One document matched: draft-ietf-geopriv-dhcp-lci-option-00.txt
Internet Engineering Task Force J. Polk
Internet Draft J. Schnizlein
Expiration: Nov 13th, 2003 M. Linsner
File: draft-ietf-geopriv-dhcp-lci-option-00.txt Cisco Systems
Location Configuration Information for GEOPRIV
May 13th, 2003
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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Abstract
This document specifies a Dynamic Host Configuration Protocol Option
for the geographic location of the client. The Location
Configuration Information (LCI) includes latitude, longitude, and
altitude, with resolution indicators for each, as well as for the
datum of the location.
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Conventions . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Rationale . . . . . . . . . . . . . . . . . . . . . . . 4
2. Location Configuration Information (LCI) Elements . . . . . . 4
2.1 Elements of the Location Configuration Information . . . 5
3. Purpose of Resolution Value per La/Lo/Alt Element . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Author Information . . . . . . . . . . . . . . . . . . . . . 9
Appendix Calculations of Imprecision possible with the DHC LCI . 10
A.1 LCI of "White House" (Example 1) . . . . . . . . . . . . 10
A.2 LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 12
8. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 13
1.0 Introduction
This document specifies a Dynamic Host Configuration Protocol [1]
Option for the 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 [2]. 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.
The Location Configuration Information (LCI) format presented here
could be considered a subset of the information which would be
included in a GEOPRIV Location Object. This LCI is part of the
generation of location by the GEOPRIV origin.
An important feature of this document is it places location
information completely under control of the end device rather than
storing this Location Configuration Information in an outside
service for retrieval by the end device. Storage outside the end
device during times of emergency can cause unnecessary delay, or
failure during communication.
Another important feature of this LCI is its inclusion of a
resolution parameter for each of the dimensions of location. The
GEOPRIV working group has a stated requirement [3] to enable
decreasing the precision of a location element. Because this
resolution parameter need not apply to all dimensions equally, a
resolution value is included for each of the 3 location elements.
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This resolution method provides a natural ability for the device to
hide from the center point of the bounding area as this resolution
method is determined via the inherent affects of binary mathematics,
using the power of 2.
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 16 bytes long.
Finally, in the appendix this document provides some arithmetic
examples of just how the imprecision can be introduced in any or all
of the La/Lo/Alt values without the IP device needing to be
preprogrammed with bogus location information, and just how
imprecise the La/Lo/Alt values can be.
This document does not cover any policy regarding the use of this
other than a few as potential suggestions to convey the meaning
intended by the document.
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 [4].
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 it's current geo-location, if the user and/or application
so desires.
The goal of this option is to enable a wired Ethernet host to
provide its location to an emergency responder, as one example.
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Wireless hosts can utilize this option to gain knowledge of the
location of the radio access point used during host configuration,
but will need some more exotic mechanisms, maybe GPS, or maybe a
future DHCP option, which includes a list of geo-locations like that
defined here, which has 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 the string encoding of
digits in [5]. 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. Each parameter is 40
bits total, in length.
Altitude is represented in measurement units (MU) indicated by the
MU field, which is 4 bits long. Two measurement units are defined
here, meters (code=1) and floors (code=2), both of which are 2s-
complement fixed-point with 8 bits of fraction. Additional
measurement units MAY be assigned by IANA. The floor of a building
is often the relevant location information, and not necessarily
computable from meters of altitude.
Each of these 3 variables is preceded by an accuracy sub-field of 6
bits, indicating the number of bits of resolution. This resolution
sub-field accommodates the GEOPRIV requirement [3] 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.
2.0 DHC Location Configuration Information Elements
DHCP is a binary Protocol; GEOPRIV is text-based. Most coordinate
systems translate fairly easily between binary-based and text-based
location output (i.e. even emergency services within the US). The
authors believe 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.
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The proposed LCI format is:
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 TBD | 16 | LaRes | Latitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude (cont'd) | LoRes | +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MU | AltRes | Altitude |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Alt (cont'd) | Datum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.1 Elements of the Location Configuration Information
Code TBD: The code for this DHCP option is TBD by IANA.
16: The length of this option is 16 bytes.
LaRes: Latitude resolution. 6 bits indicating the valid 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 sending device (meaning the Geopriv target towards the
requestor).
The examples below in section 4.0, are to illustrate that a smaller
value in the resolution field increases the area within which the
device is located (without deception).
Values of resolution above decimal 34 are Undefined and reserved
because that is the largest number of bits in the Latitude field.
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. Geo-location formats provide for positive numbers to be
north of the equator and negative numbers to be 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 (detailed in the first example in
section 4.0). A value of 34 in the LaRes field indicates a precision
within 3.11 mm in Latitude.
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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 sending device (meaning the GEOPRIV target towards the
requestor).
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. Geo-location formats provide for positive
numbers to be east of the prime meridian and negative (2s
complement) numbers to be west of the prime meridian.
Entering a value of 2 in the LoRes field will result in the
precision of no greater than 1/6th that of the globe (see first
example in section 4.0 for more here). A value of 34 in the LoRes
field indicates a precision within 2.42 mm in longitude (at the
equator). Because lines of longitude converge at the poles, the
distance is smaller (resolution greater) for locations away from the
equator.
