Internet DRAFT - draft-ietf-ipv6-3gpp-recommend


 Internet-Draft                                     M. Wasserman, Editor
 Document: draft-ietf-ipv6-3gpp-recommend-02.txt              Wind River
 Expires:  October 2002                                       April 2002

                 Recommendations for IPv6 in 3GPP Standards

 1  Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026 [RFC2026].

    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups.  Note that
    other groups may also distribute working documents as Internet-

    Internet-Drafts are draft documents valid for a maximum of six
    months and may be updated, replaced, or obsoleted by other
    documents at any time.  It is inappropriate to use Internet-Drafts
    as reference material or to cite them other than as "work in

    The list of current Internet-Drafts can be accessed at
    The list of Internet-Draft Shadow Directories can be accessed at

 2  Abstract

    This document contains recommendations from the Internet
    Engineering Task Force (IETF) IPv6 Working Group to the Third
    Generation Partnership Project (3GPP) community regarding the use
    of IPv6 in the 3GPP standards. Specifically, this document
    recommends that the 3GPP:

         1. Specify that multiple prefixes may be assigned to each
            primary PDP context,
         2. Require that a given prefix must not be assigned to more
            than one primary PDP context, and
         3. Allow 3GPP nodes to use multiple identifiers within those
            prefixes, including randomly generated identifiers.

    The IPv6 Working Group supports the use of IPv6 within 3GPP and
    offers these recommendations in a spirit of open cooperation
    between the IPv6 Working Group and the 3GPP community.  Since the
    original publication of this document as an Internet-Draft, the
    3GPP has adopted the primary recommendations of this document.

 3  Copyright Notice

    Copyright (C) The Internet Society (2001).  All Rights Reserved.

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 4  Conventions Used In This Document

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    this document are to be interpreted as described in RFC 2119

 5  Table of Contents

    1       Status of this Memo.......................................1
    2       Abstract..................................................1
    3       Copyright Notice..........................................1
    4       Conventions Used In This Document.........................2
    5       Table of Contents.........................................2
    6       Introduction..............................................3
    6.1     What is the 3GPP?.........................................3
    6.2     What is the IETF?.........................................4
    6.3     Terminology...............................................4
    6.3.1   3GPP Terminology..........................................5
    6.3.2   IETF Terminology..........................................5
    6.4     Overview of the IPv6 Addressing Architecture..............6
    6.5     An IP-Centric View of the 3GPP System.....................7
    6.5.1   Overview of the UMTS Architecture.........................7
    6.5.2   The PDP Context...........................................9
    6.5.3   IPv6 Address Autoconfiguration in GPRS...................11
    7       Recommendations to the 3GPP..............................13
    7.1     Limitations of 3GPP Address Assignment...................13
    7.2     Advertising Multiple Prefixes............................14
    7.3     Assigning a Prefix to Only One Primary PDP Context.......14
    7.3.1   Is a /64 per PDP Context Too Much?.......................14
    7.3.2   Prefix Information in the SGSN...........................15
    7.4     Multiple Identifiers per PDP Context.....................15
    8       Additional IPv6 Work Items...............................17
    9       Security Considerations..................................17
    10      Appendix A:  Analysis of Findings........................18
    10.1    Address Assignment Solutions.............................18
    11      References...............................................20
    12      Authors and Acknowledgements.............................22
    13      Editor's Contact Information.............................22

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 6  Introduction

    In May 2001, the IPv6 Working Group (WG) held an interim meeting in
    Redmond, WA to discuss the use of IPv6 within the 3GPP standards.
    The first day of the meeting was a joint discussion with 3GPP
    during which an architectural overview of 3GPP's usage of IPv6 was
    presented, and there was much discussion regarding particular
    aspects of IPv6 usage within 3GPP. At that meeting, a decision was
    made to form a design team to write a document offering advice from
    the IPv6 WG to the 3GPP community regarding their use of IPv6. This
    document is the result of that effort.

    This document offers recommendations to the 3GPP community from the
    IETF IPv6 Working Group.  It is organized into three main sections:

         1. An introduction (this section) that provides background
            information regarding the IETF IPv6 WG and the 3GPP and
            includes a high-level overview of the technologies discussed
            in this document.

         2. Recommendations from the IPv6 WG to the 3GPP community.
            These can be found in section 7.

         3. Further work items that should be considered by the IPv6 WG.
            These items are discussed in section 8.

    It is the purpose of this document to provide advice from the IPv6
    Working Group to the 3GPP community.  We have limited the contents
    of this document to items that are directly related to the use of
    IPv6 within 3GPP.  This document defines no standards, and it is
    not a definitive source of information regarding IPv6 or 3GPP.  We
    have not chosen to explore 3GPP-related issues with other IETF
    protocols (i.e. SIP, IPv4, etc.), as they are outside the scope of
    the IPv6 Working Group.

