draft-ietf-geopriv-rfc3825bis-07.txt   draft-ietf-geopriv-rfc3825bis-08.txt 
GEOPRIV Working Group J. Polk GEOPRIV Working Group J. Polk
INTERNET-DRAFT Cisco Systems INTERNET-DRAFT Cisco Systems
Obsoletes: 3825 (if approved) J. Schnizlein Obsoletes: 3825 (if approved) J. Schnizlein
Category: Standards Track Individual Contributor Category: Standards Track Individual Contributor
Expires: August 5, 2010 M. Linsner Expires: August 15, 2010 M. Linsner
5 February 2010 Cisco Systems 13 February 2010 Cisco Systems
M. Thomson M. Thomson
Andrew Andrew
B. Aboba (ed) B. Aboba (ed)
Microsoft Corporation Microsoft Corporation
Dynamic Host Configuration Protocol Options for Dynamic Host Configuration Protocol Options for
Coordinate-based Location Configuration Information Coordinate-based Location Configuration Information
draft-ietf-geopriv-rfc3825bis-07.txt draft-ietf-geopriv-rfc3825bis-08.txt
Abstract Abstract
This document specifies Dynamic Host Configuration Protocol Options This document specifies Dynamic Host Configuration Protocol Options
(both DHCPv4 and DHCPv6) for the coordinate-based geographic location (both DHCPv4 and DHCPv6) for the coordinate-based geographic location
of the client. The Location Configuration Information (LCI) includes 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 indicators for each. Separate parameters indicate the reference
datum for each of these values. datum for each of these values.
Status of This Memo Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 5, 2010. This Internet-Draft will expire on August 15, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2.2 DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . 7 2.2 DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . 7
2.3 Latitude and Longitude Fields . . . . . . . . . . . . . 9 2.3 Latitude and Longitude Fields . . . . . . . . . . . . . 9
2.4 Altitude . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4 Altitude . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Datum . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.5 Datum . . . . . . . . . . . . . . . . . . . . . . . . . 14
3. Security Considerations. . . . . . . . . . . . . . . . . . . . 15 3. Security Considerations. . . . . . . . . . . . . . . . . . . . 15
4. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 15 4. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 15
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Normative References . . . . . . . . . . . . . . . . . . 16 6.1. Normative References . . . . . . . . . . . . . . . . . . 16
6.2. Informational References . . . . . . . . . . . . . . . . 17 6.2. Informational References . . . . . . . . . . . . . . . . 17
Appendix A. Calculations of Resolution . . . . . . . . . . . . . . 18 Appendix A. GML Mapping . . . . . . . . . . . . . . . . . . . . . 18
A.1. LCI of "White House" (Example 1) . . . . . . . . . . . . 18 A.1. GML Templates . . . . . . . . . . . . . . . . . . . . . 18
A.2. LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 20 Appendix B. Calculations of Resolution . . . . . . . . . . . . . . 22
Appendix B. Calculations of Uncertainty . . . . . . . . . . . . . 22 B.1. LCI of "White House" (Example 1) . . . . . . . . . . . . 22
B.1 LCI of "Sydney Opera House" (Example 3) . . . . . . . . 22 B.2. LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 24
Appendix C. Changes from RFC 3825 . . . . . . . . . . . . . . . . 26 Appendix C. Calculations of Uncertainty . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 C.1 LCI of "Sydney Opera House" (Example 3) . . . . . . . . 26
Appendix D. Changes from RFC 3825 . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction 1. Introduction
The physical location of a network device has a range of The physical location of a network device has a range of
applications. In particular, emergency telephony applications rely applications. In particular, emergency telephony applications rely
on knowing the location of a caller in order to determine the correct on knowing the location of a caller in order to determine the correct
emergency center. emergency center.
The location of a device can be represented either in terms of The location of a device can be represented either in terms of
geospatial (or geodetic) coordinates, or as a civic address. geospatial (or geodetic) coordinates, or as a civic address.
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encompasses the target location. encompasses the target location.
The DHCPv4 option format defined in this document supports both The DHCPv4 option format defined in this document supports both
resolution and uncertainty parameters. Version 0 of the DHCPv4 resolution and uncertainty parameters. Version 0 of the DHCPv4
option format defined in this document includes a resolution option format defined in this document includes a resolution
parameter for each of the dimensions of location. Since this parameter for each of the dimensions of location. Since this
resolution parameter need not apply to all dimensions equally, a resolution parameter need not apply to all dimensions equally, a
resolution value is included for each of the 3 location elements. resolution value is included for each of the 3 location elements.
The DHCPv6 option format (which supports only version 1) as well as The DHCPv6 option format (which supports only version 1) as well as
version 1 of the DHCPv4 option format utilizes an uncertainty version 1 of the DHCPv4 option format utilizes an uncertainty
parameter. Appendix A of this document provides examples showing the parameter. Appendix A describes the mapping of DHCP option values to
calculation of resolution values. Appendix B provides an example GML. Appendix B of this document provides examples showing the
calculation of resolution values. Appendix C provides an example
demonstrating calculation of uncertainty values. demonstrating calculation of uncertainty values.
2. DHCP Option Format 2. DHCP Option Format
This section defines the format for the DHCPv4 and DHCPv6 options. This section defines the format for the DHCPv4 and DHCPv6 options.
These options utilize a similar format, differing primarily in the These options utilize a similar format, differing primarily in the
option code. option code.
2.1. DHCPv6 Option 2.1. DHCPv6 Option
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| Alt.(cont'd) |Ver| Res |Datum| | Alt.(cont'd) |Ver| Res |Datum|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code: 8 bits. The code for the DHCPv4 option (123). Code: 8 bits. The code for the DHCPv4 option (123).
Length: 8 bits. The length of the DHCPv4 option, in octets. Length: 8 bits. The length of the DHCPv4 option, in octets.
For versions 0 and 1, the option length is 16. For versions 0 and 1, the option length is 16.
