Internet Engineering Task Force (IETF) A. Allen, Ed. Request for Comments: 7255 Blackberry Category: Informational May 2014 ISSN: 2070-1721 Using the International Mobile station Equipment Identity (IMEI) Uniform Resource Name (URN) as an Instance ID
AbstractThis specification defines how the Uniform Resource Name (URN) reserved for the Global System for Mobile Communications Association (GSMA) identities and its sub-namespace for the International Mobile station Equipment Identity (IMEI) can be used as an instance-id. Its purpose is to fulfill the requirements for defining how a specific URN needs to be constructed and used in the '+sip.instance' Contact header field parameter for outbound behavior. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. 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). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see 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/rfc7255.
Copyright Notice Copyright (c) 2014 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 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 1. Introduction ....................................................2 2. Terminology .....................................................3 3. Background ......................................................3 4. 3GPP Use Cases ..................................................5 5. User Agent Client Procedures ....................................5 6. User Agent Server Procedures ....................................6 7. 3GPP SIP Registrar Procedures ...................................6 8. Security Considerations .........................................7 9. Acknowledgements ................................................7 10. References .....................................................8 10.1. Normative References ......................................8 10.2. Informative References ....................................8 RFC 7254  can be used as an instance-id as specified in RFC 5626  and also as used by RFC 5627 . RFC 5626  specifies the '+sip.instance' Contact header field parameter that contains a URN as specified in RFC 2141 . The instance-id uniquely identifies a specific User Agent (UA) instance. This instance-id is used as specified in RFC 5626  so that the Session Initiation Protocol (SIP) registrar (as specified in RFC 3261 ) can recognize that the contacts from multiple registrations correspond to the same UA. The instance-id is also used as specified
by RFC 5627  to create Globally Routable User Agent URIs (GRUUs) that can be used to uniquely address a UA when multiple UAs are registered with the same Address of Record (AoR). RFC 5626  requires that a UA SHOULD create a Universally Unique Identifier (UUID) URN as specified in RFC 4122  as its instance-id but allows for the possibility to use other URN schemes. Per RFC 5626, "If a URN scheme other than UUID is used, the UA MUST only use URNs for which an RFC (from the IETF stream) defines how the specific URN needs to be constructed and used in the "+sip.instance" Contact header field parameter for outbound behavior". This specification meets this requirement by specifying how the GSMA IMEI URN is used in the '+sip.instance' Contact header field parameter for outbound behavior, and RFC 7254  specifies how the GSMA IMEI URN is constructed. The GSMA IMEI is a URN for the IMEI -- a globally unique identifier that identifies mobile devices used in the GSM, Universal Mobile Telecommunications System (UMTS), and 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) networks. The IMEI allocation is managed by the GSMA to ensure that the IMEI values are globally unique. Details of the formatting of the IMEI as a URN are specified in RFC 7254 , and the definition of the IMEI is contained in 3GPP TS 23.003 . Further details about the GSMA's role in allocating the IMEI, and the IMEI allocation guidelines, can be found in GSMA PRD TS.06 . RFC 2119 .
The latest enhancement, known as LTE, introduces even higher data rates and dispenses with the circuit switched infrastructure completely. This means that with LTE networks, voice calls will need to be conducted using IP and IMS. However, the transition to all IP SIP-based IMS networks worldwide will take a great many years, and mobile devices, being mobile, will need to operate in both IP/SIP/IMS mode and circuit switched mode. This means that calls and sessions will need to be handed over between IP/SIP/IMS mode and circuit switched mode mid-call or mid-session. Also, since many existing GSM and UMTS radio access networks are unable to support IP/SIP/IMS-based voice services in a commercially acceptable manner, some sessions could have some media types delivered via IP/IMS simultaneously with voice media delivered via the circuit switched domain to the same mobile device. To achieve this, the mobile device needs to be simultaneously attached via both the IP/SIP/IMS domain and the circuit switched domain. To meet this need, the 3GPP has specified how to maintain session continuity between the IP/SIP/IMS domain and the circuit switched domain in 3GPP TS 24.237 , and in 3GPP TS 24.292  has specified how to access IMS hosted services via both the IP/SIP/IMS domain and the circuit switched domain. In order for the mobile device to access SIP/IMS services via the circuit switched domain, the 3GPP has specified a Mobile Switching Center (MSC) server enhanced for IMS Centralized Services (ICS) and a MSC server enhanced for Single Radio Voice Call Continuity (SR-VCC) that control mobile voice call setup over the circuit switched radio access while establishing the corresponding voice session in the core network using SIP/IMS. To enable this, the MSC server enhanced for ICS or the MSC server enhanced for SR-VCC performs SIP registration on behalf of the mobile device, which is also simultaneously directly registered with the IP/SIP/IMS domain. The only mobile device identifier that is transportable using GSM/UMTS/LTE signaling is the IMEI; therefore, the instance-id included by the MSC server enhanced for ICS or the MSC server enhanced for SR-VCC when acting on behalf of the mobile device, and the instance-id directly included by the mobile device, both need to be based on the IMEI. Additionally, in order to meet the above requirements, the same IMEI that is obtained from the circuit switched signaling by the MSC server needs to be obtainable from SIP signaling so that it can be determined that both the SIP signaling and circuit switched signaling originate from the same mobile device. For these reasons, 3GPP TS 24.237  and 3GPP TS 24.292  already specify the use of the URN namespace for the GSMA IMEI URN as specified in RFC 7254  as the instance-id used by GSM/UMTS/LTE