    The IPv6 Working Group fully supports the use of IPv6 within 3GPP,
    and we encourage 3GPP implementers and operators to participate in
    the IETF process.  We are offering these suggestions in a spirit of
    open cooperation between the IPv6 Working Group and the 3GPP
    community, and we hope that our ongoing cooperation will help to
    strengthen both sets of standards.

    The 3GPP address allocation information in this document is based
    on the 3GPP document TS 23.060 version 4.1.0 [OLD-TS23060].  At the
    3GPP plenary meeting TSG #15 in March 2002, the 3GPP adopted the
    two primary recommendations contained in this document, allocating
    a unique prefix to each primary PDP context when IPv6 stateless
    address autoconfiguration is used, and allowing the terminals to
    use multiple interface identifiers.  These changes were
    retroactively applied from 3GPP release 99 onwards, in TS23.060
    versions 3.11.0, 4.4.0 and 5.1.0 [NEW-TS23060].

 6.1 What is the 3GPP?

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    The Third Generation Partnership Project (3GPP) is a global
    standardization partnership founded in late 1998. Its
    Organizational Partners have agreed to co-operate in the production
    of technical specifications for a Third Generation Mobile System
    based on the evolved GSM core networks.

    The 3GPP Organizational Partners consist of several different
    standardization organizations: ETSI from Europe, Standards
    Committee T1 Telecommunications (T1) in the USA, China Wireless
    Telecommunication Standard Group (CWTS), Korean Telecommunications
    Technology Association (TTA), the Association of Radio Industries
    and Businesses (ARIB) and the Telecommunication Technology
    Committee(TTC) in Japan.

    The work is coordinated by a Project Co-ordination Group (PCG), and
    structured into Technical Specification Groups (TSGs). There are
    five TSGs: Core Network (TSG CN), Radio Access Networks (TSG RAN),
    Services and System Aspects (TSG SA), GSM/EDGE Radio Access Network
    (GERAN), and the Terminals (TSG T). The TSGs are further divided
    into Working Groups (WGs). The technical work is done in the
    working groups, and later approved in the TSGs.

    3GPP working methods are different from IETF working methods.  The
    major difference is where the major part of the work is done. In
    3GPP, the work is done in face-to-face meetings, and the mailing
    list is used mainly for distributing contributions, and for
    handling documents that were not handled in the meeting due to lack
    of time. Decisions are usually made by consensus, though voting
    does exist. However, it is rather rare to vote. 3GPP documents are
    public and can be accessed via the 3GPP web site [3GPP-URL].

 6.2 What is the IETF?

    The Internet Engineering Task Force (IETF) is a large open
    international community of network designers, operators, vendors,
    and researchers concerned with the evolution of the Internet
    architecture and the smooth operation of the Internet. The IETF is
    also the primary standards body developing Internet protocols and
    standards.  It is open to any interested individual.  More
    information about the IETF can be found at the IETF web site [IETF-

    The actual technical work of the IETF is done in working groups,
    which are organized by topic into several areas (e.g., routing,
    transport, security, etc.). The IPv6 Working Group is chartered
    within the Internet area of the IETF. Much of the work is handled
    via mailing lists, and the IETF holds meetings three times per

 6.3 Terminology

    This section defines the 3GPP and IETF terminology used in this
    document.  The 3GPP terms and their meanings have been taken from

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 6.3.1   3GPP Terminology

    APN          Access Point Name. The APN is a logical name referring
                 to a GGSN and an external network.

    CS           Circuit Switched

    GERAN        GSM/EDGE Radio Access Network

    GGSN         Gateway GPRS Support Node.  A router between the GPRS
                 network and an external network (i.e. the Internet).

    GPRS         General Packet Radio Services

    GTP-U        General Tunneling Protocol - User Plane

    MT           Mobile Termination.  For example, a mobile phone

    PDP          Packet Data Protocol

    PDP Context  A PDP connection between the UE and the GGSN.

    PS           Packet Switched

    SGSN         Serving GPRS Support Node

    TE           Terminal Equipment.  For example, a laptop attached
                 through a 3GPP handset.

    UE           User Equipment (TE + MT + USIM).  An example would be
                 a mobile handset with a USIM card inserted and a
                 laptop attached.

    UMTS         Universal Mobile Telecommunications System

    USIM         Universal Subscriber Identity Module.  Typically, a
                 card that is inserted into a mobile phone handset.

