Subject: RE: [Geopriv] GeoPriv :- draft-winterbottom-location-uri

From: "Martin Thomson" <[email-masked]>
Date: Mon, 25 Jul 2005 10:51:42 +1000

Hi John,

I've chosen a few points to elaborate on, I think that it might help to
break this down into smaller chunks.

> Indeed, much of the rationale for by-reference appears to rely on the 
> idea that de-referencing the reference occurs at some different time 
> and/or place than the target, which could avoid unnecessarily 
> traversing of a level of indirection by getting just its location 
> rather than a reference to its location.

The idea of location by-reference enables the separation of the user of
location information and the owner of said data.  The host is the owner, but
unless it needs to use location information, why bother going to the effort
of creating it?  What is often left unacknowledged is the potential cost of
determining location - a GPS fix from a cold start can take approximately 45
seconds (time on a consumer GPS product).

Perhaps you could consider the case where a target needs location by-value
immediately as a special case.

> > In any event, the deployment realities are not the only reason to
> > study location by-reference. Mobile handsets whose location changes 
> > are a good argument for not statically provisioning location 
> > information at the moment a device autoconfigures on a network.
> 
> Of course this is true.  I have not heard anyone advocate 
> that the only 
> time a package of geographic information like the one 
> specified in RFC 
> 3825 should be transmitted to an Internet host would be when 
> it gets it 
> IP address.  The timing of when a host requests its location seems to 
> me a different question from the indirection of an intervening 
> reference.

This raises an interesting point that location by-reference handles rather
well.  Since location information is a continuous datum that could change
constantly, timeliness of information is particularly pertinent.  For this
reason, polling approaches as you recommend are less than optimal.  The SIP
location event package proposed by Rohan highlights this quite well.
Location by-reference gives a user of location information (for now, just
assume that this could be anyone, including the target) the ability to
request location information when it is needed only.  Requesting when needed
means that the information is timely, and that the resources required to
determine location are only expended as necessary.

Cheers,
Martin
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---

From: John Schnizlein <[email-masked]>
Date: Thu, 28 Jul 2005 20:09:58 -0400

There are probably situations in which an Internet user would value 
giving a location reference rather than a location to some other party. 
Because there are also probably situations where the user would value 
getting the location as directly as possible, and controlling to whom 
it is given, this alternative should not be precluded.

The attempt to portray these mechanisms in opposition creates 
unnecessary conflict.

On Jul 24, 2005, at 8:51 PM, Martin Thomson wrote:
>
> I've chosen a few points to elaborate on, I think that it might help 
> to break this down into smaller chunks.
>
> The idea of location by-reference enables the separation of the user 
> of location information and the owner of said data.  The host is the 
> owner, but unless it needs to use location information, why bother 
> going to the effort of creating it?

A host would (bother to) determine its location when it has stopped 
moving so that it would have the information "in hand" and not have to 
determine the location at the point when it wanted to send it to some 
application.

>   What is often left unacknowledged is the potential cost of 
> determining location - a GPS fix from a cold start can take 
> approximately 45 seconds (time on a consumer GPS product).

Is the cost of determining location then better left to the party 
requesting the location of some other host?  Do you expect GPS to be 
involved in the location determination process?

> Perhaps you could consider the case where a target needs location 
> by-value immediately as a special case.

One use for the actual location rather than a reference might be to 
send as part of a request for help in an emergency.  If time is short, 
it would be better to send the already known location than to have to 
wait for the location determination in addition to the emergency 
response time.

Another value of enabling the host to determine its own location, and 
send it where it wants when it wants, is that it enables each host to 
perform this determination at its own discretion.  Relying on a 
Location Server to determine location during an emergency introduces 
the risk that my request arrived at shared Location Server at the tail 
end of a burst of requests.  The unnecessary sharing of the location 
determination process would add an unpredictable delay.

> > that the only time a package of geographic information
> > like the one specified in RFC 3825 should be transmitted
> > to an Internet host would be when it gets its IP address. 
> > The timing of when a host requests its location seems to
> This raises an interesting point that location by-reference handles 
> rather well.  Since location information is a continuous datum that 
> could change constantly, timeliness of information is particularly 
> pertinent. 

If a target's location is changing constantly, it seems to me that the 
location determination process will face a challenge in any case. Who 
would you prefer to control when the determination takes place, the 
owner or the other party?  Remember that the user's control over their 
location information is the point of GeoPriv.

>  For this reason, polling approaches as you recommend are less than 
> optimal. 

I have not recommended a polling approach. Location values as well as 
location references can be requested on demand.

>  The SIP location event package proposed by Rohan highlights this 
> quite well.  Location by-reference gives a user of location 
> information (for now, just assume that this could be anyone, including 
> the target) the ability to request location information when it is 
> needed only.  Requesting when needed means that the information is 
> timely, and that the resources required to determine location are only 
> expended as necessary.

The location-by-reference approach puts control over how timely and 
accurate the location determination is, which may trade off against the 
expense of performing the determination under the location server. The 
alternative allows the user to expend resources differently to suit 
different purposes.

The essential philosophical difference is who is to be empowered with 
information location, the user or the party that wants to learn the 
user's location?  I guess there is another possibility - empowering the 
operator of the location server, but that should be a non-goal.

John