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Internet Engineering Task Force (IETF)                     A. Allen, Ed.Request for Comments: 7255                                    BlackberryCategory: Informational                                         May 2014ISSN: 2070-1721Using the International Mobile station Equipment Identity (IMEI)Uniform Resource Name (URN) as an Instance IDAbstract   This 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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7255.Allen                         Informational                     [Page 1]

RFC 7255            Using IMEI URN as an Instance ID            May 2014Copyright Notice   Copyright (c) 2014 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Table of Contents1. Introduction ....................................................22. Terminology .....................................................33. Background ......................................................34. 3GPP Use Cases ..................................................55. User Agent Client Procedures ....................................56. User Agent Server Procedures ....................................67. 3GPP SIP Registrar Procedures ...................................68. Security Considerations .........................................79. Acknowledgements ................................................710. References .....................................................810.1. Normative References ......................................810.2. Informative References ....................................81.  Introduction   This 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) as specified inRFC 7254 [1] can be   used as an instance-id as specified inRFC 5626 [2] and also as used   byRFC 5627 [3].RFC 5626 [2] specifies the '+sip.instance' Contact header field   parameter that contains a URN as specified inRFC 2141 [4].  The   instance-id uniquely identifies a specific User Agent (UA) instance.   This instance-id is used as specified inRFC 5626 [2] so that the   Session Initiation Protocol (SIP) registrar (as specified inRFC 3261   [9]) can recognize that the contacts from multiple registrations   correspond to the same UA.  The instance-id is also used as specifiedAllen                         Informational                     [Page 2]

RFC 7255            Using IMEI URN as an Instance ID            May 2014   byRFC 5627 [3] 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 [2] requires that a UA SHOULD create a Universally Unique   Identifier (UUID) URN as specified inRFC 4122 [6] as its instance-id   but allows for the possibility to use other URN schemes.  PerRFC 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, andRFC 7254 [1]  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 inRFC 7254 [1], and the definition of the IMEI is   contained in 3GPP TS 23.003 [10].  Further details about the GSMA's   role in allocating the IMEI, and the IMEI allocation guidelines, can   be found in GSMA PRD TS.06 [11].2.  Terminology   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 inRFC 2119 [7].3.  Background   GSM, UMTS, and LTE capable mobile devices represent 90% of the mobile   devices in use worldwide.  Every manufactured GSM, UMTS, or LTE   mobile device has an allocated IMEI that uniquely identifies this   specific mobile device.  Among other things, in some regulatory   jurisdictions the IMEI is used to identify that a stolen mobile   device is being used, to help to identify the subscription that is   using it, and to prevent use of the mobile device.  While GSM was   originally a circuit switched system, enhancements such as the   General Packet Radio Service (GPRS) and UMTS have added IP data   capabilities that, along with the definition of the IP Multimedia   Subsystem (IMS), have made SIP-based calls and IP multimedia sessions   from mobile devices possible.Allen                         Informational                     [Page 3]

RFC 7255            Using IMEI URN as an Instance ID            May 2014   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 [12], and in 3GPP TS 24.292 [13] 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 [12] and 3GPP TS 24.292 [13]   already specify the use of the URN namespace for the GSMA IMEI URN as   specified inRFC 7254 [1] as the instance-id used by GSM/UMTS/LTEAllen                         Informational                     [Page 4]

RFC 7255            Using IMEI URN as an Instance ID            May 2014   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.4.  3GPP Use Cases   1.  The mobile device includes its IMEI in the SIP REGISTER request       so that the SIP registrar can perform a check of the Equipment       Identity Register (EIR) to verify whether this mobile device is       allowed to access the network for non-emergency services or is       barred from doing so (e.g., because the device has been stolen).       If the mobile device is not allowed to access the network for       non-emergency services, the SIP registrar can reject the       registration and thus prevent a barred mobile device from       accessing the network for non-emergency services.   2.  The mobile device includes its IMEI in SIP INVITE requests used       to establish emergency sessions.  This is so that the Public       Safety Answering Point (PSAP) can obtain the IMEI of the mobile       device for identification purposes if required by regulations.   3.  The IMEI that is included in SIP INVITE requests by the mobile       device and used to establish emergency sessions is also used in       cases of unauthenticated emergency sessions to enable the network       to identify the mobile device.  This is especially important if       the unauthenticated emergency session is handed over from the       packet switched domain to the circuit switched domain.  In this       scenario, the IMEI is the only identifier that is common to both       domains, so the Emergency Access Transfer Function (EATF) in the       network, which in such cases coordinates the transfer between       domains, can use the IMEI to determine that the circuit switched       call is from the same mobile device that was in the emergency       session in the packet switched domain.5.  User Agent Client Procedures   A User Agent Client (UAC) that has an IMEI as specified in 3GPP TS   23.003 [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 inRFC 7254 [1] when performing the   registration procedures specified inRFC 5626 [2] orRFC 5627 [3], 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 beAllen                         Informational                     [Page 5]

