 1/draftietfgeoprivrfc3825bis07.txt 20100213 20:11:23.000000000 +0100
+++ 2/draftietfgeoprivrfc3825bis08.txt 20100213 20:11:23.000000000 +0100
@@ 1,33 +1,33 @@
GEOPRIV Working Group J. Polk
INTERNETDRAFT Cisco Systems
Obsoletes: 3825 (if approved) J. Schnizlein
Category: Standards Track Individual Contributor
Expires: August 5, 2010 M. Linsner
5 February 2010 Cisco Systems
+Expires: August 15, 2010 M. Linsner
+13 February 2010 Cisco Systems
M. Thomson
Andrew
B. Aboba (ed)
Microsoft Corporation
Dynamic Host Configuration Protocol Options for
Coordinatebased Location Configuration Information
 draftietfgeoprivrfc3825bis07.txt
+ draftietfgeoprivrfc3825bis08.txt
Abstract
This document specifies Dynamic Host Configuration Protocol Options
(both DHCPv4 and DHCPv6) for the coordinatebased geographic location
of the client. The Location Configuration Information (LCI) includes
 latitude, longitude, and altitude, with resolution or uncertainty
+ Latitude, Longitude, and Altitude, with resolution or uncertainty
indicators for each. Separate parameters indicate the reference
datum for each of these values.
Status of This Memo
This InternetDraft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
InternetDrafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
@@ 38,21 +38,21 @@
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use InternetDrafts as reference
material or to cite them other than as "work in progress."
The list of current InternetDrafts can be accessed at
http://www.ietf.org/ietf/1idabstracts.txt.
The list of InternetDraft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
 This InternetDraft will expire on August 5, 2010.
+ This InternetDraft will expire on August 15, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/licenseinfo) in effect on the date of
publication of this document. Please review these documents
@@ 84,27 +84,29 @@
2.2 DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . 7
2.3 Latitude and Longitude Fields . . . . . . . . . . . . . 9
2.4 Altitude . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Datum . . . . . . . . . . . . . . . . . . . . . . . . . 14
3. Security Considerations. . . . . . . . . . . . . . . . . . . . 15
4. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 15
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Normative References . . . . . . . . . . . . . . . . . . 16
6.2. Informational References . . . . . . . . . . . . . . . . 17
 Appendix A. Calculations of Resolution . . . . . . . . . . . . . . 18
 A.1. LCI of "White House" (Example 1) . . . . . . . . . . . . 18
 A.2. LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 20
 Appendix B. Calculations of Uncertainty . . . . . . . . . . . . . 22
 B.1 LCI of "Sydney Opera House" (Example 3) . . . . . . . . 22
 Appendix C. Changes from RFC 3825 . . . . . . . . . . . . . . . . 26
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
+ Appendix A. GML Mapping . . . . . . . . . . . . . . . . . . . . . 18
+ A.1. GML Templates . . . . . . . . . . . . . . . . . . . . . 18
+ Appendix B. Calculations of Resolution . . . . . . . . . . . . . . 22
+ B.1. LCI of "White House" (Example 1) . . . . . . . . . . . . 22
+ B.2. LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 24
+ Appendix C. Calculations of Uncertainty . . . . . . . . . . . . . 26
+ C.1 LCI of "Sydney Opera House" (Example 3) . . . . . . . . 26
+ Appendix D. Changes from RFC 3825 . . . . . . . . . . . . . . . . 30
+ Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
The physical location of a network device has a range of
applications. In particular, emergency telephony applications rely
on knowing the location of a caller in order to determine the correct
emergency center.
The location of a device can be represented either in terms of
geospatial (or geodetic) coordinates, or as a civic address.
@@ 180,22 +182,23 @@
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 defined in this document 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 3 location elements.
The DHCPv6 option format (which supports only version 1) as well as
version 1 of the DHCPv4 option format utilizes an uncertainty
 parameter. Appendix A of this document provides examples showing the
 calculation of resolution values. Appendix B provides an example
+ 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.
2. DHCP Option Format
This section defines the format for the DHCPv4 and DHCPv6 options.
These options utilize a similar format, differing primarily in the
option code.
2.1. DHCPv6 Option
@@ 265,43 +268,43 @@
 Alt.(cont'd) Ver Res Datum
+++++++++++++++++
Code: 8 bits. The code for the DHCPv4 option (123).
Length: 8 bits. The length of the DHCPv4 option, in octets.
For versions 0 and 1, the option length is 16.
LatUnc: 6 bits. When the Ver field = 0, this field represents
Latitude resolution. When the Ver field = 1,
 this field represents Latitude uncertainty.
+ this field represents latitude uncertainty.
Latitude: a 34 bit fixed point value consisting of 9 bits of
integer and 25 bits of fraction. Latitude SHOULD be
normalized to within +/ 90 degrees. Positive numbers
are north of the equator and negative numbers are south
of the equator.
LongUnc: 6 bits. When the Ver field = 0, this field represents
 Longitude resolution. When the Ver field = 1,
 this field represents Longitude uncertainty.
+ longitude resolution. When the Ver field = 1,
+ this field represents longitude uncertainty.
Longitude: a 34 bit fixed point value consisting of 9 bits of
integer and 25 bits of fraction. Longitude SHOULD be
normalized to within +/ 180 degrees. Positive values
are East of the prime meridian and negative
(2s complement) numbers are West of the prime meridian.
AType: Altitude Type (4 bits).
AltUnc: 6 bits. When the Ver field = 0, this field represents
Altitude resolution. When the Ver field = 1,
 this field represents Altitude uncertainty.
+ this field represents altitude uncertainty.
Altitude: A 30 bit value defined by the AType field.
Ver: The Ver field is two bits, providing for four potential
versions. This specification defines the behavior of
version 0 (originally specified in [RFC3825]) as well as
version 1. The Ver field is always located at the same
offset from the beginning of the option, regardless of
the version in use.
@@ 352,93 +355,94 @@
in error up to a full degree of latitude and longitude, and a full
increment of altitude. This results in a version 0only client
either not obtaining location information (with no ability to
indicate to the server that version 1 was unsupported), or
misinterpreting the option.
Therefore, in situations where some DHCPv4 clients are known to
support only version 0, by default the DHCPv4 server SHOULD send a
version 0 response. It is also RECOMMENDED that DHCPv4 client
implementations support version 1, so the versioning capability added
 by this document does not cause errors interpreting the latitude,
 longitude and altitude values.
+ by this document does not cause errors interpreting the Latitude,
+ Longitude and Altitude values.
Moving forward, clients not understanding a datum value MUST assume a
World Geodesic System 1984 (WGS84) [WGS84] datum (EPSG [EPSG] 4326 or
 4979, depending on whether there is an altitude value present) and
+ 4979, depending on whether there is an Altitude value present) and
proceed accordingly. Assuming that a less accurate location value is
better than none, this ensures that some (perhaps less accurate)
location is available to the client.
2.3. Latitude and Longitude Fields
The Latitude and Longitude values in this specification are encoded
as 34 bit, twos complement, fixed point values with 9 integer bits
and 25 fractional bits. The exact meaning of these values is
determined by the datum; the description in this section applies to
the datums defined in this document.
New datums MUST define the way that the 34 bit values and the
respective 6 bit uncertainties are interpreted. This document uses
the same definition for all datums it specifies.
Latitude values MUST be constrained to the range from 90 to +90
degrees. Positive latitudes are north of the equator; negative
 latitude are south of the equator.
+ latitudes are south of the equator.
Longitude values SHOULD be normalized to the range from 180 to +180
degrees. Values outside this range are normalized by adding or
subtracting 360 until they fall within this range. Positive
longitudes are east of the Prime Meridian (Greenwich); negative
longitudes are west of the Prime Meridian.
 When encoding, latitude and longitude values are rounded to the
+ When encoding, Latitude and Longitude values are rounded to the
nearest 34bit binary representation. This imprecision is considered
acceptable for the purposes to which this form is intended to be
applied and is ignored when decoding.
2.3.1. Latitude and Longitude Resolution
 In the version 0 DHCPv4 Option, the Latitude, Longitude and Altitude
 fields are each preceded by an accuracy subfield of 6 bits,
 indicating the number of bits of resolution. The resolution sub
 fields accommodate the desire to easily adjust the precision of a
+ The Latitude (LatUnc), Longitude (LongUnc) and Altitude (AltUnc)
+ Uncertainty fields are encoded as 6 bit, unsigned integer values. In
+ the version 0 DHCPv4 Option, the LatUnc, LongUnc and AltUnc fields
+ are used to encode the number of bits of resolution. The resolution
+ subfields accommodate the desire to easily adjust the precision of a
reported location. Contents beyond the claimed resolution MAY be
randomized to obscure greater precision that might be available.
 When encoded within the version 0 DHCPv4 Option, the LatUnc value
 encodes the number of highorder Latitude bits that should be
 considered valid. Any bits entered to the right of this limit should
 not be considered valid and might be purposely false, or zeroed by
 the sender. The examples in Appendix A illustrate that a smaller
 value in the resolution field increases the area within which the
 device is located. A value of 2 in the LatUnc field indicates a
 precision of no greater than 1/6th that of the globe (see the first
 example of Appendix A). A value of 34 in the LatUnc field indicates
 a precision of about 3.11 mm in Latitude at the equator.

