Re: [sipcore] draft-ietf-sipcore-location-conveyance-04
Anders Kristensen <ankriste@cisco.com> Thu, 28 October 2010 04:51 UTC
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Date: Wed, 27 Oct 2010 21:52:37 -0700
From: Anders Kristensen <ankriste@cisco.com>
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Subject: Re: [sipcore] draft-ietf-sipcore-location-conveyance-04
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I haven't really followed the discussion closely but I'll say this anyway. Many header fields are of a form similar to Geolocation, essentially lists of URI, and allow for parameters. But I think the parameters are pretty much always associated with individual entries in the list and may be present for more than one. From what I can tell, in the case of Geolocation, the routing-allowed param is not really attached to any particular entry in the list suggesting that maybe it doesn't belong in the same header field. I think that's the thinking that lead Paul to options 4 or 5 which seem much preferable to me. That allows Geolocation to fit the text in RFC 3261 that talks about combining header fields: Specifically, any SIP header whose grammar is of the form header = "header-name" HCOLON header-value *(COMMA header-value) allows for combining header fields of the same name into a comma- separated list. Granted, there's no rule that says that header fields with comma-separated values *must* fit the above grammar but ISTM that it's a pretty established pattern which is worth observing. Thanks, Anders On 10/27/2010 9:10 PM, James M. Polk wrote: > At 06:50 PM 10/27/2010, Paul Kyzivat wrote: >> I have a bunch inline here. > > I'll say ;-) > >> This supersedes my earlier suggested ABNF change. > > ack > > >> On 10/27/2010 2:32 PM, James M. Polk wrote: >>> Paul >>> >>> in-line >>> >>> At 08:36 PM 10/26/2010, Paul Kyzivat wrote: >>>> I took a quick look at the new version, and it seems to have cleanup a >>>> lot. But there *still* seems to be a problem with the syntax. >>>> (Interplay between ABNF and text.) From the text, I find: >>>> >>>> The placement of the "routing-allowed" header field parameter, >>>> strongly encouraged by [RFC5606], is outside the locationValue, and >>>> MUST always be last in the header field value. The routing-allowed >>>> parameter MUST be present, even when no locationValue is present. >>>> >>>> This is questionably supported by the ABNF: >>>> >>>> Geolocation-header = "Geolocation" HCOLON Geolocation-value >>>> Geolocation-value = ( locationValue [ COMMA locationValue ] ) >>>> / routing-param >>> >>> the above, I believe - but am open to be corrected by those better at >>> ABNF syntax that I, says >>> >>> - the Geolocation header can optionally have one or more locationValues >>> - which are where the location URIs go >> >> The above says *a* Geolocation header can have >> - one or two locationValues >> - OR one routing-param >> >> (The slash means OR) >> >> But it doesn't state that the Geolocation header itself can appear >> only once. And obviously if the goal is to have a locationValue AND a >> routing-param in the message, then with the above syntax at least TWO >> Geolocation headers will be required. >> >>> - but that the Geolocation header *will* have a routing-param >>> - which is the "routing-allowed" paramter that RFC 5606 wanted included >> >> Since the slash means OR, it doesn't mean it *will*. >> >>> The text of the ID then says that only zero, one or two locationValues >>> are allowed, which we all agreed to in Maastricht (in SIPCORE and >>> ECRIT/GEOPRIV). >>> >>>> locationValue = LAQUOT locationURI RAQUOT >>>> *(SEMI geoloc-param) >>>> locationURI = sip-URI / sips-URI / pres-URI >>>> / http-URI / HTTPS-URI >>>> / cid-url ; (from RFC 2392) >>>> / absoluteURI ; (from RFC 3261) >>>> geoloc-param = generic-param; (from RFC 3261) >>>> routing-param = "routing-allowed" EQUAL "yes" / "no" >>>> >>>> It only works if you presume that there are separate occurrences of >>>> GeoLocation-header in the message, one with just locations, another >>>> with just the routing-param. >>> >>> I don't get that part of your point, but I guess Martin's next message >>> says I need to