GEOPRIV Working Group J. Polk INTERNET-DRAFT Cisco Systems Obsoletes: 3825 (if approved) J. Schnizlein Category: Standards Track ISOC Expires: April 7, 2010 M. Linsner 7 October 2009 Cisco Systems M. Thomson Andrew B. Aboba (ed) Microsoft Corporation Dynamic Host Configuration Protocol Option for Coordinate-based Location Configuration Information draft-ietf-geopriv-rfc3825bis-02.txt Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 7, 2010. Polk, et al. Standards Track [Page 1] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document specifies Dynamic Host Configuration Protocol Options (both DHCPv4 and DHCPv6) for the coordinate-based geographic location of the client. The Location Configuration Information (LCI) includes latitude, longitude, and altitude, with resolution or uncertainty indicators for each. Separate parameters indicate the reference datum for each of these values. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Resolution and Uncertainty . . . . . . . . . . . . . . . 4 2. DHCP Option Format . . . . . . . . . . . . . . . . . . . . . . 4 2.1 DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . 5 2.2 DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . 6 2.3 Latitude and Longitude Fields . . . . . . . . . . . . . 8 2.4 Altitude . . . . . . . . . . . . . . . . . . . . . . . . 10 2.5 Datum . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. Security Considerations. . . . . . . . . . . . . . . . . . . . 12 4. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 12 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. Normative References . . . . . . . . . . . . . . . . . . 14 6.2. Informational References . . . . . . . . . . . . . . . . 14 Appendix A. Calculations of Imprecision possible with the DHC LCI 15 A.1. LCI of "White House" (Example 1) . . . . . . . . . . . . 15 A.2. LCI of "Sears Tower" (Example 2) . . . . . . . . . . . . 17 Appendix B. Changes from RFC 3825 . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 Polk, et al. Standards Track [Page 2] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 1. Introduction The physical location of a network device has a range of applications. In particular, emergency telephony applications rely on knowing the location of a caller in order to determine the correct emergency center. The location of a device can be represented either in terms of geospatial (or geodetic) coordinates, or as a civic address. Different applications may be more suited to one form of location information; therefore, both the geodetic and civic forms may be used simultaneously. 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 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. 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]. Polk, et al. Standards Track [Page 3] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 1.2. Resolution and Uncertainty The DHCPv4 option format defined in this document utilizes both resolution and uncertainty parameters. The DHCPv6 option format only utilizes an uncertainty parameter. 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. Appendix A of this document provides some arithmetic examples of the implication of different resolution values on the La/Lo/Alt. The DHCPv6 option format as well as version 1 of the DHCPv4 option format utilizes an uncertainty parameter. In the context of location technology, uncertainty is a quantification of errors. Any method for determining location is subject to some sources of error; uncertainty describes the amount of error that is present. Uncertainty might be the coverage area of a wireless transmitter, the extent of a building or a single room. Uncertainty is usually represented as an area within which the target is located. In this document, each of the three axes can be assigned an uncertainty value. In effect, this describes a rectangular prism. When representing locations from sources that can quantify uncertainty, the goal is to find the smallest possible rectangular prism that this format can describe. This is achieved by taking the minimum and maximum values on each axis and ensuring that the final encoding covers these points. This increases the region of uncertainty, but ensures that the region that is described encompasses the target location. 2. DHCP Option Format This section defines the format for the DHCPv4 and DHCPv6 options. These options use the same basic format, differing only in the option code. Polk, et al. Standards Track [Page 4] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 2.1. DHCPv6 Option The DHCPv6 [RFC3315] option 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code (TBD) | OptLen (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LatUnc | Latitude + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lat (cont'd) | LongUnc | Longitude + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Longitude (cont'd) | AT | AltUnc | Altitude + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Altitude (cont'd) | Datum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code: GEOCONF_GEODETIC (8 bits). OptLen: Option Length (8 bits). This option is fixed size, the value of this octet will always be 16. LatUnc: Latitude Uncertainty (6 bits). Latitude: Latitude (34 bits). LongUnc: Longitude Uncertainty (6 bits). Longitude: Longitude (34 bits). AType: Altitude Type (4 bits). AltUnc: Altitude Uncertainty (6 bits). Altitude: Altitude (30 bits). Datum: Datum (8 bits). Polk, et al. Standards Track [Page 5] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 2.2. DHCPv4 Option The DHCPv4 option 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 | Length | LatUnc | Latitude + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Latitude (cont'd) | LongUnc | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Longitude | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AType | AltUnc | Altitude + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Alt.