Re: [sipcore] Comments on draft-ietf-sipcore-rfc4244bis-02

"DRAGE, Keith (Keith)" <keith.drage@alcatel-lucent.com> Wed, 03 November 2010 10:41 UTC

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From: "DRAGE, Keith (Keith)" <keith.drage@alcatel-lucent.com>
To: Mary Barnes <mary.ietf.barnes@gmail.com>, "Elwell, John" <john.elwell@siemens-enterprise.com>
Date: Wed, 3 Nov 2010 11:41:41 +0100
Thread-Topic: [sipcore] Comments on draft-ietf-sipcore-rfc4244bis-02
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Subject: Re: [sipcore] Comments on draft-ietf-sipcore-rfc4244bis-02
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> > 1. As a general comment that I have made before, the
> document still talks about 'header' in many places where it
> is not referring to the entire header for a SIP message, but
> only to a particular header field such as History-Info.
> History-Info is only one field within the entire SIP header.
> See RFC 3261 section 6 - definitions of header and header
> field. Although RFC 3261 is not 100% consistent, in general
> things like Contact, To, From etc. are referred to as header
> fields, and hence History-Info should be too. Section 4.3 of
> RFC 4485 also calls for attention to be given to the correct
> use of terms header, header field and header field parameter,
> although it fails to say what the correct use is and one has
> to rely on RFC 3261.
> [MB] I replied to this in the other email. But, yes, this doc
> does use Header to mean Header field, but that's done in many
> other documents.
> However, I can change all of those to say "header field" if
> it makes a difference in understanding the document. [This
> might be something to put on the RFC editor list if folks are
> insisting that we always use "Header field"]  The term header
> field parameter AFAIK is only used to refer to the two new
> header field parameters defined in this document.
> [/MB].

If you look at the definitions in RFC 3261 you will find that "header" and "header field" are terms with two very different meanings, so I would support the change to "header field".

> -----Original Message-----
> From: sipcore-bounces@ietf.org
> [mailto:sipcore-bounces@ietf.org] On Behalf Of Mary Barnes
> Sent: Tuesday, November 02, 2010 7:25 PM
> To: Elwell, John
> Cc: sipcore@ietf.org
> Subject: Re: [sipcore] Comments on draft-ietf-sipcore-rfc4244bis-02
>
> Hi John,
>
> Responses inline below [MB].  I will skip the ones that I
> replied to in the other response [MB].
>
> Thanks,
> Mary.
>
> On Mon, Nov 1, 2010 at 5:13 PM, Elwell, John
> <john.elwell@siemens-enterprise.com> wrote:
> > Despite the effort that has gone into addressing comments
> raised by people on -01, I still find -02 hard to understand
> in places. I have not had time to review the whole document,
> but here are some comments up to section 7. Just as I
> finished writing this I saw Mary's response to my comments on
> -01, which I will respond to tomorrow. Apologies for any
> overlap between the two.
> >
> >
> > 1. As a general comment that I have made before, the
> document still talks about 'header' in many places where it
> is not referring to the entire header for a SIP message, but
> only to a particular header field such as History-Info.
> History-Info is only one field within the entire SIP header.
> See RFC 3261 section 6 - definitions of header and header
> field. Although RFC 3261 is not 100% consistent, in general
> things like Contact, To, From etc. are referred to as header
> fields, and hence History-Info should be too. Section 4.3 of
> RFC 4485 also calls for attention to be given to the correct
> use of terms header, header field and header field parameter,
> although it fails to say what the correct use is and one has
> to rely on RFC 3261.
> [MB] I replied to this in the other email. But, yes, this doc
> does use Header to mean Header field, but that's done in many
> other documents.
> However, I can change all of those to say "header field" if
> it makes a difference in understanding the document. [This
> might be something to put on the RFC editor list if folks are
> insisting that we always use "Header field"]  The term header
> field parameter AFAIK is only used to refer to the two new
> header field parameters defined in this document.
> [/MB].