LatUnc: 6 bits. When the Ver field = 0, this field represents LatUnc: 6 bits. When the Ver field = 0, this field represents
Latitude resolution. When the Ver field = 1, 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 Latitude: a 34 bit fixed point value consisting of 9 bits of
integer and 25 bits of fraction. Latitude SHOULD be integer and 25 bits of fraction. Latitude SHOULD be
normalized to within +/- 90 degrees. Positive numbers normalized to within +/- 90 degrees. Positive numbers
are north of the equator and negative numbers are south are north of the equator and negative numbers are south
of the equator. of the equator.
LongUnc: 6 bits. When the Ver field = 0, this field represents LongUnc: 6 bits. When the Ver field = 0, this field represents
Longitude resolution. When the Ver field = 1, longitude resolution. When the Ver field = 1,
this field represents Longitude uncertainty. this field represents longitude uncertainty.
Longitude: a 34 bit fixed point value consisting of 9 bits of Longitude: a 34 bit fixed point value consisting of 9 bits of
integer and 25 bits of fraction. Longitude SHOULD be integer and 25 bits of fraction. Longitude SHOULD be
normalized to within +/- 180 degrees. Positive values normalized to within +/- 180 degrees. Positive values
are East of the prime meridian and negative are East of the prime meridian and negative
(2s complement) numbers are West of the prime meridian. (2s complement) numbers are West of the prime meridian.
AType: Altitude Type (4 bits). AType: Altitude Type (4 bits).
AltUnc: 6 bits. When the Ver field = 0, this field represents AltUnc: 6 bits. When the Ver field = 0, this field represents
Altitude resolution. When the Ver field = 1, 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. Altitude: A 30 bit value defined by the AType field.
Ver: The Ver field is two bits, providing for four potential Ver: The Ver field is two bits, providing for four potential
versions. This specification defines the behavior of versions. This specification defines the behavior of
version 0 (originally specified in [RFC3825]) as well as version 0 (originally specified in [RFC3825]) as well as
version 1. The Ver field is always located at the same version 1. The Ver field is always located at the same
offset from the beginning of the option, regardless of offset from the beginning of the option, regardless of
the version in use. the version in use.
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in error up to a full degree of latitude and longitude, and a full in error up to a full degree of latitude and longitude, and a full
increment of altitude. This results in a version 0-only client increment of altitude. This results in a version 0-only client
either not obtaining location information (with no ability to either not obtaining location information (with no ability to
indicate to the server that version 1 was unsupported), or indicate to the server that version 1 was unsupported), or
misinterpreting the option. misinterpreting the option.
Therefore, in situations where some DHCPv4 clients are known to Therefore, in situations where some DHCPv4 clients are known to
support only version 0, by default the DHCPv4 server SHOULD send a support only version 0, by default the DHCPv4 server SHOULD send a
version 0 response. It is also RECOMMENDED that DHCPv4 client version 0 response. It is also RECOMMENDED that DHCPv4 client
implementations support version 1, so the versioning capability added implementations support version 1, so the versioning capability added
by this document does not cause errors interpreting the latitude, by this document does not cause errors interpreting the Latitude,
longitude and altitude values. Longitude and Altitude values.
Moving forward, clients not understanding a datum value MUST assume a Moving forward, clients not understanding a datum value MUST assume a
World Geodesic System 1984 (WGS84) [WGS84] datum (EPSG [EPSG] 4326 or 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 proceed accordingly. Assuming that a less accurate location value is
better than none, this ensures that some (perhaps less accurate) better than none, this ensures that some (perhaps less accurate)
location is available to the client. location is available to the client.
2.3. Latitude and Longitude Fields 2.3. Latitude and Longitude Fields
The Latitude and Longitude values in this specification are encoded The Latitude and Longitude values in this specification are encoded
as 34 bit, twos complement, fixed point values with 9 integer bits as 34 bit, twos complement, fixed point values with 9 integer bits
and 25 fractional bits. The exact meaning of these values is and 25 fractional bits. The exact meaning of these values is
determined by the datum; the description in this section applies to determined by the datum; the description in this section applies to
the datums defined in this document. the datums defined in this document.
New datums MUST define the way that the 34 bit values and the New datums MUST define the way that the 34 bit values and the
respective 6 bit uncertainties are interpreted. This document uses respective 6 bit uncertainties are interpreted. This document uses
the same definition for all datums it specifies. the same definition for all datums it specifies.
Latitude values MUST be constrained to the range from -90 to +90 Latitude values MUST be constrained to the range from -90 to +90
degrees. Positive latitudes are north of the equator; negative 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 Longitude values SHOULD be normalized to the range from -180 to +180
degrees. Values outside this range are normalized by adding or degrees. Values outside this range are normalized by adding or
subtracting 360 until they fall within this range. Positive subtracting 360 until they fall within this range. Positive
longitudes are east of the Prime Meridian (Greenwich); negative longitudes are east of the Prime Meridian (Greenwich); negative
longitudes are west of the Prime Meridian. 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 34-bit binary representation. This imprecision is considered nearest 34-bit binary representation. This imprecision is considered
acceptable for the purposes to which this form is intended to be acceptable for the purposes to which this form is intended to be
applied and is ignored when decoding. applied and is ignored when decoding.
2.3.1. Latitude and Longitude Resolution 2.3.1. Latitude and Longitude Resolution
In the version 0 DHCPv4 Option, the Latitude, Longitude and Altitude The Latitude (LatUnc), Longitude (LongUnc) and Altitude (AltUnc)
fields are each preceded by an accuracy sub-field of 6 bits, Uncertainty fields are encoded as 6 bit, unsigned integer values. In
indicating the number of bits of resolution. The resolution sub- the version 0 DHCPv4 Option, the LatUnc, LongUnc and AltUnc fields
fields accommodate the desire to easily adjust the precision of a are used to encode the number of bits of resolution. The resolution
sub-fields accommodate the desire to easily adjust the precision of a
reported location. Contents beyond the claimed resolution MAY be reported location. Contents beyond the claimed resolution MAY be
randomized to obscure greater precision that might be available. randomized to obscure greater precision that might be available.
