draft-ietf-geopriv-rfc3825bis-01.txt   draft-ietf-geopriv-rfc3825bis-02.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 ISOC Category: Standards Track ISOC
Expires: January 12, 2010 M. Linsner Expires: April 7, 2010 M. Linsner
12 July 2009 Cisco Systems 7 October 2009 Cisco Systems
Bernard Aboba (ed) M. Thomson
Andrew
B. Aboba (ed)
Microsoft Corporation Microsoft Corporation
Dynamic Host Configuration Protocol Option for Dynamic Host Configuration Protocol Option for
Coordinate-based Location Configuration Information Coordinate-based Location Configuration Information
draft-ietf-geopriv-rfc3825bis-01.txt draft-ietf-geopriv-rfc3825bis-02.txt
Status of This Memo Status of This Memo
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Abstract Abstract
This document specifies a Dynamic Host Configuration Protocol Option This document specifies Dynamic Host Configuration Protocol Options
for the coordinate-based geographic location of the client. The (both DHCPv4 and DHCPv6) for the coordinate-based geographic location
Location Configuration Information (LCI) includes latitude, of the client. The Location Configuration Information (LCI) includes
longitude, and altitude, with resolution indicators for each. The latitude, longitude, and altitude, with resolution or uncertainty
reference datum for these values is also included. indicators for each. Separate parameters indicate the reference
datum for each of these values.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Resolution and Uncertainty . . . . . . . . . . . . . . . 4
1.3. Rationale . . . . . . . . . . . . . . . . . . . . . . . 4 2. DHCP Option Format . . . . . . . . . . . . . . . . . . . . . . 4
2. Location Configuration Information (LCI) Elements. . . . . . . 5 2.1 DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . 5
2.1. Elements of the Location Configuration Information . . . 5 2.2 DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . 6
2.2 Version Support . . . . . . . . . . . . . . . . . . . . 8 2.3 Latitude and Longitude Fields . . . . . . . . . . . . . 8
3. Security Considerations. . . . . . . . . . . . . . . . . . . . 9 2.4 Altitude . . . . . . . . . . . . . . . . . . . . . . . . 10
4. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 10 2.5 Datum . . . . . . . . . . . . . . . . . . . . . . . . . 11
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 3. Security Considerations. . . . . . . . . . . . . . . . . . . . 12
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . 11 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Informational References . . . . . . . . . . . . . . . . 11 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Calculations of Imprecision possible with the DHC LCI 12 6.1. Normative References . . . . . . . . . . . . . . . . . . 14
A.1. LCI of "White House" (Example 1) . . . . . . . . . . . . 12 6.2. Informational References . . . . . . . . . . . . . . . . 14
A.2. LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 14 Appendix A. Calculations of Imprecision possible with the DHC LCI 15
Appendix B. Changes from RFC 3825 . . . . . . . . . . . . . . . . 15 A.1. LCI of "White House" (Example 1) . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 A.2. LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 17
Appendix B. Changes from RFC 3825 . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
This document specifies a Dynamic Host Configuration Protocol The physical location of a network device has a range of
[RFC2131] Option for the coordinate-based geographic location of the applications. In particular, emergency telephony applications rely
client, to be provided by the server. on knowing the location of a caller in order to determine the correct
emergency center.
The DHCP server is assumed to have determined the location from the The location of a device can be represented either in terms of
Circuit-ID Relay Agent Information Option (RAIO) defined (as SubOpt geospatial (or geodetic) coordinates, or as a civic address.
1) in [RFC3046]. In order to translate the circuit (switch port Different applications may be more suited to one form of location
identifier) into a location, the DHCP server is assumed to have information; therefore, both the geodetic and civic forms may be used
access to a service that maps from circuit-ID to the location at simultaneously.
which the circuit connected to that port terminates in the building,
for example, the location of the wall jack. This document specifies Dynamic Host Configuration Protocol (DHCPv4)
[RFC2131] and DHCPv6 [RFC3315]) options for the coordinate-based
geographic location of the client, to be provided by the server.
"Dynamic Host Configuration Protocol (DHCPv4 and DHCPv6) Option for
Civic Addresses Configuration Information" [RFC4776] specifies DHCP
options for civic addresses.
