Subject: RE: [dhcwg] Geographic position option

From: "Bernie Volz (EUD)" <[email-masked]>
Date: Fri, 16 Aug 2002 10:16:06 -0500

Sam:

If you want to submit this, you need to send it to [email-masked]. (I think they'd prefer an attachment - .txt file - rather than embedded text.)

If you want this to be a DHC WG item, you need to request that (which is perhaps exactly why you send the email). You can submit the draft (as an individual contribution) in any case.

My questions regarding this draft are:
1. What use is the location of the DHCP server? Isn't there some assumption implied here that the server is "close" to the client and hence the client could use the server's location information as an indication of where it is located (and hence use these location based services)?

However, I don't see that the location of a client and the location of a server are necessarily related. Sure, there are lots of instances where they are physically close (such as an office building). But there are many other indicates where they are not (for example in a cable modem environment). And, how does a client determine this?

2. More text on what a client does with this information would be useful. For example, does the client use it as in (1) above or could a client use this to chose a DHCP server (for example, one that it is "closest" to it if it knows its own location)? I'm not sure what value this has, but it would be good to be clear about how clients use this option.

3. Is there any assumption that this positioning information might be extended to other devices? For example, could the DHCP server tell the clients where a DNS server or printer is located? (Why this would be of use I have no idea.) Anyway, can more than one Geographic Position Sentence be specified? If so, how? Please note that DHCP doesn't allow multiple options to be present to represent separate instances of the option (all of the option strings are assumed to be concatenatable).

The reason I ask is that the first parameter is "DHCPPS", so by implication this could mean others might be possible. Though, you do say "which always must have a value of "DHCPPS"".

Personally, I'm not so sure of the importance of this option.

- Bernie

-----Original Message-----
From: Sam Critchley [mailto:[email-masked]]
Sent: Friday, August 16, 2002 10:52 AM
To: [email-masked]
Subject: [dhcwg] Geographic position option

Hi,

Included below is a draft proposing an option to allow a DHCP server to
pass its geographic location to a DHCP client.

From RFC 2489:

"Preferably, the author will submit the Internet Draft to the DHC Working
Group,..."

and

"The specification is reviewed by the DHC WG (if it exists) or by the
IETF."

So, I'd be interested in people's comments on this document. What should I
do with the document now?

Many thanks,

Sam

Here is the draft:

************************************************************************

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
   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.

   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
   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.

3.	Author's Address

   Sam Critchley
   Worldcom EMEA Network Service
   Joan Muyskenweg 22
   1096 CJ Amsterdam
   The Netherlands

   Phone: +31 20 711 6082
   Email: [email-masked]

***************************************************************************

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---

From: Sam Critchley <[email-masked]>
Date: Fri, 16 Aug 2002 17:42:02 +0200 (MET DST)

Hi Bernie,

Thanks for the help and the comments.

> If you want this to be a DHC WG item, you need to request that (which is perhaps exactly why you send the email). You can submit the draft (as an individual contribution) in any case.

Okay, I guess I'll go with the flow here... although I assume that if I
send it to [email-masked] as an individual contribution then at
least it gets a URL that people can refer to rather than having to include
the text in every message...

> 1. What use is the location of the DHCP server? Isn't there some assumption implied here that the server is "close" to the client and hence the client could use the server's location information as…

Sure, this assumption is definitely there. For example, if someone with a
laptop and a 802.11b card logged on to an 802.11b AP whilst travelling to
a city they weren't familiar with, they could use LBS without having to
manually configure their computer.

> However, I don't see that the location of a client and the location of a server are necessarily related. Sure, there are lots of instances where they are physically close (such as an office buildin…

I agree that in many cases the DHCP server and client will not be
geographically close (such as in dial-up access or with cable modems as
you say), and it may be preferable to manually input the host's location
at the application level.

The original reason for writing this draft was following some discussion
on an LBS mailing-list, as to whether a similar system would be available
for 802.11 mobile devices as for mobile telephony-style devices, which use
technologies such as E-OTD and A-GPS to derive location. It turned out
that there isn't really a standardised technology to do this, and that
there were two options:

i) Do something in DHCP
ii) Use the NAT setup and a browser environment variable.

The disadvantages of the second are that not everyone has a NAT setup, and
that http isn't the only service which might want to use LBS.

> 2. More text on what a client does with this information would be useful. For example, does the client use it as in (1) above or could a client use this to chose a DHCP server (for example, one tha…

I think probably the first, rather than the second. What I had in mind was
that an application running on the client host would have an interface to
the location information, and would be able to use that when presented
with a "location request" from a LBS server. Unfortunately I'm not really
an expert on the stack required to do that but presumably it would be the
same as many IP-based applications?

> The reason I ask is that the first parameter is "DHCPPS", so by implication this could mean others might be possible. Though, you do say "which always must have a value of "DHCPPS"".

Well, I only really intended this to be used in a DHCP Server -> Client
relationship in order to satisfy the question (initially) of how a mobile
802.11 host might make use of LBS without manual input of location such as
street address etc. However, it's possible that there would be other uses.
That's also why I put in an option to have a sentence other than "DHCPPS",
just in case someone comes up with another one in the future.

> Personally, I'm not so sure of the importance of this option.

Well, I think there would be demand for this mainly for 802.11a/b/g
roaming at the moment. One of the differences between cellular-based
roaming for mobile devices and 802.11 is that there's no location
mechanism in place for 802.11... the kinds of services this enables are
very popular in, for example, South Korea, where over 1 million
GPS-enabled handsets are in use already on the KDDI CDMA network.

Thanks,

Sam

> do with the document now?

******************************************************
Sam Critchley           Technology Integration Manager
                        Network Services EMEA
[email-masked]  Worldcom
                       	Joan Muyskenweg 22
Tel: +31 20 711 6082    1096 CJ Amsterdam
                        The Netherlands
******************************************************