Individual Submission                                   J. Korhonen, Ed.
Internet-Draft                                    Nokia Siemens Networks
Intended status: Informational                               J. Soininen
Expires: November 3, 2011 January 7, 2012                                  Renesas Mobile
                                                                B. Patil
                                                           T. Savolainen
                                                                G. Bajko
                                                                   Nokia
                                                            K. Iisakkila
                                                          Renesas Mobile
                                                             May 2,
                                                            July 6, 2011

                   IPv6 in 3GPP Evolved Packet System
                      draft-ietf-v6ops-3gpp-eps-01
                      draft-ietf-v6ops-3gpp-eps-02

Abstract

   Internet connectivity and use

   Use of data services in 3GPP based mobile
   networks has increased rapidly as a result of smart phones, phones and broadband
   service services via HSPA
   and HSPA+ networks, competitive service offerings by
   operators HSPA+, in particular Internet services, has increased rapidly and a large number of applications.  Operators who
   operators that have deployed networks based on 3GPP network
   architectures are facing IPv4 address
   shortages.  With the impending exhaustion of available IPv4 addresses
   from shortages at the Internet
   registries there is an increased emphasis for operators and are feeling a pressure to migrate to IPv6.  This
   document describes the support for IPv6 in 3GPP network
   architectures.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 3, 2011. January 7, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  3GPP Terminology and Concepts  . . . . . . . . . . . . . . . .  5
     2.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  The concept of APN . . . . . . . . . . . . . . . . . . . .  8  9
   3.  IP over 3GPP GPRS  . . . . . . . . . . . . . . . . . . . . . .  9 10
     3.1.  Introduction to 3GPP GPRS  . . . . . . . . . . . . . . . .  9 10
     3.2.  PDP Context  . . . . . . . . . . . . . . . . . . . . . . . 10 12
   4.  IP over 3GPP EPS . . . . . . . . . . . . . . . . . . . . . . . 11 12
     4.1.  Introduction to 3GPP EPS . . . . . . . . . . . . . . . . . 11 13
     4.2.  PDN Connection . . . . . . . . . . . . . . . . . . . . . . 12 14
     4.3.  EPS bearer model . . . . . . . . . . . . . . . . . . . . . 13 14
   5.  Address Management . . . . . . . . . . . . . . . . . . . . . . 13 15
     5.1.  IPv4 Address Configuration . . . . . . . . . . . . . . . . 14 15
     5.2.  IPv6 Address Configuration . . . . . . . . . . . . . . . . 14 15
     5.3.  Prefix Delegation  . . . . . . . . . . . . . . . . . . . . 15 16
     5.4.  IPv6 Neighbor Discovery Considerations . . . . . . . . . . 15 16
   6.  3GPP Dual-Stack Approach to IPv6 . . . . . . . . . . . . . . . 16 17
     6.1.  3GPP Networks Prior to Release-8 . . . . . . . . . . . . . 16 17
     6.2.  3GPP Release-8 and -9 Networks . . . . . . . . . . . . . . 17 18
     6.3.  PDN Connection Establishment Process . . . . . . . . . . . 18 19
     6.4.  Mobility of 3GPP IPv4v6 Type of Bearers  . . . . . . . . . 21 22
   7.  Dual-Stack Approach to IPv6 Transition in 3GPP Networks  . . . 21 22
   8.  Deployment issues  . . . . . . . . . . . . . . . . . . . . . . 22 23
     8.1.  Overlapping IPv4 Addresses . . . . . . . . . . . . . . . . 22 23
     8.2.  IPv6 for transport . . . . . . . . . . . . . . . . . . . . 23 24
     8.3.  Operational Aspects of Running Dual-Stack Networks . . . . 24 25
     8.4.  Operational Aspects of Running a Network with IPv6
           Only
           IPv6-only Bearers  . . . . . . . . . . . . . . . . . . . . . . . 24 25
     8.5.  Restricting Outbound IPv6 Roaming  . . . . . . . . . . . . 25 26
     8.6.  Inter-rat  Inter-RAT Handovers and IP Versions  . . . . . . . . . . . 26 27
     8.7.  Provisioning of IPv6 Subscribers and Various
           Combinations During Initial Network Attachment . . . . . . 27 28
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 28 30
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 28 30
   11. Summary and Conclusion . . . . . . . . . . . . . . . . . . . . 28 30
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29 30
   13. Informative References . . . . . . . . . . . . . . . . . . . . 29 30
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 32

1.  Introduction

   IPv6 has been specified in the 3rd Generation Partnership Project
   (3GPP) standards since the early architectures developed for R99
   General Packet Radio Service (GPRS).  However, the support for IPv6
   in commercially deployed networks by the end of 2010 is nearly non-
   existent. remains low.  There are many
   factors that can be attributed to the lack of IPv6 deployment in 3GPP
   networks.  The most relevant one is essentially the same as the
   reason for IPv6 not being deployed by other networks as well, i.e.
   the lack of business and commercial incentives for deployment. 3GPP
   network architectures have also evolved since 1999 (since R99).  The
   most recent version of the 3GPP architecture, the Evolved Packet
   System (EPS), which is commonly referred to as SAE, LTE or Release-8,
   is a packet centric architecture.  The number of subscribers and
   devices that are using the 3GPP networks for Internet connectivity
   and data services has also increased significantly.  With the
   subscriber growth numbers projected to increase even further and the
   IPv4 addresses depletion problem looming in the near term, 3GPP
   operators and vendors have started the process of identifying the
   scenarios and solutions needed to transition to IPv6.

