Re: [sipcore] WGLC: draft-ietf-sipcore-rfc4244bis

Shida Schubert <shida@ntt-at.com> Mon, 27 June 2011 05:07 UTC

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From: Shida Schubert <shida@ntt-at.com>
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Date: Mon, 27 Jun 2011 11:06:18 +0900
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Cc: "SIPCORE \(Session Initiation Protocol Core\) WG" <sipcore@ietf.org>, SIPCORE Chairs <sipcore-chairs@tools.ietf.org>
Subject: Re: [sipcore] WGLC: draft-ietf-sipcore-rfc4244bis
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Hi Andrew;

 My comments below. 

On Jun 24, 2011, at 11:31 PM, Andrew Allen wrote:

> Shida
>  
> Response below.
>  
> Andrew
>  
> From: Shida Schubert [mailto:shida@ntt-at.com] 
> Sent: Friday, June 24, 2011 7:40 AM
> To: Andrew Allen
> Cc: SIPCORE Chairs; SIPCORE (Session Initiation Protocol Core) WG
> Subject: Re: [sipcore] WGLC: draft-ietf-sipcore-rfc4244bis
>  
>  
> Hi Andrew;
>  
>  Thanks for your review. 
>  
>  My comments inline. 
>  
> On Jun 22, 2011, at 12:35 AM, Andrew Allen wrote:
> 
> 
> Seems I missed the WGLC deadline by a day or so but here are the comments from my review:
>  
> Section 5
>  
> "mp": The hi-targeted-to-URI represents a user other than the
>  user associated with the Request-URI in the incoming request
>   that was retargeted.
> 
> The term “user” here is confusing. Does it mean the human user (who might have multiple AoRs/URIs which may or may not be known to the retargeting proxy as AoRs/URIs that all map to the same human user)? When retargeting is the proxy supposed to assess whether the new target URI represents the same human user or not in order to determine whether to include the “mp” parameter or not? I’m not sure what terminology would be best but I think “user” is likely to cause confusion.
> The above issue also reoccurs in section 7
>  
>  Your assumption is same as my understanding of this terminology as well. 
>  
>  It could be an individual or it could be a corporate entity.  
> 
> [AA] So does the proxy that is doing the re-targeting need to have definitive knowledge that the two URIs are for the same individual (or corporate entity)? I am not convinced that a proxy will always know that this is the case. Often call forwarding is done based on some kind of user configuration. In some cases the user sets up the forwarding to another URI of (owned by) the same human user but in other cases it is not the same human user. For example I can choose to have all my calls forwarded to some other person (such as wife, friend, or even a hotel where I am staying). I don’t know how a proxy can tell that the URI is for the same human user or not in such circumstances.  I think this area needs further explanation.

 It assumes that Proxy has way to know whether this is the same user or not. 
 
 It could be that the user would indicate that the retargeting target is a same 
user when he/she configures the retargeting. And sometime proxy knows that 
it is a same user because it is configured as an alias to the original AoR etc.

 I agree some text needs to be added. 

>  
> Section 15
> “Entities that have not implemented this specification MUST ignore these parameters”?  We can’t make any normative requirements on entities that have not implemented this specification! Therefore the MUST should be removed. I think you mean to state that according to RFC 3261 and RFC 4244 entities that are not compliant with this specification will ignore these parameters.
>  
>  Yes. 
> 
> [AA] OK so this will be rephrased to remove the MUST?

 Yes. It makes no sense to mandate something from non-RFC4244bis compliant proxy. 

