GEOPRIV Working Group                                            J. Polk
INTERNET-DRAFT                                             Cisco Systems
Obsoletes: 3825 (if approved)                              J. Schnizlein
Category: Standards Track                                           ISOC
Expires: December 15, 2009 January 12, 2010                                     M. Linsner
5 June
12 July 2009                                               Cisco Systems
                                                      Bernard Aboba (ed)
                                                   Microsoft Corporation

             Dynamic Host Configuration Protocol Option for
          Coordinate-based Location Configuration Information

                  draft-ietf-geopriv-rfc3825bis-00.txt

                  draft-ietf-geopriv-rfc3825bis-01.txt

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Abstract

   This document specifies a Dynamic Host Configuration Protocol Option
   for the coordinate-based geographic location of the client.  The
   Location Configuration Information (LCI) includes latitude,
   longitude, and altitude, with resolution indicators for each.  The
   reference datum for these values is also included.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . .  3
       1.2.  Motivation . . . . . . . . . . . . . . . . . . . . . . .  3
       1.3.  Rationale  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Location Configuration Information (LCI) Elements. . . . . . .  5
       2.1.  Elements of the Location Configuration Information . . .  5
       2.2   Version Support  . . . . . . . . . . . . . . . . . . . .  8
   3.  Security Considerations. . . . . . . . . . . . . . . . . . . .  8  9
   4.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . .  9 10
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9 10
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 11
       6.1.  Normative References . . . . . . . . . . . . . . . . . . 10 11
       6.2.  Informational References . . . . . . . . . . . . . . . . 10 11
   Appendix A. Calculations of Imprecision possible with the DHC LCI  11  12
       A.1.  LCI of "White House" (Example 1) . . . . . . . . . . . . 11 12
       A.2.  LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 13 14
   Appendix B. Changes from RFC 3825  . . . . . . . . . . . . . . . . 14 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 16

1.  Introduction

   This document specifies a Dynamic Host Configuration Protocol
   [RFC2131] Option for the coordinate-based geographic location of the
   client, to be provided by the server.

   The DHCP server is assumed to have determined the location from the
   Circuit-ID Relay Agent Information Option (RAIO) defined (as SubOpt
   1) in [RFC3046].  In order to translate the circuit (switch port
   identifier) into a location, the DHCP server is assumed to have
   access to a service that maps from circuit-ID to the location at
   which the circuit connected to that port terminates in the building,
   for example, the location of the wall jack.

   An important feature of this specification is that after the relevant
   DHC exchanges have taken place, the location information is stored on
   the end device rather than somewhere else, where retrieving it might
   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

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  Motivation

   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
   location of the radio access point used during host configuration,
   but would need some more exotic mechanisms, maybe GPS, or maybe a
   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

   Within the LCI described here, Latitude and Longitude are represented
   in fixed-point 2s-complement binary degrees, for the economy of a
   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
   field, which is 4 bits long.  Two Altitude Types are defined here,
   meters (code=1) and floors (code=2), both of which are 2s-complement
   fixed-point with 22 bits of integer part and 8 bits of fractional
   part.  Additional Altitude Types MAY be assigned by IANA.  The
   "floors" Altitude Type is provided because altitude in meters may not
   be known within a building, and a floor indication may be more
   useful.

   GPS systems today can use WGS84 for horizontal and vertical datums;
   [WGS84] defines WGS84 as a three-dimensional datum.  For other datum
   values that do not include a vertical component, both the horizontal
   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,
   indicating the number of bits of resolution.  This resolution sub-
   field accommodates the desire to easily adjust the precision of a
   reported location.  Contents beyond the claimed resolution MAY be
   randomized to obscure greater precision that might be available.

2.  DHC Location Configuration Information Elements

   DHCP is a binary Protocol; using protocols of LCI are likely to be
   text based.  Since most coordinate systems translate easily between
   binary-based and text-based location output (even emergency services
   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
   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:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Code 123    |      16    Length     |   LaRes   |     Latitude      +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Latitude (cont'd)              |    LoRes  |   +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Longitude                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   AT  |   AltRes  |                Altitude                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Alt (cont'd) |     Datum     | |Ver| Res |Datum|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.1.  Elements of the Location Configuration Information

   Code 123:  The code for this DHCP option.