add a "COMMA" after the ']' but before the ')'. Would >>> this satisfy your issue? >> >> Adding the COMMA and removing the slash would require the >> routing-param, and would separate it from the location-value. But then >> if you only wanted the routing-param without any locationValues you >> would have to write: >> >> Geolocation:,routing-allowed=no >> >> which is at least a bit weird, which I think is what Martin meant. >> >>>> The routing-param certainly can't be "last in the header field value" >>>> except in the degenerate sense, since it must be first and only in a >>>> Geolocation-header. >>> >>> If the routing-param was intended to be first, wouldn't it appear first >>> on this line? >> >> My point was that the syntax as written only allows routing-param by >> itself in a geolocation-header. E.g. >> >> Geolocation:routing-allowed=no >> >> It can't share a single Geolocation header with a locationValue. Hence >> it is *both* first and last in that header. >> >>>> Geolocation-value = ( locationValue [ COMMA locationValue ] ) >>>> / routing-param >>> >>> but it doesn't, so I'm confused. >> >> Again, the slash means OR. So you have: >> >> Geolocation-value = ( locationValue [ COMMA locationValue ] ) >> OR >> Geolocation-value = routing-param >> >> (Though you can't write it that way in ABNF. >> >>>> Below are some specific cases - both valid and invalid. In each case I >>>> show some headers bracketed by "...". That is intended to mean other >>>> headers in a message, but all in the same message. (And when I show >>>> multiple headers, there could be other non-geoloc headers interleaved.) >>>> >>>> * The following are legal according to the above, and probably within >>>> expected usage: >>>> >>>> ... >>>> Geolocation: cid:foo@example.com >>>> Geolocation: routing-allowed=yes >>>> ... >>>> >>>> ... >>>> Geolocation: cid:foo@example.com,cid:bar@example.com >>>> Geolocation: routing-allowed=yes >>>> ... >>>> >>>> ... >>>> Geolocation: routing-allowed=no >>>> ... >>>> >>>> * IIUC the following are allowed by the above both syntactically and >>>> according to the text, but is presumably not *intended* to be valid. >>>> (Its legal because the in each instance of Geolocation-header its >>>> last.) >>>> >>>> ... >>>> Geolocation: routing-allowed=no >>>> Geolocation: routing-allowed=yes >>>> ... >>>> >>>> The following is also allowed - I don't know if its intended or not: >>>> >>>> ... >>>> Geolocation: routing-allowed=yes >>>> Geolocation: cid:foo@example.com,cid:bar@example.com >>>> ... >>>> >>>> * The following is allowed by the ABNF though disallowed by the text: >>>> >>>> ... >>>> Geolocation: cid:foo@example.com,cid:bar@example.com >>>> Geolocation: cid:baz@example.com >>>> ... >>>> >>>> * The following is *not* allowed by the ABNF. I suspect it might be >>>> intended to be valid, but I'm far from sure about it: >>>> >>>> ... >>>> Geolocation: cid:foo@example.com,routing-allowed=yes >>>> ... >>> >>> to get this above example "allowed", would I correct the existing ABNF >>> to be >>> >>>> Geolocation-value = ( locationValue [ COMMA locationValue ] COMMA ) >>>> / routing-param >>> >>> ? >> >> No. *That* would allow all of the following but not the example above: >> >> Geolocation: cid:foo@example.com, >> Geolocation: cid:foo@example.com,cid:bar@example.com, >> Geolocation: routing-allowed=yes >> >>>> In addition to that, the text is very explicit that: >>>> >>>> The routing-allowed >>>> parameter MUST be present, even when no locationValue is present. >>>> >>>> but then it says: >>>> >>>> If no routing-allowed parameter >>>> is present in a SIP request, a SIP intermediary MAY insert this >>>> value with a RECOMMENDED value of "no" by default. >>>> >>>> So its required, but we have rules to follow if its missing. But I >>>> don't understand how it *can* be required, since the sender of the >>>> request may not understand/support Geolocation and so won't include it. >>> >>> What we're trying to do here is explicitly give instructions to SIP >>> intermediary implementers to include the routing-allowed parameter if >>> one isn't present, with a default value of =no. >> >> I went back and reread the section containing this