Re: [Geopriv] Location-by-value in a SIP Location Header

James M. Polk wrote:
> Henning
> 
> Remind us what the unique use-case is for a data URL, where neither a 
> by-reference URI nor a by-value PIDF-LO can be used?

The use case is proxy-inserted location, where the proxy does not have 
access to a globally-accessible HTTP server where it can deposit this 
information. This could be a proxy behind a (corporate) firewall or NAT, 
for example.


> 
> In other words, why is this needed, and what would it be used for that 
> every element necessary couldn't use one of the two methods of Location 
> Conveyance already specified in the doc?

See above. The incremental complexity is essentially zero.

> 
> Complexity is an issue in location conveyance - especially during 
> emergency calling, but I've heard you state this isn't an issue with a 
> data URL.  Are you sure?  Are others sure?

I don't get your complexity point. The complexity of a data URL is 
likely to be significantly lower than

- setting up a custom web server outside the security or NAT perimeter
- that allows remote writes by the proxy server
- using a proxy-to-webserver protocol that isn't standardized
- using a webserver-to-proxy protocol (to get the object identifier 
back) that isn't standardized, either
- automatically cleaning up location state just at the right time (not 
too early to avoid resolution problems and not too late to avoid 
exposure and denial-of-service problems where the attacker uses bogus 
SIP INVITEs to create lots of location entries)
- and hoping that the server is always accessible, so that emergency 
calls don't fail

The data URL solution is self-contained; the reference solution is 
basically of the "and then magic happens" kind, where the proposed 
solution only provides a tiny part of what's needed to actually build a 
real system.

Henning

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