 When encoded within the version 0 DHCPv4 Option, the LongUnc value
 encodes the number of highorder Longitude bits that should be
 considered valid. Any bits entered to the right of this limit should
 not be considered valid and might be purposely false, or zeroed by
 the sender. A value of 2 in the LongUnc field indicates precision of
+ In the version 0 DHCPv4 Option, the LatUnc value encodes the number
+ of highorder latitude bits that should be considered valid. Any
+ bits entered to the right of this limit should not be considered
+ valid and might be purposely false, or zeroed by the sender. The
+ examples in Appendix B illustrate that a smaller value in the
+ resolution field increases the area within which the device is
+ located. A value of 2 in the LatUnc field indicates a precision of
no greater than 1/6th that of the globe (see the first example of
 Appendix A). A value of 34 in the LongUnc field indicates a
 precision of about 2.42 mm in longitude (at the equator). Because
 lines of longitude converge at the poles, the distance is smaller
 (better precision) for locations away from the equator.
+ Appendix B). A value of 34 in the LatUnc field indicates a precision
+ of about 3.11 mm in latitude at the equator.
+
+ In the version 0 DHCPv4 Option, the LongUnc value encodes the number
+ of highorder longitude bits that should be considered valid. Any
+ bits entered to the right of this limit should not be considered
+ valid and might be purposely false, or zeroed by the sender. A value
+ of 2 in the LongUnc field indicates precision of no greater than
+ 1/6th that of the globe (see the first example of Appendix B). A
+ value of 34 in the LongUnc field indicates a precision of about 2.42
+ mm in Longitude (at the equator). Because lines of longitude
+ converge at the poles, the distance is smaller (better precision) for
+ locations away from the equator.
2.3.2. Latitude and Longitude Uncertainty
 The latitude and longitude uncertainty fields are encoded as 6 bit,
 unsigned integer values. These values quantify the amount of
 uncertainty in each of the latitude and longitude values
+ In the DHCPv6 option and the version 1 DHCPv4 option, the Latitude
+ and Longitude Uncertainty fields (LatUnc and LongUnc) quantify the
+ amount of uncertainty in each of the Latitude and Longitude values
respectively. A value of 0 is reserved to indicate that the
uncertainty is unknown; values greater than 34 are reserved.
A point within the region of uncertainty is selected to be the
encoded point; the centroid of the region is often an appropriate
choice. The value for uncertainty is taken as the distance from the
selected point to the furthest extreme of the region of uncertainty
on that axis.
The following figure shows a twodimensional figure that is projected
@@ 501,138 +505,137 @@
Note that the result of encoding this value increases the range of
uncertainty to the next available power of two; subsequent repeated
encodings and decodings do not change the value. Only increasing
uncertainty means that the associated confidence does not have to
decrease.
2.4. Altitude
The altitude is expressed as a 30 bit, fixed point, twos complement
 integer with 22 integer bits and 8 fractional bits. How the altitude
+ integer with 22 integer bits and 8 fractional bits. How the Altitude
value is interpreted depends on the type of altitude and the selected
datum.
 New altitude types and datums MUST define the way that the 30 bit
+ New Altitude Types and datums MUST define the way that the 30 bit
value and the associated 6 bit uncertainty are interpreted.
 Three altitude types are defined in this document: unknown (0),
 meters (1) and floors (2). Additional altitude types MUST be defined
+ Three Altitude Types are defined in this document: unknown (0),
+ meters (1) and floors (2). Additional Altitude Types MUST be defined
in a Standards Track RFC.
2.4.1. No Known Altitude (AT = 0)
In some cases, the altitude of the location might not be provided. An
 altitude type of 0 indicates that the altitude is not given to the
 client. In this case, the altitude and altitude uncertainty fields
+ Altitude Type of 0 indicates that the altitude is not given to the
+ client. In this case, the Altitude and Altitude Uncertainty fields
can contain any value and MUST be ignored.
2.4.2. Altitude in Meters (AT = 1)
 If the altitude type has a value of 1, the altitude is measured in
+ If the Altitude Type has a value of 1, the Altitude is measured in
meters. The altitude is measured in relation to the zero set by the
vertical datum.
2.4.3. Altitude in Floors (AT = 2)
 A value of 2 for altitude type indicates that the altitude value is
+ A value of 2 for altitude type indicates that the Altitude value is
measured in floors. This value is relevant only in relation to a
building; the value is relative to the ground level of the building.
In this definition, numbering starts at ground level, which is floor
0 regardless of local convention.
Noninteger values can be used to represent intermediate or sub
floors, such as mezzanine levels. For instance, a mezzanine between
floors 4 and 5 could be represented as 4.1.
2.4.4. Altitude Resolution
 When encoded within the version 0 DHCPv4 Option, the AltUnc value
 encodes the number of highorder Altitude bits that should be
 considered valid. Values above 30 (decimal) are undefined and
 reserved.
+ In the version 0 DHCPv4 Option, the AltUnc value encodes the number
+ of highorder altitude bits that should be considered valid. Values
+ above 30 (decimal) are undefined and reserved.
 If AT = 1, an AltUnc value 0.0 would indicate unknown altitude. The
 most precise Altitude would have an AltUnc value of 30. Many values
+ If AT = 1, an AltUnc value 0.0 would indicate unknown Altitude. The
+ most precise altitude would have an AltUnc value of 30. Many values
of AltUnc would obscure any variation due to vertical datum
differences.
The AltUnc field SHOULD be set to maximum precision when AT = 2
(floors) when a floor value is included in the DHCP Reply, or when AT
= 0, to denote that the floor isn't known. An altitude coded as AT =
2, AltRes = 30, and Altitude = 0.0 is meaningful even outside a
building, and represents ground level at the given latitude and
longitude.
2.4.5. Altitude Uncertainty
 Altitude uncertainty uses the same form of expression as latitude and
 longitude uncertainty. Like latitude and longitude, a value of 0 is
 reserved to indicate that uncertainty is not known; values above 30
 are also reserved. Altitude uncertainty only applies to altitude
 type 1.
+ In the DHCPv6 option or the version 1 DHCPv4 option, the AltUnc value
+ quantifies the amount of uncertainty in the Altitude value. As with
+ LatUnc and LongUnc, a value of 0 for AltUnc is reserved to indicate
