Subject: [Sip] RFC4474 and E.164

From: "Dan Wing" <[email-masked]>
Date: Wed, 5 Dec 2007 11:13:23 -0800

Jon,

At the microphone I believe you were referring to section 11 of RFC4474.  The
first paragraph is relevant to today's discussion in SIP and I highlighted a
specific sentence.  The highlighted sentence does not consider session border
controllers which, on today's deployments, _are_ the majority of cases
(majority of call minutes and the majority of phone calls):

   11.  Identity and the TEL URI Scheme

   Since many SIP applications provide a Voice over IP (VoIP) service,
   telephone numbers are commonly used as identities in SIP deployments.
   In the majority of cases, this is not problematic for the identity
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   mechanism described in this document.  Telephone numbers commonly
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   appear in the username portion of a SIP URI (e.g.,
   'sip:[email-masked];user=phone').  That username
   conforms to the syntax of the TEL URI scheme (RFC 3966 [13]).  For
   this sort of SIP address-of-record, chicago.example.com is the
   appropriate signatory.

The rest of the section is available at:
http://tools.ietf.org/html/rfc4474#section-11
but discusses only the TEL URI (which has no domain name).

We will need more text in Jason's document to discuss this in more detail.

-d

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---

From: "Peterson, Jon" <[email-masked]>
Date: Fri, 7 Dec 2007 11:06:03 -0500

I'm certainly not going to claim that Section 11 of RFC4474, or my older work in RFC3824, adequately describes the situation with telephone numbers in SIP today. The sentence you highlight below was intended to suggest that the appearance of telephone numbers as the user part of a SIP URI, rather than as a bare TEL URI with no host portion, constitutes the "majority of cases". It was not making a statement either way about whether or not SBCs are involved in the majority of calls. The guidance given in RFC4474 for signing such telephony-related SIP URIs for Identity is obviously non-optimal when an intermediary such as an SBC must modify content covered by the signature, but of course, that is also true for all the rest of the guidance in RFC4474.

My primary concern in the microphone discussion was to separate out the difficulties of managing telephone numbers in this context from (in my perspective) the unrelated and excessive dilution of necessary security properties which was proposed to accommodate SBCs.

Jon Peterson
NeuStar, Inc.

> -----Original Message-----
> From: Dan Wing [mailto:[email-masked]]
> Sent: Wednesday, December 05, 2007 11:13 AM
> To: [email-masked]; Peterson, Jon
> Cc: 'Jason Fischl'; [email-masked]; 'Cullen Jennings'
> Subject: RFC4474 and E.164 
> 
> 
> Jon,
>