    UTRAN        Universal Terrestrial Radio Access Network

 6.3.2   IETF Terminology

    IPv6         Internet Protocol version 6 [RFC 2460]

    NAS          Network Access Server

    NAT          Network Address Translator

    NAT-PT       Network Address Translation with Protocol Translation.
                 An IPv6 transition mechanism. [NAT-PT]

    PPP          Point-to-Point Protocol [PPP]

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    SIIT         Stateless IP/ICMP Transition Mechanism [SIIT]

 6.4 Overview of the IPv6 Addressing Architecture

    The recommendations in this document are primarily related to IPv6
    address assignment.  To fully understand the recommended changes,
    it is necessary to understand the IPv6 addressing architecture, and
    current IPv6 address assignment mechanisms.

    The IPv6 addressing architecture represents a significant evolution
    from IPv4 addressing [ADDRARCH]. It is required that all IPv6 nodes
    be able to assemble their own addresses from interface identifiers
    and prefix information. This mechanism is called IPv6 Host
    Autoconfiguration [AUTOCONF], and it allows IPv6 nodes to configure
    themselves without the need for stateful configuration servers
    (i.e. DHCPv6) or statically configured addresses.

    Interface identifiers can be globally unique, such as modified EUI-
    64 addresses [ADDRARCH], or non-unique, such as randomly generated
    identifiers.  Hosts that have a globally unique identifier
    available may also choose to use randomly generated addresses for
    privacy [PRIVADDR] or for other reasons.  IPv6 hosts are free to
    generate new identifiers at any time, and Duplicate Address
    Detection (DAD) is used to protect against the use of duplicate
    identifiers on a single link [IPV6ND].

    A constant link-local prefix can be combined with any interface
    identifier to build an address for communication on a locally
    attached link.  IPv6 routers may advertise additional prefixes
    (site-local and/or global prefixes)[IPV6ND].  Hosts can combine
    advertised prefixes with their own interface identifiers to create
    addresses for site-local and global communication.

    IPv6 introduces architectural support for scoped unicast addressing
    [SCOPARCH].  A single interface will typically have multiple
    addresses for communication within different scopes:  link-local,
    site-local and/or global [ADDRARCH].  Link-local addresses allow
    for local communication, even when an IPv6 router is not present.
    Some IPv6 protocols (i.e. routing protocols) require the use of
    link-local addresses.  Site-local addressing allows communication
    to be administratively contained within a single site.  Link-local
    or site-local connections may also survive changes to global prefix
    information (e.g. site renumbering).

    IPv6 explicitly associates each address with an interface.
    Multiple-interface hosts may have interfaces on more than one link
    or in more than one site.  Links and sites are internally
    identified using zone identifiers.  Proper routing of non-global
    traffic and proper address selection are ensured by the IPv6 scoped
    addressing architecture [SCOPARCH].

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    IPv6 introduces the concept of privacy addresses [PRIVADDR].  These
    addresses are generated from an advertised global prefix and a
    randomly generated identifier, and are used for anonymous access to
    Internet services.  Applications control the generation of privacy
    addresses, and new addresses can be generated at any time.

    The IPv6 site renumbering specification [SITEREN] relies upon the
    fact that IPv6 nodes will generate new addresses when new prefixes
    are advertised on the link, and that they will deprecate addresses
    that use deprecated prefixes.

    In the future, additional IPv6 specifications may rely upon the
    ability of IPv6 nodes to use multiple prefixes and/or multiple
    identifiers to dynamically create new addresses.

 6.5 An IP-Centric View of the 3GPP System

    The 3GPP specifications define a Third Generation Mobile System.
    An overview of the packet switched (PS) domain of the 3GPP Release
    99 system is described in the following sections. The authors hope
    that this description is sufficient for the reader who is
    unfamiliar with the UMTS packet switched service to understand how
    the UMTS system works, and how IPv6 is currently defined to be used
    within it.

 6.5.1   Overview of the UMTS Architecture

    The UMTS architecture can be divided into two main domains -- the
    packet switched (PS) domain, and the circuit switched (CS) domain.
    In this document, we will concentrate on the PS domain, or General
    Packet Radio Services (GPRS).

 |  TE  |
  ------   Uu  -----------   Iu  -----------   Gn  -----------   Gi
 |  MT  |--+--|   UTRAN   |--+--|   SGSN    |--+--|   GGSN    |--+--
  ------       -----------       -----------       -----------

