Subject: Re: [IPTEL] rfc2806bis-05 comments: parameters and telephone-subscriber

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 01 Oct 2002 21:58:37 -0400

Digging through old mail...

You raise a good point. Unfortunately, there doesn't seem to be a 
concise way to say in RFC 2234 notation "elements A, B, and C in any 
order, with each appearing no more than once". There are two 
alternatives that I can see:

- 1st option -

*([A] [B] [C])

with the constraint of 'at most once' expressed outside the BNF. This is 
how SIP and other protocols with similar at-most-once/any-order syntax 
handle this.

- 2nd option -

[A] [B] [C] / [A] [C] [B] / [B] [A] [C] / [B] [C] [A] / etc.

Clearly, the latter gets tedious very quickly.

For now, I will pick the 1st option, but clever alternatives are 
appreciated.

Brett Tate wrote:
> rfc2806bis-05 BNF describes an explicit ordering 
> of the parameters in regards to isdn-subaddress, 
> context, and param.  If this explicit ordering 
> was not intended, the BNF should be changed or 
> explicit text should be added to indicate that 
> the above parameters are not required to be
> in an explicit order.
> 
> Adding back a telephone-subscriber definition 
> might help accommodate the above.  It would also 
> help in correlating rfc3261's telephone-subscriber 
> reference to rfc2806bis.
> 
> -brett
> 
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