   16:

   Length:   The length of this option, in octets.  For versions 0
             and 1, the option length is 16 bytes. 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
              valid bits in the altitude.  Values above 30 (decimal) are
              undefined and reserved.

   AltRes does not define Geographic Privacy policy.

   AT:        Altitude Type for altitude.  Codes defined are:

   1: Meters - in 2s-complement fixed-point 22-bit integer part with 8-
              bit fraction

   If AT = 1, an AltRes value 0.0 would indicate unknown altitude.  The
   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
              8-bit fraction

   AT = 2 for Floors enables representing altitude in a form more
   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.
   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
   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
   values.

   Larger values represent floors that are above (higher in altitude)
   floors with lower values.

   The AltRes field SHOULD be set to maximum precision when AT = 2
   (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
   DHC Option MUST be done through a Standards Track RFC.

   The Ver field is two bits, providing for four potential versions.

   This specification defines the behavior of version 0 (originally
   specified in [RFC3825]) as well as version 1.  The Ver field is
   always located at the same offset from the beginning of the option,
   regardless of the version in use.

   The Res field which is 3 bits, is reserved.  These bits have been
   used by [IEEE-802.11y], but are not defined within this
   specification.

   Datum: The Map Datum used for the coordinates given in this Option

   The datum must include both a horizontal and a vertical reference.
   Since the WGS 84 reference datum is three-dimensional, it includes
   both.  For any additional datum parameters, the datum codepoint must
   specify both horizontal datum and vertical datum references.

   The Datum byte has 256 field is 3 bits, providing 8 possibilities, of which 3 have
   been registered with IANA by this document (all derived from
   specification in [EPSG]):

      1: WGS 84  (Geographical 3D) - World Geodesic System 1984, CRS
                 Code 4327, Prime Meridian Name: Greenwich

      2: NAD83 - North American Datum 1983, CRS Code 4269, Prime
                 Meridian Name: Greenwich; The associated vertical datum
                 is the North American Vertical Datum of 1988 (NAVD88)

                 This datum pair is to be used when referencing
                 locations on land, not near tidal water (which would
                 use Datum = 3 below)

      3: NAD83 - North American Datum 1983, CRS Code 4269, Prime
                 Meridian Name: Greenwich; The associated vertical datum
                 is Mean Lower Low Water (MLLW)

                 This datum pair is to be used when referencing
                 locations on water/sea/ocean

   Any additional LCI datum(s) to be defined for use via this DHC Option
   MUST be done through a Standards Track RFC.

2.2.  Version Support

2.2.1.  Client Version Support

   Clients implementing this specification MUST support receiving
   responses of versions 0 and 1. Since this specification utilizes the
   same DHCP option code as [RFC3825], the option format does not
   provide a means for the client to indicate the highest version that
   it supports to the server.

2.2.2.  Server Version Selection

   A DHCP server that provides location information cannot provide
   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
   same response or a separate response) causes a DHCP client to replace
   the information in the old Option with the information in the new
   Option.

   A server uses configuration to determine which version to send in a
   response. For example, where a mixture of v0 and v1 clients are
   expected, the server could be configured to send v0 or v1 depending
   on configuration (possibly making the choice based on information
   such as the client MAC address). Where few v0 clients are expected,
   the server could be configured to send only v1 responses.

   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
   v0-only client not obtaining location information, with no ability to
   indicate to the server that v1 was unsupported.  Therefore, in
   situations where some clients are known to support only v0, by
   default the server SHOULD send a v0 response.

3.  Security Considerations

   Where critical decisions might be based on the value of this GeoConf
   option, DHCP authentication in [RFC3118] SHOULD be used to protect
   the integrity of the DHCP options.

   Since there is no privacy protection for DHCP messages, an
   eavesdropper who can monitor the link between the DHCP server and
   requesting client can discover this LCI.