                   Figure 1:  Simplified GPRS Architecture

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 |      |
 |  App |- - - - - - - - - - - - - - - - - - - - - - - - -(to app peer)
 |      |
 |------|                                              -------------
 |  IP  |- - - - - - - - - - - - - - - - - - - - - - -|      IP     |->
 | v4/6 |                                             |     v4/6    |
 |------|      -------------       -------------      |------       |
 |      |     |  \ Relay /  |     |  \ Relay /  |     |      |      |
 |      |     |   \     /   |     |   \     /   |     |      |      |
 |      |     |    \   /    |     |    \   /    |     |      |      |
 | PDCP |- - -| PDCP\ /GTP_U|- - -|GTP_U\ /GTP_U|- - -|GTP_U |      |
 |      |     |      |      |     |      |      |     |      |      |
 |------|     |------|------|     |------|------|     |------|      |
 |      |     |      |  UDP |- - -|  UDP |  UDP |- - -| UDP  |      |
 |      |     |      |------|     |------|------|     |------|      |
 |  RLC |- - -|  RLC |  IP  |- - -|  IP  |  IP  |- - -| IP   |      |
 |      |     |      | v4/6 |     | v4/6 | v4/6 |     |v4/6  |      |
 |------|     |------|------|     |------|------|     |------|------|
 |  MAC |     |  MAC | AAL5 |- - -| AAL5 |  L2  |- - -| L2   |  L2  |
 |------|     |------|------|     |------|------|     |------|------|
 |  L1  |- - -|  L1  |  ATM |- - -|  ATM |  L1  |- - -| L1   |  L1  |
  ------       -------------       -------------       -------------

    UE             UTRAN                SGSN                GGSN
                       Figure 2:  GPRS Protocol Stacks

    |      |
    | App. |- - - - - - - - - - - - - - - - - - - - - - (to app peer)
    |      |
    |      |
    |  IP  |- - - - - - - - - - - - - - - - - - - - - - (to GGSN)
    | v4/6 |
    |      |     |             |
    |------|     |-------------|
    |      |     |  \ Relay /  |
    |      |     |   \     /   |
    |      |     |    \   /    |
    |      |     |     \ / PDCP|- - - (to UTRAN)
    |      |     |      |      |
    |  PPP |- - -|  PPP |------|
    |      |     |      |  RLC |- - - (to UTRAN)
    |      |     |      |------|
    |      |     |      |  MAC |
    |------|     |------|------|
    |  L1a |- - -|  L1a |  L1b |- - - (to UTRAN)
     ------       -------------
       TE              MT
    (laptop)        (handset)

                 Figure 3:  Laptop Attached to 3GPP Handset

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    The GPRS core network elements shown in Figures 1 and 2 are the
    User Equipment (UE), Serving GPRS Support Node (SGSN) and Gateway
    GPRS Support Node (GGSN). The UTRAN comprises Radio Access Network
    Controllers (RNC) and the UTRAN base stations.

    GGSN A specialized router that functions as the gateway between the
         GPRS network and the external networks, e.g. Internet. It also
         gathers charging information about the connections. In many
         ways the GGSN is similar to a Network Access Server (NAS).

    SGSN The SGSN's main functions include authentication,
         authorization, mobility management, and collection of billing
         information. The SGSN is connected to the SS7 network and
         through that to the Home Location Register (HLR), so that it
         can perform user profile handling, authentication, and

    GTP-U is a simple tunnelling protocol running over UDP/IP
    and used to route packets between RNC, SGSN and GGSN within the
    same, or between different, UMTS backbone(s). A GTP-U tunnel is
    identified at each end by a Tunnel Endpoint Identifier (TEID).

    Only the most significant elements of the GPRS system are discussed
    in this document. More information about the GPRS system can be
    found in [OLD-TS23060].

 6.5.2   The PDP Context

    The most important 3GPP concept in this context is a PDP Context. A
    PDP Context is a connection between the UE and the GGSN, over which
    the packets are transferred. There are two kinds of PDP Contexts --
    primary, and secondary.

    The primary PDP Context initially defines the link to the GGSN. For
    instance, an IP address is assigned to each primary PDP Context. In
    addition, one or more secondary PDP Contexts can be added to a
    primary PDP Context, sharing the same IP address. These secondary
    PDP Contexts can have different Quality of Service characteristics
    than the primary PDP Context.

    Together a primary PDP Context and zero or more secondary PDP
    Contexts define, in IETF terms, a link. GPRS links are point-to-
    point. Once activated, all PDP contexts have equal status, meaning
    that a primary PDP context can be deleted while keeping the link
    between the UE and the GGSN, as long as there are other (secondary)
    PDP contexts active for the same IP address.

    There are currently three PDP Types supported in GPRS -- IPv4,
    IPv6, and PPP. This document will only discuss the IPv6 PDP Type.

    There are three basic actions that can be performed on a PDP
    Context: PDP Context Activation, Modification, and Deactivation.
    These actions are described in the following.

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    Activate PDP Context

                 Opens a new PDP Context to a GGSN.  If a new primary
                 PDP Context is activated, there is a new link created
                 between a UE and a GGSN. A UE can open multiple
                 primary PDP Contexts to one or more GGSNs.