> >
> > Also there are some instances of "header parameter field",
> which is not a normal term - it should be "header field parameter".
> [MB] That's a typo. [/MB]
> >
> > 2. There is some confusion concerning Reason - sometimes it
> is referred to as a parameter (e.g., 7.1 3rd bullet, 7.1 last
> paragraph), sometimes as reason header, sometimes as reason,
> sometimes as Reason header, sometimes as Reason...
> [MB] Logically, Reason is a "parameter" for the hi-entries.
> However, rather than redefine the "parameter", we reuse the
> Reason header by escaping it in the URI - the term Reason
> header was used for brevity.
> I did add text in the -02 to clarify that in cases where it
> is confusing. I can change all instances to refer to "escape
> a Reason header in the hi-targeted-uri" rather than just "add
> a Reason header".
> [/MB]
> >
> > 3. The word "entry" is used inconsistently. Mostly it
> occurs in "hi-entry", which is fine. But we also have
> "targeted-to-URI entry", "entry" (alone), History-Info entry
> (which is probably fine, as long as we say what it is),
> "header entry". Also "hi-entries".
> [MB] Which term do you prefer?  I will change all the
> entry(s) to hi-entry. The targeted-to-URI entry possibly
> should be hi-targeted-to-uri. [/MB]
>
> >
> > 4. As another general comment, there are too many normative
> statements using the passive voice, and therefore hard to
> understand. To quote one example of the sort of ambiguity
> that can arise from using passive, in 7.3.2:
> > "For retargets that are the result of an explicit SIP response, a
> >   Reason MUST be associated with the hi-targeted-to-uri."
> > Is this saying that an entity that inserts History-Info
> MUST include in hi-targeted-uri an escaped Reason header
> field? Or is this saying that a recipient of Reason MUST
> associate it with an hi-targeted-to-uri. I guess the first
> interpretation is more plausible, but why not say what is
> meant, rather than fudging it?
> [MB] The Reason header is added to the hi-entry whose
> hi-targeted-to-URI is being retargeted due to the response.
> It is added by the entity receiving the response.  Note that
> it is added to the entry prior to the entry that is being
> added as a result of the retargeting due to the response -
> i.e., it's not added to the "current" hi-entry.  It's added
> to the previous.  The sentences following the one that you
> highlight are intended to say just that.
> That's why the term "associated" is loosely used because the
> next sentences are the normative part. So, really, that first
> sentence shouldn't be "MUST be" and would be more accurate to
> say "is". [/MB]
> >
> > 5. Section 1:
> > "there is a need for a standard mechanism within
> >   SIP for communicating the retargeting history of such a request"
> > What is meant by "such a request"? We have not previously
> mentioned "request". The preceding text has talked about
> calls, not requests, but perhaps it should talk about requests.
> [MB] I will change "such a request" to "call requests". [/MB]
> >
> > 6. Section 3:
> > "Current network applications provide the ability for elements
> >   involved with the call to exchange  additional
> information relating
> > to
> >   how and why the call was routed to a particular destination"
> > Change "exchange" to "obtain". I think that would fit
> better with the examples that follow.
> [MB] Okay. [/MB]
> >
> > 7. Section 3:
> > "Capturing aliases and Globally Routable User Agent URIs (GRUUs)
> >      [RFC5627], which can be overwritten by a home proxy
> upon receipt"
> > The term "home proxy" is not used in RFC 3261.
> [MB] I will change to "proxy in the home domain" which is a
> term used in RFC 5627 (earlier versions of GRUU did use the
> term "home proxy")[/MB]
> >
> > 8. Section 4:
> > "The  following information is carried in the History-Info header as
> >   detailed in Section 7.1:"
> > I think it would be better to say "For each target used for
> forwarding a request, the  following information is carried
> in the History-Info header as detailed in Section 7.1:"
> > This would make it clear that there can be more than one
> instance of this information.
> [MB] Okay. [/MB]
> >
> > 9. Section 4;
> > "Target : A parameter indicating ..."