When encoded within the version 0 DHCPv4 Option, the LatUnc value In the version 0 DHCPv4 Option, the LatUnc value encodes the number
encodes the number of high-order Latitude bits that should be of high-order latitude bits that should be considered valid. Any
considered valid. Any bits entered to the right of this limit should bits entered to the right of this limit should not be considered
not be considered valid and might be purposely false, or zeroed by valid and might be purposely false, or zeroed by the sender. The
the sender. The examples in Appendix A illustrate that a smaller examples in Appendix B illustrate that a smaller value in the
value in the resolution field increases the area within which the resolution field increases the area within which the device is
device is located. A value of 2 in the LatUnc field indicates a located. A value of 2 in the LatUnc field indicates a precision of
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 high-order 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 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 Appendix B). A value of 34 in the LatUnc field indicates a precision
precision of about 2.42 mm in longitude (at the equator). Because of about 3.11 mm in latitude at the equator.
lines of longitude converge at the poles, the distance is smaller
(better precision) for locations away from the equator. In the version 0 DHCPv4 Option, the LongUnc value encodes the number
of high-order 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 2.3.2. Latitude and Longitude Uncertainty
The latitude and longitude uncertainty fields are encoded as 6 bit, In the DHCPv6 option and the version 1 DHCPv4 option, the Latitude
unsigned integer values. These values quantify the amount of and Longitude Uncertainty fields (LatUnc and LongUnc) quantify the
uncertainty in each of the latitude and longitude values amount of uncertainty in each of the Latitude and Longitude values
respectively. A value of 0 is reserved to indicate that the respectively. A value of 0 is reserved to indicate that the
uncertainty is unknown; values greater than 34 are reserved. uncertainty is unknown; values greater than 34 are reserved.
A point within the region of uncertainty is selected to be the A point within the region of uncertainty is selected to be the
encoded point; the centroid of the region is often an appropriate encoded point; the centroid of the region is often an appropriate
choice. The value for uncertainty is taken as the distance from the choice. The value for uncertainty is taken as the distance from the
selected point to the furthest extreme of the region of uncertainty selected point to the furthest extreme of the region of uncertainty
on that axis. on that axis.
The following figure shows a two-dimensional figure that is projected The following figure shows a two-dimensional figure that is projected
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Note that the result of encoding this value increases the range of Note that the result of encoding this value increases the range of
uncertainty to the next available power of two; subsequent repeated uncertainty to the next available power of two; subsequent repeated
encodings and decodings do not change the value. Only increasing encodings and decodings do not change the value. Only increasing
uncertainty means that the associated confidence does not have to uncertainty means that the associated confidence does not have to
decrease. decrease.
2.4. Altitude 2.4. Altitude
The altitude is expressed as a 30 bit, fixed point, twos complement 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 value is interpreted depends on the type of altitude and the selected
datum. 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. value and the associated 6 bit uncertainty are interpreted.
Three altitude types are defined in this document: unknown (0), Three Altitude Types are defined in this document: unknown (0),
meters (1) and floors (2). Additional altitude types MUST be defined meters (1) and floors (2). Additional Altitude Types MUST be defined
in a Standards Track RFC. in a Standards Track RFC.
2.4.1. No Known Altitude (AT = 0) 2.4.1. No Known Altitude (AT = 0)
In some cases, the altitude of the location might not be provided. An 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 Altitude Type of 0 indicates that the altitude is not given to the
client. In this case, the altitude and altitude uncertainty fields client. In this case, the Altitude and Altitude Uncertainty fields
can contain any value and MUST be ignored. can contain any value and MUST be ignored.
2.4.2. Altitude in Meters (AT = 1) 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 meters. The altitude is measured in relation to the zero set by the
vertical datum. vertical datum.
2.4.3. Altitude in Floors (AT = 2) 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 measured in floors. This value is relevant only in relation to a
building; the value is relative to the ground level of the building. building; the value is relative to the ground level of the building.
In this definition, numbering starts at ground level, which is floor In this definition, numbering starts at ground level, which is floor
0 regardless of local convention. 0 regardless of local convention.
Non-integer values can be used to represent intermediate or sub- Non-integer values can be used to represent intermediate or sub-
floors, such as mezzanine levels. For instance, a mezzanine between floors, such as mezzanine levels. For instance, a mezzanine between
floors 4 and 5 could be represented as 4.1. floors 4 and 5 could be represented as 4.1.
2.4.4. Altitude Resolution 2.4.4. Altitude Resolution
When encoded within the version 0 DHCPv4 Option, the AltUnc value In the version 0 DHCPv4 Option, the AltUnc value encodes the number
encodes the number of high-order Altitude bits that should be of high-order altitude bits that should be considered valid. Values
considered valid. Values above 30 (decimal) are undefined and above 30 (decimal) are undefined and reserved.
reserved.
If AT = 1, an AltUnc value 0.0 would indicate unknown altitude. The 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 most precise altitude would have an AltUnc value of 30. Many values
of AltUnc would obscure any variation due to vertical datum of AltUnc would obscure any variation due to vertical datum
differences. differences.
The AltUnc field SHOULD be set to maximum precision when AT = 2 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 (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 = = 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 2, AltRes = 30, and Altitude = 0.0 is meaningful even outside a
building, and represents ground level at the given latitude and building, and represents ground level at the given latitude and
longitude. longitude.
2.4.5. Altitude Uncertainty 2.4.5. Altitude Uncertainty
Altitude uncertainty uses the same form of expression as latitude and In the DHCPv6 option or the version 1 DHCPv4 option, the AltUnc value
longitude uncertainty. Like latitude and longitude, a value of 0 is quantifies the amount of uncertainty in the Altitude value. As with
reserved to indicate that uncertainty is not known; values above 30 LatUnc and LongUnc, a value of 0 for AltUnc is reserved to indicate
are also reserved. Altitude uncertainty only applies to altitude that Altitude Uncertainty is not known; values above 30 are also
type 1. 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: 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. This value uses the same units as the associated altitude.