    Modify PDP Context

                 Changes the characteristics of a PDP Context, for
                 example QoS attributes.

    Deactivate PDP Context

                 Deactivates a PDP Context. If a primary PDP Context
                 and all secondary PDP contexts associated with it are
                 deactivated, a link between the UE and the GGSN is

    The APN is a name which is logically linked to a GGSN. The APN may
    identify a service or an external network. The syntax of the APN
    corresponds to a fully qualified domain name. At PDP context
    activation, the SGSN performs a DNS query to find out the GGSN(s)
    serving the APN requested by the terminal. The DNS response
    contains a list of GGSN addresses from which the SGSN selects one
    (in a round-robin fashion).

                 ---------                           --------
                |         |                         |  GGSN  |
                |         |           LINK 1        |        |
                |      -======== PDP Context A ========-   - - -> ISP X
                |         |                         |        |
                |         |                         |        |
                |         |                         |        |
                |       /======= PDP Context B =======\      |
                |      -  |           LINK 2        |  -   - - -> ISP Y
                |       \======= PDP Context C =======/      |
                |         |                         |        |
                |   MT    |                          --------
                |         |                          --------
  --------      |         |                         |  GGSN  |
 |        |     |         |           LINK 3        |        |
 |        |     |      -======== PDP Context D ========-     |
 |   TE   |     |         |                         |        |
 |(laptop)|     |         |                         |      - - -> ISP Z
 |        |     |         |           LINK 4        |        |
 |     -====PPP====-----======== PDP Context E ========-     |
 |        |     |         |                         |        |
 |        |     |         |                         |        |
  --------       ---------                           --------

           Figure 3:  Correspondence of PDP Contexts to IPv6 Links

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 6.5.3   IPv6 Address Autoconfiguration in GPRS

    GPRS supports static and dynamic address allocation. Two types of
    dynamic address allocation are supported -- stateless, and
    stateful. Stateful address configuration uses an external protocol
    to connect to a server that gives the IP address, e.g. DHCP.

    The stateless IPv6 autoconfiguration works differently in GPRS than
    in Ethernet networks. GPRS nodes have no unique identifier, whereas
    Ethernet nodes can create an identifier from their EUI-48 address.
    Because GPRS networks are similar to dialup networks, the stateless
    address autoconfiguration in GPRS was based on PPPv6 [PPPV6].

    3GPP address autoconfiguration has the following steps:

         1. The Activate PDP Context message is sent to the SGSN (PDP
            Type=IPv6, PDP Address = 0, etc.).

         2. The SGSN sends a Create PDP Context message to the GGSN with
            the above parameters.

         3. GGSN chooses an interface identifier for the PDP Context and
            creates the link-local address. It answers the SGSN with a
            Create PDP Context response (PDP Address = link-local

         4. The SGSN sends an Activate PDP Context accept message to the
            UE (PDP Address = link-local address).

         5. The UE keeps the link-local address, and extracts the
            interface identifier for later use. The UE may send a Router
            Solicitation message to the GGSN (first hop router).

         6. After the PDP Context Activation the GGSN sends a Router
            Advertisement to the UE.

         7. The UE should be configured not to send Neighbor
            Solicitation message. However, if one is sent the GGSN will
            silently discard it.

         8. The GGSN updates the SGSN with the whole IPv6 address.

    Each connected handset or laptop will create a primary PDP context
    for communication on the Internet.  A handset may create many
    primary and/or secondary PDP contexts throughout the life of its
    connection with a GGSN.

    Within 3GPP, the GGSN assigns a single 64-bit identifier to each
    primary PDP context.  The GGSN also advertises a single /64 prefix
    to the handset, and these two items are assembled into a single
    IPv6 address.  Later, the GGSN modifies the PDP context entry in
    the SGSN to include the whole IPv6 address, so that the SGSN can
    know the single address of each 3GPP node (e.g. for billing

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    purposes).  This address is also used in the GGSN to identify the
    PDP context associated with each packet.  It is assumed that 3GPP
    nodes will not generate any addresses, except for the single
    identifier/prefix combination assigned by the GGSN.  DAD is not
    performed, as the GGSN will not assign the same address to multiple

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 7  Recommendations to the 3GPP

    In the spirit of productive cooperation, the IPv6 Working Group
    recommends that the 3GPP consider three changes regarding the use
    of IPv6 within GPRS.  Specifically, we recommend that the 3GPP

         1. Specify that multiple prefixes may be assigned to each
            primary PDP context,

         2. Require that a given prefix must not be assigned to more
            than one primary PDP context, and

         3. Allow 3GPP nodes to use multiple identifiers within those
            prefixes, including randomly generated identifiers.

