Internet Engineering Task Force
Internet Draft                                            H. Schulzrinne
                                                             Columbia U.
February 19, 2003
Expires: August 2003

                     DHCP Option for Civil Location


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Internet Draft      DHCP Option for Civil Addresses    February 19, 2003


   This document specifies a Dynamic Host Configuration Protocol option
   for the civil (country, street and community) location of the client.

1 Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
   indicate requirement levels for compliant implementations.

2 Introduction

   Many end system services can benefit by knowing the approximate
   location of the end device. In particular, IP telephony devices need
   to know their location to contact the appropriate emergency response
   agency and to be found by emergency responders.

   There are two common ways to identify the location of an object,
   either through geospatial coordinates or by so-called civil
   coordinates.  Geospatial coordinates indicate longitude, latitude and
   altitude, while civil coordinates indicate a street address.

        This is commonly, but not necessearily, closely related to
        the postal address, used by the local postal service to
        deliver mail.  However, not all postal addresses correspond
        to street addresses. For example, the author's address is a
        postal address that does not appear on any street or
        building sign. Naturally, post office boxes would be
        unsuitable for the purposes described here.

   A related draft [7] describes a DHCP [2] option for conveying
   geospatial information to a device. This draft describes how DHCP can
   be used to convey the civil location to devices. Both can be used
   simultaneously, increasing the chance to deliver accurate and timely
   location information to emergency responders.

   End systems that obtain location information via the mechanism
   described here then use other protocol mechanisms to communicate this
   information to the emergency call center.

   Civil information is useful since it often provides additional,
   human-usable information particularly within buildings. Also,
   compared to geospatial information, it is readily obtained for most
   occupied structures and can often be interpreted even if incomplete.

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   For example, for many large university or corporate campuses,
   geocoding information to building and room granularity may not be
   readily available.

   Unlike geospatial information, the format for civil information
   differs from country to country. Thus, this draft establishes an IANA
   registry for civil location data fields. The initial set of data
   fields is derived from standards published by the United States
   National Emergency Numbering Association (NENA) [3]. It is
   anticipated that other countries can reuse many of the data elements.

3 Format of the DHCP Civil Location Option

         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    |       N       |          Countrycode          |
         |    What       |        civil address elements                ...

   Each civil address element has the following format:

         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
         |   CAtype      |   CAlength    |      CAvalue                 ...

        Code TBD: The code for this DHCP option is TBD by IANA.

        N: The length of this option is variable.

        Countrycode: The two-letter ISO country code in capital ASCII
             letter, e.g., DE or US.

        What: The 'what' element describes which location the DHCP
             refers to. Currently, three options are defined: the
             location of the DHCP server (0), the location of the
             network element believed to be closest to the client (1) or
             the location of the client (2). Option (2) SHOULD be used,
             but may not be known. Options (1) and (2) SHOULD NOT be

H. Schulzrinne                                                [Page 3]

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             used unless it is known that the DHCP client is in close
             physical proximity to the server or network element.

             In some cases, the local wiring plant makes it
             difficult to ascertain the device location with
             certainty. In that case, it is still preferable to
             indicate the DHCP server, Ethernet switch or router,
             but indicate the uncertainty. This avoids that the
             emergency responders try to break into the LAN closet.

        CAtype: A one-octet descriptor of the data civil address value.

        CAlength: The length, in octets, of the CAvalue, not including
             the CAlength field itself. Data SHOULD be encoded in

        CAvalue: The civil address value, encoded as UTF-8, and written
             in uppercase letters where applicable.

4 Civil Address Components

   Since each country has different administrative hierarchies, with
   often the same (English) names, this specification adopts a simple
   hierarchical notation that is then instantiated for each country. We
   assume that five levels are sufficient for sub-national divisions
   above the street level.

   All elements are OPTIONAL and can appear in any order. Abbreviations
   do not need a trailing period.

   CAtype  label  description
        1  A1     national subdivisions (state, region, province, prefecture)
        2  A2     county, parish, gun (JP), district (IN)
        3  A3     city, township, shi (JP)
        4  A4     city division, borough, city district, ward, chou (JP)
        5  A5     neighborhood, block
        6  A6     street

   For specific countries, the administrative sub-divisions are
   described below.