+ that Altitude Uncertainty is not known; values above 30 are also
+ reserved. Altitude Uncertainty only applies to Altitude Type 1.
 The amount of altitude uncertainty can be determined by the following
+ The amount of Altitude Uncertainty can be determined by the following
formula, where x is the encoded integer value:
 uncertainty = 2 ^ ( 21  x )
+ Uncertainty = 2 ^ ( 21  x )
This value uses the same units as the associated altitude.
Similarly, a value for the encoded integer value can be derived by
the following formula:
x = 21  ceil( log2( x ) )
2.5. Datum
 The datum field determines how coordinates are organized and related
+ The Datum field determines how coordinates are organized and related
to the real world. Three datums are defined in this document, based
on the definitions in [OGP.Geodesy]:
1: WGS84 (Latitude, Longitude, Altitude):
The World Geodesic System 1984 [WGS84] coordinate reference
system.
This datum is identified by the European Petroleum Survey Group
(EPSG)/International Association of Oil & Gas Producers (OGP) with
the code 4979, or by the URN "urn:ogc:def:crs:EPSG::4979".
 Without altitude, this datum is identified by the EPSG/OGP code
+ Without Altitude, this datum is identified by the EPSG/OGP code
4326 and the URN "urn:ogc:def:crs:EPSG::4326".
2: NAD83 (Latitude, Longitude) + NAVD88:
This datum uses a combination of the North American Datum 1983
 (NAD83) for horizontal (latitude and longitude) values, plus the
+ (NAD83) for horizontal (Latitude and Longitude) values, plus the
North American Vertical Datum of 1988 (NAVD88) vertical datum.
This datum is used for referencing location on land (not near
tidal water) within North America.
NAD83 is identified by the EPSG/OGP code of 4269, or the URN
"urn:ogc:def:crs:EPSG::4269". NAVD88 is identified by the EPSG/
OGP code of 5703, or the URN "urn:ogc:def:crs:EPSG::5703".
3: NAD83 (Latitude, Longitude) + MLLW:
This datum uses a combination of the North American Datum 1983
 (NAD83) for horizontal (latitude and longitude) values, plus the
+ (NAD83) for horizontal (Latitude and Longitude) values, plus the
Mean Lower Low Water (MLLW) vertical datum.
This datum is used for referencing location on or near tidal water
within North America.
NAD83 is identified by the EPSG/OGP code of 4269, or the URN
"urn:ogc:def:crs:EPSG::4269". MLLW does not have a specific code
or URN.
All hosts MUST support the WGS84 datum (Datum 1).
 New datum codes can be registered in the IANA registry (Section 4) by
+ New Datum codes can be registered in the IANA registry (Section 4) by
a Standards Track RFC.
3. Security Considerations
Where critical decisions might be based on the value of this option,
DHCP authentication as defined in "Authentication for DHCP Messages"
[RFC3118] and "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)"
[RFC3315] SHOULD be used to protect the integrity of the DHCP
options.
@@ 652,23 +655,23 @@
defined in this document. Assignment of a DHCPv6 option code is
requested.
The GeoConf Option defines two fields for which IANA maintains a
registry: The Altitude (AT) field and the Datum field (see Section
2). The datum indicator MUST include specification of both
horizontal and vertical datum. New values for the Altitude (AT)
field are assigned through "Standards Action" [RFC5226]. The initial
values of the Altitude registry are as follows:
 AT = 1 meters of Altitude defined by the vertical datum specified.
+ AT = 1 meters of altitude defined by the vertical datum specified.
 AT = 2 building Floors of Altitude.
+ AT = 2 building floors of altitude.
Datum = 1 denotes the vertical datum WGS 84 as defined by the EPSG as
their CRS Code 4327; CRS Code 4327 also specifies WGS 84 as
the vertical datum
Datum = 2 denotes the vertical datum NAD83 as defined by the EPSG as
their CRS Code 4269; North American Vertical Datum of 1988
(NAVD88) is the associated vertical datum for NAD83
Datum = 3 denotes the vertical datum NAD83 as defined by the EPSG as
@@ 683,25 +686,26 @@
Options, with values as follows:
0: DHCPv4 Implementations conforming to [RFC3825]
1: Implementations of this specification (for both DHCPv4 and DHCPv6)
Any additional Ver field values to be defined for use with the DHCPv4
or DHCPv6 Options MUST be done through a Standards Track RFC.
5. Acknowledgments
 The authors would like to thank Patrik Falstrom, Ralph Droms, Ted
 Hardie, Jon Peterson, and Nadine Abbott for their inputs and
 constructive comments regarding this document. Additionally, the
 authors would like to thank Greg Troxel for the education on vertical
 datums, as well as Carl Reed.
+ The authors would like to thank Randall Gellens, Patrik Falstrom,
+ Ralph Droms, Ted Hardie, Jon Peterson, and Nadine Abbott for their
+ inputs and constructive comments regarding this document.
+ Additionally, the authors would like to thank Greg Troxel for the
+ education on vertical datums, as well as Carl Reed. Thanks to
+ Richard Barnes for his contribution on GML mapping for resolution.
6. References
6.1. Normative References
[EPSG] European Petroleum Survey Group, http://www.epsg.org/ and
http://www.epsgregistry.org/
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
@@ 757,30 +761,210 @@
and DHCPv6) Option for Civic Addresses Configuration
Information", RFC 4776, November 2006.
[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
Format for Presence Information Data Format Location Object
(PIDFLO)", RFC 5139, February 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 5226, May 2008.
Appendix A. Calculations of Resolution
+Appendix A. GML Mapping
+
+ The GML representation of a decoded DHCP option depends on what
+ fields are specified. The DHCP format for location logically
+ describes a geodetic prism, rectangle, or point, depending on whether
+ Altitude and uncertainty values are provided. In the absence of
+ uncertainty information, the value decoded from the DHCP form can be
+ expressed as a single point; this is true regardless of whether the
+ version 0 or version 1 interpretations of the uncertainty fields are
+ used. If the point includes Altitude, it uses a three dimensional
+ CRS, otherwise it uses a two dimensional CRS. If all fields are
+ included along with uncertainty, the shape described is a rectangular
+ prism. Note that this is necessary given that uncertainty for each
+ axis is provided independently.
+
+ If Altitude or Altitude Uncertainty (AltUnc) is not specified, the
+ shape is described as a rectangle using the "gml:Polygon" shape. If
+ Altitude is available, a three dimensional CRS is used, otherwise a
+ two dimensional CRS is used.
+
+ For Datum values of 2 or 3 (NAD83), there is no available CRS URN
+ that covers three dimensional coordinates. By necessity, locations
+ described in these datums can be represented by two dimensional
