Internet Engineering Task Force (IETF) R. Atarius, Ed.

Internet Engineering Task Force (IETF) R. Atarius, Ed.
Request for Comments: 8465 September 2018
Category: Informational
ISSN: 2070-1721

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

Abstract

This document specifies how the Uniform Resource Name (URN) namespace
reserved for the Third Generation Partnership Project 2 (3GPP2)
identities and its Namespace Specific String (NSS) for the Mobile
Equipment Identity (MEID) can be used as an Instance ID. The purpose
of this Instance ID 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 candidates for any level of Internet
Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8465.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.

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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. 3GPP2 Use Cases . . . . . . . . . . . . . . . . . . . . . . . 4
5. User Agent Client Procedures . . . . . . . . . . . . . . . . 5
6. User Agent Server Procedures . . . . . . . . . . . . . . . . 5
7. 3GPP/3GPP2 SIP Registrar Procedures . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8

1. Introduction

This document 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 RFC 8464 [10] can be used
as an Instance ID as specified in RFC 5626 [4] and also as used by
RFC 5627 [5].

RFC 5626 [4] specifies the "+sip.instance" Contact header field
parameter that contains a URN as specified in RFC 8141 [6]. The
Instance ID uniquely identifies a specific User Agent (UA) instance.
This Instance ID is used as specified in RFC 5626 [4] so that the
Session Initiation Protocol (SIP) registrar (as specified in RFC 3261
[2]) can recognize that the contacts from multiple registrations
correspond to the same UA. The Instance ID is also used as specified
by RFC 5627 [5] 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 [4] requires that a UA SHOULD create a Universally Unique
Identifier (UUID) URN as specified in RFC 4122 [9] as its Instance ID
but allow for the possibility to use other URN schemes.

RFC 5626 [4] states:

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.

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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 RFC 8464 [10] 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 RFC 8464 [10] and the definition of the MEID is
contained in 3GPP2 S.R0048-A [13].

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [1] [7] when, and only when, they appear in all capitals, as
shown here.

3. Background

Mobile communication has been rapidly improved from low-bit-rate
circuit-switched systems to the higher-data-rate packet-switched
system. The packet-switched system has added the mobile capability
of Internet Protocol (IP) connectivity; 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, SIP-based IMS networks will
take a great many years from the time of writing to transition to the
use of all IP; 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-A [14].

In order for the mobile device to access SIP/IMS voice service via
the circuit-switched domain, 3GPP2 has specified that a Mobile
Switching Center (MSC) server will control mobile voice call setup

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over the circuit-switched radio access while establishing the
corresponding voice session in the core network using SIP/IMS. The
specified MSC server operates either via an IMS Media Gateway Control
Function (MGCF) or directly if it is enhanced by SIP interface. To
enable this, the mobile device MUST be identified in both the 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.

4. 3GPP2 Use Cases

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.

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5. User Agent Client Procedures

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 [13]. 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 RFC 8464 [10] when performing the registration
procedures specified in RFC 5626 [4] or RFC 5627 [5] (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),
preconfiguration, 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 carrier's
packet data network. When registering with a non-3GPP or non-3GPP2
IMS network, a UAC SHOULD use a UUID as an Instance ID as specified
in RFC 5626 [4].

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. Regulations can require that the MEID be provided to the
PSAP. Any future exceptions to this prohibition require 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 3GPP2 MEID URN in the Contact header field
of responses except when the response is related to an emergency
session. Regulations 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 usage.

7. 3GPP/3GPP2 SIP Registrar Procedures

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 RFC 8464 [10], the SIP
registrar follows the procedures specified in RFC 5626 [4]. The MEID

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URN MAY be validated as described in the RFC 8464 [10]. If the UA
indicates that it supports the extension in RFC 5627 [5] and the SIP
Registrar allocates a GRUU according to the procedures specified in
RFC 5627 [5], 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 [11] subclause 5.4.7A.2 specifies the mechanism for
obfuscating the MEID when creating the "gr" parameter.

8. IANA Considerations

This document has no IANA actions.

9. Security Considerations

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 user's privacy. RFC 5626 [4] 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; 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 [3]. 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 [5] provides a means to create URIs that address the user
at a specific device or UA.

Entities that log the Instance ID need to protect them as personally
identifiable information. Regulations can require carriers to log
SIP MEIDs.

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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 8446 [8]
or any other security mechanism that provides equivalent levels of
protection such as hop-by-hop security based upon IP Security
(IPsec).

10. References

10.1. Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261,
June 2002, <https://www.rfc-editor.org/info/rfc3261>.

[3] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Registrations", RFC 3680, DOI 10.17487/RFC3680,
March 2004, <https://www.rfc-editor.org/info/rfc3680>.

[4] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed., "Managing
Client-Initiated Connections in the Session Initiation Protocol
(SIP)", RFC 5626, DOI 10.17487/RFC5626, October 2009,
<https://www.rfc-editor.org/info/rfc5626>.

[5] Rosenberg, J., "Obtaining and Using Globally Routable User Agent
URIs (GRUUs) in the Session Initiation Protocol (SIP)",
RFC 5627, DOI 10.17487/RFC5627, October 2009,
<https://www.rfc-editor.org/info/rfc5627>.

[6] Saint-Andre, P. and J. Klensin, "Uniform Resource Names (URNs)",
RFC 8141, DOI 10.17487/RFC8141, April 2017,
<https://www.rfc-editor.org/info/rfc8141>.

[7] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key
Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.

[8] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

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[9] Leach, P., Mealling, M., and R. Salz, "A Universally Unique
IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.

[10] Atarius, R., "A URN Namespace for Device Identity and Mobile
Equipment Identity (MEID)", RFC 8464, DOI 10.17487/RFC8464,
September 2018, <https://www.rfc-editor.org/info/rfc8464>.

[11] 3GPP, "IP multimedia call control protocol based on Session
Initiation Protocol (SIP) and Session Description Protocol
(SDP); Stage 3", 3GPP 24.229, Version 10.13.0, Release 10,
September 2013,
<ftp://ftp.3gpp.org/Specs/archive/24_series/24.229/>.

10.2. Informative References

[12] Allen, A., Ed., "Using the International Mobile station
Equipment Identity (IMEI) Uniform Resource Name (URN) as an
Instance ID", RFC 7255, DOI 10.17487/RFC7255, May 2014,
<https://www.rfc-editor.org/info/rfc7255>.

[13] 3GPP2, "3G Mobile Equipment Identifier (MEID) - Stage 1, Version
4.0", Stage 1, Version 4.0, 3GPP2 S.R0048-A, June 2005.

[14] 3GPP2, "Voice Call Continuity between IMS and Circuit Switched
Systems - Version 1.0", Version 1.0, 3GPP2 S.X0042-A 1.0, August
2008, <https://www.3gpp2.org/Public_html/Specs/
X.S0042-A_v1.0_080904.pdf>.

Acknowledgments

This document draws heavily on RFC 8464 [10] and also on the style
and structure used in RFC 7255 [12].

The author thanks Andrew Allen for the detailed comments.

Author's Address

Roozbeh Atarius (editor)

Email: [email protected]

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