Re: [Gen-art] Gen-ART LC review of draft-ietf-geopriv-http-location-delivery-07

"Mary Barnes" <mary.barnes@nortel.com> Fri, 16 May 2008 19:44 UTC

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From: "Mary Barnes" <mary.barnes@nortel.com>
To: "Ben Campbell" <ben@estacado.net>
Cc: Cullen Jennings <fluffy@cisco.com>, Jon Peterson <jon.peterson@neustar.biz>, General Area Review Team <gen-art@ietf.org>, james.winterbottom@andrew.com, "Stark, Barbara" <bs7652@att.com>, martin.thomson@andrew.com
Subject: Re: [Gen-art] Gen-ART LC review of draft-ietf-geopriv-http-location-delivery-07
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Hi Ben,

Just a few more comments embedded below [MB3], again snipping what I
think we've agreed. 

Mary.

-----Original Message-----
From: Ben Campbell [mailto:ben@estacado.net] 
Sent: Wednesday, May 14, 2008 1:30 PM
To: Barnes, Mary (RICH2:AR00)
Cc: General Area Review Team; Robert Sparks; Jon Peterson; Cullen
Jennings; james.winterbottom@andrew.com; martin.thomson@andrew.com;
Stark, Barbara
Subject: Re: Gen-ART LC review of
draft-ietf-geopriv-http-location-delivery-07


On May 14, 2008, at 11:24 AM, Mary Barnes wrote:

> Hi Ben,
>
> Thanks for the response. Additional responses are embedded below 
> [MB2].
> I've snipped the things with which we have agreement to keep the 
> thread a bit shorter.
>
> Mary.
>
> -----Original Message-----
> From: Ben Campbell [mailto:ben@estacado.net]
> Sent: Friday, May 09, 2008 3:35 PM
> To: Barnes, Mary (RICH2:AR00)
> Cc: General Area Review Team; Robert Sparks; Jon Peterson; Cullen 
> Jennings; james.winterbottom@andrew.com; martin.thomson@andrew.com; 
> Stark, Barbara
> Subject: Re: Gen-ART LC review of
> draft-ietf-geopriv-http-location-delivery-07
>
> Further comments inline:
>
> Thanks!
>
> Ben.
>
> On May 9, 2008, at 2:02 PM, Mary Barnes wrote:
>
>> Hi Ben,
>>
>> Thank you for your detailed review. After consulting with the 
>> contributors, we've come up with the responses embedded below [MB].
>>
>> Thanks,
>> Mary.
>>
>> -----Original Message-----
>> From: Ben Campbell [mailto:ben@estacado.net]
>> Sent: Tuesday, May 06, 2008 5:02 PM
>> To: Barnes, Mary (RICH2:AR00); james.winterbottom@andrew.com; 
>> martin.thomson@andrew.com; barbara.stark@bellsouth.com; General Area 
>> Review Team
>> Cc: Robert Sparks; Jon Peterson; Cullen Jennings
>> Subject: Gen-ART LC review of
>> draft-ietf-geopriv-http-location-delivery-07
>>
>> I have been selected as the General Area Review Team (Gen-ART) 
>> reviewer for this draft (for background on Gen-ART, please see 
>> http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html).
>>
>> Please resolve these comments along with any other Last Call comments

