Subject: RE: [dhcwg] Working Group Last Call: Location Configuration Info rmation for GEOPRIV

From: "Abbott, Nadine B." <[email-masked]>
Date: Wed, 02 Jul 2003 13:42:39 -0400

Marc,

FYI and Question:

For wireless 9-1-1 calls, the geodetic location is provided from the
wireless carriers in a binary coded form over SS7 (ISUP or TCAP/E2, carried
in Calling Geodetic Location parameter; see ANSI T1.628-2000 for the coding
of the CGL--similar, but not the same as the DHCP-LO).  The location
information is processed by an E9-1-1 Database for delivery to Public Safety
Answering Points (PSAPs).
The geodetic location information that is provided to 9-1-1 Public Safety
Answering Points via queries to these E9-1-1 DBs uses the following NENA
formats:

Longitude:
11 bytes; Numeric; 
Longitude/X coordinate. Right Justified; pad field with zeros to left of
decimal degrees. +long: east of Greenwich; -long: west of Greenwich.  (Can
be used
for wireline as well as wireless) Sample: +000.######

Latitude 
10 bytes; Numeric; 
Latitude/Y coordinate. Right Justified; pad field with zeros to left of
decimal
degrees. +lat: north of equator; -lat: south of equator. (Can be used for
wireline as well as wireless) Sample: +00.######

Elevation 
5 bytes; Numeric;
Elevation/Altitude indicated as height above mean sea level, measured in
meters (Can be used for wireline) Sample: #####

Datum 
2 bytes; alphanumeric;
Specifies the map projection and coordinate system recommended for the
display of the Longitude and Latitude coordinates. Two systems are
commonly used for North America. The code 83 identifies North American
Datum for 1983 (NAD83). Code 84 identifies the World Geodetic System
for 1984 (WGS84). Other codes may be added as additional datum become
available through authorized entities.
Where x =
83 = NAD83
84 = WGS84

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For a 9-1-1 call, if IP devices are populated with coordinate information in
a different format from that expected by PSAP mapping applications, then
somewhere between caller and PSAP, the geodetic location information
provided by the DHCP location object procedures will need to be put into a
format that can be processed by PSAP applications.  If you assume that the
location object information is routed via the E9-1-1 DBs, perhaps the
conversion could be performed there.  If you envision that geodetic location
is carried with the call establishment signaling, where do you assume that
the conversion between the DHCP-LO format and the formats expected by PSAP
applications will take place?  

Thanks,
Nadine Abbott
Telcordia Technologies

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From: Marc Linsner <[email-masked]>
Date: Wed, 02 Jul 2003 20:25:32 -0400

Yes, we did look at the T1.628 geo-loc format.  As John Schnizlein
already stated, we found it to be inefficient in many respects.  We also
discussed other uses of our newly described format and decided it needed
to be able to define a higher resolution than what is allowed by T1.628.

The new format: better than 7 decimal places of degrees of resolution;
ability to identify floors of a building (something that is impossible
for a PSAP to accomplish with a simple altitude value); ability to state
the resolution (accuracy) of the location value from 1/6 of the globe to
~3mm.  All this in only 16 bytes!

The bottom line: The application at the PSAP will need to be able to
interpret the new format.  Interpretation of this format should be
relatively easy for today's class of cpus.  At this point, looking at
the length of the data object should be a good clue for a GIS
application programmer to decide which format they're dealing with.  Or,
a few short subroutines to run against the object will be able to decide
in a short time the format.  I don't foresee the need to do any
conversion outside of the PSAP GIS mapping software.  If a network
routing node needs to perform a lookup based on the new format,
conversion to the needed format for lookup will be easy at that point
also or by the lookup service provider.  After all, MS Word can
understand text, word, html, rtf, etc. docs; a $50K GIS package should
be able to handle a couple of different data formats.

-Marc Linsner-

> available through authorized entities.
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> For a 9-1-1 call, if IP devices are populated with coordinate
information
> in