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Roach 5 Intended status: Standards Track Mozilla 6 Expires: April 30, 2015 October 27, 2014 8 Clarifications for the use of REFER with RFC6665 9 draft-sparks-sipcore-refer-clarifications-05 11 Abstract 13 An accepted SIP REFER method creates an implicit subscription using 14 the SIP-Specific Event Notification Framework. That framework was 15 revised by RFC6665. This document highlights the implications of the 16 requirement changes in RFC6665, and updates the definition of the 17 REFER method, RFC3515, to clarify and disambiguate the impact of 18 those changes. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on April 30, 2015. 37 Copyright Notice 39 Copyright (c) 2014 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Conventions and Definitions . . . . . . . . . . . . . . . . . 2 55 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 3. Use of GRUU is mandatory . . . . . . . . . . . . . . . . . . 2 57 4. Dialog reuse is prohibited . . . . . . . . . . . . . . . . . 3 58 5. Security Considerations . . . . . . . . . . . . . . . . . . . 3 59 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 60 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 7.1. Normative References . . . . . . . . . . . . . . . . . . 4 62 7.2. Informative References . . . . . . . . . . . . . . . . . 4 63 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 65 1. Conventions and Definitions 67 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 68 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 69 document are to be interpreted as described in [RFC2119]. 71 2. Introduction 73 An accepted SIP REFER method creates an implicit subscription using 74 the SIP-Specific Event Notification Framework. That framework was 75 revised by [RFC6665]. This document highlights the implications of 76 the requirement changes in RFC6665, and updates [RFC3515] to clarify 77 and disambiguate the impact of those changes. 79 3. Use of GRUU is mandatory 81 Section 4.5.1 of [RFC6665] makes GRUU [RFC5627] mandatory to 82 implement and use as the local target in the subscription created by 83 the REFER request. 85 A user agent constructing any REFER that can result in an implicit 86 subscription MUST populate its Contact header field with a GRUU. 88 As RFC6665 details, this is necessary to ensure that NOTIFY requests 89 sent in the implicitly created subscription arrive at this user agent 90 without creating a second usage inside an existing dialog. Using the 91 "norefersub" option tag [RFC4488] does not change this requirement, 92 even if used in a "Require" header field. Even if the recipient 93 supports the "norefersub" mechanism, and accepts the request with the 94 option tag in the "Require" header field, it is allowed to return a 95 "Refer-Sub" header field with a value of "true" in the response, and 96 create an implicit subscription. 98 A UA that will accept a REFER request needs to include a GRUU in the 99 Contact header field of all INVITE requests. This ensures that out- 100 of-dialog REFER requests corresponding to any resulting INVITE 101 dialogs arrive at this UA. Future extensions (such as 102 [I-D.sparks-sipcore-refer-explicit-subscription]) might relax this 103 requirement by defining a REFER request that cannot create an 104 implicit subscription. 106 4. Dialog reuse is prohibited 108 If a peer in an existing dialog has provided a GRUU as its Contact, 109 sending a REFER that might result in an additional dialog usage 110 within that dialog is prohibited. This is a direct consequence of 111 [RFC6665] requiring the use of GRUU, and the requirements in section 112 4.5.2 of that document. 114 A user agent constructing a REFER request that could result in an 115 implicit subscription MUST build it as an out-of-dialog message as 116 defined in [RFC3261]. Thus, the REFER request will have no tag 117 parameter in its To: header field. 119 A user agent wishing to identify an existing dialog (such as for call 120 transfer as defined in [RFC5589] MUST use the "Target-Dialog" 121 extension defined in [RFC4538] to do so, and user agents accepting 122 REFER MUST be able to process that extension in requests they 123 receive. 125 If a user agent can be certain that no implicit subscription will be 126 created as a result of sending a REFER request (such as by requiring 127 an extension that disallows any such subscription), the REFER request 128 MAY be sent within an existing dialog. Such a REFER will be 129 constructed with its Contact header field populated with the dialog's 130 Local URI as specified in section 12 of [RFC3261]. 132 As described in section 4.5.2 of [RFC6665], there are cases where a 133 user agent may fall back to sharing existing dialogs for backwards- 134 compatibility purposes. This applies to REFER only when the peer has 135 not provided a GRUU as its Contact in the existing dialog (i.e. when 136 the peer is a pre-RFC6665 implementation). 138 5. Security Considerations 140 This document introduces no new security considerations directly. 141 The updated considerations in [RFC6665] apply to the implicit 142 subscription created by an accepted REFER request. 144 6. IANA Considerations 146 This document has no actions for IANA. 148 7. References 150 7.1. Normative References 152 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 153 Requirement Levels", BCP 14, RFC 2119, March 1997. 155 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 156 A., Peterson, J., Sparks, R., Handley, M., and E. 157 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 158 June 2002. 160 [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer 161 Method", RFC 3515, April 2003. 163 [RFC4538] Rosenberg, J., "Request Authorization through Dialog 164 Identification in the Session Initiation Protocol (SIP)", 165 RFC 4538, June 2006. 167 [RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User 168 Agent URIs (GRUUs) in the Session Initiation Protocol 169 (SIP)", RFC 5627, October 2009. 171 [RFC6665] Roach, A., "SIP-Specific Event Notification", RFC 6665, 172 July 2012. 174 7.2. Informative References 176 [I-D.sparks-sipcore-refer-explicit-subscription] 177 Sparks, R., "Explicit Subscriptions for the REFER Method", 178 draft-sparks-sipcore-refer-explicit-subscription-00 (work 179 in progress), June 2014. 181 [RFC4488] Levin, O., "Suppression of Session Initiation Protocol 182 (SIP) REFER Method Implicit Subscription", RFC 4488, May 183 2006. 185 [RFC5589] Sparks, R., Johnston, A., and D. Petrie, "Session 186 Initiation Protocol (SIP) Call Control - Transfer", BCP 187 149, RFC 5589, June 2009. 189 Authors' Addresses 191 Robert Sparks 192 Oracle 193 7460 Warren Parkway 194 Suite 300 195 Frisco, Texas 75034 196 US 198 Email: rjsparks@nostrum.com 200 Adam Roach 201 Mozilla 202 Dallas, TX 203 US 205 Phone: +1 650 903 0800 x863 206 Email: adam@nostrum.com