Internet DRAFT - draft-sparks-sipcore-refer-clarifications
draft-sparks-sipcore-refer-clarifications
Network Working Group R. Sparks
Internet-Draft Oracle
Updates: 3515 (if approved) A. Roach
Intended status: Standards Track Mozilla
Expires: April 30, 2015 October 27, 2014
Clarifications for the use of REFER with RFC6665
draft-sparks-sipcore-refer-clarifications-05
Abstract
An accepted SIP REFER method creates an implicit subscription using
the SIP-Specific Event Notification Framework. That framework was
revised by RFC6665. This document highlights the implications of the
requirement changes in RFC6665, and updates the definition of the
REFER method, RFC3515, to clarify and disambiguate the impact of
those changes.
Status of This Memo
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This Internet-Draft will expire on April 30, 2015.
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Table of Contents
1. Conventions and Definitions . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Use of GRUU is mandatory . . . . . . . . . . . . . . . . . . 2
4. Dialog reuse is prohibited . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 3
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
An accepted SIP REFER method creates an implicit subscription using
the SIP-Specific Event Notification Framework. That framework was
revised by [RFC6665]. This document highlights the implications of
the requirement changes in RFC6665, and updates [RFC3515] to clarify
and disambiguate the impact of those changes.
3. Use of GRUU is mandatory
Section 4.5.1 of [RFC6665] makes GRUU [RFC5627] mandatory to
implement and use as the local target in the subscription created by
the REFER request.
A user agent constructing any REFER that can result in an implicit
subscription MUST populate its Contact header field with a GRUU.
As RFC6665 details, this is necessary to ensure that NOTIFY requests
sent in the implicitly created subscription arrive at this user agent
without creating a second usage inside an existing dialog. Using the
"norefersub" option tag [RFC4488] does not change this requirement,
even if used in a "Require" header field. Even if the recipient
supports the "norefersub" mechanism, and accepts the request with the
option tag in the "Require" header field, it is allowed to return a
"Refer-Sub" header field with a value of "true" in the response, and
create an implicit subscription.
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A UA that will accept a REFER request needs to include a GRUU in the
Contact header field of all INVITE requests. This ensures that out-
of-dialog REFER requests corresponding to any resulting INVITE
dialogs arrive at this UA. Future extensions (such as
[I-D.sparks-sipcore-refer-explicit-subscription]) might relax this
requirement by defining a REFER request that cannot create an
implicit subscription.
4. Dialog reuse is prohibited
If a peer in an existing dialog has provided a GRUU as its Contact,
sending a REFER that might result in an additional dialog usage
within that dialog is prohibited. This is a direct consequence of
[RFC6665] requiring the use of GRUU, and the requirements in section
4.5.2 of that document.
A user agent constructing a REFER request that could result in an
implicit subscription MUST build it as an out-of-dialog message as
defined in [RFC3261]. Thus, the REFER request will have no tag
parameter in its To: header field.
A user agent wishing to identify an existing dialog (such as for call
transfer as defined in [RFC5589] MUST use the "Target-Dialog"
extension defined in [RFC4538] to do so, and user agents accepting
REFER MUST be able to process that extension in requests they
receive.
If a user agent can be certain that no implicit subscription will be
created as a result of sending a REFER request (such as by requiring
an extension that disallows any such subscription), the REFER request
MAY be sent within an existing dialog. Such a REFER will be
constructed with its Contact header field populated with the dialog's
Local URI as specified in section 12 of [RFC3261].
As described in section 4.5.2 of [RFC6665], there are cases where a
user agent may fall back to sharing existing dialogs for backwards-
compatibility purposes. This applies to REFER only when the peer has
not provided a GRUU as its Contact in the existing dialog (i.e. when
the peer is a pre-RFC6665 implementation).
5. Security Considerations
This document introduces no new security considerations directly.
The updated considerations in [RFC6665] apply to the implicit
subscription created by an accepted REFER request.
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6. IANA Considerations
This document has no actions for IANA.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[RFC4538] Rosenberg, J., "Request Authorization through Dialog
Identification in the Session Initiation Protocol (SIP)",
RFC 4538, June 2006.
[RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent URIs (GRUUs) in the Session Initiation Protocol
(SIP)", RFC 5627, October 2009.
[RFC6665] Roach, A., "SIP-Specific Event Notification", RFC 6665,
July 2012.
7.2. Informative References
[I-D.sparks-sipcore-refer-explicit-subscription]
Sparks, R., "Explicit Subscriptions for the REFER Method",
draft-sparks-sipcore-refer-explicit-subscription-00 (work
in progress), June 2014.
[RFC4488] Levin, O., "Suppression of Session Initiation Protocol
(SIP) REFER Method Implicit Subscription", RFC 4488, May
2006.
[RFC5589] Sparks, R., Johnston, A., and D. Petrie, "Session
Initiation Protocol (SIP) Call Control - Transfer", BCP
149, RFC 5589, June 2009.
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Authors' Addresses
Robert Sparks
Oracle
7460 Warren Parkway
Suite 300
Frisco, Texas 75034
US
Email: rjsparks@nostrum.com
Adam Roach
Mozilla
Dallas, TX
US
Phone: +1 650 903 0800 x863
Email: adam@nostrum.com
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