mobile devices, the MSC server enhanced for SR-VCC, and the MSC server enhanced for ICS, for SIP/IMS registrations and emergency- related SIP requests. 10] and that is registering with a 3GPP IMS network MUST include in the "sip.instance" media feature tag the GSMA IMEI URN according to the syntax specified in RFC 7254  when performing the registration procedures specified in RFC 5626  or RFC 5627 , or any other procedure requiring the inclusion of the "sip.instance" media feature tag. The UAC SHOULD NOT include the optional 'svn' parameter in the GSMA IMEI URN in the "sip.instance" media feature tag, since the software version can change as a result of upgrades to the device firmware that would create a new instance-id. Any future non-zero values of the 'vers' parameter, or the future definition of additional parameters for the GSMA IMEI URN that are intended to be
used as part of an instance-id, will require that an update be made to this RFC. The UAC MUST provide character-by-character identical URNs in each registration according to RFC 5626 . Hence, any optional or variable components of the URN (e.g., the 'vers' parameter) MUST be presented with the same values and in the same order in every registration as in the first registration. A UAC MUST NOT use the GSMA IMEI URN as an instance-id, except when registering with a 3GPP IMS network. When a UAC is operating in IMS mode, it will obtain from the Universal Integrated Circuit Card (UICC) (commonly known as the SIM card) the domain of the network with which to register. This is a carrier's IMS network domain. The UAC will also obtain the address of the IMS edge proxy to send the REGISTER request containing the IMEI using information elements in the Attach response when it attempts to connect to the carrier's packet data network. When registering with a non-3GPP IMS network, a UAC SHOULD use a UUID as an instance-id as specified in RFC 5626 . A UAC MUST NOT include the "sip.instance" media feature tag containing the GSMA IMEI URN in the Contact header field of non- REGISTER requests, except when the request is related to an emergency session. Regulatory requirements can require that the IMEI be provided to the PSAP. Any future exceptions to this prohibition will require the publication of an RFC that addresses how privacy is not violated by such usage. RFC 7254  the SIP registrar follows the procedures specified in RFC 5626 . The IMEI URN MAY be validated as described in RFC 7254 . If the UA indicates that it supports the extension in RFC 5627  and the SIP registrar allocates a public GRUU according to the procedures specified in RFC 5627 , the instance-id MUST be obfuscated when creating the 'gr' parameter in order not to reveal the IMEI to other UAs when the
public GRUU is included in non-REGISTER requests and responses. 3GPP TS 24.229  subclause 5.4.7A.2 specifies the mechanism for obfuscating the IMEI when creating the 'gr' parameter. RFC 5626  states that "One case where a UA could prefer to omit the "sip.instance" media feature tag is when it is making an anonymous request or some other privacy concern requires that the UA not reveal its identity". The same concerns apply when using the GSMA IMEI URN as an instance-id. Publication of the GSMA IMEI URN to networks to which the UA is not attached, or with which the UA does not have a service relationship, is a security breach, and the "sip.instance" media feature tag MUST NOT be forwarded by the service provider's network elements when forwarding requests or responses towards the destination UA. Additionally, an instance-id containing the GSMA IMEI URN identifies a mobile device and not a user. The instance-id containing the GSMA IMEI URN MUST NOT be used alone as an address for a user or as an identification credential for a user. The GRUU mechanism specified in RFC 5627  provides a means to create URIs that address the user at a specific device or User Agent. Entities that log the instance-id need to protect them as personally identifiable information. Regulatory requirements can require that carriers log SIP IMEIs. In order to protect the "sip.instance" media feature tag containing the GSMA IMEI URN from being tampered with, those REGISTER requests containing the GSMA IMEI URN MUST be sent using a security mechanism such as Transport Layer Security (TLS) (RFC 5246 ) or another security mechanism that provides equivalent levels of protection such as hop-by-hop security based upon IPsec.
 Montemurro, M., Ed., Allen, A., McDonald, D., and P. Gosden, "A Uniform Resource Name Namespace for the Global System for Mobile Communications Association (GSMA) and the International Mobile station Equipment Identity (IMEI)", RFC 7254, May 2014.  Jennings, C., Mahy, R., and F. Audet, "Managing Client- Initiated Connections in the Session Initiation Protocol (SIP)", RFC 5626, October 2009.  Rosenberg, J., "Obtaining and Using Globally Routable User Agent URIs (GRUUs) in the Session Initiation Protocol (SIP)", RFC 5627, October 2009.  Moats, R., "URN Syntax", RFC 2141, May 1997.  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008.  Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, July 2005.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  3GPP, "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3", 3GPP TS 24.229 (Release 8), March 2014, <ftp://ftp.3gpp.org/Specs/archive/24_series/ 24.229/>.  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.  3GPP, "Numbering, addressing and identification", 3GPP TS 23.003 (Release 8), March 2014, <ftp://ftp.3gpp.org/Specs/ archive/23_series/23.003/>.  GSM Association, "IMEI Allocation and Approval Guidelines", PRD TS.06 (DG06) Version 6.0, July 2011, <http://www.gsma.com/newsroom/wp-content/uploads/2012/06/ ts0660tacallocationprocessapproved.pdf>.
 3GPP, "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3", 3GPP TS 24.237 (Release 8), September 2013, <ftp://ftp.3gpp.org/Specs/archive/ 24_series/24.237/>.  3GPP, "IP Multimedia (IM) Core Network (CN) subsystem Centralized Services (ICS); Stage 3", 3GPP TS 24.292 (Release 8), December 2013, <ftp://ftp.3gpp.org/Specs/ archive/24_series/24.292/>.