Internet DRAFT - draft-critchley-dhc-location-option
draft-critchley-dhc-location-option
Network Working Group Sam Critchley
Internet Draft Worldcom, Inc
August, 2002
Expires January, 2003
The Geographic Position Option for DHCP
<draft-critchley-dhc-location-option-00.txt>
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 10 of RFC2026.
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/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Abstract
This document describes a DHCP option in which the geographic
position of the DHCP server is passed to the DHCP client in order
to allow the client to make use of Location-Based Services.
1. Introduction
Mobile telephony networks are able to make use of certain
technologies which supply the geographic location of a mobile
suscriber's handset to a Location-Based Services (LBS) provider. The
mobile subscriber is then able to take advantage of such services
as point-of-interest (POI) location, mapping, route-determination,
traffic services and location-aware mobile instant messaging.
There is currently no standardised mechanism in place to supply
a geographic location to Internet hosts not connected to mobile
telephony network, including, but not limited to, hosts connecting
using IEEE 802.11x wireless protocols, and those connected to
wire-based networks but configured with non-static IP addresses.
Consequently, these hosts are more limited in their ability to
take advantage of LBS, including having to manually enter a
geographic position or street address in many cases.
This document defines a DHCP option by which a DHCP server can pass
Critchley [Page 1]
its geographical location, in the form of a latitude, longitude and
altitude position, to its clients.
This document does not seek to define a method to allow a host to
pass its location to a LBS server, as there are already in place
several standards which propose these mechanisms, such as the Mobile
Location Protocol (MLP) developed by the Location Interoperability
Forum (LIF), although it does make one security recommendation in
this area.
Furthermore, this document does not attempt to propose a mechanism
which would perform in the same manner as critical emergency location
services such as the Enhanced 911 (E-911) service being implemented
in US mobile telephony networks, nor does it propose a mechanism
to be used for highly accurate positioning applications, such as that
provided by the Global Positioning System (GPS).
However, the Geographic Position Option for DHCP does propose a
mechanism which, in many cases, will provide a position to the same
degree of accuracy as that provided by mobile telephony networks'
geographic location mechanisms.
2. The Geographic Position Option for DHCP
2.1 DHCP Option field definitions.
This option contains the following fields:
a) Option Code - TBD
b) Option length in bytes
c) DHCP Server Geographic Position Sentence
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 | Length | Geographic Position Sentence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Geographic Position Sentence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.2 DHCP Server Geographic Position Sentence
The DHCP Server Geographic Position Sentence takes the form of a
comma-separated ASCII string of position terms. This is in some ways
similar to the format used in the National Marine Electronics
Association's NMEA 0183 and NMEA 2000 standards, commonly used by
GPS navigation devices for passing location information to other
devices.
Critchley [Page 2]
The sentence takes the following form:
DHCPPS,A,B,C,D,E,F,G,H,I,J,K
Where the following are field definitions:
- DHCPPS - DHCP Position Sentence. Indicates to the DHCP client that
this is a sentence designed to provide the geographic position of
the DHCP server to the DHCP client, as opposed to any other
information.
- A - Latitude. Expressed in decimal degrees, to a maximum of 6
decimal places.
- B - Latitude N/S. Whether the latitude figure expressed is North or
South of the equator, expressed simply as the letter "N" or the
letter "S" in upper case.
- C - Longitude. Expressed in decimal degrees, to a maximum of 6
decimal places.
- D - Longitude E/W. Whether the longitude figure expressed is East
or West of the Greenwhich Meridian, expressed simply as the letter
"E" or the letter "W" in upper case.
- E - Altitude. The altitude, expressed to a maximum of 2 decimal
places, and preceded with a "+" or a "-" symbol to indicate whether
the value is above mean sea level (positive) or below mean sea level
(negative).
- F - Altitude unit. The upper-case letter "M" to indicate that the
unit is in Metres, or the upper-case letters "FT" to indicate that
the unit is in feet.
- G - Horizontal Accuracy. The horizontal accuracy of the latitude
and longitude position obtained by the DHCP client from the DHCP
server. Intended to represent the maximum horizontal distance that
a DHCP client will be from its DHCP server, and useful, for example,
in the case of DHCP scenarios such as IEEE 802.11b setups using
bridging, and where the DHCP client can expect to be some distance
from the DHCP server. Figure given to a maximum of three decimal
places.
- H - Horizontal Accuracy unit. The upper-case letter "M" to indicate
that the unit is in metres, the upper-case letters "KM" to indicate
that the unit is in kilometres, the upper-case letters "FT" to
indicate that the unit is in feet, or the upper-case letters "ML" to
indicate that the unit is in miles.
- I - Vertical Accuracy. The vertical accuracy of the Altitude
position obtained by the DHCP client from the DHCP server. Intended
to represent the maximum vertical distance that a DHCP client will be
located from its DHCP server, and useful, for example, in the case
of network segments located in tall buildings.
- J - Vertical Accuracy unit. The upper-case letter "M" to indicate
that the unit is in metres, the upper-case letters "KM" to indicate
that the unit is in kilometres, the upper-case letters "FT" to
Critchley [Page 3]
indicate that the unit is in feet, or the upper-case letters "ML" to
indicate that the unit is in miles.
- K - Geodesic Datum. The standard abbreviated form of the geodesic
datum used to calculate position. This term has a default value of
"WGS84" should no datum be specified.
The DHCP Server Geographic Position Sentence would normally have a
maximum length of between 49 and 64 bytes, depending on the values
used.
Apart from the first term of the DHCP Server Geographic Position
Sentence, which always must have a value of "DHCPPS", and must be
present, the presence of a value in all other fields is optional.
However, all fields, whether a value is present or not, must be
comma-separated. Furthermore, it is understood that a DHCPPS
containing few or no values might be of little use in determining
the position of the DHCP client.
2.2.1 Example of a DHCP Server Geographic Position Sentence
DHCPPS,52.3742,N,4.8925,E,+3.12,M,50.9,M,5,M,WGS84
This sentence indicates that the DHCP server is located at 52.3742
degrees North, 4.8925 degrees East, at 3.12 metres above mean sea
level, that the DHCP client is a maximum of 50.9 metres horizontally
from the DHCP server, a maximum of 5 metres altitude above or below
the DHCP server, and that the datum used to calculate this position
was WGS-84.
2.3 Security Concerns
Whilst this document does not seek to define a method to allow a
host to pass its location to a LBS server, it does note that
there are possible security concerns involved in the location of
an Internet host being passed to an LBS server. In the case of mobile
telephony networks, most subscriber locations are passed to an LBS
server from a mobile provider's location server, not directly from
the mobile handset, and the list of permitted LBS servers is strictly
controlled. However, in the case of a Geographic Position option for
DHCP, this security infrastructure may not be in place, and it is
therefore recommended that any client application supplying a
DHCP-acquired position to an LBS server should implement an adequate
security mechanism to protect users from any possible wrongdoing.
Such mechanisms might include implementing a list of permitted LBS
servers, popup alerts when passing a host's location to an LBS
server, or the ability to turn on/off the passing of location
information.
Critchley [Page 4]
3. Author's Address
Sam Critchley
Worldcom EMEA Network Service
Joan Muyskenweg 22
1096 CJ Amsterdam
The Netherlands
Phone: +31 20 711 6082
Email: Sam.Critchley@wcom.com
Critchley [Page 5]
^L