>  
>  
> There is a backward compatibility concern which I think should be addressed. With 4244bis the URI in the Request-URI is now clearly to be included in the History-Info when the Request-URI is replaced by the Contact address. This was not the case in RFC 4244 where in many (if not most) implementations rewriting the request-URI with the Contact was not considered retargeting. Some existing UA implementations may have assumed that the last History-Info entry cannot be their own Contact Address but will always be their AoR. For example a UA may only look at the next highest History-Info header field from the bottom most one in order to determine whether the call arrived as a result of forwarding or not from within their home domain and what the URI was that it was forwarded from. Since outside the home domain of the UA up to now the use of History-Info has not been deterministic some UAs may have only looked at the last couple of History-Info header fields in order to determine what happened to the request after it arrived within their domain. In these kinds of scenarios having a proxy now add an additional History-Info header field (for the rewriting of the Request-URI to the Contact) in 4244bis may break the logic of such UAs. I am not saying we shouldn’t do this but I think some text about such possible problems with existing implementations should be indicated in the backwards compatibility section.
>  
>  The definition of retargeting in RFC4244 was not clear and it is definitely not 
> defined in RFC3261, so I can understand why some may implement it the way 
> you mentioned it. Although example in RFC4244 clearly inserts contact address 
> as the History-Info. 
>  
>  Never the less, we will add some text with regards to this in the backward 
> compatibility section.
> 
> [AA] OK
>  
> Section B.1
>  
> In this example, the Office and Home are not the
>    same AOR as sip:bob@example.com, but rather different AORs that have
>    been configured as alternate addresses for Bob in the proxy.  In
>    other words, Office and Bob are not bound through SIP Registration
> with Bob's AOR.
>  
> The opportunity is missed to explain here that this means that the “rc” parameter is not added. I think it would help to understand if that was highlighted.
>  
>  You are right, but Dale and Hadriel pointed the issue here with not marking 
> hi-entry, so we are likely to change these texts as we are likely to change the 
> semantics of "rc", from the looks of the discussion. 
>  
>  We will reflect the followings errors you found. 
>  
>  As for the details in call-flow B.2 and B.3, the idea is to focus only on 
> H-I so it is easier for implementors to see what gets recorded. Do you prefer 
> the extended version similar to B.1? 
>  
> [AA] Yes I prefer the extended version as this is consistent with the flows in most other SIP RFCs and also with RFC 4244. At the very least the Request-URI, History-Info, and Contact headers need to be shown as these all interact in a meaningful way in History Info.

 Okay, if that is what people want, we can change it to the extended version. 

 Regards
  Shida

>  
>  Regards
>   Shida
> 
> 
>  
>  
>  
> FLOW F1
>  
> INVITE sip:alice@example.com   should be INVITE sip:bob@example.com
>  
>  
> FLOW F5
>  
> Request-URI for the ACK looks wrong to me shouldn’t it be bob@192.0.2.4?
>  
>  
> FLOW F6
>  
> The URI in the Request-URI and the URI in the bottom most History-Info header field are not the same (R-URI = office@192.0.2.3 and H-I =office@192.0.2.5). These should be the same – suggest change R-URI tooffice@192.0.2.5 so as to avoid need to change H-I in the other flows and also since 192.0.2.3 is Alice’s UA!!.
>  
>  
> FLOW F13
>  
> Again Request-URI for the ACK looks wrong to me shouldn’t it behome@192.0.2.6?
>  
>  
> Examples in B.2 and B.3 do not have the same level of detail as in B.1 or RFC 4244.
>  
>  
> Editorials
> Last paragraph of 10.1 .2 “compenent” should be “component”
> First and 2nd paragraph of 10.3 “add an hi-index”/”adds an hi-entry” should be “a” not “an”
>  
> Regards
> Andrew
>  
> From: sipcore-bounces@ietf.org [mailto:sipcore-bounces@ietf.org] On Behalf OfPaul Kyzivat
> Sent: Sunday, June 05, 2011 7:34 PM
> To: SIPCORE (Session Initiation Protocol Core) WG
> Cc: draft-ietf-sipcore-rfc4244bis@tools.ietf.org; SIPCORE Chairs; Robert Sparks
> Subject: [sipcore] WGLC: draft-ietf-sipcore-rfc4244bis
>  
> [as co-chair]
> 
> The current editor of draft-ietf-sipcore-rfc4244bis believes that the document has no remaining technical issues, and is ready for evaluation. Today, we are starting a two-week working group last call period. This last call period ends on Sunday, June 19.
> 
> The latest version of the document can be retrieved here:
> 
> http://tools.ietf.org/html/draft-ietf-sipcore-rfc4244bis
> 
> Any comments on the document should be sent to the SIPCORE mailing list.
> 
>     Thanks,
>     Paul
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