Similarly, a value for the encoded integer value can be derived by Similarly, a value for the encoded integer value can be derived by
the following formula: the following formula:
x = 21 - ceil( log2( x ) ) x = 21 - ceil( log2( x ) )
2.5. Datum 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 to the real world. Three datums are defined in this document, based
on the definitions in [OGP.Geodesy]: on the definitions in [OGP.Geodesy]:
1: WGS84 (Latitude, Longitude, Altitude): 1: WGS84 (Latitude, Longitude, Altitude):
The World Geodesic System 1984 [WGS84] coordinate reference The World Geodesic System 1984 [WGS84] coordinate reference
system. system.
This datum is identified by the European Petroleum Survey Group This datum is identified by the European Petroleum Survey Group
(EPSG)/International Association of Oil & Gas Producers (OGP) with (EPSG)/International Association of Oil & Gas Producers (OGP) with
the code 4979, or by the URN "urn:ogc:def:crs:EPSG::4979". 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". 4326 and the URN "urn:ogc:def:crs:EPSG::4326".
2: NAD83 (Latitude, Longitude) + NAVD88: 2: NAD83 (Latitude, Longitude) + NAVD88:
This datum uses a combination of the North American Datum 1983 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. North American Vertical Datum of 1988 (NAVD88) vertical datum.
This datum is used for referencing location on land (not near This datum is used for referencing location on land (not near
tidal water) within North America. tidal water) within North America.
NAD83 is identified by the EPSG/OGP code of 4269, or the URN 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/ "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". OGP code of 5703, or the URN "urn:ogc:def:crs:EPSG::5703".
3: NAD83 (Latitude, Longitude) + MLLW: 3: NAD83 (Latitude, Longitude) + MLLW:
This datum uses a combination of the North American Datum 1983 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. Mean Lower Low Water (MLLW) vertical datum.
This datum is used for referencing location on or near tidal water This datum is used for referencing location on or near tidal water
within North America. within North America.
NAD83 is identified by the EPSG/OGP code of 4269, or the URN 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 "urn:ogc:def:crs:EPSG::4269". MLLW does not have a specific code
or URN. or URN.
All hosts MUST support the WGS84 datum (Datum 1). 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. a Standards Track RFC.
3. Security Considerations 3. Security Considerations
Where critical decisions might be based on the value of this option, Where critical decisions might be based on the value of this option,
DHCP authentication as defined in "Authentication for DHCP Messages" DHCP authentication as defined in "Authentication for DHCP Messages"
[RFC3118] and "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)" [RFC3118] and "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)"
[RFC3315] SHOULD be used to protect the integrity of the DHCP [RFC3315] SHOULD be used to protect the integrity of the DHCP
options. options.
skipping to change at page 15, line 36 skipping to change at page 15, line 39
defined in this document. Assignment of a DHCPv6 option code is defined in this document. Assignment of a DHCPv6 option code is
requested. requested.
The GeoConf Option defines two fields for which IANA maintains a The GeoConf Option defines two fields for which IANA maintains a
registry: The Altitude (AT) field and the Datum field (see Section registry: The Altitude (AT) field and the Datum field (see Section
2). The datum indicator MUST include specification of both 2). The datum indicator MUST include specification of both
horizontal and vertical datum. New values for the Altitude (AT) horizontal and vertical datum. New values for the Altitude (AT)
field are assigned through "Standards Action" [RFC5226]. The initial field are assigned through "Standards Action" [RFC5226]. The initial
values of the Altitude registry are as follows: 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 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 their CRS Code 4327; CRS Code 4327 also specifies WGS 84 as
the vertical datum the vertical datum
Datum = 2 denotes the vertical datum NAD83 as defined by the EPSG as Datum = 2 denotes the vertical datum NAD83 as defined by the EPSG as
their CRS Code 4269; North American Vertical Datum of 1988 their CRS Code 4269; North American Vertical Datum of 1988
(NAVD88) is the associated vertical datum for NAD83 (NAVD88) is the associated vertical datum for NAD83
Datum = 3 denotes the vertical datum NAD83 as defined by the EPSG as Datum = 3 denotes the vertical datum NAD83 as defined by the EPSG as
skipping to change at page 16, line 18 skipping to change at page 16, line 21
Options, with values as follows: Options, with values as follows:
0: DHCPv4 Implementations conforming to [RFC3825] 0: DHCPv4 Implementations conforming to [RFC3825]
1: Implementations of this specification (for both DHCPv4 and DHCPv6) 1: Implementations of this specification (for both DHCPv4 and DHCPv6)
Any additional Ver field values to be defined for use with the DHCPv4 Any additional Ver field values to be defined for use with the DHCPv4
or DHCPv6 Options MUST be done through a Standards Track RFC. or DHCPv6 Options MUST be done through a Standards Track RFC.
5. Acknowledgments 5. Acknowledgments
The authors would like to thank Patrik Falstrom, Ralph Droms, Ted The authors would like to thank Randall Gellens, Patrik Falstrom,
Hardie, Jon Peterson, and Nadine Abbott for their inputs and Ralph Droms, Ted Hardie, Jon Peterson, and Nadine Abbott for their
constructive comments regarding this document. Additionally, the inputs and constructive comments regarding this document.
authors would like to thank Greg Troxel for the education on vertical Additionally, the authors would like to thank Greg Troxel for the
datums, as well as Carl Reed. education on vertical datums, as well as Carl Reed. Thanks to
Richard Barnes for his contribution on GML mapping for resolution.
6. References 6. References
6.1. Normative References 6.1. Normative References
[EPSG] European Petroleum Survey Group, http://www.epsg.org/ and [EPSG] European Petroleum Survey Group, http://www.epsg.org/ and
http://www.epsg-registry.org/ http://www.epsg-registry.org/
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
skipping to change at page 18, line 5 skipping to change at page 18, line 5
and DHCPv6) Option for Civic Addresses Configuration and DHCPv6) Option for Civic Addresses Configuration
Information", RFC 4776, November 2006. Information", RFC 4776, November 2006.