> > This overloads the word target. Perhaps a better generic
> term for these parameters would be "Derivation".
> [MB] I will just change to "Indicates.." which matches the
> form of the other bullets in that list. [/MB]
> >
> > 10. Section 4:
> > "A SIP entity changing the target of a
> >   request in response to a redirect or REFER"
> > A REFER does not cause an entity to change the target of a
> request - it causes an entity to generate a new request. H-I
> will indeed be added, but that is covered by the statement
> above about creating a new request.
> [MB] Yep. [/MB]
> >
> > 11. "propagates any
> >   History-Info header from the initial Request in the new request":
> > Contrary to what it says in the first half of the sentence,
> this does indeed acknowledge that we have a new request as a
> result of REFER. However, the statement is incorrect because
> there is no normative statement (e.g., in section 5)
> concerning this special behaviour for REFER. There is merely
> a requirement in Appendix A.
> [MB] I'll add text. [/MB]
> >
> > 12. Section 4:
> > "Note that an hi-entry is not included for the fork to
> >   sip:bob@192.0.2.7 "
> > This is misleading, because there is indeed H-I sent to
> 192.0.2.7. I think what it should say is that the H-I sent to
> 192.0.2.3 and subsequently sent back to Alice does not
> contain an entry for target 192.0.2.7.
> [MB] yep. [/MB]
> >
> > 12bis. Section 5.1:
> > "In addition, the UAC
> >   SHOULD add  a History-Info header"
> > Why is this only a SHOULD, not a MUST? What would be the exceptions?
> [MB] This was issue  #28  where Dale suggested it be change
> from a "MAY" to a "SHOULD" (with which you agreed in the
> email thread).  But, I don't have a problem to change this to
> a MUST. [/MB]
> >
> > 13. Section 5.1:
> > "As a result, intermediaries and
> >   the UAS at least know the original Request-URI, and if
> the Request-
> >   URI was modified by a previous hop. "
> > This is inaccurate, since intermediaries may have removed
> H-I for privacy or other reasons. Best to delete the sentence.
> [MB] Okay. HOwever, entries should not be removed for privacy
> - that was a change from RFC 4244 - they MUST be anonymized.  [/MB]
> >
> > 14. Section 5.1:
> > "A UAC that wants to ensure  that privacy not
> >   be applied to its identity MUST include a Privacy header with a
> > priv-
> >   value of "none"."
> > I am not sure that 'none' ensures anything - it is only a
> request according to RFC 3323.
> [MB] Then I'll change it from "ensure" to "request". [/MB]
> >
> > 15. Section 5.1:
> > "A new hi-entry  MUST then be added for the URI from
> >   the Contact header (which becomes the new Request-URI) "
> > The Contact header field could contain >1 URIs. I think
> what we want to say is that the UAC MUST populate the
> new-hi-entry with the URI chosen as the Request-URI for the
> new request.
> [MB] Yes. [/MB]
> >
> > 16. Section 5.1:
> > "If the Contact header contained any of
> >   the header parameter fields defined in this specification"
> > Don't understand. The parameters defined in this
> specification are parameters of the History-Info header
> field, so would not appear in a Contact header field.
> Admittedly there is some mention in 7.3.4 of using the
> parameters in a Contact header field, but there is nothing
> that specifies the extended syntax of the Contact header field.
> [MB] The header field parameters are defined for the Contact
> header (and History-Info) in the IANA section.  It is
> introduced in 7.1 and the usage thereof described in 7.3.4.  [/MB]
> >
> > 17. Section 5.1:
> > "MUST include the header parameter field  as a header
> parameter field
> >   associated with the current hi-entry as described in
> Section 7.3.4."
> > Is "current hi-entry" the "new hi-entry" from a couple of
> sentences earlier?
> [MB] Yes. Do you have a terminology preference? [/MB]
> >
> > 18. Section 5.2.1:
> > "The last hi-entry reflects the most recent
> >   target and MUST contain the Request-URI for the received request,"
> > If I interpret this correctly, this is talking about what
> the UAS receives. What the UAS receives is outside the
> control of the UAS, so we can't use RFC 2119 language. Should
> be "will".
