Subject: [Ecrit] Proposed requirement: split responsibility

From: Henning Schulzrinne <[email-masked]>
Date: Sat, 21 May 2005 21:32:27 +0200

We discussed towards the end at the interim meeting, but I don't think 
we have documented this requirement:

Lx (?): Split responsibility

The mapping protocol MUST allow that within a single level of the civic 
address hierarchy, multiple mapping servers handle subsets of the data 
elements.

Motivation: For example, two directories for the same city or county may 
handle different streets within that city or county.

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From: Andrew Newton <[email-masked]>
Date: Sun, 22 May 2005 11:03:06 -0400

On May 21, 2005, at 3:32 PM, Henning Schulzrinne wrote:

> The mapping protocol MUST allow that within a single level of the 
> civic address hierarchy, multiple mapping servers handle subsets of 
> the data elements.
>
> Motivation: For example, two directories for the same city or county 
> may handle different streets within that city or county.

Why are you limiting this to civic?  I would think that it would be 
just as important for geo as well.

-andy

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From: Henning Schulzrinne <[email-masked]>
Date: Sun, 22 May 2005 16:53:26 -0400

>
>
>> We discussed towards the end at the interim meeting, but I don't  
>> think we have documented this requirement:
>>
>> civic address hierarchy, multiple mapping servers handle subsets  
>> of the data elements.
>>
>> Motivation: For example, two directories for the same city or  
>> county may handle different streets within that city or county.
>>
>>
>

The "classical" example for this split responsibility was that, say,  
for one city, streets south of the railroad were part of PSAP1, while  
streets north were in PSAP2, usually based on PSTN wire center  
boundaries.  This meant that you'd either have to have a directory  
that contains all streets (easy case) or have to have two directories  
and somehow direct requests to the right directory.

Since geo doesn't have the civic hierarchy of country - state -  
county - city - street, it is less clear to me what the equivalent  
problem would be for geo. For this same case, in geo, you'd just have  
two polygons, one for the area north of the railroad, the other for  
the one south.

You do sometimes have polygons with holes for coverage regions, e.g.,  
where an airport has its own fire department/PSAP, while the  
surrounding county is served by the county sheriff, FD, etc.

(A somewhat related, but different, topic is that of conflicting  
jurisdictions, the Kashmir and Jerusalem cases. They would indeed  
have multiple servers be responsible for exactly the same geographic  
area.)

Can you give an example of what you had in mind?

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From: Andrew Newton <[email-masked]>
Date: Mon, 23 May 2005 11:54:57 -0400

> Can you give an example of what you had in mind?

In the example you gave, I would assume that just because "the powers 
that be" divided the PSAP along street north of the railroad vs south 
of the railroad still means that some users are gonna use geographical 
coordinates to give their location vs. a full civil address.

-andy

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From: Ted Hardie <[email-masked]>
Date: Mon, 23 May 2005 10:09:11 -0700

At 11:54 AM -0400 5/23/05, Andrew Newton wrote:
>In the example you gave, I would assume that just because "the 
>powers that be" divided the PSAP along street north of the railroad 
>vs south of the railroad still means that some users are gonna use 
>geographical coordinates to give their location vs. a full civil 
>address.
>
>-andy

The question goes back to split responsibility of the mapping server, though.
If a geoloc-capable mapping server said:  I can be responsible for this set of
polygons, but I'm going to refer you for the polygons you actually sent me,
I think this meets the split responsibility case.

Note that this doesn't necessarily map to the psap splits.  A mapping 
server could
have knowledge of a specific area, including which psaps served which numbers
on the street, but split that responsibility with another server which also
served different territory covered by the same psaps.  As a thought experiment,
imagine someone splitting a city into two geographically equal halves along
east-west lines for the purposes of assigning mapping server responsibility.
Unless the psap division followed exactly the same lines, each of the two
would have territory that used a psap that also served territory under the
other mapping server's responsibility.
				Ted

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From: "Brian Rosen" <[email-masked]>
Date: Mon, 23 May 2005 13:19:13 -0400

I agree that we need BOTH civic and geo routing, and thus we need both civic
and geo databases that determine boundaries.  Civic is based on country,
state/province, county, city, street, and house number.  Geo is based on
point-in-polygon algorithms.

It's possible that we use a nested set of polygons (country, state, county,
city, ...), but the number of polygons down to psap is thousands, perhaps a
small number of 10,000s.  That's small enough that a GIS system can store
all of them and do an intersection against them all simultaneously.
Most GIS systems are pretty smart about efficiently organizing such data.
They can find the right polygon in a dozen milliseconds of compute time.

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of
> Andrew Newton
> Sent: Monday, May 23, 2005 11:55 AM
> To: Henning Schulzrinne
> Cc: [email-masked]
> Subject: Re: [Ecrit] Proposed requirement: split responsibility
> 
>

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From: "Brian Rosen" <[email-masked]>
Date: Mon, 23 May 2005 13:28:20 -0400

See my reply to Andrew on polygons; we probably don't need this complexity.

Your example however is illustrative of how the NENA i2 mechanism works on
civic boundaries.  It assigns state/county/city areas to a specific part of
the database.  There is a "root server", which, when queried, returns a list
of servers that have data for a specified city/county/state.  Where the
boundary doesn't exactly match the city/county/state boundary, you get more
than one server in the response.  Each of the servers can forward the
request to the actual server, if it knows. 

I don't like this mechanism as much as the DNS proposal I have made, which
always gets the query to the authoritative server with one request by the
client, but it works.

Brian

> Ted Hardie
> Sent: Monday, May 23, 2005 1:09 PM
> To: Andrew Newton; Henning Schulzrinne
> Cc: [email-masked]

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From: Henning Schulzrinne <[email-masked]>
Date: Tue, 24 May 2005 06:50:59 -0400

Certainly. These two coordinate systems are largely independent and  
you could even have two separate mapping server hierarchies (referral  
chains) for each type of coordinate. In other words, as Brian noted,  
you could have a single geo-based mapping server for a whole state/ 
province and a hierarchy of county, city and borough for civic. Maybe  
this is another requirement that needs to be made explicit.

(There's some argument to be made for such differences. Geospatial  
boundaries are likely going to be more stable. As an example, town  
boundaries in New Jersey probably haven't changed since the 1800's  
and geographic PSAP service areas since the advent of 911, while we  
still get new streets and subdivisions as the last farm plots are  
converted to McMansions.)

This doesn't affect the issue at hand, however. See my longer message  
for details.