Re: [Geopriv] Location in SIP and "retransmission-allowed"

From: Henning Schulzrinne ^lt;hgs@cs.columbia.edu>
Date: Wed May 02 2007 - 09:04:20 EDT

Another thought on this topic, which seems to have gotten lost. In
the end, this is all about trust. We sometimes have the notion that
SIP proxies are kind of like routers, operated by random entities
that we don't control. However, that's a clear misunderstanding of
how SIP request routing works. Those familiar with SIP will have seen
the SIP trapezoid picture, consisting of a proxy in the outbound
domain (typically, my VSP) and in the destination domain.

For the topic at hand, as I noted, there are two cases:

(1) The destination URL is a service URN. If not resolved by the UA,
it needs to be resolved by the very first (outbound) proxy. Thus,
this proxy needs to do a location-based lookup. There simply is no
choice other than failing the call, assuming that there is no
worldwide catch-all call center for that service. Thus, any privacy
indication in this case is simply a waste of time, since you might as
well have a "fail this call, please" flag.

(2) The second case is that of a second-level resolution, i.e., after
the service URN has been resolved to a specific SIP URL. This could
be the emergency service network or PizzaHut's internal network. In
other words, this occurs if I place a call so
sip:deliver@pizzahut.com which is then delivered to
sip:brooklyn@nyc.pizzahut.com, say.

In this second case, however, the trust domain for the UA and the
proxy is exactly the same organization. In other words, as a caller,
I have decided to hand my location information to PizzaHut so that
they can deliver their service to me. The proxy is owned by PizzaHut.
Thus, it seems rather strange that I would give PizzaHut my location
information for pizza delivery, but not to route the call. This gets
even stranger if it were ok that PizzaHut were to operate a back-to-
back UA, extract the information, and then, as a UA, re-issue the
call. On top of that, in this particular case, the LoST server
hierarchy is likely to be operated by PizzaHut, too.

I think we need to rely on organizational boundaries, rather than
whether there's an Ethernet cable between the proxy and the location
lookup service or other angels-on-a-pin distinctions. As far as I
know, all privacy restrictions in the real world operate like that.
In other words, the typical privacy rule that (a good) company X has
is something like "we'll use the information you provide us with as
necessary to provide the service you contracted for, but we won't
hand the information to third parties, unless compelled to do so by
law, or to our marketing department unless you opt in".

Henning

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Received on Wed, 2 May 2007 09:04:20 -0400

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