[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location [RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
Format for Presence Information Data Format Location Object Format for Presence Information Data Format Location Object
(PIDF-LO)", RFC 5139, February 2008. (PIDF-LO)", RFC 5139, February 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 5226, May 2008. 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 currently-defined 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):
<gs:Prism srsName="urn:ogc:def:crs:EPSG::4979"
xmlns:gs="http://www.opengis.net/pidflo/1.0"
xmlns:gml="http://www.opengis.net/gml">
<gs:base>
<gml:Polygon>
<gml:exterior>
<gml:LinearRing>
<gml:posList>
$lowLatitude$ $lowLongitude$ $lowAltitude$
$lowLatitude$ $highLongitude$ $lowAltitude$
$highLatitude$ $highLongitude$ $lowAltitude$
$highLatitude$ $lowLongitude$ $lowAltitude$
$lowLatitude$ $lowLongitude$ $lowAltitude$
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gs:base>
<gs:height uom="urn:ogc:def:uom:EPSG::9001">
$highAltitude - lowAltitude$
</gs:height>
</gs:Prism>
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:
<gml:Polygon srsName="$2D-CRS-URN$"
xmlns:gml="http://www.opengis.net/gml">>
<gml:exterior>
<gml:LinearRing>
<gml:posList>
$lowLatitude$ $lowLongitude$
$lowLatitude$ $highLongitude$
$highLatitude$ $highLongitude$
$highLatitude$ $lowLongitude$
$lowLatitude$ $lowLongitude$
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
The value "2D-CRS-URN" is defined by the datum value: If the datum is
WGS84 (value 1), then the 2D-CRS-URN is "urn:ogc:def:crs:EPSG::4326".
If the datum is NAD83 (value 2 or 3), then the 2D-CRS-URN is
"urn:ogc:def:crs:EPSG::4269".
A Polygon shape with the WGS84 three-dimensional 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 three-dimentional 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 three-dimensional CRS; otherwise, it uses a two-
dimensional CRS.
<gml:Point srsName="$CRS-URN$"
xmlns:gml="http://www.opengis.net/gml">
<gml:pos>$Latitude$ $Longitude$ $[Altitude]$</gml:pos>
</gml:Point>
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 34-bit 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 fixed-point 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 following examples for two different locations demonstrate how
the Resolution values for Latitude, Longitude, and Altitude (used the Resolution values for Latitude, Longitude, and Altitude (used
in the version 0 DHCPv4 option) can be used. In both examples, in the version 0 DHCPv4 option) can be used. In both examples,
the geo-location values were derived from maps using the WGS84 the geo-location values were derived from maps using the WGS84
map datum, therefore in these examples, the Datum field would map datum, therefore in these examples, the Datum field would
have a value = 1 (00000001, or 0x01). 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 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 found on the Internet or mapping software, but was picked as an
easily identifiable location on our planet. easily identifiable location on our planet.
Postal Address: Postal Address:
White House White House
1600 Pennsylvania Ave. NW 1600 Pennsylvania Ave. NW
Washington, DC 20006 Washington, DC 20006
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Latitude = 0001001101110011000001111111001000 Latitude = 0001001101110011000001111111001000
Longitude 77.03723 degrees West (or -77.03723 degrees) Longitude 77.03723 degrees West (or -77.03723 degrees)
Using 2s complement, 34 bit fixed point, 25 bit fraction Using 2s complement, 34 bit fixed point, 25 bit fraction
Longitude = 0xf65ecf031, Longitude = 0xf65ecf031,
Longitude = 1101100101111011001111000000110001 Longitude = 1101100101111011001111000000110001
Altitude 15 Altitude 15
In this example, we are not inside a structure, therefore we will 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. Geological survey map, Washington West quadrangle.
AltUnc = 30, 0x1e, 011110 AltUnc = 30, 0x1e, 011110
AT = 1, 0x01, 000001 AT = 1, 0x01, 000001
Altitude = 15, 0x0F00, 00000000000000000000000001111100000000 Altitude = 15, 0x0F00, 00000000000000000000000001111100000000
If: LatUnc is expressed as value 2 (0x02 or 000010) and LongUnc is 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 expressed as value 2 (0x02 or 000010), then it would describe a
geo-location region that is north of the equator and extends from geo-location region that is north of the equator and extends from
-1 degree (west of the meridian) to -128 degrees. This would -1 degree (west of the meridian) to -128 degrees. This would
include the area from approximately 600km south of Saltpond, include the area from approximately 600km south of Saltpond,
Ghana, due north to the North Pole and approximately 4400km Ghana, due north to the North Pole and approximately 4400km
south-southwest of Los Angeles, CA due north to the North Pole. south-southwest of Los Angeles, CA due north to the North Pole.
This would cover an area of about one-sixth of the globe, This would cover an area of about one-sixth of the globe,
approximately 20 million square nautical miles (nm). approximately 20 million square nautical miles (nm).
If: LatUnc is expressed as value 3 (0x03 or 000011) and LongUnc is 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 expressed as value 3 (0x03 or 000011), then it would describe a
geo-location area that is north from the equator to 63 degrees geo-location 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, includes south of a line from Anchorage, AL to eastern Nunavut,
CN, and from the Amazons of northern Brazil to approximately CN, and from the Amazons of northern Brazil to approximately
4400km south-southwest of Los Angeles, CA. This area would 4400km south-southwest of Los Angeles, CA. This area would
include North America, Central America, and parts of Venezuela include North America, Central America, and parts of Venezuela
and Columbia, except portions of Alaska and northern and eastern and Columbia, except portions of Alaska and northern and eastern
Canada, approximately 10 million square nm. Canada, approximately 10 million square nm.
