Re: [sipcore] location-conveyance-03 just submitted

I was hoping this would settle out the right way, but alas....

First of all, I don't think value + reference from the same source is really all that important.  It can be accomplished with a reference that returns what the value would have been to unauthenticated dereferencers.  It's more efficient to use value+reference, but not by much.

However. in the end, I think (despite my being a coauthor), the mechanism in -03 is insufficient.  If you want to treat emergency call as a corner case, that is okay, but it's an important one.

I don't think intermediaries will 424 and ask the UAC to compose something they like.  I think they will drop the existing header and replace it with what they want it to be.  

I think the requirement is either two PIDFs in one geolocation header, or or two parameters in one header.  That get us into "used for routing", but assuming the intermediary will 424 rather than replace is, in my opinion, fantasy.

Brian

On Jul 25, 2010, at 10:18 AM, Thomson, Martin wrote:

> I feel like some of this is old ground, but I chalk that up to you doing all these replies while you were offline.
> 
> (I'll note that some of your recent responses are in response to emails that you have already responded to.)
> 
>>> Dynamism is the easiest one to pin down.  It's
>>> obviously very important to the emergency
>>> scenario - the ability of a PSAP to acquire
>>> updated location information in a timely fashion
>>> is central to many of their use cases.
>> 
>> Martin - how long are you expecting this initial
>> INVITE to go from the UAC to the PSAP?
>> 
>> You're giving the impression that a second or two
>> matters or the UAC will be in a completely
>> different location, meaning the wrong PSAP will be contacted.
> 
> It's not the transit time that is the problem, it’s the uses of location after that.  The call can certainly last longer than a few seconds.
> 
>>> In either case, it's possible to leave the
>>> intermediary out of consideration and
>>> concentrate on the information that the UAC provides.
>> 
>> but what about environments (or networks) that
>> don't trust the UE (or UAC) at all. I'd argue
>> that's much more probable -- because that's how 3GPP treats their
>> phones.
> 
> Then they have some reconsidering to do in how they deploy this spec.  There are methods for dealing with this that might be more practical in those environments, but less so on the wider Internet.  Digital signatures, for example.
> 
> ... 
>>> The interactions with the intermediary add
>>> complexity to the scenario, including some
>>> privacy model problems, primarily with retransmission.
>> 
>> meaning UDP vs TCP?
> 
> Meaning <retransmission-allowed>.  I would hope that people know how to use UDP and TCP by now.
> 
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