The geodetic coordinate options defined in this document and the
civic address options defined in [RFC4776] enable a DHCP client to
obtain its location. For example, a wired Ethernet host might use
these options for location determination. In this case, the location
information could be derived from a wiremap by the DHCP server, using
the Circuit-ID Relay Agent Information Option (RAIO) defined (as Sub-
Option 1) in RFC 3046 [RFC3046]. The DHCP server could correlate the
Circuit-ID with the geographic location where the identified circuit
terminates (such as the location of the wall jack).
The options defined in this document have limited applicability for
mobile hosts. Typically DHCP clients refresh their configuration in
response to changes in interface state or pending lease expirations.
As a result, when a mobile host changes location without subsequently
completing another DHCP exchange, location configuration information
initially obtained via DHCP could become outdated.
An important feature of this specification is that after the relevant An important feature of this specification is that after the relevant
DHC exchanges have taken place, the location information is stored on DHC exchanges have taken place, the location information is stored on
the end device rather than somewhere else, where retrieving it might the end device rather than somewhere else, where retrieving it might
be difficult in practice. be difficult in practice.
Another important feature of this LCI is its inclusion of a
resolution parameter for each of the dimensions of location. Because
this resolution parameter need not apply to all dimensions equally, a
resolution value is included for each of the 3 location elements.
Resolution does not define Geographic Privacy policy.
The resulting location information using this resolution method is a
small fixed length Configuration Information that can be easily
carried in protocols, such as DHCP, which have limited packet size
because this LCI is only 18 bytes long.
Finally, Appendix A of this document provides some arithmetic
examples of the implication of different resolution values on the
La/Lo/Alt.
1.1. Conventions used in this document 1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
1.2. Motivation 1.2. Resolution and Uncertainty
As applications such as IP Telephony are replacing conventional
telephony, users are expecting the same (or greater) level of
services with the new technology. One service offered by
conventional telephony that is missing in any standardized fashion
within IP Telephony is for a user to be automatically located by
emergency responders, in a timely fashion, when the user summons help
(by dialing 911 in North America, for example). Unless strict
administrative rules are followed, the mobility of a wired Ethernet
device within a campus negates any opportunity for an emergency
responder to locate the device with any degree of expediency. Users
do not want to give up the mobility IP Telephony offers. Informing
the host device of its geo-location at host configuration time will
allow the device to utilize this geo-location information to inform
others of its current geo-location, if the user and/or application so
desires.
The goal of this option is to enable a wired Ethernet host to obtain
its location, which it could provide to an emergency responder, as
one example.
Wireless hosts can utilize this option to gain knowledge of the The DHCPv4 option format defined in this document utilizes both
location of the radio access point used during host configuration, resolution and uncertainty parameters. The DHCPv6 option format only
but would need some more exotic mechanisms, maybe GPS, or maybe a utilizes an uncertainty parameter.
future DHCP option, which includes a list of geo-locations like that
defined here, containing the locations of the radio access points
that are close to the client.
1.3. Rationale 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. Resolution does not define Geographic Privacy
policy.
Within the LCI described here, Latitude and Longitude are represented Appendix A of this document provides some arithmetic examples of the
in fixed-point 2s-complement binary degrees, for the economy of a implication of different resolution values on the La/Lo/Alt.
smaller option size compared to a string encoding of digits in
[RFC1712]. The integer parts of these fields are 9 bits long to
accommodate +/- 180 degrees. The fractional part is 25 bits long,
better than the precision of 7 decimal digits. The length of each
field is 40 bits, 34 of which is the sum of the integer (9) and
fractional (25) bits, plus 6 bits of resolution.
Altitude is determined by the Altitude Type (AT) indicated by the AT The DHCPv6 option format as well as version 1 of the DHCPv4 option
field, which is 4 bits long. Two Altitude Types are defined here, format utilizes an uncertainty parameter. In the context of location
meters (code=1) and floors (code=2), both of which are 2s-complement technology, uncertainty is a quantification of errors. Any method
fixed-point with 22 bits of integer part and 8 bits of fractional for determining location is subject to some sources of error;
part. Additional Altitude Types MAY be assigned by IANA. The uncertainty describes the amount of error that is present.
"floors" Altitude Type is provided because altitude in meters may not Uncertainty might be the coverage area of a wireless transmitter, the
be known within a building, and a floor indication may be more extent of a building or a single room.
useful.
