Re: [sipcore] Location Conveyance -04 submitted, here's the changes

"James M. Polk" <jmpolk@cisco.com> Wed, 27 October 2010 19:02 UTC

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Date: Wed, 27 Oct 2010 14:04:31 -0500
To: "Elwell, John" <john.elwell@siemens-enterprise.com>, "James M. Polk" <jmpolk@cisco.com>, "sipcore@ietf.org" <sipcore@ietf.org>
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Subject: Re: [sipcore] Location Conveyance -04 submitted, here's the changes
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At 08:17 AM 10/27/2010, Elwell, John wrote:
>I am happy to see that http and https are added as schemes in 
>locationURI. However, looking at 4.6, I am still uncomfortable that 
>SIP-, SIPS- and PRES-URI are recommended and but HTTP- and HTTPS-URI 
>are not recommended (by virtue of the fact they are only MAY 
>strength, for use when one disregards the SHOULD for SIP-, SIPS- and PRES-).

well... this is a SIP document, why shouldn't a SIP-based URI be 
recommended? Do you want me to say HTTP:/HTTPS: is allowed in some other way?


>We had an earlier thread starting here:
>http://www.ietf.org/mail-archive/web/sipcore/current/msg03149.html
>in which questions were asked about what one must support. The text 
>in 4.6 says nothing about what a LR must support. The implication is 
>that it either has two support all of the 5 schemes listed for 
>sending in a request, or it can choose which to support and reject 
>any that it doesn't support.

right now it is the latter, but I would - if I must - propose making 
SIP:/SIPS:/PRES: mandatory if there is any URI scheme that is (again, 
this is a SIP doc).


>In practice, as pointed out on the thread, the schemes effectively 
>boil down to 2 mechanisms: SIP and HTTP (if we for now ignore the 
>absoluteURI option, which effectively leaves it open ended). So 
>perhaps it is not unreasonable to mandate support for all 5 schemes 
>(both mechanisms) by a recipient, although it does raise the bar 
>somewhat for recipient implementations.

Several of us have and currently believe that is raising the bar a 
little too high.

>I recall there was some interest on the thread in limiting to a 
>single MUST support, and some interest in that scheme being HTTP(S). 
>I am not sure we reached consensus on this. I don't have a strong 
>opinion, but we certainly need some text to clarify things one way 
>or the other.
>
>Furthermore, it is unclear which code to use in a 494 response when 
>rejecting an unsupported scheme - presumably the top level 400, but 
>that says nothing about why dereference failed. Even if all the 
>named schemes were MUST support (so you would never reject these), 
>there could be other schemes under absoluteURI that you would want to reject.

The conclusion from the San Diego adhoc bof on this ID was to limit 
the number of error types to specific different actionable ones. At 
that adhoc, I had roughly 22 different error types, one set included 
the ability to indicate which URI scheme wasn't supported and which 
ones were. That idea was roundly rejected (most strongly by our 
newest co-author Jon Peterson).  I believe it was Henning (and maybe 
Hannes) that wanted the error codes limited as well, and to allow 
this RFC-to-be to be extended with an XML body in the response that 
included a much more detailed error explanation and ways detailed in 
how to resolve the problem.

No one has written that ID yet, so I don't know where that thought is now.

That said, -04 doesn't have a 494 response articulated because 
location specific rejections are for the 424 (Bad Location 
Information) response. Jon and I talked just last week about what do 
we do when an LR supports one URI scheme and receives another URI 
scheme (i.e., supports SIP:/SIPS:/PRES: URIs but gets an HTTP:/HTTPS: 
URI). We couldn't come up with anything that didn't have a lot of 
holes in it, so we left it for now.

James


>John
>
>
> > -----Original Message-----
> > From: sipcore-bounces@ietf.org
> > [mailto:sipcore-bounces@ietf.org] On Behalf Of James M. Polk
> > Sent: 27 October 2010 05:32
> > To: sipcore@ietf.org
> > Subject: [sipcore] Location Conveyance -04 submitted, here's
> > the changes
> >
> > SIPCORE
> >
> > I've submitted the next version of Location Conveyance (-04)
> > http://www.ietf.org/internet-drafts/draft-ietf-sipcore-locatio
> > n-conveyance-04.txt
> > and I believe this version has addressed each open item from the
> > mailing list, as well as what was discussed and agreed to in the
> > Maastricht meeting.
> >
> > I have attempted to identify each open issue with the specific
> > resolution here (in no particular order):
> >
> > - Martin wanted Section 3 to be broken up into subsections, each
> > revolving around each of the 4 diagrams. I have done this.
> >
> > - allowed a maximum of two (up from one) locationValues to be present
> > in the Geolocation header value. The text however recommends against
> > inserting a second value. This was agreed to in Maastricht.
> >
> > - Because we're allowing a max of two locationValues, they can be in
> > separate Geolocation headers in the SIP request. This scenario
> > necessitates bring a previous version's paragraph in stating that a
> > 'SIP intermediary MUST inspect all instances of each Geolocation
> > header before considering the routing-allowed parameter to be
> > considered =yes', to ensure there isn't a conflict in the 'other'
> > Geolocation header that states the policy is =no.
> >
> > - with the ability to add a second locationValue, it is necessary to
> > warn against doing this (confusion at the LRs).
> >
> > - Added the "you break it you bought it" philosophy to SIP
> > intermediaries that choose to insert a second location where one
> > already existed, especially for inserting a location URI in the
> > downstream SIP request.
> >
> > - Fixed the ABNF to handle zero, one or two (but no more)
> > locationValues according to the agreement in Maastricht.  There is a
> > one-off use case which won't be in play very often, but is a WG item
> > in ECRIT that several wanted to allow the possibility for (involving
> > allowing one coarse and one highly accurate location in the
> > same SIP request).
> >
> > - Paul K. wanted the use-case in which a SIP intermediary inserts a
> > locationValue where one didn't exist previously, and received a 424
> > (Bad Location Information) to that inserted location, from having the
> > 424 propagate towards the UAC (as the UAC might not know what to do
> > with a 424). This is now covered in Section 4.3.
> >
> > - changed existing text to "MUST NOT" from "does not" about a 424 not
> > terminating an existing dialog (just increased the strength of this.
> >
> > - I added the 424 to the table 2 entry in which the Geolocation
> > header can be in only this response.
> >
> > - I added text stating the conditions for adding a Geolocation header
> > value to the 424, to make it clear what is and what isn't
> > allowed for this.
> >
> > - Martin wanted me to add back in the top level Geolocation-Error
> > codes 100, 200, 300 and 400, which I did in section 4.3.
> >
> > - rejected the idea that the geolocation option-tag hasn't
> > been justified.
> >
> > - Added RFCs 2616, 2818 and HELD Deref ID to the references section
> > because I added the ability to include HTTP: and HTTPS: URIs, and
> > stated if received, they should be dereferenced according to the HELD
> > Deref doc.
> >
> > - changed the Section 5 examples how Martin wanted them.
> >
> > - Stated that GEO-URIs are not appropriate for the SIP Geolocation
> > header, according to the discussion during the Maastricht
> > Geopriv meeting.
> >
> > - we changed the privacy section, and included a ref to the Geopriv
> > Arch doc, according to the agreement in Geopriv at Maastricht.
> >
> >
> > Comments are encouraged
> >
> > We plan to request (3rd?) WGLC during the SIPCORE meeting in Beijing
> > (to give folks a sense of our plans).
> >
> > James/Brian/Jon
> >
> >
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> >