    Making these changes would provide several advantages for 3GPP
    implementers and users:

         Laptops that connect to 3GPP handsets will work without any
         software changes. Their implementation of standard IPv6 over
         PPP,  address assignment, and autoconfiguration mechanisms
         will work without any modification. This will eliminate the
         need for vendors and operators to build and test special 3GPP
         drivers and related software.  As currently specified, the
         3GPP standards will be incompatible with laptop
         implementations that generate their own identifiers for
         privacy or other purposes.

         IPv6 software implementations could be used in 3GPP handsets
         without any modifications to the IPv6 protocol mechanisms.
         This will make it easier to build and test 3GPP handsets.

         Applications in 3GPP handsets will be able to take advantage
         of different types of IPv6 addresses (e.g., static addresses,
         temporary addresses for privacy, site-scoped addresses for
         site only communication, etc.)

         The GPRS system will be better positioned to take advantage of
         new IPv6 features that are built around the current addressing

 7.1 Limitations of 3GPP Address Assignment

    The current 3GPP address assignment mechanism has the following

         The GGSN only advertises a single /64 prefix, rather than a
         set of prefixes.  This will prevent the participation of 3GPP
         nodes (e.g. handsets or 3GPP-attached laptops) in IPv6 site
         renumbering, or in other mechanisms that expect IPv6 hosts to
         create addresses based on multiple advertised prefixes.

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         A 3GPP node is assigned a single identifier and is not allowed
         to generate additional identifiers.  This will prevent the use
         of privacy addresses by 3GPP nodes.  This also makes 3GPP
         mechanisms not fully compliant with the expected behavior of
         IPv6 nodes, which will result in incompatibility with popular
         laptop IPv6 stacks.  For example, a laptop that uses privacy
         addresses for web browser connections could not currently not
         currently establish a web browser connection over a 3GPP link.

    These limitations could be avoided by enabling the standard IPv6
    address allocation mechanisms in 3GPP nodes.  The GGSN could
    advertise one or more prefixes for the local link in standard IPv6
    Router Advertisements, and IPv6 addresses could be assembled, as
    needed, by the IPv6 stack on the handset or laptop.  An interface
    identifier could still be assigned by the GGSN, as is currently
    specified in the 3GPP standards.  However, the handset or laptop
    could generate additional identifiers, as needed for privacy or
    other reasons.

 7.2 Advertising Multiple Prefixes

    For compliance with current and future IPv6 standards, the IPv6 WG
    recommends that the 3GPP allow multiple prefixes to be advertised
    for each primary PDP context.  This would have several advantages,

         3GPP nodes could participate in site renumbering and future
         IPv6 mechanisms that rely on the use of multiple global
         prefixes on a single link.

         Site-local prefixes could be advertised on 3GPP links, if
         desired, allowing for site-constrained communication that
         could survive changes to global prefix information (e.g. site

 7.3 Assigning a Prefix to Only One Primary PDP Context

    The IPv6 WG recommends that the 3GPP treat a primary PDP context,
    along with its secondary PDP contexts, as a single IPv6 link, and
    that the GGSN view each primary PDP context as a single subnet.
    Accordingly, a given global (or site-local) prefix should not be
    assigned to more than one PDP context.

    Because multiple IPv6 hosts may attach through a 3GPP handset, the
    IPv6 WG recommends that one or more /64 prefixes should be assigned
    to each primary PDP context.  This will allow sufficient address
    space for a 3GPP-attached node to allocate privacy addresses and/or
    route to a multi-link subnet [MULTLINK], and will discourage the
    use of NAT within 3GPP-attached devices.

 7.3.1   Is a /64 per PDP Context Too Much?

    If an operator assigns a /64 per PDP context, can we be assured
    that there is enough address space for millions of mobile devices?

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    This question can be answered in the positive using the Host
    Density (HD) Ratio for address assignment efficiency [HD]. This is
    a measure of the number of addresses that can practically and
    easily be assigned to hosts, taking into consideration the
    inefficiencies in usage resulting from the various address
    assignment processes. The HD ratio was empirically derived
    from actual telephone number and data network address assignment

    We can calculate the number of easily assignable /64's making the
    following assumptions:

         An HD ratio of 0.8 (representing the efficiency that can be
         achieved with no particular difficulty).

         Only addresses with the 3-bit prefix 001 (the Aggregatable
         Global Unicast Addresses defined by RFC 2373) are used,
         resulting in 61 bits of assignable address space.

    Using these assumptions, a total of 490 trillion (490x10^12) /64
    prefixes can be assigned. This translates into around 80,000 PDP
    Contexts per person on the earth today. Even assuming that a
    majority of these IPv6 /64 prefixes will be used by non-3GPP
    networks, there is still clearly a sufficient number of /64

    Given this, it can be safely concluded that the IPv6 address space
    will not be exhausted if /64 prefixes are allocated to primary PDP

    For more information regarding policies for IPv6 address
    assignment, refer to the IAB/IESG recommendations regarding address
    assignment [IABAA], and the APNIC, ARIN and RIPE address allocation
    policy [AAPOL].