GPS systems today can use WGS84 for horizontal and vertical datums; Uncertainty is usually represented as an area within which the target
[WGS84] defines WGS84 as a three-dimensional datum. For other datum is located. In this document, each of the three axes can be assigned
values that do not include a vertical component, both the horizontal an uncertainty value. In effect, this describes a rectangular prism.
and vertical datum of reference will be specified in the IANA record.
Each of these 3 elements begins with an accuracy sub-field of 6 bits, When representing locations from sources that can quantify
indicating the number of bits of resolution. This resolution sub- uncertainty, the goal is to find the smallest possible rectangular
field accommodates the desire to easily adjust the precision of a prism that this format can describe. This is achieved by taking the
reported location. Contents beyond the claimed resolution MAY be minimum and maximum values on each axis and ensuring that the final
randomized to obscure greater precision that might be available. encoding covers these points. This increases the region of
uncertainty, but ensures that the region that is described
encompasses the target location.
2. DHC Location Configuration Information Elements 2. DHCP Option Format
DHCP is a binary Protocol; using protocols of LCI are likely to be This section defines the format for the DHCPv4 and DHCPv6 options.
text based. Since most coordinate systems translate easily between These options use the same basic format, differing only in the option
binary-based and text-based location output (even emergency services code.
within the US), translation/conversion is a non-issue with DHCP's
binary format.
This binary format provides a fortunate benefit in a mechanism for 2.1. DHCPv6 Option
making a true/correct location coordinate imprecise. It further
provides the capability to have this binary representation be
deterministically imprecise.
The LCI format is as follows: The DHCPv6 [RFC3315] option format is as follows:
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 | Length | LaRes | Latitude + | Option Code (TBD) | OptLen (16) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude (cont'd) | LoRes | + | LatUnc | Latitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude | | Lat (cont'd) | LongUnc | Longitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AT | AltRes | Altitude | | Longitude (cont'd) | AT | AltUnc | Altitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Altitude (cont'd) | Datum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Alt (cont'd) |Ver| Res |Datum|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.1. Elements of the Location Configuration Information
Code 123: The code for this DHCP option.
Length: The length of this option, in octets. For versions 0
and 1, the option length is 16.
LaRes: Latitude resolution. 6 bits indicating the number of
valid bits in the fixed-point value of Latitude.
This value is the number of high-order 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.
LaRes does not define Geographic Privacy policy. Values above
decimal 34 are undefined and reserved.
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.
A value of 2 in the LaRes field indicates a precision of no greater
than 1/6th that of the globe (in the first example of Appendix A). A
value of 34 in the LaRes field indicates a precision of about 3.11 mm
in Latitude at the equator.
LoRes: Longitude resolution. 6 bits indicating the number of
valid bits in the fixed-point value of Longitude.
This value is 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.
LoRes does not define Geographic Privacy policy. Values above
decimal 34 are undefined and reserved.
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.
A value of 2 in the LoRes field indicates precision of no greater
than 1/6th that of the globe (see the first example of Appendix A).
A value of 34 in the LoRes 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.
Altitude: A 30 bit value defined by the AT field
AltRes: Altitude resolution. 6 bits indicating the number of Code: GEOCONF_GEODETIC (8 bits).
valid bits in the altitude. Values above 30 (decimal) are
undefined and reserved.
AltRes does not define Geographic Privacy policy. OptLen: Option Length (8 bits). This option is fixed size, the
value of this octet will always be 16.
AT: Altitude Type for altitude. Codes defined are: LatUnc: Latitude Uncertainty (6 bits).
1: Meters - in 2s-complement fixed-point 22-bit integer part with 8- Latitude: Latitude (34 bits).
bit fraction
If AT = 1, an AltRes value 0.0 would indicate unknown altitude. The LongUnc: Longitude Uncertainty (6 bits).
most precise Altitude would have an AltRes value of 30. Many values
of AltRes would obscure any variation due to vertical datum
differences.
2: Floors - in 2s-complement fixed-point 22-bit integer part with Longitude: Longitude (34 bits).
8-bit fraction
AT = 2 for Floors enables representing altitude in a form more AType: Altitude Type (4 bits).
relevant in buildings which have different floor-to-floor dimensions.
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. Inside a building, 0.0 represents
the floor level associated with ground level at the main entrance.
This document defines a number; one must arrive at the number by
counting floors from the floor defined to be 0.0.
The values represented by this AT will be of local significance. AltUnc: Altitude Uncertainty (6 bits).