> [MB] Yep. [/MB]
> >
> > 19. Section 5.2.1:
> > "e.g., the last proxy does
> >   not support History-Info"
> > In the previous sentence we used the term "previous
> entity", so it would be better to stick to that term rather
> than "last proxy".
> [MB] Okay. [/MB]
> >
> > 20. Section 5.2.1:
> > "hi-index attribute"
> > and
> > "hi-target attribute"
> > Up till now we have called these parameters rather than attributes
> [MB] I'll change to parameter [/MB].
> >
> > 21. Section 5.2.1:
> > "The
> >   addition of the missing hi-entry ensures that the most complete
> >   information can be provided in the response ..."
> > Not sure that it is "most complete" - "more complete" would
> be better, since there could still be some missing entries
> from upstream.
> [MB] Most complete as "possible" - but I can change to "more". [/MB]
> >
> > 22. Section 5.2.1:
> > "Prior to any application usage of the information, the
> validity MUST
> >   be ascertained"
> > What MUST ascertain the validity - the UAS or the
> application? Use active voice. How does it do this? Is this
> testable? I don't believe we can use RFC2119 language here.
> [MB] That is saying that the UAS MUST check that the entries
> that it is aware of contain the information that might be
> needed by an application (i.e., the last entry, target header
> field parameters, etc.). It's testable from a software
> implementation perspective - not a protocol perspective.  I
> can change the MUST to a lower case recommended .. ie., it is
> recommended that the UAS...Note, that this was one of the
> SHOULDS (from RFC 4244) that folks wanted to change to MUST.  [/MB]
> >
> > 23. Section 5.2.2:
> > "If the "histinfo" option tag is received in a request, the UAS MUST
> >   include any History-Info received in the request in the subsequent
> >   response"
> > This is incorrect for a B2BUA - a B2BUA should be allowed
> to use information received from its other interface. Also it
> is not necessarily correct for a regular UAS, since I would
> have thought a UAS should be required to include the hi-entry
> inserted in accordance with 5.2.1, rather than using just the
> H-I received.
> [MB] We can reword something like the following to capture
> your concern:
>
>    If the "histinfo" option tag is received in a request, the UAS MUST
>    include any History-Info received in the request and any hi-entries
>    added by the UAS in the subsequent response.  In addition, in
>    the case of a B2BUA, the UAS MAY include any hi-entries
>    received by the UAC in a response in the subsequent response
>    sent by the UAS.
>
> [/MB]
>
> >
> > 24. Section 5.2.2:
> > "The processing of History-Info in responses follows the methodology
> >   described in Section 16.7 of [RFC3261], "
> > We can't refer to 16.7 of RFC 3261, because that is for
> proxies, not UASs.
> [MB] See reply in other email response [/MB]
> >
> > 25. Section 5.3:
> > "the redirect server MUST add the appropriate target header
> >   field parameter to each Contact header as described in
> Section 7.3.4."
> > I don't think 7.3.4 tells me how to do this. Section 7.3.4
> does mention the Contact header field, but only in the
> context of adding these parameters to the History-Info header
> field (if I understand correctly).
> [MB] 7.3.4 tells you which one to add based upon the
> mechanism by which the targets are determined.  The header
> field parameter is added based upon the same criteria. [/MB]
> >
> > 26. Section 6:
> > "A Reason MAY be associated with the hi-targeted-to-uri
> that has been
> >   retargeted as shown in the example in Appendix B.1."
> > It would be good to be more precise, since B.1 is long -
> refer to A6, perhaps.
> [MB] Okay. [/MB]
> >
> > 27. Section 6.1.1:
> > "The proxy MUST include an hi-index attribute
> >      with a value of "1""
> > It says we are inserting an entry, not replacing any
> existing entries. Value "1" will not apply if there is an
> existing entry.
