Subject: [Sip] Refer-To header/RFC3261 ambiguity?

From: "Paul D.Smith" <[email-masked]>
Date: Tue, 8 Feb 2005 09:37:01 -0000

All,

We've recently hit a problem with REFER interoperability, on receipt
of a REFER request with a Refer-To header like this:

   Refer-To: sip:[email-masked];user=phone?Replaces=something

The issue is whether the ";user=phone" should be parsed as a URI
parameter or a header parameter.  Obviously the intent here is that it
is a URI parameter, but allowing this runs counter to existing SIP
precedent.

The problem appears to be that the specification of the Refer-To
header (in RFC 3515 section 2.1) is missing some key words that other
headers of similar format (namely the To, From, Contact and Reply-To
headers) have in RFC 3261.

RFC3261 section 20 states:

   The Contact, From, and To header fields contain a URI.  If the URI
   contains a comma, question mark or semicolon, the URI MUST be
   enclosed in angle brackets (< and >).  Any URI parameters are
   contained within these brackets.  If the URI is not enclosed in angle
   brackets, any semicolon-delimited parameters are header-parameters,
   not URI parameters.

RFC3261 section 20.31 (Reply-To) states:

   Even if the "display-name" is empty, the "name-addr" form MUST be
   used if the "addr-spec" contains a comma, question mark, or
   semicolon.  Syntax issues are discussed in Section 7.3.1.

Note that To, Reply-To, From and Contact are the only RFC3261 headers
that are defined as "addr-spec / name-addr ...", similarly to 
Refer-To.

For the RFC 3261 headers - if we are understanding correctly - these
words exist in order to force the protocol to be clear about the
structural difference between

   Contact: <sip:[email-masked];transport=UDP>

and

   Contact: <sip:[email-masked]>;expires=30

It seems that it would be a good idea to impose the same requirement
for the Refer-To header.  Our guess, therefore, is that RFC 3515
should have the same words for the Refer-To header as RFC 3261 has for
the To/From/Contact headers.  Are we right?

Regards,
Paul D Smith
Network Protocols Group 
Data Connection Ltd (DCL)
Tel: +44 20 8366 1177  Email: [email-masked] 
Fax: +44 20 8363 1039  Web:   http://www.dataconnection.com

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---

From: Scott Lawrence <[email-masked]>
Date: Tue, 08 Feb 2005 08:10:24 -0500

> the To/From/Contact headers.  Are we right?

I think it would be an even better fix to change the 3261 text to
clarify that the rule applies to any use of addr-spec or name-addr.

---

From: Robert Sparks <[email-masked]>
Date: Wed, 9 Feb 2005 13:00:27 -0600

I thought there were outstanding bugs to clarify this wherever possible.
I didn't find them on a quick scan, so I added 765.

As we are waiting for the opportunity to put those clarifications in
place, help spread the word:

->ANYWHERE<- in the header that name-addr / addr-spec is used,
if you want URI parameters, they have to appear inside <>s, otherwise
they are header parameters.

RjS