   To minimize the unintended exposure of location information, the LCI
   option SHOULD be returned by DHCP servers only when the DHCP client
   has included this option in its 'parameter request list' (section 3.5
   [RFC2131]).

   When implementing a DHC server that will serve clients across an
   uncontrolled network, one should consider the potential security
   risks.

4.  IANA Considerations

   IANA has assigned a DHCP option code of 123 for the GeoConf option
   defined in this document.

   The GeoConf Option defines two fields for which IANA maintains a
   registry: The Altitude (AT) field (see Section 2) and the Datum field
   (see Section 2).  The datum indicator MUST include specification of
   both horizontal and vertical datum.  New values for the Altitude (AT)
   field are assigned through "Standards Action" [RFC5226].  The initial
   values of the Altitude registry are as follows:

   AT = 1  meters of Altitude defined by the vertical datum specified.

   AT = 2  building Floors of Altitude.

   Datum = 1 denotes the vertical datum WGS 84 as defined by the EPSG as
           their CRS Code 4327; CRS Code 4327 also specifies WGS 84 as
           the vertical datum

   Datum = 2 denotes the vertical datum NAD83 as defined by the EPSG as
           their CRS Code 4269; North American Vertical Datum of 1988
           (NAVD88) is the associated vertical datum for NAD83

   Datum = 3 denotes the vertical datum NAD83 as defined by the EPSG as
           their CRS Code 4269; Mean Lower Low Water (MLLW) is the
           associated vertical datum for NAD83

   Any additional LCI datum(s) to be defined for use via this DHC Option
   MUST be done through a Standards Track RFC.

   This document defines the Ver field, with values as follows:

   0: Implementations conforming to [RFC3825]
   1: Implementations of this specification

   Any additional Ver field values to be defined for use with this DHC
   Option MUST be done through a Standards Track RFC.

5.  Acknowledgements

   The authors would like to thank Patrik Falstrom, Ralph Droms, Ted
   Hardie, Jon Peterson, and Nadine Abbott for their inputs and
   constructive comments regarding this document.  Additionally, the
   authors would like to thank Greg Troxel for the education on vertical
   datums, as well as Carl Reed.

6.  References

6.1.  Normative References

[EPSG]    European Petroleum Survey Group, http://www.epsg.org/ and
          http://www.epsg-registry.org/

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
          March 1997.

[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
          January 2001.

[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
          RFC 3118, June 2001.

[WGS84]   US National Imagery and Mapping Agency, "Department of Defense
          (DoD) World Geodetic System 1984 (WGS 84), Third Edition",
          NIMA TR8350.2, January 2000,
          https://www1.nga.mil/PRODUCTSSERVICES/GEODESYGEOPHYSICS/
          WORLDGEODETICSYSTEM/Pages/default.aspx and
          http://www.ngs.noaa.gov/faq.shtml#WGS84

6.2.  Informational References

[IEEE-802.11y]
          Information technology - Telecommunications and information
          exchange between systems - Local and metropolitan area
          networks - Specific requirements - Part 11: Wireless LAN
          Medium Access Control (MAC) and Physical Layer (PHY)
          specifications Amendment 3: 3650-3700 MHz Operation in USA,
          November 2008.

[NENA]    National Emergency Number Association (NENA) www.nena.org NENA
          Technical Information Document on Model Legislation Enhanced
          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
          Configuration Protocol Option for Coordinate-based Location
          Configuration Information", RFC 3825, July 2004.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
          Considerations Section in RFCs", RFC 5226, May 2008.

Appendix A. Calculations of Imprecision Possible with the DHC LCI

   The following examples for two different locations demonstrate how
   the Resolution values for Latitude, Longitude, and Altitude can be
   used.  In both examples the geo-location values were derived from
   maps using the WGS84 map datum, therefore in these examples, the
   datum field would have a value = 1 (00000001, or 0x01).

A.1.  Location Configuration Information of "White House" (Example 1)

   The address was NOT picked for any political reason and can easily be
   found on the Internet or mapping software, but was picked as an
   easily identifiable location on our planet.

