A Clarification on the Use of Globally Routable User Agent URIs (GRUUs) in the SIP Event Notification Framework
RFC 7621

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Internet Engineering Task Force (IETF)                        A.B. Roach
Request for Comments: 7621                                       Mozilla
Updates: 6665                                                August 2015
Category: Standards Track
ISSN: 2070-1721

A Clarification on the Use of Globally Routable User Agent URIs (GRUUs)
                in the SIP Event Notification Framework

Abstract

   Experience since the publication of the most recent SIP Events
   framework (in July 2012) has shown that there is room for
   interpretation around the use of Globally Routable User Agent URIs in
   that specification.  This document clarifies the intended behavior.

   This document updates RFC 6665.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7621.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Roach                        Standards Track                    [Page 1]
RFC 7621              SIP Events GRUU Clarification          August 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Clarification of GRUU Handling  . . . . . . . . . . . . . . .   2
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   3
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   This document is intended to clarify a point of implementor confusion
   arising from lack of clarity in [RFC6665].

2.  Clarification of GRUU Handling

   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].

   Section 4.5.1 of [RFC6665] contains the following normative
   requirement on implementations:

      Notifiers MUST implement the Globally Routable User Agent URI
      (GRUU) extension defined in [RFC5627], and MUST use a GRUU as
      their local target.  This allows subscribers to explicitly target
      desired devices.

   The second sentence of this paragraph attempted to set context for
   the normative statement: the reason GRUUs are required in this
   context is to allow you to send SUBSCRIBE or REFER requests to a
   specific user agent, with the target of the subscription request
   being something like an INVITE dialog on that device.  Consequently,
   the requirement to include a GRUU as a local target was intended to
   apply not just to the local target for SUBSCRIBE-created dialogs, but
   to *all* dialogs, even those created by INVITE.  This requirement has
   been interpreted in a variety of ways by implementors, so a
   clarification is in order.

   Discussion subsequent to the publication of [RFC6665] has highlighted
   obscure cases in which implementations might be notifiers in some
   contexts, but may not wish to act as notifiers in others.  Under
   these narrow circumstances, the restriction described above is not
   necessary for dialogs about which the notifier will never accept
   subscriptions (although the use of GRUUs in such a context causes no
   harm, either).

Roach                        Standards Track                    [Page 2]
RFC 7621              SIP Events GRUU Clarification          August 2015

   This document updates [RFC6665] to clarify the actual requirements.
   The replacement text is as follows:

      Notifiers MUST implement the Globally Routable User Agent URI
      (GRUU) extension defined in [RFC5627].  Notifiers MUST use a GRUU
      as their local target for all dialog-forming methods and all
      target-refresh methods, except for those dialogs for which they
      will reject all subscription requests (implicit or explicit).  For