RFC 7255            Using IMEI URN as an Instance ID            May 2014   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 toRFC 5626 [2].  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 inRFC 5626 [2].   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.6.  User Agent Server Procedures   A User Agent Server (UAS) MUST NOT include its "sip.instance" media   feature tag containing the GSMA IMEI URN in the Contact header field   of responses, except when the response 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.7.  3GPP SIP Registrar Procedures   In 3GPP IMS, when the SIP registrar receives in the Contact header   field a "sip.instance" media feature tag containing the GSMA IMEI URN   according to the syntax specified inRFC 7254 [1] the SIP registrar   follows the procedures specified inRFC 5626 [2].  The IMEI URN MAY   be validated as described inRFC 7254 [1].  If the UA indicates that   it supports the extension inRFC 5627 [3] and the SIP registrar   allocates a public GRUU according to the procedures specified inRFC 5627 [3], the instance-id MUST be obfuscated when creating the   'gr' parameter in order not to reveal the IMEI to other UAs when theAllen                         Informational                     [Page 6]

RFC 7255            Using IMEI URN as an Instance ID            May 2014   public GRUU is included in non-REGISTER requests and responses.  3GPP   TS 24.229 [8] subclause 5.4.7A.2 specifies the mechanism for   obfuscating the IMEI when creating the 'gr' parameter.8.  Security Considerations   Because IMEIs, like other formats of instance-ids, can be correlated   to a user, they are personally identifiable information and therefore   MUST be treated in the same way as any other personally identifiable   information.  In particular, the "sip.instance" media feature tag   containing the GSMA IMEI URN MUST NOT be included in requests or   responses intended to convey any level of anonymity, as this could   violate the user's privacy.RFC 5626 [2] 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 inRFC 5627 [3]   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 [5]) or another   security mechanism that provides equivalent levels of protection such   as hop-by-hop security based upon IPsec.9.  Acknowledgements   The author would like to thank Paul Kyzivat, Dale Worley, Cullen   Jennings, Adam Roach, Keith Drage, Mary Barnes, Peter Leis, James Yu,   S. Moonesamy, Roni Even, and Tim Bray for reviewing this document and   providing their comments.Allen                         Informational                     [Page 7]

RFC 7255            Using IMEI URN as an Instance ID            May 201410.  References10.1.  Normative References   [1]  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.   [2]  Jennings, C., Mahy, R., and F. Audet, "Managing Client-        Initiated Connections in the Session Initiation Protocol (SIP)",RFC 5626, October 2009.   [3]  Rosenberg, J., "Obtaining and Using Globally Routable User Agent        URIs (GRUUs) in the Session Initiation Protocol (SIP)",RFC5627, October 2009.   [4]  Moats, R., "URN Syntax",RFC 2141, May 1997.   [5]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)        Protocol Version 1.2",RFC 5246, August 2008.   [6]  Leach, P., Mealling, M., and R. Salz, "A Universally Unique        IDentifier (UUID) URN Namespace",RFC 4122, July 2005.   [7]  Bradner, S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, March 1997.   [8]  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/>.   [9]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,        Peterson, J., Sparks, R., Handley, M., and E.  Schooler, "SIP:        Session Initiation Protocol",RFC 3261, June 2002.10.2.  Informative References   [10] 3GPP, "Numbering, addressing and identification", 3GPP TS 23.003        (Release 8), March 2014, <ftp://ftp.3gpp.org/Specs/archive/23_series/23.003/>.   [11] 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>.Allen                         Informational                     [Page 8]

RFC 7255            Using IMEI URN as an Instance ID            May 2014   [12] 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/>.   [13] 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/>.Author's Address   Andrew Allen (editor)   Blackberry   1200 Sawgrass Corporate Parkway   Sunrise, Florida  33323   USA   EMail: aallen@blackberry.comAllen                         Informational                     [Page 9]