Since buildings and floors can vary due to lack of common control,
the values chosen to represent the characteristics of an individual
building will be derived and agreed upon by the operator of the
Building and the intended users of the data. Attempting to
standardize this type of function is beyond the scope this document.
Sub-floors can be represented by non-integer values. Example: a Altitude: Altitude (30 bits).
mezzanine between floor 1 and floor 2 could be represented as a value
= 1.1. Example: (2) mezzanines between floor 4 and floor 5 could be
represented as values = 4.1 and 4.2 respectively.
Floors located below ground level could be represented by negative Datum: Datum (8 bits).
values.
Larger values represent floors that are above (higher in altitude) 2.2. DHCPv4 Option
floors with lower values.
The AltRes field SHOULD be set to maximum precision when AT = 2 The DHCPv4 option format is as follows:
(floors) when a floor value is included in the DHCP Reply, or the AT
= 0 to denote the floor isn't known.
Any additional LCI Altitude Types(s) to be defined for use via this 0 1 2 3
DHC Option MUST be done through a Standards Track RFC. 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 | Length | LatUnc | Latitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude (cont'd) | LongUnc | +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AType | AltUnc | Altitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Alt.(cont'd) |Ver| Res |Datum|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Ver field is two bits, providing for four potential versions. Code: 8 bits. The code for the DHCPv4 option (123).
This specification defines the behavior of version 0 (originally Length: 8 bits. The length of the DHCPv4 option, in octets.
specified in [RFC3825]) as well as version 1. The Ver field is For versions 0 and 1, the option length is 16.
always located at the same offset from the beginning of the option,
regardless of the version in use.
The Res field which is 3 bits, is reserved. These bits have been LatUnc: 6 bits. When the Ver field = 0, this field represents
used by [IEEE-802.11y], but are not defined within this Latitude resolution. When the Ver field = 1,
specification. this field represents Latitude uncertainty.
Datum: The Map Datum used for the coordinates given in this Option 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.
The datum must include both a horizontal and a vertical reference. LongUnc: 6 bits. When the Ver field = 0, this field represents
Since the WGS 84 reference datum is three-dimensional, it includes Longitude resolution. When the Ver field = 1,
both. For any additional datum parameters, the datum codepoint must this field represents Longitude uncertainty.
specify both horizontal datum and vertical datum references.
The Datum field is 3 bits, providing 8 possibilities, of which 3 have Longitude: a 34 bit fixed point value consisting of 9 bits of integer
been registered with IANA by this document (all derived from and 25 bits of fraction. Longitude SHOULD be normalized
specification in [EPSG]): to within +/- 180 degrees. Positive values are East of
the prime meridian and negative (2s complement) numbers
are West of the prime meridian.
1: WGS 84 (Geographical 3D) - World Geodesic System 1984, CRS AType: Altitude Type (4 bits).
Code 4327, Prime Meridian Name: Greenwich
2: NAD83 - North American Datum 1983, CRS Code 4269, Prime AltUnc: 6 bits. When the Ver field = 0, this field represents
Meridian Name: Greenwich; The associated vertical datum Altitude resolution. When the Ver field = 1,
is the North American Vertical Datum of 1988 (NAVD88) this field represents Altitude Uncertainty.
This datum pair is to be used when referencing Altitude: A 30 bit value defined by the AType field.
locations on land, not near tidal water (which would
use Datum = 3 below)
3: NAD83 - North American Datum 1983, CRS Code 4269, Prime Ver: The Ver field is two bits, providing for four potential
Meridian Name: Greenwich; The associated vertical datum versions. This specification defines the behavior of
is Mean Lower Low Water (MLLW) 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.
This datum pair is to be used when referencing Res: The Res field which is 3 bits, is reserved. These bits
locations on water/sea/ocean have been used by [IEEE-802.11y], but are not defined
within this specification.
Any additional LCI datum(s) to be defined for use via this DHC Option Datum: 3 bits. The Map Datum used for the coordinates given in
MUST be done through a Standards Track RFC. this Option.
2.2. Version Support 2.2.1. Version Support
2.2.1. Client Version Support 2.2.1.1. Client Version Support
Clients implementing this specification MUST support receiving Clients implementing this specification MUST support receiving
responses of versions 0 and 1. Since this specification utilizes the responses of versions 0 and 1. Since this specification utilizes the
same DHCP option code as [RFC3825], the option format does not same DHCP option code as [RFC3825], the option format does not
provide a means for the client to indicate the highest version that provide a means for the client to indicate the highest version that
it supports to the server. it supports to the server.