        US: The mapping to NENA designations is shown in parentheses.
             A1=state (STA), using the the two-letter state and
             possession abbreviations recommended by the United States
             Postal Service Publication 28 [4], Appendix B; A2=county

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             (CNA); A3=civil community name (city or town) (MCN);
             A6=street (STN). A4 and A5 are not used. The civil
             community name (MCN) reflects the political boundaries.
             These may differ from postal delivery assignments for
             historical or practical reasons.

        CA: The mapping to NENA designations is shown in parentheses.
             A1=province (STA), A2=county (CNA), A3=city or town (MCN).

        JP: A1=metropolis (To, Fu) or prefecture (Ken, Do); A2=city
             (Shi) or rural area (Gun); A3=ward (Ku) or village (Mura);
             A4=town (Chou or Machi); A5=city district (Choume);
             A6=block (Banchi or Ban).

        DE: A1=state (Bundesstaat); A2=county (Kreis); A3=city (Stadt,
             Gemeinde); A6=street (Strasse).

   Additional CA types appear in many countries and are simply omitted
   where they are not used:

   CAtype  NENA  description                           examples
       16  PRD   leading street direction              N
       17  POD   trailing street suffix                SW
       18  STS   street suffix                         AVE, PLATZ
       19  HNO   house number                          123
       20  HNS   house number suffix                   A, 1/2
       21  LMK   landmark or vanity address            SHADELAND CRESCENT APTS
       22  LOC   additional location information       APT 17
       23  NAM   name (residence and office occupant)  JOE'S BARBERSHOP
       24  ZIP   postal/zip code                       10027-1234

   These CA types correspond to items from the NENA "Recommended Formats
   & Protocols For ALI Data Exchange, ALI Response & GIS Mapping" [3],
   but are applicable to most countries. The "NENA" column refers to the
   data dictionary name in Exhibit 18 of [3].

   The NAM object is used to aid user location ("Joe Miller" "Alice's
   Dry Cleaning"). It does not identify the person using a
   communications device, but rather the person or organization
   associated with the address.

   For POD and PRD, in English-speaking countries, the abbreviations N,
   E, S, W, and NE, NW, SE, SW should be used.

   STS designates a street suffix. In the United States (US), the
   abbreviations recommended by the United States Postal Service

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   Publication 28 [4], Appendix C, SHOULD be used.

   The DHCP long-options mechanism described in RFC 3396 [5] MUST be
   used if the civil address option exceeds the maximum DHCP option size
   of 255 octets.

5 Security Considerations

   The information in this option may be used for a variety of tasks. In
   some cases, integrity of the information may be of great importance.
   In such cases, DHCP authentication in [6] SHOULD be used to protect
   the integrity of the DHCP options.

6 Acknowledgments

   Rohan Mahy provided helpful comments.

7 Authors' Addresses

   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue
   New York, NY 10027
   electronic mail:

8 Normative References

   [1] S. Bradner, "Key words for use in RFCs to indicate requirement
   levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.

   [2] R. Droms, "Dynamic host configuration protocol," RFC 2131,
   Internet Engineering Task Force, Mar. 1997.

   [3] National Emergency Number Association, "Nena recommended formats
   & protocols for ali data exchange, ali response & gis mapping,"
   Standard NENA-02-010, NENA, Washington, DC, 2002 Jan.

   [4] United States Postal Service, "Postal addressing standards,"
   Publication 28, USPS, Washington, DC, Nov. 2000.

   [5] T. Lemon and S. Cheshire, "Encoding long options in the dynamic
   host configuration protocol (DHCPv4)," RFC 3396, Internet Engineering
   Task Force, Nov. 2002.

   [6] R. Droms and W. Arbaugh, eds., "Authentication for DHCP
   messages," RFC 3118, Internet Engineering Task Force, June 2001.

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9 Informative References

   [7] J. Polk et al., "DHCP option for geographic location," Internet
   Draft, Internet Engineering Task Force, Oct. 2002.  Work in progress.

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H. Schulzrinne                                                [Page 7]

                           Table of Contents

   1          Terminology .........................................    2
   2          Introduction ........................................    2
   3          Format of the DHCP Civil Location Option ............    3
   4          Civil Address Components ............................    4
   5          Security Considerations .............................    6
   6          Acknowledgments .....................................    6
   7          Authors' Addresses ..................................    6
   8          Normative References ................................    6
   9          Informative References ..............................    7

H. Schulzrinne                                                [Page 1]