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Copyright Notice

Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

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

Table of Contents

1.  Terminology
2.  Introduction
3.  Format of the DHCP Civil Location Option
3.1  Overall Format
3.2  Element Format
3.3  Civil Address Components
4.  Example
5.  Security Considerations
6.  IANA Considerations
§  Normative References
§  Informative References
§  Author's Address
A.  Acknowledgments
§  Intellectual Property and Copyright Statements

1. Terminology

In this document, the key words "MUST", "MUSTNOT", "REQUIRED", "SHALL", "SHALLNOT", "SHOULD", "SHOULDNOT", "RECOMMENDED", "MAY", 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.

A related draft [9] describes a DHCPv4 [2] option for conveying geospatial information to a device. This draft describes how DHCPv4 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 or to convey it as part of presence information.

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. 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 Number Association (NENA) [11]. It is anticipated that other countries can reuse many of the data elements.

The same civil address information can often be rendered in multiple languages and scripts. For example, Korean addresses are often shown in Hangul, Latin and Kanji, while some older cities have multiple language variants (Munich, Muenchen and Monaco, for example). Since DHCPv4 does not currently support a mechanism to query for a specific script or language, the DHCP server SHOULD provide all common renderings to the client and MUST provide at least the rendering in the language and script appropriate to the location indicated. For example, for use in presence information, the target may be visiting from a foreign country and want to convey the information in a format suitable for watchers in its home country. For emergency services, the rendering in the local language is likely to be most appropriate. To provide multiple renderings, the client repeats sequences of address elements, prefixing each with a 'langtag' element (see Section 3.2).

The DHCP long-options mechanism described in RFC 3396[3] MUST be used if the civil address option exceeds the maximum DHCP option size of 255 octets.

3. Format of the DHCP Civil Location Option

3.1 Overall 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Code TBD    |       N       |          Countrycode          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    What       |        civil address elements                ... 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 3166 country code in capital ASCII letters, 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) SHOULDNOT be used unless it is known that the DHCP client is in close physical proximity to the server or network element.

Civil address element:

Zero or more elements comprising the civil address, with the format as described below.

3.2 Element Format

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                 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 uppercase.

CAvalue:

The civil address value, encoded as UTF-8[5], and written in uppercase letters where applicable. The script indication is written in mixed-case, with the first letter a capital letter.

Elements SHOULD be included in numeric order from lowest to highest of their CAtype if the server only provides one language and script rendition. In general, an element is labeled in its language and script by the most recent 'language tag' (CAtype = 0) element preceding it. Since not all elements depend on the script and language, a client accumulates the elements by CAtype and then selects the most desirable language and script rendition if there are multiple elements for the same CAtype.

3.3 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.

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

CA (Canada):

The mapping to NENA designations is shown in parentheses. A1=province (STA); A2=county (CNA); A3=city or town (MCN); A6=street (STN).

DE (Germany):

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

JP (Japan):

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).

KR (Korea):

A1=province (Do); A2=county (gun); A3=city or village (ri); A4=urban district (gu); A5=neighborhood (dong); A6=street (no, ro, ga or gil).

US (United States):

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 [10], Appendix B; A2=county (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.

Additional CA types appear in many countries and are simply omitted where they are not needed or known:

The CA types labeled in the second column correspond to items from the NENA "Recommended Formats & Protocols For ALI Data Exchange, ALI Response & GIS Mapping" [11], but are applicable to most countries. The "NENA" column refers to the data dictionary name in Exhibit 18 of [11].

The "langtag" item (CAtype 0) optionally identifies the script that should be used in rendering the address information, drawing from the tags for identifying languages in [7]. If omitted, the default value for this tag is "en-Latn".

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 Publication 28 [10], Appendix C, SHOULD be used.

The "type of place" item (CAtype 25) describes the type of place described by the civil coordinates. For example, it describes whether it is a home, office, street or other public space. The values are drawn from the items in the rich presence[12] document. This information makes it easy, for example, for the DHCP client to then populate the presence information.

4. Example

Rather than showing the precise byte layout of a DHCP option, we show a symbolic example below.

TBD

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 RFC3118[4] SHOULD be used to protect the integrity of the DHCP options.

6. IANA Considerations

TBD

Normative References

Informative References

Author's Address

Appendix A. Acknowledgments

Rohan Mahy and Stefan Berger provided helpful comments.

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