need to go into a
 new rev right now, since the change is pretty minor, but if you could at
 least send out an acknowledgement, that would be helpful.

 Thanks,
 --Richard

 [BA] The NITs have been fixed in my private -13 copy which I'll submit
 once the window opens again during IETF week.

 I went back to the archives of IETF 71, and reviewed the presentation.

 Here is a potential revision to Section 1.2 to address the comments:

 1.2. Resolution and Uncertainty

    The DHCP options defined in this document include fields quantifying
    the resolution or uncertainty associated with a target location.  No
    inferences relating to privacy policies can be drawn from either
    uncertainty or resolution values.

    As utilized in this document, resolution refers to the accuracy of a
    reported location, as expressed by the number of valid bits in each
    of the Latitude, Longitude and Altitude fields.

    In the context of location technology, uncertainty is a
    quantification of errors.  Any method for determining location is
    subject to some sources of error; uncertainty describes the amount of
    error that is present.  Uncertainty might be the coverage area of a
    wireless transmitter, the extent of a building or a single room.

    Uncertainty is usually represented as an area within which the target
    is located.  In this document, each of the three axes can be assigned
    an uncertainty value.  In effect, this describes a rectangular prism,
    which may be used as a coarse representation of a more complex shape
    that fits within it.  See Section 2.3.2 for more detail on the
    correspondence between shapes and uncertainty.

    When representing locations from sources that can quantify
    uncertainty, the goal is to find the smallest possible rectangular
    prism that this format can describe.  This is achieved by taking the
    minimum and maximum values on each axis and ensuring that the final
    encoding covers these points.  This increases the region of
    uncertainty, but ensures that the region that is described
    encompasses the target location.

    The DHCPv4 option format defined in this document supports both
    resolution and uncertainty parameters.  Version 0 of the DHCPv4
    option format includes a resolution parameter for each of the
    dimensions of location.  Since this resolution parameter need not
    apply to all dimensions equally, a resolution value is included for
    each of the three location elements. However, due to the definition
    of resolution, using version 0 of the DHCP option format, it may
    not be possible to define a PIDF-LO that captures both the
    location as well as the uncertainty region surrounding it.

    Since version 0 of the DHCPv6 option format is not defined, the
    DHCPv6 option does not support a resolution parameter.  Version 1
    of the DHCPv4 and DHCPv6 option format utilizes an uncertainty
    parameter.  Using version 1 of the DHCP option format, it is
    typically possible to define a PIDF-LO that encloses
    the location as well as the uncertainty region surrounding it.

    Appendix A describes the mapping of DHCP option values
    to GML.  Appendix B of this document provides examples showing
    the calculation of resolution values. Appendix C provides an
    example demonstrating calculation of uncertainty values.

-- 
---------------------------------------+------------------------------------
 Reporter:  bernard_aboba@…            |       Owner:  bernard_aboba@…           
     Type:  defect                     |      Status:  new                       
 Priority:  major                      |   Milestone:  draft-ietf-geopriv-3825bis
Component:  rfc3825bis                 |     Version:  1.0                       
 Severity:  Submitted WG Document      |    Keywords:                            
---------------------------------------+------------------------------------

Ticket URL: <https://wiki.tools.ietf.org/wg/geopriv/trac/ticket/39#comment:1>
geopriv <http://tools.ietf.org/geopriv/>

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From: "geopriv issue tracker" <[email-masked]>
Date: Sat, 30 Oct 2010 21:35:57 -0000

#39: AD review

Changes (by bernard_aboba@…):

  * owner:  bernard_aboba@… => martin.thomson@…

Comment:

 Here is the complete proposed text for Section 1.2, incorporating Martin's
 suggested text as well:

    The DHCPv4 option format defined in this document supports both
    resolution and uncertainty parameters.  Version 0 of the DHCPv4
    option format includes a resolution parameter for each of the
    dimensions of location.  Since this resolution parameter need not
    apply to all dimensions equally, a resolution value is included for
    each of the three location elements.  Since version 0 of the DHCPv6
    option format is not defined, the DHCPv6 option does not support a
    resolution parameter.  Version 1 of the DHCPv4 and DHCPv6 option
    format utilizes an uncertainty parameter.  Appendix A describes the
    mapping of DHCP option values to GML.  Appendix B of this document
    provides examples showing the calculation of resolution values.
    Appendix C provides an example demonstrating calculation of
    uncertainty values.

    Since the PIDF-LO format [RFC4119][RFC5491] is used to conveying
    location and the associated uncertainty within an emergency call
    [Convey], a mechanism is needed to convert the information contained
    with the DHCPv4 and DHCPv6 options to PIDF-LO.  This document
    describes the following conversions:

      version 0 to PIDF-LO
      version 1 to PIDF-LO
      PIDF-LO to version 1

    Conversion to PIDF-LO does not increase uncertainty; conversion from
    PIDF-LO to version 1 increases uncertainty by less than a factor of 2
    in each dimension.  Since it is not possible to translate an
    arbitrary PIDF-LO to version 0 with a bounded increase in
    uncertainty, the conversion to version 0 is not specified.  Note also
    that in the conversion of version 0 to PIDF-LO it may not always be
    possible to produce a PIDF-LO that captures both the location as well
    as the uncertainty region surrounding it.

 Reporter:  bernard_aboba@…            |       Owner:  martin.thomson@…          

Ticket URL: <http://trac.tools.ietf.org/wg/geopriv/trac/ticket/39#comment:2>
geopriv <http://tools.ietf.org/geopriv/>

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From: "Thomson, Martin" <[email-masked]>
Date: Mon, 1 Nov 2010 06:39:42 +0800

>     as the uncertainty region surrounding it.

WFM.  In retrospect, the last sentence doesn't make a lot of sense.  It could be safely removed.

--Martin