2.2.2. Server Version Selection 2.2.1.2. Server Version Selection
A DHCP server that provides location information cannot provide A DHCP server that provides location information cannot provide
options with both v0 and v1 formats in the same response. This is not options with both v0 and v1 formats in the same response. This is not
useful since receiving two copies of the same Option (either in the useful since receiving two copies of the same Option (either in the
same response or a separate response) causes a DHCP client to replace same response or a separate response) causes a DHCP client to replace
the information in the old Option with the information in the new the information in the old Option with the information in the new
Option. Option.
A server uses configuration to determine which version to send in a A server uses configuration to determine which version to send in a
response. For example, where a mixture of v0 and v1 clients are response. For example, where a mixture of v0 and v1 clients are
skipping to change at page 9, line 30 skipping to change at page 8, line 5
such as the client MAC address). Where few v0 clients are expected, such as the client MAC address). Where few v0 clients are expected,
the server could be configured to send only v1 responses. the server could be configured to send only v1 responses.
Servers that opt to send location in v1 format are likely to cause Servers that opt to send location in v1 format are likely to cause
clients that support only v0 to reject the Option. This results in a clients that support only v0 to reject the Option. This results in a
v0-only client not obtaining location information, with no ability to v0-only client not obtaining location information, with no ability to
indicate to the server that v1 was unsupported. Therefore, in indicate to the server that v1 was unsupported. Therefore, in
situations where some clients are known to support only v0, by situations where some clients are known to support only v0, by
default the server SHOULD send a v0 response. default the server SHOULD send a v0 response.
2.3. Latitude and Longitude Fields
The Latitude and Longitude values in this format 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.
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
nearest 34-bit 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 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
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 two-dimensional figure that is projected
to each axis. In the figure, "X" marks the point that is selected;
the ranges marked with "U" is the uncertainty.
___ ___________
^ | / |
| | / |
| | / |
U | / |
| | ( |
V | | |
--X | X |
| | `---------.
| | |
| | |
| | |
- `-------------------------'
|---------X---------------|
|<------U------>|
Uncertainty applies to each axis independently.
The amount of uncertainty can be determined from the encoding by
taking 2 to the power of 8, less the encoded value. As is shown in
the following formula, where "x" is the encoded integer value:
uncertainty = 2 ^ ( 8 - x )
The result of this formula is expressed in degrees of latitude or
longitude. The uncertainty is added to the base latitude or
longitude value to determine the maximum value in the uncertainty
range; similarly, the uncertainty is subtracted from the base value
to determine the minimum value. Note that because lines of longitude
converge at the poles, the actual distance represented by this
uncertainty changes with the distance from the equator.
If the maximum or minimum latitude values derived from applying
uncertainty are outside the range of -90 to +90, these values are
trimmed to within this range. If the maximum or minimum longitude
values derived from applying uncertainty are outside the range of
-180 to +180, then these values are normalized to this range by
adding or subtracting 360 as necessary.
The encoded value is determined by subtracting the next highest whole
integer value for the base 2 logarithm of uncertainty from 8. As is
shown by the following formula, where uncertainty is the midpoint of
the known range less the lower bound of that range:
x = 8 - ceil( log2( uncertainty ) )
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
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
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
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
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
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
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.
Non-integer 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 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.
The amount of altitude uncertainty can be determined by the following
formula, where x is the encoded integer value:
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
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
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
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
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 5) by
a Standards Track RFC.
3. Security Considerations 3. Security Considerations
Where critical decisions might be based on the value of this GeoConf Where critical decisions might be based on the value of this GeoConf
option, DHCP authentication in [RFC3118] SHOULD be used to protect option, DHCP authentication in [RFC3118] SHOULD be used to protect
the integrity of the DHCP options. the integrity of the DHCP options.
Since there is no privacy protection for DHCP messages, an Since there is no privacy protection for DHCP messages, an
eavesdropper who can monitor the link between the DHCP server and eavesdropper who can monitor the link between the DHCP server and
requesting client can discover this LCI. requesting client can discover this LCI.
skipping to change at page 11, line 24 skipping to change at page 14, line 5
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997. March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
January 2001. January 2001.
