Re: [sipcore] draft-barnes-sipcore-rfc4244bis

Paul Kyzivat <pkyzivat@cisco.com> Thu, 02 July 2009 18:39 UTC

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Date: Thu, 02 Jul 2009 14:39:45 -0400
From: Paul Kyzivat <pkyzivat@cisco.com>
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To: Dale Worley <dworley@nortel.com>
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Cc: SIPCORE <sipcore@ietf.org>
Subject: Re: [sipcore] draft-barnes-sipcore-rfc4244bis
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Dale,

I agree with your concern about the BNF. A requirement about the 
ordering of the params is problematic.

OTOH, this is a revision to an existing RFC which had that ordering 
requirement. Its possible that relaxing it might lead to interop problems.

Perhaps the best one can do is put in a recommendation to make the index 
first.

Regarding indicating that the index is required: it can be done in text, 
but it can also be done in the BNF, as follows:

    History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)

    hi-entry = hi-targeted-to-uri hi-param-list

    hi-targeted-to-uri = name-addr

    hi-param-list = *(SEMI hi-option) SEMI hi-index *(hi-option)

    hi-option = hi-target / hi-aor / hi-extension

    hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)

    hi-target = "rc" / "cc" / "mp" / "rt"

    hi-aor = "aor"

    hi-extension = generic-param


	Thanks,
	Paul


Dale Worley wrote:
> Regarding the BNF for the History-Info header (section 4.1 in the draft
> version of -02):
> 
> The current BNF requires that the "index" parameter appear immediately
> after the URI, whereas other parameters appear after it:
> 
>    History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)
> 
>    hi-entry = hi-targeted-to-uri SEMI hi-index *(SEMI hi-param)
> 
>    hi-targeted-to-uri = name-addr
> 
>    hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)
> 
>    hi-param = hi-target/hi-aor/hi-extension
> 
>    hi-target = "rc" / "cc" / "mp" / "rt"
> 
>    hi-aor = "aor"
> 
>    hi-extension = generic-param
> 
> IMHO, this is not a good way to organize the grammar, as it makes it
> difficult to generate hi-entry's with generic code (there needs to be
> some way to constrain the "index" parameter to be first), and violates
> the general rule that the order of parameters is not significant.
> 
> I propose to adjust the BNF to:
> 
>    History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)
> 
>    hi-entry = hi-targeted-to-uri *(SEMI hi-param)
> 
>    hi-targeted-to-uri = name-addr
> 
>    hi-param = hi-index / hi-target / hi-aor / hi-extension
> 
>    hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)
> 
>    hi-target = "rc" / "cc" / "mp" / "rt"
> 
>    hi-aor = "aor"
> 
>    hi-extension = generic-param
> 
> Of course, the "index" parameter is still mandatory per the semantic
> constraints listed earlier in section 4.1.
> 
> I've also inserted into the hi-index BNF some spaces around the
> instances of "/" for better readability.
> 
> Dale
> 
> 
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