AltRes: Altitude resolution. 6 bits indicating the number of valid
bits in the altitude. Values above 30 (decimal) are
undefined and reserved.
MU: Measurement unit for altitude. Codes defined are:
1: Meters - in 2s-complement fixed-point 22-bit integer part with
8-bit fraction
If MU = 1, an AltRes value 0 would indicate unknown altitude. The
most precise Altitude would have an AltRes value of 30.
2: Floors - in 2s-complement fixed-point 22-bit integer part with
8-bit fraction
MU = 2 for Floors enables representing altitude in a form more
relevant in buildings which have different floor-to-floor
dimensions. An altitude coded as MU=2, AltRes = 30, and Altitude =
0, represents the ground level outside as well as the ground floor
within a building). This encoding is useful where the precise
altitude is less important than the location at ground level.
Any additional Geopriv Measurement Unit(s) to be defined for use via
this DHC Option MUST be done through a Standards Track RFC.
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Datum: The Map Datum used for the coordinates given in this Option
The Datum byte has 255 possibilities, of which 3 are to be
registered with IANA by this document (all derived from
specification in [8]):
1: WGS 84 (Geographical 3D) - World Geodesic System 1984, CRS
Code 4327, Prime Meridian Name: Greenwich
2: ED50 - European Datum 1950(77), CRS Code 4154, Prime Meridian
Name: Greenwich
3: ED87 - European Datum 1987, CRS Code 4231, Prime Meridian
Name: Greenwich
Any additional Geopriv datum(s) to be defined for use via this DHC
Option MUST be done through a Standards Track RFC.
3.0 Purpose of Resolution Value per La/Lo/Alt Element
GEOPRIV specified [3] the requirement that any location expressed
from or proxied on behalf of a device through the GEOPRIV Protocol
can have the accuracy or precision of that device's location
limited. The owner of the device, or the domain of the device
determines the policy for divulging how precise the location is for
any/all given requesters of that device's location.
One aspect within the GEOPRIV WG is the precision of a device's
ability to present its location coordinates might have a domain
policy override the individual policy in the sense of maximum
resolution possible. In other words, a user of a device might not
mind providing a quite precise location return to a location
request, but the local domain might not want that level of precision
by its policy. In this case, the resolution value provided in the
DHCP Reply can set this maximum precision value, perhaps allowing
the user of the Target device to make the values more imprecise
based on who is requesting their location. The document does not go
further down this thought for good reason.
4.0 Security Considerations
Where critical decisions might be based on the value of this
GeoLoc option, DHCP authentication in [7] SHOULD be used to
protect the integrity of the DHCP options.
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5.0 IANA Considerations
The DHCP option code for the GeoLoc option is TBD.
This document calls for the IANA registration of the following:
MU = 1 is meters of Altitude from mean low tide. Semantics are
included in this document (section 2.1)
MU = 2 is building Floors of Altitude. Semantics are included in
this document (section 2.1)
Datum = 1 is denoting WGS 84 (Geographical 3D) as defined by the
EPSG as their CRS Code 4327
Datum = 2 is denoting ED50(77) as defined by the EPSG as their CRS
Code 4154
Datum = 3 is denoting ED87 as defined by the EPSG as their CRS Code
4231
6.0 References
[1] Droms R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997
[2] Patrick M., "DHCP Relay Agent Information Option", RFC 3046,
January 2001
[3] Cuellar J., Morris J., Mulligan D., "GEOPRIV Requirements",
Internet Draft, "Work in Progress", June 2002
[4] Bradner S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997
[5] Farrell C., Schulze M., Pleitner S. and Baldoni D., "DNS
Encoding of Geographical Location", RFC 1712, November 1994.
[6] National Emergency Number Association (NENA) www.nena.org
NENA Technical Information Document on Model Legislation
Enhanced 911 for Multi-Line Telephone Systems
(http://www.nena.org/9%2D1%2D1techstandards/TechInfoDocs/
MLTS_ModLeg_Nov200.PDF)
[7] Droms R., "Authentication for DHCP Messages", RFC 3118, June
2001
[8] European Petroleum Survey Group, http://www.epsg.org/ and
http://www.ihsenergy.com/epsg/geodetic2.html
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7.0 Author Information
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
jmpolk@cisco.com
John Schnizlein
Cisco Systems
9123 Loughran Road
Fort Washington, MD 20744 USA
john.schnizlein@cisco.com
Marc Linsner
Cisco Systems
Marco Island, FL 34145 USA
marc.linsner@cisco.com
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Appendix: 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
MU = 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
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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
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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 [6],
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 asked for 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
103th 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 measurement unit value is 2 indicating floors. The AltRes
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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
MU = 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.).
8. Full Copyright Statement
"Copyright (C) The Internet Society (February 23rd, 2001).
All Rights Reserved.
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Standards process must be followed, or as required to translate
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The limited permissions granted above are perpetual and will not
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ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
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The Expiration date for this Internet Draft is:
Nov 13th, 2003
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