   Postal Address:
      White House
      1600 Pennsylvania Ave. NW
      Washington, DC 20006

   Standing on the sidewalk, north side of White House, between
   driveways.

      Latitude 38.89868 degrees North (or +38.89868 degrees)
      Using 2s complement, 34 bit fixed point, 25 bit fraction
      Latitude = 0x04dcc1fc8,
      Latitude = 0001001101110011000001111111001000

   Longitude 77.03723 degrees West (or -77.03723 degrees)
      Using 2s complement, 34 bit fixed point, 25 bit fraction
      Longitude = 0xf65ecf031,
      Longitude = 1101100101111011001111000000110001

   Altitude 15

   In this example, we are not inside a structure, therefore we will
   assume an altitude value of 15 meters, interpolated from the US
   Geological survey map, Washington West quadrangle.

      AltRes = 30, 0x1e, 011110
      AT = 1, 0x01, 000001
      Altitude = 15, 0x0F00, 00000000000000000000000001111100000000

   If: LaRes is expressed as value 2 (0x02 or 000010) and LoRes is
       expressed as value 2 (0x02 or 000010), then it would describe a
       geo-location region that is north of the equator and extends from
       -1 degree (west of the meridian) to -128 degrees.  This would
       include the area from approximately 600km south of Saltpond,
       Ghana, due north to the North Pole and approximately 4400km
       south-southwest of Los Angeles, CA due north to the North Pole.
       This would cover an area of about one-sixth of the globe,
       approximately 20 million square nautical miles (nm).

   If: LaRes is expressed as value 3 (0x03 or 000011) and LoRes is
       expressed as value 3 (0x03 or 000011), then it would describe a
       geo-location area that is north from the equator to 63 degrees
       north, and -65 degrees to -128 degrees longitude.  This area
       includes south of a line from Anchorage, AL to eastern Nunavut,
       CN, and from the Amazons of northern Brazil to approximately
       4400km south-southwest of Los Angeles, CA.  This area would
       include North America, Central America, and parts of Venezuela
       and Columbia, except portions of Alaska and northern and eastern
       Canada, approximately 10 million square nm.

   If: LaRes is expressed as value 5 (0x05 or 000101) and LoRes is
       expressed as value 5 (0x05 or 000101), then it would describe a
       geo-location area that is latitude 32 north of the equator to
       latitude 48 and extends from -64 degrees to -80 degrees
       longitude.  This is approximately an east-west boundary of a time
       zone, an area of approximately 700,000 square nm.

   If: LaRes is expressed as value 9 (0x09 or 001001) and LoRes is
       expressed as value 9 (0x09 or 001001), which includes all the
       integer bits, then it would describe a geo-location area that is
       latitude 38 north of the equator to latitude 39 and extends from
       -77 degrees to -78 degrees longitude.  This is an area of
       approximately 9600 square km (111.3km x 86.5km).

   If: LaRes is expressed as value 18 (0x12 or 010010) and LoRes is
       expressed as value 18 (0x12 or 010010), then it would describe a
       geo-location area that is latitude 38.8984375 north to latitude
       38.9003906 and extends from -77.0390625 degrees to -77.0371094
       degrees longitude.  This is an area of approximately 36,600
       square meters (169m x 217m).

   If: LaRes is expressed as value 22 (0x16 or 010110) and LoRes is
       expressed as value 22 (0x16 or 010110), then it would describe a
       geo-location area that is latitude 38.896816 north to latitude
       38.8985596 and extends from -77.0372314 degrees to -77.0371094
       degrees longitude.  This is an area of approximately 143 square
       meters (10.5m x 13.6m).

   If: LaRes is expressed as value 28 (0x1c or 011100) and LoRes is
       expressed as value 28 (0x1c or 011100), then it would describe a
       geo-location area that is latitude 38.8986797 north to latitude
       38.8986816 and extends from -77.0372314 degrees to -77.0372296
       degrees longitude.  This is an area of approximately 339 square
       centimeters (20.9cm x 16.23cm).