If: LatUnc is expressed as value 5 (0x05 or 000101) and LongUnc is 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 expressed as value 5 (0x05 or 000101), then it would describe a
geo-location area that is latitude 32 north of the equator to geo-location area that is Latitude 32 north of the equator to
latitude 48 and extends from -64 degrees to -80 degrees Latitude 48 and extends from -64 degrees to -80 degrees
longitude. This is approximately an east-west boundary of a time Longitude. This is approximately an east-west boundary of a time
zone, an area of approximately 700,000 square nm. zone, an area of approximately 700,000 square nm.
If: LatUnc is expressed as value 9 (0x09 or 001001) and LongUnc is If: LatUnc is expressed as value 9 (0x09 or 001001) and LongUnc is
expressed as value 9 (0x09 or 001001), which includes all the expressed as value 9 (0x09 or 001001), which includes all the
integer bits, then it would describe a geo-location area that is integer bits, then it would describe a geo-location area that is
latitude 38 north of the equator to latitude 39 and extends from Latitude 38 north of the equator to Latitude 39 and extends from
-77 degrees to -78 degrees longitude. This is an area of -77 degrees to -78 degrees Longitude. This is an area of
approximately 9600 square km (111.3km x 86.5km). approximately 9600 square km (111.3km x 86.5km).
If: LatUnc is expressed as value 18 (0x12 or 010010) and LongUnc is 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 expressed as value 18 (0x12 or 010010), then it would describe a
geo-location area that is latitude 38.8984375 north to latitude geo-location area that is Latitude 38.8984375 north to Latitude
38.9003906 and extends from -77.0390625 degrees to -77.0371094 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). square meters (169m x 217m).
If: LatUnc is expressed as value 22 (0x16 or 010110) and LongUnc is 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 expressed as value 22 (0x16 or 010110), then it would describe a
geo-location area that is latitude 38.896816 north to latitude geo-location area that is Latitude 38.896816 north to Latitude
38.8985596 and extends from -77.0372314 degrees to -77.0371094 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). meters (10.5m x 13.6m).
If: LatUnc is expressed as value 28 (0x1c or 011100) and LongUnc is 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 expressed as value 28 (0x1c or 011100), then it would describe a
geo-location area that is latitude 38.8986797 north to latitude geo-location area that is Latitude 38.8986797 north to Latitude
38.8986816 and extends from -77.0372314 degrees to -77.0372296 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). centimeters (20.9cm x 16.23cm).
If: LatUnc is expressed as value 30 (0x1e or 011110) and LongUnc is 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 expressed as value 30 (0x1e or 011110), then it would describe a
geo-location area that is latitude 38.8986797 north to latitude geo-location area that is Latitude 38.8986797 north to Latitude
38.8986802 and extends from -77.0372300 degrees to -77.0372296 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). centimeters (50mm x 39mm).
If: LatUnc is expressed as value 34 (0x22 or 100010) and LongUnc is 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 expressed as value 34 (0x22 or 100010), then it would describe a
geo-location area that is latitude 38.8986800 north to latitude geo-location area that is Latitude 38.8986800 north to Latitude
38.8986802 and extends from -77.0372300 degrees to -77.0372296 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). millimeters (3.11mm x 2.42mm).
In the (White House) example, the requirement of emergency responders In the (White House) example, the requirement of emergency responders
in North America via their NENA Model Legislation [NENA] could be met 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 by a LatUnc value of 21 and a LongUnc value of 20. This would yield
a geo-location that is latitude 38.8984375 north to latitude a geo-location that is Latitude 38.8984375 north to Latitude
38.8988616 north and longitude -77.0371094 to longitude -77.0375977. 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 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. 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 In this example, a service provider could enforce that a device send
a Location Configuration Information with this minimum amount of a Location Configuration Information with this minimum amount of
resolution for this particular location when calling emergency resolution for this particular location when calling emergency
services. services.
A.2. Location Configuration Information of "Sears Tower" (Example 2) B.2. Location Configuration Information of "Sears Tower" (Example 2)
Postal Address: Postal Address:
Sears Tower Sears Tower
103rd Floor 103rd Floor
233 S. Wacker Dr. 233 S. Wacker Dr.
Chicago, IL 60606 Chicago, IL 60606
Viewing the Chicago area from the Observation Deck of the Sears Viewing the Chicago area from the Observation Deck of the Sears
Tower. Tower.
skipping to change at page 21, line 7 skipping to change at page 25, line 7
Using 2s complement, 34 bit fixed point, 25 bit fraction Using 2s complement, 34 bit fixed point, 25 bit fraction
Latitude = 0x053c1f751, Latitude = 0x053c1f751,
Latitude = 0001010011110000011111011101010001 Latitude = 0001010011110000011111011101010001
Longitude 87.63602 degrees West (or -87.63602 degrees) Longitude 87.63602 degrees West (or -87.63602 degrees)
Using 2s complement, 34 bit fixed point, 25 bit fraction Using 2s complement, 34 bit fixed point, 25 bit fraction
Longitude = 0xf50ba5b97, Longitude = 0xf50ba5b97,
Longitude = 1101010000101110100101101110010111 Longitude = 1101010000101110100101101110010111
Altitude 103 Altitude 103
In this example, we are inside a structure, therefore we will assume 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 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 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. accurately represent the floor of the structure where we are located.
AltUnc = 30, 0x1e, 011110 AltUnc = 30, 0x1e, 011110
AT = 2, 0x02, 000010 AT = 2, 0x02, 000010
Altitude = 103, 0x00006700, 000000000000000110011100000000 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 available to us was supplied by a generic mapping service that shows
a single geo-loc for all of the Sears Tower. Therefore we are going a single geo-loc for all of the Sears Tower. Therefore we are going
to show LatUnc as value 18 (0x12 or 010010) and LongUnc as value 18 to show LatUnc as value 18 (0x12 or 010010) and LongUnc as value 18
(0x12 or 010010). This would be describing a geo-location area that (0x12 or 010010). This would be describing a geo-location area that
is latitude 41.8769531 to latitude 41.8789062 and extends from is Latitude 41.8769531 to Latitude 41.8789062 and extends from
-87.6367188 degrees to -87.6347657 degrees longitude. This is an -87.6367188 degrees to -87.6347657 degrees Longitude. This is an
area of approximately 373412 square feet (713.3 ft. x 523.5 ft.). 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 The following example demonstrates how uncertainty values for
Latitude, Longitude, and Altitude (used in the DHCPv6 Option as Latitude, Longitude, and Altitude (LatUnc, LongUnc and AltUnc
well as the version 1 DHCPv4 option) can be calculated. 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) (Example 3)
This section describes an example of encoding and decoding the This section describes an example of encoding and decoding the
geodetic DHCP Option. The textual results are expressed in GML geodetic DHCP Option. The textual results are expressed in GML
[OGC.GML-3.1.1] form, suitable for inclusion in PIDF-LO [RFC4119]. [OGC.GML-3.1.1] form, suitable for inclusion in PIDF-LO [RFC4119].