>> you may receive.
>>
>>
>> Document: draft-ietf-geopriv-http-location-delivery-07
>> Reviewer: Ben Campbell
>> Review Date:  2008-05-06
>> IETF LC End Date: 2008-05-07
>> IESG Telechat date: (if known)
>>
>> Summary:
>>
>> This document is almost ready for publication as a proposed standard.
>> I have a few questions and comments that should be considered prior 
>> to
>
>> publication.
>>
>> Comments:
>>
> ----snipped by mary for [MB3] responses
>
>
>>
>>
>> Section 4.3.1: Should there be normative advice in this section?
>> [MB] I'm not clear as to whether you're suggesting we should or 
>> should
>
>> not have normative text in this section. We do have normative 
>> statements in the first paragraph, but there aren't in the second.
>> Part of the issue is this text was carefully crafted as a result of 
>> WG
>
>> consensus, thus it's perhaps not as strong as some would like. The 
>> language was softened in this section during the -03 to -04 changes.
>> The justification was that we can't mandate behaviors on elements 
>> unless it's specific to the actual protocol. [/MB]
>
> So I reread the section, and cannot actually find the place I thought 
> needed more normative behavior--I think it was a misread on my part.
> However, in the process of re-reading it, I wonder if there is not a 
> conflict between the normative advice about the client performing 
> discovery prior to the establishment of the VPN, and the architectural

> advice about what VPN device behavior, since if the device follows the

> recommended behavior the VPN response to discovery would never get 
> excercised.
>
> I am guessing the intent is to say that the special "closed network"
> guidance is for situations where one might have a good reason to 
> ignore the RECOMMENDED advice about client behavior. If that is 
> correct, some more precise words to that effect might help.
>
> [MB2] The second paragraph in section 4.3.1 is actually independent of

> the first (in some sense).  The first paragraph is saying that if you 
> use a VPN Tunnel (like I do when I work from home), you really should 
> determine your Location before you setup your tunnel.  The second 
> paragraph builds on that concept and is describing a configuration 
> whereby another entity that establishes a VPN (i.e., the devices 
> aren't aware that a VPN is being used) serves as the LIS for those 
> Devices, rather than tunneling location requests to a LIS that might 
> not be geographically relevant.
>
> In the first paragraph we do specify what might happen if you don't 
> follow the RECOMMENDED behavior - you might not get the right location

> (eg., in my case the firetruck goes to Richardson instead of Flower 
> Mound right now). Maybe your concern is that we don't re-iterate that 
> same point for the second paragraph (i.e., if the VPN device doesn't 
> serve as a LIS and just tunnels those requests, many devices will get 
> the wrong location).

I think maybe the key point that needs more emphasis is that the second
paragraph is for situations where the device is not aware of the VPN
being used.

[MB3] So, I will add the following to the end of the second paragraph:
   Otherwise, the other devices would be totally unaware that they 
   could receive inaccurate location information. 
[/MB3]


>
>
> [/MB2]
>
>>
>>
>> Section 6.2 and 6.2.1: I don't see an obvious way to say I only want 
>> to get location by value. Is that intentional?
>> [MB] Correct. You cannot ask for just "any" location by value. You 
>> can
>
>> ask for just one type of location or both types using "exact", but 
>> you
>
>> can't do an either/or.  If you want either/or, then you may also get 
>> a
>
>> locationURI by just using "any". It makes the protocol slightly more 
>> complicated to allow that, when it didn't seem like that would be a 
>> high runner - e.g., if neither of the location by values were 
>> available, then wouldn't you want to use a locationURI, so this in 
>> the
>
>> end could save on the number of requests at the cost of sometimes 
>> getting more information than you want. [/MB]
>
> Just to make sure I understand: You can request lbyr only, by 
> asserting "locationURI" and "exact", but there is nothing I can 
> combine with "exact" to get me by-value only. Does that mean that you 
> assume it possible to have devices that only understand lbyr, but not 
> common to have devices that only understand lbyv? Or that sending by 
> value when the device doesn't want it is somehow more damaging than 
> sending by reference if the device doesn't want it?
>
> On re-reading the section, I think it would be helpful to talk a 
> little more about how the values can be combined. I am somewhat 
> confused by the fact that the class of location (geodetic, civic,etc) 
> is combined with the way it is transmitted (by value or by reference.)

