Re: [sip-clf] Request for Consensus: Adopt ASCII

"Vijay K. Gurbani" <vkg@bell-labs.com> Fri, 03 December 2010 14:44 UTC

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Date: Fri, 03 Dec 2010 08:48:03 -0600
From: "Vijay K. Gurbani" <vkg@bell-labs.com>
Organization: Bell Laboratories, Alcatel-Lucent
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To: Peter Musgrave <peter.musgrave@magorcorp.com>
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Subject: Re: [sip-clf] Request for Consensus: Adopt ASCII
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On 12/03/2010 07:07 AM, Peter Musgrave wrote:
> Hi Vijay,
>
> Maybe we can do something simple (but not perfect)
> - for empty field
> ? for unparsable field
>
> In practice a tag or other field which contains the literal text - or
> ? would not be distinguishable from empty/unparsable, but I view that
> as a very remote case. We could go down the rat-hole of escaping
> them, but then e.g. a tag could legitimately contain the exact
> escaped sequence etc. etc.

Peter: I agree that a tag field consisting of only one character --- an
unadorned "-" --- and the Call-ID field consisting of only one character
--- an unadorned "?" --- will be extremely rare in practice (although
ABNF allows them.)

If these characters are part of a sequence of other characters, then
of course, there is no ambiguity.  Ambiguity arises if they are the
only character for that field, and in such a case, we could say
something like the following:

   If the To- or From- tag fields contain only one character, and that
   character is the literal "-", the implementation SHOULD insert an
   escaped %2D in the SIPCLF record.  Similarly, if the Call-ID field
   contains only one character, and that character is the literal "?",
   the implementation SHOULD insert an escaped %3F in the SIPCLF record.

This way, the SIPCLF log record can still contain "-" and "?" and if
this is the only character in the field, then the reader can assert
that the fields were empty and unparseable, respectively.

Thanks,

- vijay
-- 
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane, Rm. 9C-533, Naperville, Illinois 60566 (USA)
Email: vkg@{alcatel-lucent.com,bell-labs.com,acm.org}
Web:   http://ect.bell-labs.com/who/vkg/