These examples all assume a datum of WGS84 (datum = 1) and an 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 example draws a rough polygon around the Sydney Opera House.
This polygon consists of the following six points: This polygon consists of the following six points:
33.856625 S, 151.215906 E 33.856625 S, 151.215906 E
33.856299 S, 151.215343 E 33.856299 S, 151.215343 E
33.856326 S, 151.214731 E 33.856326 S, 151.214731 E
33.857533 S, 151.214495 E 33.857533 S, 151.214495 E
33.857720 S, 151.214613 E 33.857720 S, 151.214613 E
33.857369 S, 151.215375 E 33.857369 S, 151.215375 E
The top of the building 67.4 meters above sea level, and a starting 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 The first step is to determine the range of Latitude and Longitude
values. Latitude ranges from -33.857720 to -33.856299; longitude values. Latitude ranges from -33.857720 to -33.856299; Longitude
ranges from 151.214495 to 151.215906. ranges from 151.214495 to 151.215906.
For this example, the point that is encoded is chosen by finding the 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 middle of each range, that is (-33.8570095, 151.2152005). This is
encoded as (1110111100010010010011011000001101, encoded as (1110111100010010010011011000001101,
0100101110011011100010111011000011) in binary, or (3BC49360D, 0100101110011011100010111011000011) in binary, or (3BC49360D,
12E6E2EC3) in hexadecimal notation (with an extra 2 bits of leading 12E6E2EC3) in hexadecimal notation (with an extra 2 bits of leading
padding on each). Altitude is set at 33.7 meters, which is padding on each). Altitude is set at 33.7 meters, which is
000000000000000010000110110011 (binary) or 000021B3 (hexadecimal). 000000000000000010000110110011 (binary) or 000021B3 (hexadecimal).
The latitude uncertainty is given by inserting the difference between The Latitude Uncertainty (LatUnc) is given by inserting the
the center value and the outer value into the formula from difference between the center value and the outer value into the
Section 2.3.1. This gives: formula from Section 2.3.1. This gives:
x = 8 - ceil( log2( -33.8570095 - -33.857720 ) ) x = 8 - ceil( log2( -33.8570095 - -33.857720 ) )
The result of this equation is 18, therefore the uncertainty is The result of this equation is 18, therefore the uncertainty is
encoded as 010010 in binary. 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 ) ) x = 8 - ceil( log2( 151.2152005 - 151.214495 ) )
The result of this equation is also 18, or 010010 in binary. 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 ) ) x = 21 - ceil( log2( 33.7 - 0 ) )
The result of this equation is 15, which is encoded as 001111 in The result of this equation is 15, which is encoded as 001111 in
binary. binary.
Adding an Altitude Type of 1 (meters) and a Datum of 1 (WGS84), this Adding an Altitude Type of 1 (meters) and a Datum of 1 (WGS84), this
gives the following DHCPv4 form: gives the following DHCPv4 form:
0 1 2 3 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 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 . | Code (123) | OptLen (16) | LatUnc | Latitude .
skipping to change at page 23, line 40 skipping to change at page 27, line 48
| AType | AltUnc | Altitude . | AType | AltUnc | Altitude .
|0 0 0 1|0 0 1 1 1 1|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1. |0 0 0 1|0 0 1 1 1 1|0 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 | . Alt (cont'd) | Datum |
.1 0 1 1 0 0 1 1|0 1 0 0 0 0 0 1| .1 0 1 1 0 0 1 1|0 1 0 0 0 0 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In hexadecimal, this is 7B104BBC 49360D49 2E6E2EC3 13C00021 B341. In hexadecimal, this is 7B104BBC 49360D49 2E6E2EC3 13C00021 B341.
The DHCPv6 form only differs in the code and option length portion. 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 If receiving the binary form created in the previous section, this
section describes how that would be interpreted. The result is then section describes how that would be interpreted. The result is then
represented as a GML object, as defined in [GeoShape]. represented as a GML object, as defined in [GeoShape].
A latitude value of 1110111100010010010011011000001101 decodes to a A Latitude value of 1110111100010010010011011000001101 decodes to a
value of -33.8570095003 (to 10 decimal places). The longitude value value of -33.8570095003 (to 10 decimal places). The Longitude value
of 0100101110011011100010111011000011 decodes to 151.2152005136. 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 in integer variables, the actual value can be derived by the
following process: following process:
1. If the highest order bit is set (i.e. the number is a twos 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 complement negative), then subtract 2 to the power of 34 (the
total number of bits). total number of bits).
2. Divide the result by 2 to the power of 25 (the number of 2. Divide the result by 2 to the power of 25 (the number of
fractional bits) to determine the final value. 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). 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 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 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). 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, 33.69921875. The encoded uncertainty of 15 gives a value of 64,
therefore the final uncertainty is 33.69921875 +/- 64 (or the range therefore the final uncertainty is 33.69921875 +/- 64 (or the range
from -30.30078125 to 97.69921875). from -30.30078125 to 97.69921875).
B.1.2.1. GML Representation of Decoded Locations C.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.