text. It is in a >> section explicitly about this header. So on reflection I suppose the >> "MUST be present" was intended to imply "in the Geolocation *header". >> I took it to mean "in the request". >> >> Requiring it to be in the header only makes sense if there can be at >> most one header. And then it only makes sense if the syntax is altered >> to allow both the routing-parameter and the locationValue in the same >> header. >> >>>> ISTM that in reality its only *required* if the is a locationValue >>>> present, and is otherwise optional. >>> >>> which is how most would read it if ... >>> >>>> If no routing-allowed parameter >>>> is present in a SIP request, a SIP intermediary MAY insert this >>>> value with a RECOMMENDED value of "no" by default. >>> >>> ... weren't present in the document. But, there is no permission to >>> allow SIP intermediaries to add the routing-allowed parameter, which we >>> wanted to cover. >> >> I'm still confused. Let me state what I think you are after: >> >> - a request may or may not contain a Geolocation header >> - a request may not contain more than one Geolocation header > > of what you have, this one is one I hadn't considered important, but if > that gets everything aligned, then I'm all for adding it in. > >> - a Geolocation header MUST contain a routing-param >> - a Geolocation header Must contain zero, one, or two locationValues >> - you prefer the routing-param to be the last field in the header >> - a proxy MAY add a Geolocation header if one is not present >> (in which case it MUST include a routing-param) >> - a proxy MAY add a locationValue to an existing Geolocation header >> if it doesn't already have two locationValues. (And I guess it >> could add two if there initially were none.) >> >> And you would like ABNF that is consistent with the above. > > with the one caveat, yes. > > >> I'm going to give you some alternatives that should all be >> syntactically correct. I'll give you one that meets the above, and >> some others that may be more appealing variations. Then we can see >> which people prefer. >> >> 1) The following tries to meet the requirements I spelled out above: >> >> Geolocation-header = "Geolocation" HCOLON Geolocation-value >> Geolocation-value = locationValue [ COMMA locationValue] >> COMMA routing-param >> / routing-param > > I hadn't even thought that was possible, but seeing it, I'm amazed I > didn't try it > > (i.e., it's another classic "I could've had a v8" moment)... > > I'm not as smart as you, Paul <:-| > >> locationValue = LAQUOT locationURI RAQUOT >> *(SEMI geoloc-param) >> locationURI = sip-URI / sips-URI / pres-URI >> / http-URI / HTTPS-URI >> / cid-url ; (from RFC 2392) >> / absoluteURI ; (from RFC 3261) >> geoloc-param = generic-param; (from RFC 3261) >> routing-param = "routing-allowed" EQUAL "yes" / "no" >> >> This must be accompanied by text stating that there MUST be at most >> one Geolocation-header in a request. > > you've sold me on this one (and yes, I examined all the others before > jumping on this first one!). Do others have strong opinions about why > not #1? > > thank you for this! > > James > > >> 2) The following is similar to (1), but allows more than two >> 'locationValue's >> >> Geolocation-header = "Geolocation" HCOLON Geolocation-value >> Geolocation-value = *(locationValue COMMA) routing-param >> locationValue = LAQUOT locationURI RAQUOT >> *(SEMI geoloc-param) >> locationURI = sip-URI / sips-URI / pres-URI >> / http-URI / HTTPS-URI >> / cid-url ; (from RFC 2392) >> / absoluteURI ; (from RFC 3261) >> geoloc-param = generic-param; (from RFC 3261) >> routing-param = "routing-allowed" EQUAL "yes" / "no" >> >> The same wording is required with it >> >> 3) The following is a copy from my earlier posting: >> >> Geolocation-header = "Geolocation" HCOLON Geolocation-value >> *( COMMA Geolocation-value) >> Geolocation-value = locationValue / routing-param >> locationValue = LAQUOT locationURI RAQUOT >> *(SEMI geoloc-param) >> locationURI = sip-URI / sips-URI / pres-URI >> / http-URI / HTTPS-URI >> / cid-url ; (from RFC 2392) >> / absoluteURI ; (from RFC 3261) >> geoloc-param = generic-param; (from RFC 3261) >> routing-param = "routing-allowed" EQUAL "yes" / "no" >> >> The above is overly forgiving, in that it permits zero or more >> locationURIs and zero or more routing-params. That then needs to be >> tightened up with text. I think the text needs to say, more or less: >> >> - if there are any locationURIs in a sip request, >> then a routing-param MUST be present in the request >> - there MUST NOT be more than one routing-param present in a >> sip request. >> - there MUST NOT be more than two locationURIs in a sip request >> (if there is really a reason for such a restriction) >> >> 4) The following is a more radical change: >> >> Geolocation-header = "Geolocation" HCOLON locationValue >> [ COMMA locationValue ] >> locationValue = LAQUOT locationURI RAQUOT >> *(SEMI geoloc-param) >> locationURI = sip-URI / sips-URI / pres-URI >> / http-URI / HTTPS-URI >> / cid-url ; (from RFC 2392) >> / absoluteURI ; (from RFC 3261) >> geoloc-param = generic-param; (from RFC 3261) >> >> Georouting-header = "Geolocation-Routing" HCOLON >> ( "yes" / "no" / gen-value ) >> >> This one needs to be accompanied by text stating that each of >> Geolocation-header and Georouting-header may appear at most once >> in a request, and that if Georouting-header is absent it defaults >> to "no". >> >> 5) A more lenient variant on (4): >> >> Geolocation-header = "Geolocation" HCOLON locationValue >> *( COMMA locationValue ) >> locationValue = LAQUOT locationURI RAQUOT >> *(SEMI geoloc-param) >> locationURI = sip-URI / sips-URI / pres-URI >> / http-URI / HTTPS-URI >> / cid-url ; (from RFC 2392) >> / absoluteURI ; (from RFC 3261) >> geoloc-param = generic-param; (from RFC 3261) >> >> Georouting-header = "Geolocation-Routing" HCOLON >> ( "yes" / "no" / gen-value ) >> >> This one needs to be accompanied by text stating that >> Georouting-header may appear at most once in a request, and that >> if Georouting-header is absent it defaults to "no". >> >> (The Geolocation-header can appear zero or more times.) >> >> This is only preferred to (4) if more than two locationValues >> are acceptable. ISTM that once we allowed two, allowing more >> makes sense, with the same limitations imposed with two - that >> its up to the recipient to figure out which to use. >> >> Of the above, I technically and esthetically prefer (5) - or (4) if >> the limitation to two URIs is important. I see no reason to *require* >> the routing-param if the default is understood to be "no". >> >> Pragmatically I think I prefer (1) - its the least variation from what >> has been recently discussed that, IMO, makes any sense. >> >> >>>> In that case, an intermediary that adds a locationValue not only MAY, >>>> but presumably MUST add a missing routing-param if it adds a >>>> locationValue. >>> >>> We can get there (i.e., allow this) without stating this is a MUST, >>> can't we? >> >>>> I have never understood why the routing-param is required to be last. >>> >>> maybe it doesn't need to be, but it certainly is easier for >>> monitoring/reading human to find if it is last when looking at a decode. >>> >>>> And as my examples show, its difficult/impossible to enforce this in >>>> ABNF. >>>> >>>> Thanks, >>>> Paul >>> > > _______________________________________________ > sipcore mailing list > sipcore@ietf.org > https://www.ietf.org/mailman/listinfo/sipcore >
- Re: [sipcore] draft-ietf-sipcore-location-conveya… Paul Kyzivat
- Re: [sipcore] draft-ietf-sipcore-location-conveya… Thomson, Martin
- Re: [sipcore] draft-ietf-sipcore-location-conveya… Paul Kyzivat
- Re: [sipcore] draft-ietf-sipcore-location-conveya… James M. Polk
- Re: [sipcore] draft-ietf-sipcore-location-conveya… James M. Polk
- Re: [sipcore] draft-ietf-sipcore-location-conveya… James M. Polk
- Re: [sipcore] draft-ietf-sipcore-location-conveya… Paul Kyzivat
- Re: [sipcore] draft-ietf-sipcore-location-conveya… James M. Polk
- Re: [sipcore] draft-ietf-sipcore-location-conveya… Anders Kristensen
- Re: [sipcore] draft-ietf-sipcore-location-conveya… Elwell, John
- Re: [sipcore] draft-ietf-sipcore-location-conveya… James M. Polk
- Re: [sipcore] draft-ietf-sipcore-location-conveya… Paul Kyzivat
- Re: [sipcore] draft-ietf-sipcore-location-conveya… James M. Polk