Subject: Re: [Iptel] comments on rfc2806bis - grammar

From: [email-masked]
Date: Tue, 3 Dec 2002 10:29:27 EST

In a message dated 12/2/2002 10:33:44 PM Eastern Standard Time, 
[email-masked] writes:

> Unfortunately, I don't see how I can specify 'at most one isub, but can 
> appear anywhere' while specifying a single context. You'd have to 
> enumerate all combinations, as in
> 
> *par [isdn-subaddress] *par context *par
> *par context *par [isdn-subaddress]
> 
> Any other ideas?
> 

[MAP] Guess I'm totally confused by this. Whatever ABN we end up with, it 
seems that it must include no more than one ISDN subadress. I don't 
understand this point of it appearing in different places and being related 
to the context. I would think that there are two separate things: "isub= " 
and "phone-context = " and they each may appear once and in either order.

Mike Pierce
Artel

---

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 03 Dec 2002 10:40:34 -0500

We've had a similar discussion in the SIP WG. ABNF is not sufficient to 
completely describe all legal (or illegal) patterns. In particular, 
expressing

'at most once, in any order'

is not easily expressible in ABNF (for more than one item). If you have 
a suggestion, please offer it. The only way I have found is to enumerate 
all combinations, which quickly gets ouf of hand, as in

context isub ext | context ext isub | ext context isub | ...

with *par sprinkled in between each element. This is probably barely 
manageable for our current set of known parameters (;phone-context ;isub 
;ext), but this will fail if another draft adds another one (say, ;cic).

[email-masked] wrote:

> [MAP] Guess I'm totally confused by this. Whatever ABN we end up with,
> it seems that it must include no more than one ISDN subadress. I don't
> understand this point of it appearing in different places and being
> related to the context. I would think that there are two separate
> things: "isub= " and "phone-context = " and they each may appear once
> and in either order.
>
> Mike Pierce
> Artel

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