> Are these not orthagonal?
>
> [MB2]
> Part of the confusion may be due to your nit on the text in that 
> section. I've proposed some modified text below that I think clarifies

> things. I've also added an additional statement about this point.
>
> [/MB2]

On rereading that section and your proposed changes, it did not help me
with the answer to _this_ comment, that is, why are we overloading the
type of location with the delivery mode. On reflection, though, I think
I may understand a piece of this, so see if this makes sense:

An effect of sending location by value is that the actual location type
may not be determined until the time of dereference. That is, the LIS
might only have a geodetic location available when it sends a URI, but
by the time the location recipient dereferences the URI, it may only
have a civic address. Does that make sense? Is there any expectation
that any location type preferences (i.e. geodetic vs
civic) expressed in the HELD query be honored at dereference time? I
suppose the dereferencer could assert entirely different preferences.

[MB3] I think you meant to say "An effect of sending location by
reference...(rather than value)..."
But, other than that, what you say makes sense. At the time the location
URI is provided, there is not necessarily a binding to a specific
location type. The specific location type is determined at the time of
dereference. And, yes, the dereference protocol allows the dereferencer
to specify the type of location they prefer. The use of the location URI
as defined in this base HELD spec is totally independent of the specific
type of location it might reference. Do you think we need to add
something somewhere to say this? 
[/MB3]

>
>>
>>
>> 6.6, last paragraph:
>>
>> "Note that the presence parameter is not explicitly shown in the XML
>>   schema Section 7 for a location response message due to XML schema
>>   constraints."
>>
>> Is that not a problem, since section 7 is the formal definition of 
>> the
>
>> protocol syntax?
>> [MB] Maybe we should change this to read:
>>   "Note that the presence parameter is not explicitly shown in the 
>> XML
>>   schema Section 7 for a location response message due to XML schema
>>   constraints related to the PIDF namespace.  Thus, the "##other"
>> namespace serves
>>   as a placeholder for the presence parameter in the schema."
>> [/MB]
>
> Okay, I guess. I am probably showing my ignorance of XML schema here.
> It just seemed strange that what I thought was an important data 
> structure for this protocol is left out of it's formal schema. I don't

> really understand schema enough to grok the "schema constraints"
> causing the issue.
>
> [MB2] I'm not an XML guru either, but my understanding is that since 
> the schema we're wanting to use is already defined elsewhere, we don't

> want to duplicate that definition. But, since PIDF is defined already,

> we can explicitly use it per the examples. [/MB2]

Ah, maybe explaining that explicitly when you mention "XML schema
constraints" would help.

[MB3] Okay, I'll change that text to the following rather than what I
originally suggested:
"Note that the presence parameter is not explicitly shown in the 
 XML schema Section 7 for a location response message, due to XML
 schema constraints (since PIDF is already defined and registered
separately).
 Thus, the "##other" namespace serves
 as a placeholder for the presence parameter in the schema."
[/MB3]


>
>
>>
>>
>>
>>
>> Section 8:
>>
>> I'm a little confused by the fact that a HELD URI can show up both in
>> a HELD response, and in LIS discovery. Does this use of a HELD URI
>> imply the use of the HELD protocol? If so, how would a HELD URI in a
>> locationReponse message be used? Since HELD uses the source IP  
>> address
>
>> for the identifier, it is not useful to transmit the URI to another
>> device, right?
>>
>> [MB] The HELD URI is defined as a fairly general URI that can be used
>> both to provide the URI for a LIS and to provide the URI associated
>> with a specific location.  And, there may be other uses - the obvious
>> one being the dereference. The correlation of the source IP address  
>> to
>
>> a specific location URI isn't something specific to HELD - it's the
>> LIS that determines the location (using source IP address) and then
>> provides the LIS associated location URI in the response.  This
>> document doesn't provide a complete description of the usages of the
>> URI (e.g.,
>> dereference) and it's not the intention to do so, so maybe that's the
>> confusion. The use of the HELD URI within this document is limited by
>> the functionality defined in this document, but shouldn't necessarily
>> limit the use of the HELD URI overall (if that makes sense). Perhaps
>> adding something like the following at the end of that first  
>> paragraph
>
>> would help:
>> NEW:
>> There are other uses of the HELD: URI, such as
>> [I-D.winterbottom-geopriv-deref-protocol].
>> Thus, the usages of the HELD: URI described in this document are not
>> intended to limit the applicability of the HELD: URI to other  
>> relevant
>
>> interfaces.
>>
>> [/MB]
>
> To test my understanding: The deref protocol is a completely different
> protocol than HELD, but the HELD URI semantics work there as well?
> That is to say, that the dereferencer is _not_ using HELD per se, but
> the URI is still useful? I was assuming that the URI type implied the
> use of HELD, which didn't seem to make sense for dereference due to  
> the
> binding to source IP.
>
> [MB2] The only dereference protocol defined right now is based on  
> HELD,
> but it doesn't have to be.  And, again there are different set of
> requirements to be supported by the deref protocol, which are not
> required to be supported by HELD as specified in this document. [/MB2]

