Subject: [Geopriv] AD review: draft-ietf-geopriv-rfc3825bis-12

From: Robert Sparks <[email-masked]>
Date: Mon, 11 Oct 2010 16:16:27 -0500

Bernard and the chairs tell me that this is ready to go again - I've requested IETF Last Call.
Please consider the following early IETF LC comments:

Comment:

This document doesn't capture the issues with the version 0 DHCPv4 
option that we discussed in Philadelphia.
(See <http://www.ietf.org/proceedings/71/slides/geopriv-2/geopriv-2.htm>). 
It may not need to, since it is not trying to specify using the version 0 
DHCPv4 option to return an area covering another area. However, given the
amount of conversation that went into understanding the limitation, some 
text explaining it seems warranted. It would also help motivate _why_ there
is now a version 1. (That said, there is text in section 1.2 that could
be read to say a version 0 response could cover an arbitrary region to
a desired level of precision - that text should be adjusted to make it
clear that's not what's being claimed).

Nits:

Section 2.4 should call out that it is defining AType values.
In this section (and elsewhere in the document), the older "AT" 
tag in the prose should be changed to use the "AType" tag in the 
new format layout. 

The last equation in section 2.4.5 has x on both sides. I suspect
log2(x) should have been log2(Uncertainty)

Please double-check the XML templates - there are a few spurious semicolons.

---

From: Bernard Aboba <[email-masked]>
Date: Thu, 28 Oct 2010 18:34:06 -0700

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.

From: [email-masked]
To: [email-masked]
Subject: Fwd: [Geopriv] AD review: draft-ietf-geopriv-rfc3825bis-12
Date: Thu, 28 Oct 2010 18:37:52 -0400

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

Begin forwarded message:From: Robert Sparks <[email-masked]>Date: October 11, 2010 5:16:27 PM EDTTo: GEOPRIV <[email-masked]>Cc: [email-masked]: [Geopriv] AD review: draft-ietf-geopriv-rfc3825bis-12
 Bernard and the chairs tell me that this is ready to go again - I've requested IETF Last Call.Please consider the following early IETF LC comments:
Comment:

Nits:

The last equation in section 2.4.5 has x on both sides. I suspect
log2(x) should have been log2(Uncertainty)
Please double-check the XML templates - there are a few spurious semicolons._______________________________________________
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