+ shapes only; that is, either a two dimensional point or a polygon.
+
+ If the Altitude Type is 2 (floors), then this value can be
+ represented using a civic address object [RFC5139] that is presented
+ alongside the geodetic object.
+
+ This Appendix describes how the location value encoded in DHCP format
+ for geodetic location can be expressed in GML. The mapping is valid
+ for the DHCPv6 option as well as versions 0 and 1 of the DHCPv4
+ option, and for the currentlydefined datum values (1, 2, and 3).
+ Further version or datum definitions should provide similar mappings.
+
+ These shapes can be mapped to GML by first computing the bounds that
+ are described using the coordinate and uncertainty fields, then
+ encoding the result in a GML Polygon or Prism shape.
+
+A.1. GML Templates
+
+ If Altitude is provided in meters (Altitude Type 1) and the datum
+ value is WGS84 (value 1), then the proper GML shape is a Prism, with
+ the following form (where $value$ indicates a value computed from the
+ DHCP option as described below):
+
+
+
+
+
+
+
+ $lowLatitude$ $lowLongitude$ $lowAltitude$
+ $lowLatitude$ $highLongitude$ $lowAltitude$
+ $highLatitude$ $highLongitude$ $lowAltitude$
+ $highLatitude$ $lowLongitude$ $lowAltitude$
+ $lowLatitude$ $lowLongitude$ $lowAltitude$
+
+
+
+
+
+
+ $highAltitude  lowAltitude$
+
+
+
+ The Polygon shape is used if Altitude is omitted or specified in
+ floors, or if either NAD83 datum is used (value 2 or 3). The
+ corresponding GML Polygon has the following form:
+
+ >
+
+
+
+ $lowLatitude$ $lowLongitude$
+ $lowLatitude$ $highLongitude$
+ $highLatitude$ $highLongitude$
+ $highLatitude$ $lowLongitude$
+ $lowLatitude$ $lowLongitude$
+
+
+
+
+
+ The value "2DCRSURN" is defined by the datum value: If the datum is
+ WGS84 (value 1), then the 2DCRSURN is "urn:ogc:def:crs:EPSG::4326".
+ If the datum is NAD83 (value 2 or 3), then the 2DCRSURN is
+ "urn:ogc:def:crs:EPSG::4269".
+
+ A Polygon shape with the WGS84 threedimensional CRS is used if the
+ datum is WGS84 (value 1) and the Altitude is specified in meters
+ (Altitude type 1), but no Altitude uncertainty is specified (that is,
+ AltUnc is 0). In this case, the value of the Altitude field is added
+ after each of the points above, and the srsName attribute is set to
+ the threedimentional WGS84 CRS, namely "urn:ogc:def:crs:EPSG::4979".
+
+ A simple point shape is used if either Latitude uncertainty (LatUnc)
+ or Longitude uncertainty (LongUnc) is not specified. With Altitude,
+ this uses a threedimensional CRS; otherwise, it uses a two
+ dimensional CRS.
+
+
+ $Latitude$ $Longitude$ $[Altitude]$
+
+
+A.1.1. Finding Low and High Values using Uncertainty Fields
+
+ The uncertainty fields (LatUnc, LongUnc, AltUnc) indicate the bounds
+ of the location region described by a DHCP location object. For
+ version 0 of the DHCPv4 option, the uncertainty fields represent
+ resolution, indicating how many bits of a value contain information.
+ Any bits beyond those indicated can be either zero or one. For the
+ DHCPv6 option and version 1 of the DHCPv4 option, the LatUnc, LongUnc
+ and AltUnc fields indicate uncertainty distances.
+
+ The two sections below describe how to compute the Latitude,
+ Longitude, and Altitude bounds (e.g., $lowlatitide$, $highAltitude$)
+ in the templates above. The first section describes how these bounds
+ are computed in the "resolution encoding" (version 0), while the
+ second section addresses the "uncertainty encoding" (version 1).
+
+A.1.1.1. Resolution Encoding
+
+ Given a number of resolution bits (i.e., the value of a resolution
+ field), if all bits beyond those bits are set to zero, this gives the
+ lowest possible value. The highest possible value can be found
+ setting all bits to one.
+
+ If the encoded value of Latitude/Longitude and resolution (LatUnc,
+ LongUnc) are treated as 34bit unsigned integers, the following can
+ be used (where ">>" is a bitwise right shift, "&" is a bitwise AND,
+ "~" is a bitwise negation, and "" is a bitwise OR).
+
+ mask = 0x3ffffffff >> resolution
+ lowvalue = value & ~mask
+ highvalue = value  mask + 1
+
+ Once these values are determined, the corresponding floating point
+ numbers can be computed by dividing the values by 2^25 (since there
+ are 25 bits of fraction in the fixedpoint representation).
+
+ Alternatively, the lowest possible value can be found by using
+ resolution to determine the size of the range. This method has the
+ advantage that it operates on the decoded floating point values. It
+ is equivalent to the first mechanism, to a possible error of 2^25
+ (2^8 for altitude).
+
+ scale = 2 ^ ( 9  resolution )
+ lowvalue = floor( value / scale ) * scale
+ highvalue = lowvalue + scale
+
+ Altitude resolution (AltUnc for v0) uses the same process with
+ different constants. There are 22 whole bits in the Altitude
+ encoding (instead of 9) and 30 bits in total (instead of 34).
+
+A.1.1.2. Uncertainty Encoding
+
+ In the uncertainty encoding, the uncertainty fields (LongUnc/LatUnc
+ in version 1) directly represent the logarithms of uncertainty
+ distances. So the low and high bounds are computed by first
+ computing the uncertainty distances, then adding and subtracting
+ these from the value provided. If "uncertainty" is the unsigned
+ integer value of the uncertainty field and "value" is the value of
+ the coordinate field:
+
+ distance = 2 ^ (8  uncertainty)
+ lowvalue = value  distance
+ highvalue = value + distance
+
+ Altitude uncertainty (AltUnc in version 1) uses the same process with
+ different constants:
+
+ distance = 2 ^ (21  uncertainty)
+ lowvalue = value  distance
+
+Appendix B. Calculations of Resolution
The following examples for two different locations demonstrate how
the Resolution values for Latitude, Longitude, and Altitude (used
in the version 0 DHCPv4 option) can be used. In both examples,
the geolocation values were derived from maps using the WGS84
map datum, therefore in these examples, the Datum field would
have a value = 1 (00000001, or 0x01).
A.1. Location Configuration Information of "White House" (Example 1)
+B.1. Location Configuration Information of "White House" (Example 1)
The address was NOT picked for any political reason and can easily be
found on the Internet or mapping software, but was picked as an
easily identifiable location on our planet.
Postal Address:
White House
1600 Pennsylvania Ave. NW
Washington, DC 20006
@@ 793,110 +977,110 @@
Latitude = 0001001101110011000001111111001000
Longitude 77.03723 degrees West (or 77.03723 degrees)
Using 2s complement, 34 bit fixed point, 25 bit fraction
Longitude = 0xf65ecf031,
Longitude = 1101100101111011001111000000110001
Altitude 15
In this example, we are not inside a structure, therefore we will
 assume an altitude value of 15 meters, interpolated from the US
