Re: [Geopriv] Long review of draft-ietf-geopriv-loc-filters-07

RFC 4661 allows you to request a notification if a value changes _to_ a value, _from_ a value, or _by_ a certain amount. For speed, you could specify <changed to="360"> to request notification if the speed changes to 100 km/h, however there's a good chance that it goes straight past the value you are interested in.

It's impossible to specify every possible target value for something continuous like speed or position. You could cover 341, 342, 343, ..., 368, 369, 370, but when the value comes up at 364.3, you still miss the notification.

The <changed by="x"> element can be used for most use cases, although some complications are inevitable. The advantage is that this is pretty simple and, for those with a 4661 implementation, zero cost. Think of it as an opportunity for other specifications to define better filters.

--Martin

> -----Original Message-----
> From: geopriv-bounces@ietf.org [mailto:geopriv-bounces@ietf.org] On
> Behalf Of Hannes Tschofenig
> Sent: Wednesday, 4 November 2009 11:30 AM
> To: 'Brian Rosen'; 'James Polk'; geopriv@ietf.org
> Subject: Re: [Geopriv] Long review of draft-ietf-geopriv-loc-filters-07
>
> Hi James,
>
> Thanks for your detailed review. I am in the process of updating it and
> have
> comments here and there.
>
> Here is one:
>
> Draft Text:
>
> --------
>
> <?xml version="1.0" encoding="UTF-8"?>
> <filter-set xmlns="urn:ietf:params:xml:ns:simple-filter">
> <ns-bindings>
> <ns-binding prefix="dyn"
> urn="urn:ietf:params:xml:schema:pidf:dynamic"/>
> </ns-bindings>
> <filter id="123" uri="sip:presentity@example.com">
> <trigger>
> <changed by="3"> [<---James]
> //dyn:speed
> </changed>
> </trigger>
> </filter>
> </filter-set>
>
> ------
>
> [James]
>
> I get the XML,
> but I don't see what the speed now is of
> the device/target?
> What if this device is moving at 200kmph,
> where would that be placed in the XML?
> Of, is this left for the application at the
> subscriber to calculate?
> If the latter is true, something needs to be
> said about this expectation.
>
> ------
>
> The filter would not tell you what the current speed is.
>
> The current document only supports 'by' and hence you cannot say
> something
> like 'tell me when he goes faster than 100kmph'.
>
> Ciao
> Hannes
>
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