 7.3.2   Prefix Information in the SGSN

    Currently, the 3GPP standards allow only one prefix and one
    identifier for each PDP context.  So, the GGSN can send a single
    IPv6 address to the SGSN, to be used for billing purposes, etc.

    Instead of using the full IPv6 address to identify a PDP context,
    the IPv6 WG recommends that the SGSN be informed of each prefix
    that is currently assigned to a PDP context.  By assigning a prefix
    to only one primary PDP context, the SGSN can associate a prefix
    list with each PDP context.

 7.4 Multiple Identifiers per PDP Context

    The IPv6 WG also recommends that the 3GPP standards be modified to
    allow multiple identifiers, including randomly generated
    identifiers, to be used within each assigned prefix.  This would
    allow 3GPP nodes to generate and use privacy addresses, and would
    be compatible with future IPv6 standards that may depend on the

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    ability of IPv6 nodes to generate new interface identifiers for

    This is a vital change, necessary to allow standards-compliant IPv6
    nodes to connect to the Internet through 3GPP handsets, without
    modification.  It is expected that most IPv6 nodes, including the
    most popular laptop stacks, will generate privacy addresses.  The
    current 3GPP specifications will not be compatible with those

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 8  Additional IPv6 Work Items

    During our work on this document, we have discovered several areas
    that could benefit from further informational or standards-track
    work within the IPv6 Working Group.

    The IPv6 WG should work to define a point-to-point architecture and
    specify how the standard IPv6 address assignment mechanisms are
    applicable to IPv6 over point-to-point links.  We should also
    review and clarify the IPv6 over PPP specification [PPP] to match
    the current IPv6 addressing architecture [ADDRARCH].

    The IPv6 WG should consider publishing an "IPv6 over PDP Contexts"
    (or similar) document.  This document would be useful for
    developers writing drivers for IPv6 stacks to work over 3GPP PDP

    The IPv6 working group should undertake an effort to define the
    minimal requirements for all IPv6 nodes.

 9  Security Considerations

    This document contains recommendations on the use of the IPv6
    protocol in 3GPP standards.  It does not specify a protocol, and it
    introduces no new security considerations.

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 10 Appendix A:  Analysis of Findings

    This section includes some analysis that may be useful to
    understanding why the IPv6 working group is making the above
    recommendations.  It also includes some other options that were
    explored, and the reasons why those options were less suitable than
    the recommendations outlined above.

 10.1    Address Assignment Solutions

    In order to allow for the configuration and use of multiple IPv6
    addresses per primary PDP Context having different interface
    identifiers, some modifications to the current 3GPP specifications
    would be required.

    The solutions to achieve this were evaluated against the following

         - Scarcity and high cost of wireless spectrum
         - Complexity of implementation and state maintenance
         - Stability of the relevant IETF standards
         - Impact on current 3GPP standards

    Two solutions to allow autoconfiguration of multiple addresses on
    the same primary PDP Context were considered:

         1. Assign one or more entire prefixes (/64s) to a PDP Context
            upon PDP Context activation and allow the autoconfiguration
            of multiple addresses.

                 a) The assignment may be performed by having the GGSN
                 advertise one or more /64 prefixes to the mobile

                 b) The assignment may be performed by building "prefix
                 delegation" functionality into the PDP Context
                 messages or by using layer 3 mechanisms such as
                 [PREFDEL]. In this way the prefix is not assigned to
                 the link between the GGSN and the mobile device (as in
                 1a) but it is assigned to the mobile device itself.
                 Note that [PREFDEL] cannot be considered stable
                 and has not at this stage been adopted by the IPv6 WG
                 as a WG document.

         2. Share the same prefix between multiple PDP Contexts
            connected to the same GGSN (and APN). Given that mobile
            devices may generate multiple addresses using more than one
            interface identifier, this would require DAD for the newly
            generated addresses over the air interface, and a proxy DAD
            function which would increase the complexity and the amount
            of state to be kept in the GGSN. Also, the GGSN would need
            to determine when the temporary addresses are no longer in
            use which would be difficult. One possible solution could be

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            using periodic unicast neighbor solicitations for the
            temporary addresses [IPV6ND].

    Considering all the factors when evaluating the solutions, the
    recommendation is to use Solution 1a.  This solution requires the
    least modification to the current 3GPP standards and maintains all
    the advantages of the other solutions.

