Using the Mobile Equipment Identity (MEID) Uniform Resource Name (URN) as an Instance ID

This specification specifies how the Uniform Resource Name (URN) namespace reserved for Third Generation Partnership Project 2 (3GPP2) identities and its Namespace Specific String (NSS) for the Mobile Equipment Identity (MEID) as specified in draft-atarius-dispatch-meid-urn 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 8141 . 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.

RFC 5626 states:

This specification meets this requirement by specifying how the 3GPP2 MEID URN is used in the "+sip.instance" Contact header field parameter for outbound behavior and draft-atarius-dispatch-meid-urn specifies how the 3GPP2 MEID URN is constructed. The 3GPP2 MEID URN is a URN for the MEID a globally unique identifier that identifies mobile devices used in the 3GPP2 networks. The MEID allocation is managed by the 3GPP2 to ensure that the MEID values are globally unique. Details of the formatting of the MEID as a URN are specified in draft-atarius-dispatch-meid-urn and the definition of the MEID is contained in 3GPP2 S.R0048-A .

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 RFC 8174 .

Mobile communication has been rapidly improved from low bit rate circuit switched system to the higher data rate packet switched system. The packet switched system has added mobile capability of Internet Protocol (IP) connectivity and thereby the IP Multimedia Subsystem (IMS) have made SIP based calls and IP multimedia sessions from mobile devices possible. 3GPP2 defines High Rate Packet Data (HRPD) with high data rates and it dispenses with the 1x Circuit Switched (1xCS) infrastructure. This means that with HRPD 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 from the time of this writing and mobile devices 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. To achieve this the mobile device needs to simultaneously communicate via both the IP/SIP/IMS domain and the circuit switched domain. To meet this need 3GPP2 has specified how to maintain voice session continuity between the IP/SIP/IMS domain and the circuit switched domain in 3GPP2 S.X0042-B . In order for the mobile device to access SIP/IMS voice service via the circuit switched domain 3GPP2 has specified that Mobile Switching Center (MSC) server either via IMS Media Gateway Control Function (MGCF) or directly, if enhanced by SIP interface, controls 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 mobile device MUST be identified in both 1xCS and IP/SIP/IMS domains. The only mobile device identifier that is transportable using 1xCS signaling is the MEID therefore the instance-id included by the MGCF or the MSC server, and the instance-id directly included by the mobile device both need to be based on the MEID. Additionally in order to meet the above requirements, the same MEID 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.

1. The mobile device includes its MEID in the SIP REGISTER request so that the SIP registrar can perform a check of the Equipment Identity Register (EIR) to verify if this mobile device is allowed or barred from accessing the network for non-emergency services (e.g., because it 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. Thus a barred mobile device is prevented from accessing the network for non-emergency services. 2. The mobile device includes its MEID in SIP INVITE requests used to establish emergency sessions. This is so that the Public Safety Answering Point (PSAP) can obtain the MEID of the mobile device for identification purposes if required by regulations. 3. The inclusion by the mobile device of its MEID in SIP INVITE requests used to establish emergency sessions is also used in the 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 MEID is the only identifier that is common to both domains. The Emergency Access Transfer Function (EATF) which coordinates the call transfer between the domains, can thus use the MEID to identify that the circuit switched call is from the same mobile device that was in the emergency session in the packet switched domain.

A single mode 3GPP2 User Agent Client (UAC) which uses only 3GPP2 technology to transmit and receive voice or data has an MEID as specified in 3GPP2 S.R0048-A . The single mode 3GPP2 UAC that is registering with a 3GPP2 IMS network includes in the "sip.instance" media feature tag the 3GPP2 MEID URN according to the syntax specified in draft-atarius-dispatch-meid-urn 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. A UAC MUST NOT use the 3GPP2 MEID URN as an instance-id except when registering with a 3GPP2 IMS network. When a UAC is operating in IMS mode it will obtain the domain of the carrier's IMS network to register with, from the Universal Integrated Circuit Card (UICC), pre-configuration, or the network at the time of establishing the Packet Data Protocol (PDP) context. These three methods are carrier specific and are only performed by the carrier IMS networks. The UAC will also obtain the address of the IMS edge proxy to send the REGISTER request containing the MEID using information elements in the Attach response when it attempts to connect to the carriers packet data network. When registering with a non-3GPP or non-3GPP2 IMS network a UAC SHOULD use a Universally Unique Identifier (UUID) as an instance-id as specified in RFC 5626 . A UAC MUST NOT include the "sip.instance" media feature tag containing the 3GPP2 MEID URN in the Contact header field of non-REGISTER requests except when the request is related to an emergency session. Regulatory requirements can require the MEID to be provided to the PSAP. Any future exceptions to this prohibition require an RFC that addresses how privacy is not violated by such a usage.

A User Agent Server (UAS) MUST NOT include its "sip.instance" media feature tag containing the 3GPP2 MEID URN in the Contact header field of responses except when the response is related to an emergency session. Regulatory requirements can require the MEID to be provided to the PSAP. Any future exceptions to this prohibition require an RFC that addresses how privacy is not violated by such a usage.

In 3GPP/3GPP2 IMS when the SIP Registrar receives in the Contact header field a "sip.instance" media feature tag containing the 3GPP2 MEID URN according to the syntax specified in draft-atarius-dispatch-meid-urn the SIP registrar follows the procedures specified in RFC 5626 . The MEID URN MAY be validated as described in the draft-atarius-dispatch-meid-urn . If the UA indicates that it supports the extension in RFC 5627 and the SIP Registrar allocates a 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 MEID 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 MEID when creating the "gr" parameter.

This document defines no items requiring action by IANA.

Since MEIDs like other formats of instance-ids can be correlated to a user, they are personally identifiable information and MUST be treated as such. In particular, the "sip.instance" media feature tag containing the 3GPP2 MEID URN MUST NOT be included in requests or responses intended to convey any level of anonymity, as this could violate the users privacy. RFC 5626 states "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 3GPP2 MEID URN as an instance-id. Publication of the 3GPP2 MEID URN to networks that the UA is not attached to or the UA does not have a service relationship with 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. The 3GPP2 MEID URN MUST NOT accidentally leak in other contexts, such as and in particular when application servers subscribe to user registration state using the event package defined in RFC 3680 . Additionally, an instance-id containing the 3GPP2 MEID URN identifies a mobile device and not a user. The instance-id containing the 3GPP2 MEID 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 carriers to log SIP MEIDs. In order to protect the "sip.instance" media feature tag containing the 3GPP2 MEID URN from being tampered with, those REGISTER requests containing the 3GPP2 MEID URN MUST be sent using a security mechanism such as Transport Layer Security (TLS) as specified in RFC 4346 or any other security mechanism that provides equivalent levels of protection such as hop-by-hop security based upon IP Security (IPsec).

This document draws heavily on draft-atarius-dispatch-meid-urn and also on the style and structure used in RFC 7255 . The author thanks for the detailed comments, provided by Andrew Allen.