Subject: Re: [Geopriv] Naive question: LCP == LbyR?

From: Hannes Tschofenig <[email-masked]>
Date: Sat, 10 Mar 2007 21:46:58 +0200

Hi Richard,

you raised a very good question and I have a short story for you.

Other SDOs look at the location-based services in a different fashion by 
assuming that the network understands the application. Consider the 3GPP 
IMS emergency service architecture as one more detailed example.

You need a protocol to fetch the location of an end host. The 
identification of the end host for location determination might use a 
variety of different identifiers, as we all know (MAC address, IP 
address, etc. see draft-ietf-geopriv-l7-lcp-ps-00.txt).

The end host provides these identifier via, for example, SIP signaling 
to the respective nodes that perform the lookup. No new identifier needs 
to be "invented" there since the existing onces do the job, namely the 
identifiers are resolvable to the location of the end host within this 
given realm.

Now, we have assumed a different architecture where the entity that 
needs todo the lookup is from a different identifier realm (i.e., it 
cannot resolve the existing identifiers to the location of the end 
host). (Note that by realm I mean that an identifier has a specific 
validity domain and semantic within this  domain. We phrased this quite 
fuzzy, for example, by saying that the LIS is in the access network and 
somehow knows how to determine the location of the end host even though 
we encountered cases where this is not true.)

What did we do?

We came up with a different identifier that has a much larger validity 
domain, a SIP URI or an HTTP URI. This is not a big thing but quite 
important. This identifier that is used as a replacement of other 
identifiers that have a limited scope allows everyone on the Internet 
(with some assumptions behind it) to perform the lookup and to determine 
the location of the end host.

Ironically, if you demand authorization for the resolution process you 
almost destroy all benefits of the newly introduced new identifier since 
you artificially re-create the relationship between the entity that is 
able to perform the resolution and the entity that knows where the end 
host is.

So, how does this all relate to your question regarding LCP == LbyR?

Ignoring some terminology aspects, and comparing LCP that retrieves an 
LO based on IP address/MAC address/etc. and a protocol that uses an HTTP 
reference to retrieve an LO one might notice that they do very similar, 
if not the same things (ignoring the scope of the identifier validity).

Does this make sense?

Ciao
Hannes

Richard Barnes wrote:
> I've got a simple question, that's basically captured by the subject 
> line: What's the difference between a Location Configuration Protocol 
> and an L-by-R Dereference Protocol?  Compare two use cases:
>
> LCP:
> Step 1. Discover LIS
> Step 2. Send query to LIS
> Step 3. Receive LO / URL
>
> L-by-R:
> Step 1. Receive location URL
> Step 2. Send query to dereference server
> Step 3. Receive LO / URL
>
> I realize that with an LCP, there's a additional need to identify the 
> target, but it seems just as easy to embed this into a URI or 
> dereference request as  to use another protocol mechanism.  And it 
> seems like using a single protocol for both would save us all some 
> time and effort.
>
> Cheers,
> --Richard
>
>
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> Geopriv mailing list
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