+ assume an Altitude value of 15 meters, interpolated from the US
Geological survey map, Washington West quadrangle.
AltUnc = 30, 0x1e, 011110
AT = 1, 0x01, 000001
Altitude = 15, 0x0F00, 00000000000000000000000001111100000000
If: LatUnc is expressed as value 2 (0x02 or 000010) and LongUnc is
expressed as value 2 (0x02 or 000010), then it would describe a
geolocation region that is north of the equator and extends from
1 degree (west of the meridian) to 128 degrees. This would
include the area from approximately 600km south of Saltpond,
Ghana, due north to the North Pole and approximately 4400km
southsouthwest of Los Angeles, CA due north to the North Pole.
This would cover an area of about onesixth of the globe,
approximately 20 million square nautical miles (nm).
If: LatUnc is expressed as value 3 (0x03 or 000011) and LongUnc is
expressed as value 3 (0x03 or 000011), then it would describe a
geolocation area that is north from the equator to 63 degrees
 north, and 65 degrees to 128 degrees longitude. This area
+ north, and 65 degrees to 128 degrees Longitude. This area
includes south of a line from Anchorage, AL to eastern Nunavut,
CN, and from the Amazons of northern Brazil to approximately
4400km southsouthwest of Los Angeles, CA. This area would
include North America, Central America, and parts of Venezuela
and Columbia, except portions of Alaska and northern and eastern
Canada, approximately 10 million square nm.
If: LatUnc is expressed as value 5 (0x05 or 000101) and LongUnc is
expressed as value 5 (0x05 or 000101), then it would describe a
 geolocation area that is latitude 32 north of the equator to
 latitude 48 and extends from 64 degrees to 80 degrees
 longitude. This is approximately an eastwest boundary of a time
+ geolocation area that is Latitude 32 north of the equator to
+ Latitude 48 and extends from 64 degrees to 80 degrees
+ Longitude. This is approximately an eastwest boundary of a time
zone, an area of approximately 700,000 square nm.
If: LatUnc is expressed as value 9 (0x09 or 001001) and LongUnc is
expressed as value 9 (0x09 or 001001), which includes all the
integer bits, then it would describe a geolocation area that is
 latitude 38 north of the equator to latitude 39 and extends from
 77 degrees to 78 degrees longitude. This is an area of
+ Latitude 38 north of the equator to Latitude 39 and extends from
+ 77 degrees to 78 degrees Longitude. This is an area of
approximately 9600 square km (111.3km x 86.5km).
If: LatUnc is expressed as value 18 (0x12 or 010010) and LongUnc is
expressed as value 18 (0x12 or 010010), then it would describe a
 geolocation area that is latitude 38.8984375 north to latitude
+ geolocation area that is Latitude 38.8984375 north to Latitude
38.9003906 and extends from 77.0390625 degrees to 77.0371094
 degrees longitude. This is an area of approximately 36,600
+ degrees Longitude. This is an area of approximately 36,600
square meters (169m x 217m).
If: LatUnc is expressed as value 22 (0x16 or 010110) and LongUnc is
expressed as value 22 (0x16 or 010110), then it would describe a
 geolocation area that is latitude 38.896816 north to latitude
+ geolocation area that is Latitude 38.896816 north to Latitude
38.8985596 and extends from 77.0372314 degrees to 77.0371094
 degrees longitude. This is an area of approximately 143 square
+ degrees Longitude. This is an area of approximately 143 square
meters (10.5m x 13.6m).
If: LatUnc is expressed as value 28 (0x1c or 011100) and LongUnc is
expressed as value 28 (0x1c or 011100), then it would describe a
 geolocation area that is latitude 38.8986797 north to latitude
+ geolocation area that is Latitude 38.8986797 north to Latitude
38.8986816 and extends from 77.0372314 degrees to 77.0372296
 degrees longitude. This is an area of approximately 339 square
+ degrees Longitude. This is an area of approximately 339 square
centimeters (20.9cm x 16.23cm).
If: LatUnc is expressed as value 30 (0x1e or 011110) and LongUnc is
expressed as value 30 (0x1e or 011110), then it would describe a
 geolocation area that is latitude 38.8986797 north to latitude
+ geolocation area that is Latitude 38.8986797 north to Latitude
38.8986802 and extends from 77.0372300 degrees to 77.0372296
 degrees longitude. This is an area of approximately 19.5 square
+ degrees Longitude. This is an area of approximately 19.5 square
centimeters (50mm x 39mm).
If: LatUnc is expressed as value 34 (0x22 or 100010) and LongUnc is
expressed as value 34 (0x22 or 100010), then it would describe a
 geolocation area that is latitude 38.8986800 north to latitude
+ geolocation area that is Latitude 38.8986800 north to Latitude
38.8986802 and extends from 77.0372300 degrees to 77.0372296
 degrees longitude. This is an area of approximately 7.5 square
+ degrees Longitude. This is an area of approximately 7.5 square
millimeters (3.11mm x 2.42mm).
In the (White House) example, the requirement of emergency responders
in North America via their NENA Model Legislation [NENA] could be met
by a LatUnc value of 21 and a LongUnc value of 20. This would yield
 a geolocation that is latitude 38.8984375 north to latitude
 38.8988616 north and longitude 77.0371094 to longitude 77.0375977.
+ a geolocation that is Latitude 38.8984375 north to Latitude
+ 38.8988616 north and Longitude 77.0371094 to Longitude 77.0375977.
This is an area of approximately 89 feet by 75 feet or 6669 square
feet, which is very close to the 7000 square feet requested by NENA.
In this example, a service provider could enforce that a device send
a Location Configuration Information with this minimum amount of
resolution for this particular location when calling emergency
services.
A.2. Location Configuration Information of "Sears Tower" (Example 2)
+B.2. Location Configuration Information of "Sears Tower" (Example 2)
Postal Address:
Sears Tower
103rd Floor
233 S. Wacker Dr.
Chicago, IL 60606
Viewing the Chicago area from the Observation Deck of the Sears
Tower.
@@ 904,94 +1088,101 @@
Using 2s complement, 34 bit fixed point, 25 bit fraction
Latitude = 0x053c1f751,
Latitude = 0001010011110000011111011101010001
Longitude 87.63602 degrees West (or 87.63602 degrees)
Using 2s complement, 34 bit fixed point, 25 bit fraction
Longitude = 0xf50ba5b97,
Longitude = 1101010000101110100101101110010111
Altitude 103
In this example, we are inside a structure, therefore we will assume
 an altitude value of 103 to indicate the floor we are on. The
+ an Altitude value of 103 to indicate the floor we are on. The
Altitude Type value is 2, indicating floors. The AltUnc field would
indicate that all bits in the Altitude field are true, as we want to
accurately represent the floor of the structure where we are located.
AltUnc = 30, 0x1e, 011110
AT = 2, 0x02, 000010