The following GML shows the value decoded in the previous example as The following GML shows the value decoded in the previous example as
a point in a three dimensional CRS: a point in a three dimensional CRS:
<gml:Point srsName="urn:ogc:def:crs:EPSG::4979" <gml:Point srsName="urn:ogc:def:crs:EPSG::4979"
xmlns:gml="http://www.opengis.net/gml"> xmlns:gml="http://www.opengis.net/gml">
<gml:pos>-33.8570095003 151.2152005136 33.69921875</gml:pos> <gml:pos>-33.8570095003 151.2152005136 33.69921875</gml:pos>
</gml:Point> </gml:Point>
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 The following example uses all of the decoded information from the
previous example: previous example:
<gs:Prism srsName="urn:ogc:def:crs:EPSG::4979" <gs:Prism srsName="urn:ogc:def:crs:EPSG::4979"
xmlns:gs="http://www.opengis.net/pidflo/1.0" xmlns:gs="http://www.opengis.net/pidflo/1.0"
xmlns:gml="http://www.opengis.net/gml"> xmlns:gml="http://www.opengis.net/gml">
<gs:base> <gs:base>
<gml:Polygon> <gml:Polygon>
<gml:exterior> <gml:exterior>
<gml:LinearRing> <gml:LinearRing>
skipping to change at page 25, line 35 skipping to change at page 30, line 5
128 128
</gs:height> </gs:height>
</gs:Prism> </gs:Prism>
Note that this representation is only appropriate if the uncertainty Note that this representation is only appropriate if the uncertainty
is sufficiently small. [GeoShape] recommends that distances between is sufficiently small. [GeoShape] recommends that distances between
polygon vertices be kept short. A GML representation like this one polygon vertices be kept short. A GML representation like this one
is only appropriate where uncertainty is less than 1 degree (an is only appropriate where uncertainty is less than 1 degree (an
encoded value of 9 or greater). encoded value of 9 or greater).
If altitude or altitude uncertainty is not specified, the shape is Appendix D. Changes from RFC 3825
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
Technical changes: Technical changes:
-08: Added Appendix A on GML mapping.
-06: Added recommendation on link layer confidentiality to the -06: Added recommendation on link layer confidentiality to the
Security Considerations section. Security Considerations section.
-05: Added version field to DHCPv6 option. -05: Added version field to DHCPv6 option.
-04: Added Appendix C providing an example relating to
-04: Added Appendix B providing an example relating to
uncertainty. Added Section 2.3.1 on Latitude and Longitude uncertainty. Added Section 2.3.1 on Latitude and Longitude
resolution and Section 2.4.4 on Altitude resolution. resolution and Section 2.4.4 on Altitude resolution.
Added definition of Resolution to Section 1.2. Added definition of Resolution to Section 1.2.
-03: Clarified potential behavior of version 0 clients receiving -03: Clarified potential behavior of version 0 clients receiving
a version 1 option and added recommendations for clients and a version 1 option and added recommendations for clients and
servers. servers.
-02: Added Section 1.2 introducing uncertainty and resolution -02: Added Section 1.2 introducing uncertainty and resolution
concepts. Added Section 2.1 defining DHCPv6 option format. concepts. Added Section 2.1 defining DHCPv6 option format.
-01: Within Section 2.1, split Datum field from RFC 3825 into three -01: Within Section 2.1, split Datum field from RFC 3825 into three
fields: Ver, Res and Datum fields. Explained that the Ver fields: Ver, Res and Datum fields. Explained that the Ver
field is always located at the same offset. Added Section 2.2 field is always located at the same offset. Added Section 2.2
relating to Version Support. relating to Version Support.
-00: None -00: None
Editorial changes: Editorial changes:
-07: Updated boilerplate, cleaned up security considerations section.
-06: Added corrections to Section 1.2 "Resolution and Uncertainty". -06: Added corrections to Section 1.2 "Resolution and Uncertainty".
Added the DHCPv6 Option Version field to the IANA Added the DHCPv6 Option Version field to the IANA
Considerations section. Considerations section.
-05: Corrected length of DHCPv6 option. Added Key to uncertainty -05: Corrected length of DHCPv6 option. Added Key to uncertainty
figure. figure.
-04: Changed all uses of the LoRes/LaRes/AltRes terminology to -04: Changed all uses of the LoRes/LaRes/AltRes terminology to
LongUnc/LatUnc/AltUnc, and clarified when these parameters LongUnc/LatUnc/AltUnc, and clarified when these parameters
were used to encode resolution vs. uncertainty. Reorganized were used to encode resolution vs. uncertainty. Reorganized
Section 1.2. Added references to RFC 4119, RFC 5139 and Section 1.2. Added references to RFC 4119, RFC 5139 and
[GeoShape]. [GeoShape].
-03: Changed "DHC" to "DHCP" in some usages. Clarified relationship -03: Changed "DHC" to "DHCP" in some usages. Clarified relationship
of resolution and uncertainty to privacy. of resolution and uncertainty to privacy.
-02: Reorganized Sections 1 and 2. -02: Reorganized Sections 1 and 2.
-01: Added references to IEEE 802.11y, RFC 3825. -01: Added references to IEEE 802.11y, RFC 3825.
-00: Changed boilerplate. Added B. Aboba as editor. Re-positioned -00: Changed boilerplate. Added B. Aboba as editor. Re-positioned
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 numbers to names, added reference to RFC 5226 (since RFC 3825
was missing a reference to RFC 2434, now obsolete), updated was missing a reference to RFC 2434, now obsolete), updated
references (and URLs). Updated author affiliations and email references (and URLs). Updated author affiliations and email
addresses. Changed references to "the appendix" to Appendix A. addresses. Changed references to "the appendix" to Appendix B.
Added additional appendix listing changes. Added this appendix listing changes.
Authors' Addresses Authors' Addresses
James M. Polk James M. Polk
Cisco Systems Cisco Systems
2200 East President George Bush Turnpike 2200 East President George Bush Turnpike
Richardson, Texas 75082 USA Richardson, Texas 75082 USA
USA USA
EMail: jmpolk@cisco.com EMail: jmpolk@cisco.com
 End of changes. 97 change blocks. 
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