(cont'd) |Ver| Res |Datum| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code: 8 bits. The code for the DHCPv4 option (123). Length: 8 bits. The length of the DHCPv4 option, in octets. For versions 0 and 1, the option length is 16. LatUnc: 6 bits. When the Ver field = 0, this field represents Latitude resolution. When the Ver field = 1, this field represents Latitude uncertainty. Latitude: a 34 bit fixed point value consisting of 9 bits of integer and 25 bits of fraction. Latitude SHOULD be normalized to within +/- 90 degrees. Positive numbers are north of the equator and negative numbers are south of the equator. LongUnc: 6 bits. When the Ver field = 0, this field represents Longitude resolution. When the Ver field = 1, this field represents Longitude uncertainty. Longitude: a 34 bit fixed point value consisting of 9 bits of integer and 25 bits of fraction. Longitude SHOULD be normalized to within +/- 180 degrees. Positive values are East of the prime meridian and negative (2s complement) numbers are West of the prime meridian. AType: Altitude Type (4 bits). AltUnc: 6 bits. When the Ver field = 0, this field represents Altitude resolution. When the Ver field = 1, this field represents Altitude Uncertainty. Polk, et al. Standards Track [Page 6] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 Altitude: A 30 bit value defined by the AType field. Ver: The Ver field is two bits, providing for four potential versions. This specification defines the behavior of version 0 (originally specified in [RFC3825]) as well as version 1. The Ver field is always located at the same offset from the beginning of the option, regardless of the version in use. Res: 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: 3 bits. The Map Datum used for the coordinates given in this Option. 2.2.1. Version Support 2.2.1.1. 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. 2.2.1.2. 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. Polk, et al. Standards Track [Page 7] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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. Polk, et al. Standards Track [Page 8] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 ___ ___________ ^ | / | | | / | | | / | 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 Polk, et al. Standards Track [Page 9] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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 Polk, et al. Standards Track [Page 10] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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. Polk, et al. Standards Track [Page 11] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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 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 Polk, et al. Standards Track [Page 12] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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. Polk, et al. Standards Track [Page 13] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 [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 (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. [RFC3825] Polk, J., Schnizlein, J. and M. Linsner, "Dynamic Host Configuration Protocol Option for Coordinate-based Location 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 Considerations Section in RFCs", RFC 5226, May 2008. Polk, et al. Standards Track [Page 14] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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 Polk, et al. Standards Track [Page 15] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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 Polk, et al. Standards Track [Page 16] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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 Polk, et al. Standards Track [Page 17] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 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.). Polk, et al. Standards Track [Page 18] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 Appendix B. Changes from RFC 3825 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 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: -02: Reorganized Sections 1 and 2. -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. Polk, et al. Standards Track [Page 19] INTERNET-DRAFT DHCP Option for Coordinate LCI 7 October 2009 Authors' Addresses James M. Polk Cisco Systems 2200 East President George Bush Turnpike Richardson, Texas 75082 USA USA EMail: jmpolk@cisco.com John Schnizlein Technology Program Manager Internet Society 1775 Wiehle Avenue Suite 201 Reston, VA 20190-5108 USA USA EMail: schnizlein@isoc.org Marc Linsner Cisco Systems Marco Island, FL 34145 USA USA EMail: marc.linsner@cisco.com Martin Thomson Andrew PO Box U40 Wollongong University Campus, NSW 2500 AU EMail: martin.thomson@andrew.com Bernard Aboba Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA USA EMail: bernarda@microsoft.com Polk, et al. Standards Track [Page 20]