Altitude = 103, 0x00006700, 000000000000000110011100000000
 For the accuracy of the latitude and longitude, the best information
+ For the accuracy of the Latitude and Longitude, the best information
available to us was supplied by a generic mapping service that shows
a single geoloc for all of the Sears Tower. Therefore we are going
to show LatUnc as value 18 (0x12 or 010010) and LongUnc as value 18
(0x12 or 010010). This would be describing a geolocation area that
 is latitude 41.8769531 to latitude 41.8789062 and extends from
 87.6367188 degrees to 87.6347657 degrees longitude. This is an
+ is Latitude 41.8769531 to Latitude 41.8789062 and extends from
+ 87.6367188 degrees to 87.6347657 degrees Longitude. This is an
area of approximately 373412 square feet (713.3 ft. x 523.5 ft.).
Appendix B. Calculations of Uncertainty
+Appendix C. Calculations of Uncertainty
 The following example demonstrates how Uncertainty values for
 Latitude, Longitude, and Altitude (used in the DHCPv6 Option as
 well as the version 1 DHCPv4 option) can be calculated.
+ The following example demonstrates how uncertainty values for
+ Latitude, Longitude, and Altitude (LatUnc, LongUnc and AltUnc
+ used in the DHCPv6 Option as well as the version 1 DHCPv4 option)
+ can be calculated.
B.1 Location Configuration Information of "Sydney Opera House"
+C.1. Location Configuration Information of "Sydney Opera House"
(Example 3)
This section describes an example of encoding and decoding the
geodetic DHCP Option. The textual results are expressed in GML
[OGC.GML3.1.1] form, suitable for inclusion in PIDFLO [RFC4119].
These examples all assume a datum of WGS84 (datum = 1) and an
 altitude type of meters (AT = 1).
+ Altitude type of meters (AT = 1).
B.1.1. Encoding a Location into DHCP Geodetic Form
+C.1.1. Encoding a Location into DHCP Geodetic Form
This example draws a rough polygon around the Sydney Opera House.
This polygon consists of the following six points:
33.856625 S, 151.215906 E
33.856299 S, 151.215343 E
33.856326 S, 151.214731 E
33.857533 S, 151.214495 E
33.857720 S, 151.214613 E
33.857369 S, 151.215375 E
The top of the building 67.4 meters above sea level, and a starting
 altitude of 0 meters above the WGS84 geoid is assumed.
+ Altitude of 0 meters above the WGS84 geoid is assumed.
 The first step is to determine the range of latitude and longitude
 values. Latitude ranges from 33.857720 to 33.856299; longitude
+ The first step is to determine the range of Latitude and Longitude
+ values. Latitude ranges from 33.857720 to 33.856299; Longitude
ranges from 151.214495 to 151.215906.
For this example, the point that is encoded is chosen by finding the
middle of each range, that is (33.8570095, 151.2152005). This is
encoded as (1110111100010010010011011000001101,
0100101110011011100010111011000011) in binary, or (3BC49360D,
12E6E2EC3) in hexadecimal notation (with an extra 2 bits of leading
padding on each). Altitude is set at 33.7 meters, which is
000000000000000010000110110011 (binary) or 000021B3 (hexadecimal).
 The latitude uncertainty is given by inserting the difference between
 the center value and the outer value into the formula from
 Section 2.3.1. This gives:
+ The Latitude Uncertainty (LatUnc) is given by inserting the
+ difference between the center value and the outer value into the
+ formula from Section 2.3.1. This gives:
+
x = 8  ceil( log2( 33.8570095  33.857720 ) )
+
The result of this equation is 18, therefore the uncertainty is
encoded as 010010 in binary.
 Similarly, longitude uncertainty is given by the formula:
+ Similarly, Longitude Uncertainty (LongUnc) is given by the formula:
+
x = 8  ceil( log2( 151.2152005  151.214495 ) )
+
The result of this equation is also 18, or 010010 in binary.
 Altitude uncertainty uses the formula from Section 2.4.4:
+ Altitude Uncertainty (AltUnc) uses the formula from Section 2.4.4:
+
x = 21  ceil( log2( 33.7  0 ) )
+
The result of this equation is 15, which is encoded as 001111 in
binary.
Adding an Altitude Type of 1 (meters) and a Datum of 1 (WGS84), this
gives the following DHCPv4 form:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+++++++++++++++++++++++++++++++++
 Code (123)  OptLen (16)  LatUnc  Latitude .
@@ 1006,79 +1197,66 @@
 AType  AltUnc  Altitude .
0 0 0 10 0 1 1 1 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1.
+++++++++++++++++++++++++++++++++
. Alt (cont'd)  Datum 
.1 0 1 1 0 0 1 10 1 0 0 0 0 0 1
+++++++++++++++++
In hexadecimal, this is 7B104BBC 49360D49 2E6E2EC3 13C00021 B341.
The DHCPv6 form only differs in the code and option length portion.
B.1.2. Decoding a Location from DHCP Geodetic Form
+C.1.2. Decoding a Location from DHCP Geodetic Form
If receiving the binary form created in the previous section, this
section describes how that would be interpreted. The result is then
represented as a GML object, as defined in [GeoShape].
 A latitude value of 1110111100010010010011011000001101 decodes to a
 value of 33.8570095003 (to 10 decimal places). The longitude value
+ A Latitude value of 1110111100010010010011011000001101 decodes to a
+ value of 33.8570095003 (to 10 decimal places). The Longitude value
of 0100101110011011100010111011000011 decodes to 151.2152005136.
 Decoding Tip: If the raw values of latitude and longitude are placed
+ Decoding Tip: If the raw values of Latitude and Longitude are placed
in integer variables, the actual value can be derived by the
following process:
1. If the highest order bit is set (i.e. the number is a twos
complement negative), then subtract 2 to the power of 34 (the
total number of bits).
2. Divide the result by 2 to the power of 25 (the number of
fractional bits) to determine the final value.
 The same principle can be applied when decoding altitude values,
+ The same principle can be applied when decoding Altitude values,
except with different powers of 2 (30 and 8 respectively).
 The latitude and longitude uncertainty are both 18, which gives an
+ The Latitude and Longitude Uncertainty are both 18, which gives an
uncertainty value using the formula from Section 2.3.1 of
 0.0009765625. Therefore, the decoded latitudes is 33.8570095003 +/
+ 0.0009765625. Therefore, the decoded Latitudes is 33.8570095003 +/
0.0009765625 (or the range from 33.8579860628 to 33.8560329378) and
 the decoded longitude is 151.2152005136 +/ 0.0009765625 (or the
+ the decoded Longitude is 151.2152005136 +/ 0.0009765625 (or the
range from 151.2142239511 to 151.2161770761).
 The encoded altitude of 000000000000000010000110110011 decodes to
+ The encoded Altitude of 000000000000000010000110110011 decodes to
33.69921875. The encoded uncertainty of 15 gives a value of 64,
therefore the final uncertainty is 33.69921875 +/ 64 (or the range
from 30.30078125 to 97.69921875).
B.1.2.1. GML Representation of Decoded Locations