> [MB] Correct. If the prior hop did not include an hi-entry,
> then one is added. Even if there are already other
> hi-entries, there is no way to know how many hops might have
> been missed and thus, the indexing needs to be reset to 1 to
> reflect such. [/MB]
> >
> > 28. Section 6.1.1:
> > "The proxy MUST add a separate hi-entry in each
> >      separate outgoing request for each of the current (outgoing)
> >      targets in the target set."
> > Ambiguous - there should be only one entry per request -
> not one per target in each request.
> > Perhaps it should say "For each outgoing request relating
> to a target in the target set, the proxy MUST add a single
> hi-entry identifying that target. For this new hi-entry, the
> proxy MUST..."
> [MB] Yes - your suggestion is more clear. [/MB]
> >
> > 29. Section 6.1.2:
> > "When re-sending a request as "
> > I don't think this is really resending - we are
> retargeting, and therefore changing some aspects of the
> original request.
> [MB] I'll change to "sending the retargeted request" [/MB]
> >
> > 30. Section 6.1.2:
> > "in the order indicated by the indexing (see
> >      Section 7.3.3)"
> > We really need a more precise reference - where in 7.3.3
> does it tell me how to use the aggregated information?
> [MB] 7.3.3. refers to RFC 3261 Step 7
>        "Aggregate Authentication Header Field Values", which states:
>          "the proxy MUST collect any WWW-
>          Authenticate and Proxy-Authenticate header field values from
>          all other 401 (Unauthorized) and 407 (Proxy Authentication
>          Required) responses received so far in this response context
>          and add them to this response without modification before
>          forwarding.  "
>
> It's actually easier to just reword that to match what is
> done for History-Info header field something like the following:
>          The SIP entity MUST collect any History-Info header
>          field values from
>          all other responses received so far in this response context
>          and add them to this response without modification before
>          forwarding.
> [/MB]
>
>
> >
> > 31. Section 6.1.2:
> > "If the received error response did not include
> >      any History-Info header fields, the proxy MUST use the same
> >      History-Info header fields that were sent in the
> outgoing request
> >      that failed to build the outgoing request."
> > First, the two instances of "outgoing request" are
> confusing - I think the second should be "new outgoing
> request" or "retargeted request".
> [MB] I'll change to "new outgoing request" since the other
> request could also have been retargeted.
> > Second, what if some responses include aggregated
> information and others don't?
> [MB]  That shouldn't matter.  The receiving entity will use
> what it can. If the normative procedures are followed, it's
> fairly deterministic as to when the aggregated information
> should be used.
> [/MB]
> >
> > 32. Section 6.1.2:
> > "Same as per Step 2 above for the normal forwarding case
> >      Section 6.1.1."
> > This is confusing, because 6.1.1 is not on "normal
> forwarding case" but on "initial requests".
> [MB]  Section 6.1.2. use of "initial" is referring to both
> the case of the "initial" hi-entry to be added (bullet 1) AND
> the case whereby a Proxy received a request and it is adding
> the "initial" hi-entry for the first ("initial") retargeting.
>  The "normal" forwarding is specifically bullet #3.  I think
> it would be clearer if we just removed the word "initial"
> from the title and first paragraph and add an explicit
> reference to bullet 3. [/MB]
> >
> > 33. Section 6.1.3:
> > "When re-sending a request as "
> > Again I don't think "re-sending" is the correct term.
> [MB] I'll change to the "generating new requests"  [/MB]
> >
> > 34. Section 6.1.3:
> > "   Step 1:  Including Previous Entries
> >      The proxy MUST include the History-Info header fields that were
> >      sent in the outgoing request that is being redirected."
> > This seems to be a significant difference from the
> 4xx/5xx/6xx case. In that case we include any hi-entries from
> downstream entities that have sent back the 4xx/5xx/6xx - why
> not in the 3xx case too?
> [MB] See response to issue 25 in your previous set of comments. [/MB]
> >
> > 35. Section 6.1.3:
> > "add a Reason header this
> >      entry"
> > Change "this" to "to this".
