Re: [Iptel] Originating trunk group without calling number (Was [Re:Comments on Trunk Group ID])

[Takuya Sawada <[e-mail]>]

Hi,

I think only (3) conforms to both 2806bis and RFC 3261.
But (3) is not tel URI at all. It is just the convention of the
SIP URI's user part usage.

Comments inline.

> Shan Lu wrote:
> 
> > Vijay,
> [...]
> > I am happy with the draft as far as destination TG is concerned. 
> > But I don't think it should prescribe a formula for originating 
> > TG whose validity is sometimes questionable.
> 
> I think you mean above that the validity of the calling party
> number is questionable, not the trunk group's?
> 
> OK, so given the ensuing discussion on the appropriateness of
> carrying a trunk group even if the calling party number is not
> available, it would seem that there are three ways to move
> forward.
> 
> I would like to reach consensus on one of them.  Let me list
> them and provide some pros and cons.
> 
> (1) As suggested by Shan Lu, using a "tel:-;tgrp=foo" in
>      the Contact URI.
> 
ABNF in 2806bis-09 explicitly does not allow the form above.

   telephone-uri        = "tel:" telephone-subscriber
   telephone-subscriber = global-number / local-number
   global-number        = global-number-digits *par
   local-number         = local-number-digits *par context *par
   context              = ";phone-context=" descriptor
   global-number-digits = "+" 1*phonedigit

> (2) In the Contact, use a tel URI of the form:
>      "tel:0000;tgrp=foo;phone-context=example.com"
> 
Contact header MUST be a SIP or SIPS URI according to RFC 3261,
section 8.1.18.
TEL URI is not allowed to appear in Contact header in INVITE request.

> (3) In the Contact, use a SIP URI of the form:
>      "sip:anonymous;tgrp=foo;phone-context=[e-mail]"
> 
This is legal but not related to tel URI...
Probably we can live with this.
But we may have another choice.

(4)
sip:0000;tgrp=foo;phone-context=[e-mail]"

I do not have any preference between (3) and (4).

Regards,
Takuya

> For (1), I wonder if the intent of the author of rfc2806-bis
> was indeed to sanction such use.  While the ABNF may allow
> it implicitly, should we endorse such a usage?  I am sure
> with enough ingenuity, production rules of many ABNFs can
> yield pretty interesting outcomes.
> 
> Maybe the WG can decide if the use of tel URI in this form
> is okay.
> 
> In (2), the "0000" in the Contact URI serves as a filler.
> The proxy receiving a request from its upstream gateway
> with such a filler will know that an calling party number
> was not provided.
> 
> Note that this case is distinct from a "0000" in the
> R-URI of a request arriving from the PSTN, which could
> signify a valid number in the domain of the proxy handling
> the request.
> 
> (3) uses a SIP URI in the Contact header, avoiding the
> ambiguities associated with (1) and (2).
> 
> My preference would be (3).
> 
> Any feedback and discussion most welcome.
> 
> Thanks,
> 
> - vijay
> -- 
> Vijay K. Gurbani  vkg@{lucent.com,research.bell-labs.com,acm.org}
> Wireless Networks Group/Internet Software and Services
> Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
> Naperville, Illinois 60566     Voice: [phone]
> 
> _______________________________________________
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--------
Takuya Sawada
KDDI Corporation (KDDI)
Garden Air Tower, 3-10-10, Iidabashi, 
Chiyoda-ku, Tokyo 102-8460, Japan
Tel: [phone]
Fax: [phone]
[e-mail]

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