 The GML representation of a decoded DHCP option depends on what
 fields are specified. Uncertainty can be omitted from all of the
 respective fields, and altitude can also be absent.

 In the absence of uncertainty information, the value decoded from the
 DHCP form can be expressed as a single point. If the point includes
 altitude, it uses a three dimensional CRS, otherwise it uses a two
 dimensional CRS.
+C.1.2.1. GML Representation of Decoded Locations
The following GML shows the value decoded in the previous example as
a point in a three dimensional CRS:
33.8570095003 151.2152005136 33.69921875
 If all fields are included along with uncertainty, the shape
 described is a rectangular prism. Note that this is necessary given
 that uncertainty for each axis is provided idependently.

The following example uses all of the decoded information from the
previous example:
@@ 1097,91 +1275,67 @@
128
Note that this representation is only appropriate if the uncertainty
is sufficiently small. [GeoShape] recommends that distances between
polygon vertices be kept short. A GML representation like this one
is only appropriate where uncertainty is less than 1 degree (an
encoded value of 9 or greater).
 If altitude or altitude uncertainty is not specified, the shape is
 described as a rectangle using the "gml:Polygon" shape. If altitude
 is available, a three dimensional CRS is used, otherwise a two
 dimensional CRS is used.

 For Datum values of 2 or 3 (NAD83), there is no available CRS URN
 that covers three dimensional coordinates. By necessity, locations
 described in these datums can be represented by two dimensional
 shapes only; that is, either a two dimensional point or a polygon.