    Effectively this would mean that each APN in a GGSN would have a
    certain number of /64 prefixes that can be handed out at PDP
    context Activation, through Router Advertisements. Therefore,
    instead of using the full IPv6 address to identify a primary PDP
    context, the IPv6 WG recommends that the GGSN use the entire prefix
    (together with other 3GPP specific information) and that the SGSN
    be informed of the prefixes that are assigned to a PDP context. By
    assigning a given prefix to only one primary PDP context, the GGSN
    and SGSN can associate a prefix list with each PDP context, as

    Note that the recommended solution does not imply or assume that
    the mobile device is a router. The MT is expected to use the /64
    for itself and may also use this prefix for devices attached to it.
    However this is not necessary if each device behind the MT is
    connected to a separate primary PDP Context and therefore can use a
    /64 which is not shared with other devices. The MT is also expected
    to handle DAD locally for devices attached to it (e.g. laptops)
    without forwarding Neighbor Solicitations over the air to the GGSN.

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 11 References

         TS 23.060, "General Packet Radio Service (GPRS); Service
         description; Stage 2", V4.1.0

         TS 23.060 version 3.11.0 (release 99), 4.4.0 (release 4)
         and 5.1.0 (release 5).



         S. Bradner, "The Internet Standards Process -- Revision 3",
         RFC 2026, BCP9, October 1996

         S. Bradner, "Key words for use in RFCs to Indicate Requirement
         Levels", RFC 2119, BCP14, March 1999.

         3GPP TR 21.905, "Vocabulary for 3GPP Specifications", V5.0.0

         S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6)
         Specification", RFC 2460, December 1998.

         G. Tsirtsis, P. Shrisuresh, "Network Address Translation -
         Protocol Translation (NAT-PT)", RFC2766, February 2000.

         Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC
         1661, July 1994.

         E. Nordmark, "Stateless IP/ICMP Translation Algorithm",  RFC
         2765, February 2000.

         R. Hinden, S. Deering, "IP Version 6 Addressing Architecture",
         RFC 2373, July 1998

         T. Narten, E. Nordmark, W. Simpson, "Neighbor Discovery for IP
         Version 6 (IPv6)", RFC 2461, December 1998

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         S. Thomson, T. Narten, "IPv6 Stateless Address
         Autoconfiguration", RFC 2462, December 1998

         T. Narten, R. Draves, "Privacy Extensions for Stateless
         Address Autoconfiguration in IPv6", RFC 3041, January 2001

         M. Crawford, "Transmission of IPv6 Packets over Ethernet
         Networks", RFC 2464, December 1998

         D. Haskin, E. Allen, "IP Version 6 over PPP", RFC2472,
         December 1998.

         C. Huitema, D. Thaler, "Multi-link Subnet Support in IPv6",
         draft-thaler-ipngwg-multilink-subnets-01.txt, July 2001

         C. Huitema, "IPv6 Site Renumbering", draft-huitema-ipv6-
         renumber-00.txt, July 2001

         C. Huitema, A. Durand, "The Host-Density Ratio for Address
         Assignment Efficiency:  An update on the H ratio", draft-
         durand-huitema-h-density-ratio-02.txt, August 2001

         IAB, IESG, "IAB/IESG Recommendations on IPv6 Address
         Allocations to Sites", RFC3177, September 2001.

         APNIC, ARIN, RIPE-NCC, "IPv6 Address Allocation and Assignment
         Global Policy".  Draft of December, 22 2001, Version 2001-12-
         22 [

         S. Deering, et. al, "IPv6 Scoped Address Architecture", draft-
         ietf-ipngwg-scoping-arch-02.txt, March 2001

         J. Arkko, et. al, "Minimum IPv6 Functionality for a Cellular
         Host", draft-manyfolks-ipv6-cellular-host-01.txt, September

         J. Martin, B. Haberman, "Automatic Prefix Delegation Protocol
         for Internet Protocol Version 6 (IPv6)", draft-haberman-
         ipngwg-auto-prefix-01.txt, July 2001

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 12 Authors and Acknowledgements

    This document was written by the IPv6 3GPP design team:

         Steve Deering, Cisco Systems

         Karim El-Malki, Ericsson Radio Systems

         Paul Francis, Tahoe Networks

         Bob Hinden, Nokia

         Christian Huitema, Microsoft

         Niall Richard Murphy, Hutchison 3G

         Markku Savela, Technical Research Centre of Finland

         Jonne Soininen, Nokia

         Margaret Wasserman, Wind River

    Information was incorporated from a presentation co-authored by:

         Juan-Antonio Ibanez, Ericsson Eurolab

 13 Editor's Contact Information

    Comments or questions regarding this document should be sent to:

    Margaret Wasserman
    Wind River
    10 Tara Blvd., Suite 330             Phone:  (603) 897-2067
    Nashua, NH  03062  USA               Email:

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