Subject: [Iptel] rfc 3966 BNF queries

From: Eugene Seah <[email-masked]>
Date: Fri, 13 Apr 2007 16:05:38 -0600

Hi, two queries here on RFC 3966 BNF issues.

Firstly, I was wondering if the optional BNF square brackets around 
"visual-separator" in RFC 3966 was correct.

i.e.
 phonedigit = DIGIT / [ visual-separator ]

There's a discrepancy here with extension BNF, since phonedigit is
essentially optional when visual-separator is made optional, meaning the 1*
prefix to phonedigit there doesn't enforce that anything goes after 
";ext=".

see:
 extension = ";ext=" 1*phonedigit

Secondly, what is the reason behind the errata posted below, concerning 
change in isdn-subaddress BNF?

Reported By: Henning Schulzrinne <[email-masked]>
Date: Tue, 01 Mar 2005 09:34:06 -0500

UNVERIFIED
Section 3 says:

isdn-subaddress      = ";isub=" 1*uric

It should say:

isdn-subaddress      = ";isub=" 1*paramchar

Thanks

-- 
Sincerely,
Eugene Seah

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From: Paul Kyzivat <[email-masked]>
Date: Fri, 13 Apr 2007 20:00:00 -0400

> extension = ";ext=" 1*phonedigit

You are right - this is really messed up. And the same is true of 
phonedigit-hex.

(Because of the way they are used this is only technically a problem 
with 'extension'.)

I think a correct way of stating this would be:

    phonedigit           = [visual-separator] DIGIT [visual-separator]
    phonedigit-hex       = [visual-separator] HEXDIG / "*" / "#"
                           [visual-separator]

	Paul

---

From: Eugene Seah <[email-masked]>
Date: Fri, 13 Apr 2007 19:00:35 -0600

>    phonedigit-hex       = [visual-separator] HEXDIG / "*" / "#"
Implying the following changes as well?

global-number-digits = "+" 1*phonedigit

local-number-digits  = 1*phonedigit-hex 

Also, any idea about part 2 of my post, namely the reason for RFC ERRATA:
";isub=" 1*paramchar instead of ";isub=" 1*uric?

Thanks.

-- 
Sincerely,
Eugene Seah

---

From: Henning Schulzrinne <[email-masked]>
Date: Fri, 13 Apr 2007 22:43:02 -0400

I agree. I guess the next step would be filing an RFC erratum.

On Apr 13, 2007, at 8:00 PM, Paul Kyzivat wrote:

>> Firstly, I was wondering if the optional BNF square brackets  
>> around "visual-separator" in RFC 3966 was correct.
>> i.e.
>> prefix to phonedigit there doesn't enforce that anything goes  
>> after ";ext=".
>> see:
> (Because of the way they are used this is only technically a  
> problem with 'extension'.)
>

---

From: Paul Kyzivat <[email-masked]>
Date: Fri, 13 Apr 2007 23:04:38 -0400

> local-number-digits  = 1*phonedigit-hex

While the existing syntax would work with just the other changes, these 
changes you suggest are simpler and would be clearer.

> ";isub=" 1*paramchar instead of ";isub=" 1*uric?

Nope - not a clue.

	Paul

---

From: lconroy <[email-masked]>
Date: Sun, 15 Apr 2007 21:20:43 +0100

Hi Eugene, folks,
    Richard Stastny pointed out to me that RFC 4715 covers ISDN
subaddressing with the tel URI (and ISUP/SIP/ISUP interworking).
  Look there for (most of) the gory details.

That's the good news.
(see also my next message)

all the best,
   Lawrence

On 13 Apr 2007, at 23:05, Eugene Seah wrote:
> Secondly, what is the reason behind the errata posted below,  
> concerning change in isdn-subaddress BNF?
>

---

From: Eugene Seah <[email-masked]>
Date: Mon, 16 Apr 2007 16:31:32 -0600

>>    phonedigit-hex       = [visual-separator] HEXDIG / "*" / "#"
Thanks for your replies, these BNF changes to 'phonedigit' and 
'phone-digit-hex' do change the permitted BNF for the 
'global-number-digits', 'local-number-digits' and 'extension' 
constructs, I just want to clarify that this change is intentional.

  global-number-digits = "+" *phonedigit DIGIT *phonedigit

  local-number-digits  =
      *phonedigit-hex (HEXDIG / "*" / "#")*phonedigit-hex

e.g. previously, a uri such as "tel:+()()1" would be allowed under the 
BNF, but with the change in 'phonedigit', visual-separators must be 
neighbored by as least one DIGIT (or  HEXDIG/"*"/"#" for local numbers).

Does that new limitation sound right or are there valid examples of 
telephone numbers where visual-separators shouldn't need to be 
neighbored by these symbols?

Thanks.

-- 
Sincerely,
Eugene Seah

---

From: Paul Kyzivat <[email-masked]>
Date: Mon, 16 Apr 2007 19:32:40 -0400

It strikes me that if this is to be judged as a "bug" then we need to 
ascertain what the *intent* was and then come up with a valid ABNF that 
realizes the intent. Otherwise we are simply devising another extension.

I don't know what the intent was. I can only guess at what seems 
"reasonable" to me.

	Paul

---

From: Henning Schulzrinne <[email-masked]>
Date: Mon, 16 Apr 2007 20:28:23 -0400

I don't recall how and why this happened, but RFC 2806 (the  
predecessor) had

phonedigit            = DIGIT / visual-separator

This would have allowed multiple separators in sequence.

I also checked the draft history, and the original version in

http://tools.ietf.org/html/draft-ietf-iptel-rfc2806bis-00 and 01

has

honedigit            =  DIGIT [ visual-separator ]

which is close to what's being proposed. This changed to the current  
format in -02.

The only change log entry is

Changes from ietf-00 to ietf-01

         o Editorial changes suggested by Francois Audet.

I also checked my mail folder and the IETF mailing archive around the  
time 02 was issued, and there's no discussion on this feature that I  
can find.

Personally, I don't see the need for multiple consecutive separators.

Henning

On Apr 16, 2007, at 7:32 PM, Paul Kyzivat wrote:

> It strikes me that if this is to be judged as a "bug" then we need  
> to ascertain what the *intent* was and then come up with a valid  
> ABNF that realizes the intent. Otherwise we are simply devising  
> another extension.
>
>>>> You are right - this is really messed up. And the same is true  
>>>> of phonedigit-hex.
>>>>
>> 'phone-digit-hex' do change the permitted BNF for the 'global- 
>> number-digits', 'local-number-digits' and 'extension' constructs,  
>> I just want to clarify that this change is intentional.
>> e.g. previously, a uri such as "tel:+()()1" would be allowed under  
>> the BNF, but with the change in 'phonedigit', visual-separators  
>> must be neighbored by as least one DIGIT (or  HEXDIG/"*"/"#" for  
>> local numbers).
>> Does that new limitation sound right or are there valid examples  
>> of telephone numbers where visual-separators shouldn't need to be