I'm still a little confused, so let me ask some architectural  
questions that go beyond this draft. Apologies for not having studied  
the dereferencing draft:

HELD identifies the device whose location is of interest by the source  
IP address of the request. This has the consequence that a device can  
only query for its own location. But I assume that device  
dereferencing lbyr is usually _not_ the principal device; that is,  
dereferencing is usually done by a third part. Does the dereferencing  
draft somehow extend HELD to allow for third party queries?

[MB3] Yes, the dereference draft does extend HELD to allow for
third-party queries, making use of the "other identifiers" deemed out of
scope for this document (there's yet another document that extends HELD
to use other identifiers).  So, other identifiers are outside the scope
of HELD as defined in this base document and the details of dereference
are outside the scope, even though the dereferencing does make use of
the HELDS: URI defined in this document. So, maybe modifying the NEW
text I suggested above might help:
NEW:
   There are other uses of the HELD: URI, such as
   [I-D.winterbottom-geopriv-deref-protocol].
   Thus, the usages of the HELD: URI described in this document are not
   intended to limit the applicability of the HELD: URI to other  
   relevant interfaces, but are necessarily restricted in scope 
   in this document to the use for the base HELD protocol. 
[/MB3]


>
>
>
> I have some mild confusion over making the URI scheme "held" when the
> URI is generally useful across other protocols, but it's probably not
> worth pushing this late in the process (and in my experience the only
> way to win "naming" games is not to play, sort of like for  global
> thermonuclear war.)
>
> [...]
>
>>
>>
>> Section 6.2. "any" value: The normative statement that the LIS SHOULD
>> return all available forms seems to mildly conflict with some of the
>> further normative statements in the paragraph.
>> [MB] I'm not sure where the conflict is here.  They are all SHOULDs
>> with a couple MAYs and the last paragraph explains the reason for the
>> SHOULDs. [/MB]
>
> [ Warning: this is highly pedantic--which is why I offered it as a nit
> rather than as a substantive comment.]
>
> I was reading it to say you SHOULD send everything you have, and going
> on to say you SHOULD send certain forms and MAY send others. Since
> anything I could possibly send must be a subset of "everything I  
> have",
> then the second SHOULD and the MAY are either non-constraining, or a
> relaxation of the initial SHOULD.
>
> I would propose either removing the first SHOULD (and maybe indicating
> how sending everything you have by definition fulfills the rest of the
> normative requirements), or making everything except the SHOULD send
> everything you have non-normative.
>
> Of course, it's possible that I am interpreting "SHOULD attempt to
> provide LI in all forms available to it" incorrectly.
>
> [MB2] The SHOULDS and MAYs below the list of specific types was  
> intended
> to apply to all the types, but really mostly apply when you request a
> specific type, since any: really does what the LIS wants to do. So,
> maybe we should clarify that and break that paragraph into the general
> statements and the statements specific to when a specific
> locationType(s) is/are requested (and the last paragraph also applies
> just to the request for specific locationType(s).

Ah, I'm not sure we are talking about the same language. My comment  
was entirely aimed at the language defining "any", not the general  
language following the list of values. (although I do think your  
proposal improves the general section.)

