Subject: RE: IG 6.79 "Cancelling Event Detection" breaks ABNF

From: "Rosen, Brian" <[email-masked]>
Date: Fri, 8 Jun 2001 08:41:02 -0400

I agree with Tom; we did a pass over the ABNF to try to make
all of the empty forms not have braces.  The choice was
completely arbitrary, and as I recall, we decided since it
didn't make any real difference, shorter was better.
If we missed one, we goofed.

Tom, the problem here seems to be real.  As Troy says, you will get
a reduce conflict in a rules-based parser with this ambiguity.
I'm pretty sure you can ignore the problem, but it's poor design
practice.  You will recall all of the effort Abdallah and Nancy
went through to test out these kinds of things as we developed
the ABNF.  The IG change wasn't verified in the same way, thus
we have this problem.  We need to decide what to do.

Brian

> -----Original Message-----
> From: Troy Cauble [mailto:[email-masked]]
> Sent: Thursday, June 07, 2001 6:39 PM
> To: Tom-PT Taylor
> Cc: Rosen, Brian; Christian Groves; MEGACO list
> Subject: Re: IG 6.79 "Cancelling Event Detection" breaks ABNF
> 
> 
> > Tom-PT Taylor wrote:
> > 
> > I'm the one responsible for all this.  I suppose I should 
> dig up the thread.
> > Anyway, the intention was definitiely to provide a way of 
> signalling empty
> > descriptors.  I think we chose rather arbitrarily between 
> the desc{} and desc
> > form, opting for the latter.
> 
> Well, an empty Signals Descriptors already uses desc{},
> shouldn't we go for the symmetry?  Didn't we just change
> the original protocol for symmetry reasons?  This would 
> be just changing the IG.
> 
> -troy
>

---

From: Troy Cauble <[email-masked]>
Date: Fri, 08 Jun 2001 11:19:24 -0400

A summary of the problems discussed in this thread.

1) In the text encoding, some empty descriptors have the form
   "Signals {}" while others have "Events".

In a Termination Audit:

2) There are two line encodings for an empty Signals descriptor
   (text and ASN.1).

3) There are two line encodings each for an empty Events descriptor
   or Event Buffer descriptor (ASN.1 only).

4) In the text encoding, EventsToken and EventBufferToken each
   have reduce/reduce conflicts because they can represent either
   an auditItem token or an empty descriptor in the auditReturnParameter.

-troy