 If the altitude type is 2 (floors), then this value can be
 represented using a civic address object [RFC5139] that is presented
 alongside the geodetic object.

Appendix C. Changes from RFC 3825
+Appendix D. Changes from RFC 3825
Technical changes:
+ 08: Added Appendix A on GML mapping.
06: Added recommendation on link layer confidentiality to the
Security Considerations section.

05: Added version field to DHCPv6 option.

 04: Added Appendix B providing an example relating to
+ 04: Added Appendix C providing an example relating to
uncertainty. Added Section 2.3.1 on Latitude and Longitude
resolution and Section 2.4.4 on Altitude resolution.
Added definition of Resolution to Section 1.2.

03: Clarified potential behavior of version 0 clients receiving
a version 1 option and added recommendations for clients and
servers.

02: Added Section 1.2 introducing uncertainty and resolution
concepts. Added Section 2.1 defining DHCPv6 option format.

01: Within Section 2.1, split Datum field from RFC 3825 into three
fields: Ver, Res and Datum fields. Explained that the Ver
field is always located at the same offset. Added Section 2.2
relating to Version Support.

00: None
Editorial changes:
+ 07: Updated boilerplate, cleaned up security considerations section.
06: Added corrections to Section 1.2 "Resolution and Uncertainty".
Added the DHCPv6 Option Version field to the IANA
Considerations section.

05: Corrected length of DHCPv6 option. Added Key to uncertainty
figure.

04: Changed all uses of the LoRes/LaRes/AltRes terminology to
LongUnc/LatUnc/AltUnc, and clarified when these parameters
were used to encode resolution vs. uncertainty. Reorganized
Section 1.2. Added references to RFC 4119, RFC 5139 and
[GeoShape].

03: Changed "DHC" to "DHCP" in some usages. Clarified relationship
of resolution and uncertainty to privacy.

02: Reorganized Sections 1 and 2.

01: Added references to IEEE 802.11y, RFC 3825.

00: Changed boilerplate. Added B. Aboba as editor. Repositioned
 Appendix A and Acknowledgments sections. Changed reference
+ Appendix B and Acknowledgments sections. Changed reference
numbers to names, added reference to RFC 5226 (since RFC 3825
was missing a reference to RFC 2434, now obsolete), updated
references (and URLs). Updated author affiliations and email
 addresses. Changed references to "the appendix" to Appendix A.
 Added additional appendix listing changes.
+ addresses. Changed references to "the appendix" to Appendix B.
+ Added this appendix listing changes.
Authors' Addresses
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
USA
EMail: jmpolk@cisco.com