   If: LaRes is expressed as value 30 (0x1e or 011110) and LoRes is
       expressed as value 30 (0x1e or 011110), then it would describe a
       geo-location area that is latitude 38.8986797 north to latitude
       38.8986802 and extends from -77.0372300 degrees to -77.0372296
       degrees longitude.  This is an area of approximately 19.5 square
       centimeters (50mm x 39mm).

   If: LaRes is expressed as value 34 (0x22 or 100010) and LoRes is
       expressed as value 34 (0x22 or 100010), then it would describe a
       geo-location area that is latitude 38.8986800 north to latitude
       38.8986802 and extends from -77.0372300 degrees to -77.0372296
       degrees longitude.  This is an area of approximately 7.5 square
       millimeters (3.11mm x 2.42mm).

   In the (White House) example, the requirement of emergency responders
   in North America via their NENA Model Legislation [NENA] could be met
   by a LaRes value of 21 and a LoRes value of 20.  This would yield a
   geo-location that is latitude 38.8984375 north to latitude 38.8988616
   north and longitude -77.0371094 to longitude -77.0375977.  This is an
   area of approximately 89 feet by 75 feet or 6669 square feet, which
   is very close to the 7000 square feet requested by NENA.  In this
   example, a service provider could enforce that a device send a
   Location Configuration Information with this minimum amount of
   resolution for this particular location when calling emergency
   services.

A.2.  Location Configuration Information of "Sears Tower" (Example 2)

   Postal Address:
      Sears Tower
      103rd Floor
      233 S. Wacker Dr.
      Chicago, IL  60606

   Viewing the Chicago area from the Observation Deck of the Sears
   Tower.

   Latitude 41.87884 degrees North (or +41.87884 degrees)
   Using 2s complement, 34 bit fixed point, 25 bit fraction
   Latitude = 0x053c1f751,
   Latitude = 0001010011110000011111011101010001
   Longitude 87.63602 degrees West (or -87.63602 degrees)
   Using 2s complement, 34 bit fixed point, 25 bit fraction
   Longitude = 0xf50ba5b97,
   Longitude = 1101010000101110100101101110010111

   Altitude 103

   In this example, we are inside a structure, therefore we will assume
   an altitude value of 103 to indicate the floor we are on.  The
   Altitude Type value is 2, indicating floors.  The AltRes field would
   indicate that all bits in the Altitude field are true, as we want to
   accurately represent the floor of the structure where we are located.

   AltRes = 30, 0x1e, 011110
   AT = 2, 0x02, 000010
   Altitude = 103, 0x00006700, 000000000000000110011100000000

   For the accuracy of the latitude and longitude, the best information
   available to us was supplied by a generic mapping service that shows
   a single geo-loc for all of the Sears Tower.  Therefore we are going
   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
   is latitude 41.8769531 to latitude 41.8789062 and extends from
   -87.6367188 degrees to -87.6347657 degrees longitude.  This is an
   area of approximately 373412 square feet (713.3 ft. x 523.5 ft.).

Appendix B. Changes from RFC 3825

   Technical changes:

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

   -00: None

   Editorial changes:

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

   -00: Changed boilerplate.  Added B. Aboba as editor. Re-positioned
        Appendix A and Acknowledgements sections.  Changed reference
        numbers to names, added reference to RFC 5226 (since RFC 3825
        was missing a reference to RFC 2434, now obsolete), updated
        references (and URLs).  Updated author affiliations and email
        addresses.  Changed references to "the appendix" to Appendix A.
        Added Appendix B listing changes.

Authors' Addresses

   James M. Polk
   Cisco Systems
   2200 East President George Bush Turnpike
   Richardson, Texas 75082 USA

   EMail: jmpolk@cisco.com

   John Schnizlein
   Technology Program Manager
   Internet Society
   1775 Wiehle Avenue
   Suite 201
   Reston, VA 20190-5108 USA

   EMail: schnizlein@isoc.org

   Marc Linsner
   Cisco Systems
   Marco Island, FL 34145 USA

   EMail: marc.linsner@cisco.com

   Bernard Aboba
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA 98052 USA

   EMail: bernarda@microsoft.com