[MB3] I think the problem was because we had tacked on additional
normative text to the any: in the list, without necessarily considering
the text we had that was applicable to any in the lower paragraphs, thus
causing some inconsistencies. [/MB3]

>
> OLD:
>   The LIS SHOULD return the requested location type or types.  The LIS
>   MAY provide additional location types, or it MAY provide alternative
>   types if the request cannot be satisfied for a requested location
>   type.  A location URI provided by the LIS is a reference to the most
>   current available LI and is not a stable reference to a specific
>   location.  The location types the LIS returns also depend on the
>   setting of the optional "exact" attribute, as described in the
>   following section.  The LIS SHOULD provide the locations in the
>   response in the same order in which they were included in the
>   "locationType" element in the request.
>
>   The "SHOULD"-strength requirements on this parameter are included to
>   allow for soft-failover.  This enables a fixed client configuration
>   that prefers a specific location type without causing location
>   requests to fail when that location type is unavailable.  For
>   example, a notebook computer could be configured to retrieve civic
>   addresses, which is usually available from typical home or work
>   situations.  However, when using a wireless modem, the LIS might be
>   unable to provide a civic address and thus provides a geodetic
>   address.
>
> NEW:
>   The LIS SHOULD return the requested location type or types.
>   The location types the LIS returns also depend on the
>   setting of the optional "exact" attribute, as described in the
>   following section.  The "exact" attribute does not apply (is
>   ignored) for a request for a location type of "any".
>
>   In the case of a request for specific locationType(s)
>   and the "exact" attribute is false, the LIS MAY
>   provide additional location types, or it MAY provide alternative
>   types if the request cannot be satisfied for a requested location
>   type.  The "SHOULD"-strength requirements on this parameter for
>   specific location types are included to
>   allow for soft-failover.  This enables a fixed client configuration
>   that prefers a specific location type without causing location
>   requests to fail when that location type is unavailable.  For
>   example, a notebook computer could be configured to retrieve civic
>   addresses, which is usually available from typical home or work
>   situations.  However, when using a wireless modem, the LIS might be
>   unable to provide a civic address and thus provides a geodetic
>   address.
>
>   It should be noted that the protocol does not support a request to
>   just receive just one of a subset of location types. For example,
>   in the case where a Device has a preference for just "geodetic" or
>   "civic", it is necessary to make
>   the request without an "exact" attribute, including both location
> types.
>   In this case, if neither is
>   available a LIS SHOULD return a locationURI if available.
>
>   A location URI provided by the LIS is a reference to the most
>   current available LI and is not a stable reference to a specific
>   location.   The LIS SHOULD provide the locations in the
>   response in the same order in which they were included in the
>   "locationType" element in the request.
>
> It might also be much nicer at this point to pull all that text for  
> any:
> (which grew based on feedback during WGLC) into it's own paragraph or
> the end of the first (really just leaving that first sentence).
> [/MB2]

I almost wonder if some sort of table showing possible results for  
each combination of values might be useful here.

[MB3] I'm not sure a table would help due to the numerous possible
combinations and the fact that the order also matters. Although, if you
think it's useful and illustrative, then we could add something like the
following: 

   In summary, when the "exact" attribute is not used, the only
advantage of specifying specific 
   locationTypes in the request is to ensure that one gets the available
locations in a specific order,
   since the LIS SHOULD return all the available location types. For
example, a location request for
   "civic" could yield any of the following location types in the
response:
   - civic
   - civic, geodetic
   - civic, locationURI
   - civic, geodetic, locationURI
   - civic, locationURI, geodetic
   - geodetic, locationURI (only if civic not available)
   - locationURI, geodetic (only if civic not available)
   - geodetic (only if civic not available)
   - locationURI (only if civic not available)

   For the above example, if the "exact" attribute was true, then the
only possible response is a 
   "civic" location or an error message. 

[/MB3]
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