> >
> > 36. "MUST forward captured History-Info in subsequent,
> >   provisional, and final responses to the request sent by
> the ultimate
> >   UAS (see Section 5.2)"
> > If a response does not contain any captured H-I (because
> the UAS doesn't support it), is there any requirement on the
> proxy to generate it from its own information?
> [MB] A proxy would have added an hi-entry for the UAS if it
> follows the normative procedures in this document. But, there
> is no way for the proxy to generate any additional hi-entries
> (in cases where the
> UAS internally retargets or B2BUA case).   [/MB]
> >
> > 37. Section 7.1:
> > "Reason: An optional parameter for History-Info,"
> > It is not in the ABNF as a parameter of History-Info - in
> fact it is an escaped header field.
> [MB] Correct - this is a summary of information associated with each
> hi-entry and it is described in   as being escaped. Logically, the
> information is there. Certainly, it's clear that it's not
> defined specifically in the ABNF for the header. [/MB]
> >
> > 38. Section 7.1:
> > "he hi-target is added for a hi-entry when it is
> >      first added in a History-Info header field, and only
> one value is
> >      permitted"
> > I believe it should say "only one parameter is permitted".
> True that parameter ('rc' or 'mp') can have only one value,
> but I don't think that is the point we are trying to make.
> [MB] Correct. [/MB]
> >
> > 39. Section 7.3.2:
> > "If the response contains a Reason header for a protocol
> >   that is not SIP (e.g., Q.850), it MUST be captured as an
> additional
> >   Reason associated with the hi-targeted-to-uri that has been
> >   retargeted, along with the SIP Response Code"
> > I think this is saying that the entity MUST include two
> Reason parameters in the hi-entry. Perhaps we should state
> that more explicitly. Also, does order matter?
> [MB] I can add (i.e., there will be two reason headers), but
> I figured when you add "an additional" to one, that it's
> obvious that there are two headers. Per RFC  , order does not
> matter. [/MB]
> >
> > 40. Section 7.3.3 item 6:
> > "When a response is built and it represents the aggregate of
> >       responses to multiple forks "
> > Suddenly we are talking about forks when previously we were
> talking about branches.
> [MB] A branch reflects a fork.  I'll clarify the text  in
> item 6, such that it reads:
> "the index MUST be captured
>        for each forked request, creating a new branch,  per
> the rules above..."
> and change the use of forks to branch in the body of item 6.
> [/MB]
> >
> > 41. Section 7.1.3, item 6:
> > "For example, if
> >       a procesing entity received failure responses for forks 1.1.1
> > and
> >       1.1.2, it would return both the 1.1.1 and 1.1.2 entries to the
> >       entity that generated the hi-entry with index of 1."
> > I can't figure this out - shouldn't "index of 1" be "index of 1.1"?
> [MB] No.  The processing entity in that sentence has the index of 1.1.
> The processing entity is the subject of that sentence and
> "it" returns the response to the entity that would have added
> the hi-entry with index of 1.[/MB]
> >
> > 42. Section 7.1.3, item 6:
> > "See
> >       Appendix B.1 for an example"
> > It is unclear where exactly in B.1 I am supposed to look -
> searching for '1.1.1' or '1.1.2' produces no results. Please
> cite the specific messages.
> [MB] Okay. [/MB]
> >
> > Although I didn't review beyond section 7, I happened to
> notice the following in Appendix B:
> > "B.  An entity (UA or proxy) retargeting in response to a redirect
> >           or REFER MUST include any Request History information from
> >           the redirect/REFER in the new request."
> > It is unclear how you can retarget in response to a REFER.
> A REFER requests leads to the generation of a new request -
> there is no retargeting.
> [MB] I'll reword that to reflect that the REFER includes the
> History-Information from previous retargets. [/MB]
> >
> > John
> > _______________________________________________
> > sipcore mailing list
> > sipcore@ietf.org
> > https://www.ietf.org/mailman/listinfo/sipcore
> >
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