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
RFC 3118, June 2001. RFC 3118, June 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[WGS84] US National Imagery and Mapping Agency, "Department of Defense [WGS84] US National Imagery and Mapping Agency, "Department of Defense
(DoD) World Geodetic System 1984 (WGS 84), Third Edition", (DoD) World Geodetic System 1984 (WGS 84), Third Edition",
NIMA TR8350.2, January 2000, NIMA TR8350.2, January 2000,
https://www1.nga.mil/PRODUCTSSERVICES/GEODESYGEOPHYSICS/ https://www1.nga.mil/PRODUCTSSERVICES/GEODESYGEOPHYSICS/
WORLDGEODETICSYSTEM/Pages/default.aspx and WORLDGEODETICSYSTEM/Pages/default.aspx and
http://www.ngs.noaa.gov/faq.shtml#WGS84 http://www.ngs.noaa.gov/faq.shtml#WGS84
6.2. Informational References 6.2. Informational References
[IEEE-802.11y] [IEEE-802.11y]
skipping to change at page 11, line 45 skipping to change at page 14, line 30
exchange between systems - Local and metropolitan area exchange between systems - Local and metropolitan area
networks - Specific requirements - Part 11: Wireless LAN networks - Specific requirements - Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY) Medium Access Control (MAC) and Physical Layer (PHY)
specifications Amendment 3: 3650-3700 MHz Operation in USA, specifications Amendment 3: 3650-3700 MHz Operation in USA,
November 2008. November 2008.
[NENA] National Emergency Number Association (NENA) www.nena.org NENA [NENA] National Emergency Number Association (NENA) www.nena.org NENA
Technical Information Document on Model Legislation Enhanced Technical Information Document on Model Legislation Enhanced
911 for Multi-Line Telephone Systems. 911 for Multi-Line Telephone Systems.
[RFC1712] Farrell, C., Schulze, M., Pleitner, S. and D. Baldoni, "DNS
Encoding of Geographical Location", RFC 1712, November 1994.
[RFC3825] Polk, J., Schnizlein, J. and M. Linsner, "Dynamic Host [RFC3825] Polk, J., Schnizlein, J. and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004. Configuration Information", RFC 3825, July 2004.
[RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
and DHCPv6) Option for Civic Addresses Configuration
Information", RFC 4776, November 2006.
[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 Imprecision Possible with the DHC LCI Appendix A. Calculations of Imprecision Possible with the DHC LCI
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 can be the Resolution values for Latitude, Longitude, and Altitude can be
used. In both examples the geo-location values were derived from used. In both examples the geo-location values were derived from
maps using the WGS84 map datum, therefore in these examples, the maps using the WGS84 map datum, therefore in these examples, the
datum field would have a value = 1 (00000001, or 0x01). datum field would have a value = 1 (00000001, or 0x01).
skipping to change at page 15, line 33 skipping to change at page 19, line 9
to show LaRes as value 18 (0x12 or 010010) and LoRes as value 18 to show LaRes as value 18 (0x12 or 010010) and LoRes 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. Changes from RFC 3825 Appendix B. Changes from RFC 3825
Technical changes: Technical changes:
-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 -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:
-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 Acknowledgements sections. Changed reference Appendix A and Acknowledgements 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 A.
Added Appendix B listing changes. Added Appendix B 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
EMail: jmpolk@cisco.com EMail: jmpolk@cisco.com
John Schnizlein John Schnizlein
Technology Program Manager Technology Program Manager
Internet Society Internet Society
1775 Wiehle Avenue 1775 Wiehle Avenue
Suite 201 Suite 201
Reston, VA 20190-5108 USA Reston, VA 20190-5108 USA
USA
EMail: schnizlein@isoc.org EMail: schnizlein@isoc.org
Marc Linsner Marc Linsner
Cisco Systems Cisco Systems
Marco Island, FL 34145 USA Marco Island, FL 34145 USA
USA
EMail: marc.linsner@cisco.com EMail: marc.linsner@cisco.com
Martin Thomson
Andrew
PO Box U40
Wollongong University Campus, NSW 2500
AU
EMail: martin.thomson@andrew.com
Bernard Aboba Bernard Aboba
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 USA Redmond, WA 98052 USA
USA
EMail: bernarda@microsoft.com EMail: bernarda@microsoft.com
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