   This document describes the establishment of IP connectivity in 3GPP
   network architectures, specifically in the context of IP bearers for
   3GPP GPRS and for 3GPP EPS.  It provides an overview of how IPv6 is
   supported as per the current set of 3GPP specifications.  Some of the
   issues and concerns with respect to deployment and shortage of
   private IPv4 addresses within a single network domain are also
   discussed.

   The IETF has specified a set of tools and mechanisms that can be
   utilized for transitioning to IPv6.  In addition to operating dual-
   stack networks during the transition from IPv4 to IPv6 phase, the two
   alternative categories for the transition are encapsulation and
   translation.  Most of the mechanisms available in the toolbox can be
   categorized into either translation or encapsulation approaches.  The IETF continues to specify additional solutions for
   enabling the transition based on the deployment scenarios and
   operator/ISP requirements.  There is no single approach for
   transition to IPv6 that can meet the needs for all deployments and
   models.  The 3GPP scenarios for transition, described in [3GPP.23.975], [TR.23975],
   can be addressed using transition mechanisms that are already
   available in the toolbox.  The objective of transition to IPv6 in
   3GPP networks is to ensure that:

   1.  Legacy devices and hosts which have an IPv4 only IPv4-only stack will
       continue to be provided with IP connectivity to the Internet and
       services,

   2.  Devices which are dual-stack can access the Internet either via
       IPv6 or IPv4.  The choice of using IPv6 or IPv4 depends on the
       capability of:

       A.  the application on the host,

       B.  the support for IPv4 and IPv6 bearers by the network and/or,

       C.  the capability of the server(s) and other end points.

   3GPP networks are capable of providing a host with IPv4 and IPv6
   connectivity today, albeit in many cases with upgrades to network
   elements such as the SGSN and GGSN.

2.  3GPP Terminology and Concepts

2.1.  Terminology

   Access Point Name

      Access Point Name (APN) is a fully qualified domain name and
      resolves to a specific gateway in an operators network.  The APNs
      are piggybacked on the administration of the DNS namespace.

   Packet Data Protocol Context

      A Packet Data Protocol (PDP) Context

   Dual Address PDN/PDP Type

      The Dual Address PDN/PDP Type (IPv4v6) is the equivalent of used in 3GPP context in
      many cases as a synonym for dual-stack i.e. a
      virtual connection between the host type
      capable of serving both IPv4 and a gateway.

   General IPv6 simultaneously.

   Evolved Packet Radio Service

      General Core

      Evolved Packet Radio Service (GPRS) Core (EPC) is a packet oriented mobile
      data service available to users an evolution of the 2G and 3G cellular
      communication systems Global System for Mobile communications
      (GSM), and specified 3GPP GPRS system
      characterized by 3GPP. higher-data-rate, lower-latency, packet-optimized
      system.  EPC comprises of subcomponents such as Mobility
      Management Entity (MME), Serving Gateway (SGW), Packet Data
      Network Gateway (PDN-GW) and Home Subscriber Server (HSS).

   Evolved Packet Data Network (PDN) System

      Evolved Packet System (EPS) is a packet based network an evolution of the 3GPP GPRS
      system characterized by higher-data-rate, lower-latency, packet-
      optimized system that either
      belongs supports multiple Radio Access Technologies
      (RAT).  The EPS comprises the Evolved Packet Core (EPC) together
      with the evolved radio access network (E-UTRA and E-UTRAN).

   Evolved UTRAN

      Evolved UTRAN (E-UTRAN) is communications network, sometimes
      referred to as 4G, and consists of eNodeBs (4G base station) which
      make up the operator or E-UTRAN radio access network.  The E-UTRAN allows
      connectivity between the mobile host/device and the core network.

   GPRS tunnelling protocol

      GPRS Tunnelling Protocol (GTP) [TS.29060] [TS.29274] is an external a
      tunnelling protocol defined by 3GPP.  It is a network based
      mobility protocol and similar to Proxy Mobile IPv6 (PMIPv6)
      [RFC5213].  However, GTP also provides functionality beyond
      mobility such as Internet inband signaling related to Quality of Service
      (QoS) and corporate intranet.  The user eventually accesses services in
      one charging among others.

   GSM EDGE Radio Access Network

      GSM EDGE Radio Access Network (GERAN) is communications network,
      commonly referred to as 2G or more PDNs. 2.5G, and consists of base stations
      and Base Station Controllers (BSC) which make up the GSM EDGE
      radio access network.  The operator's packet domain network are
      separated from packet data networks either by GGSNs or PDN
      Gateways (PDN-GW). GERAN allows connectivity between the
      mobile host/device and the core network.

   Gateway GPRS Support Node

      Gateway GPRS Support Node (GGSN) is a gateway function in GPRS,
      which provides connectivity to Internet or other PDNs.  The host
      attaches to a GGSN identified by an APN assigned to it by an
      operator.  The GGSN also serves as the topological anchor for
      addresses/prefixes assigned to the mobile host.

   General Packet Data Network Gateway Radio Service

      General Packet Data Network Gateway (PDN-GW) Radio Service (GPRS) is a gateway function in
      Evolved Packet System (EPS), which provides connectivity to
      Internet or other PDNs.  The host attaches to a PDN-GW identified
      by an APN assigned packet oriented mobile
      data service available to it users of the 2G and 3G cellular
      communication systems Global System for Mobile communications
      (GSM), and specified by an operator. 3GPP.

   High Speed Packet Access

      The PDN-GW also serves
      as High Speed Packet Access (HSPA) and the topological anchor for addresses/prefixes assigned to Evolved High Speed
      Packet Access (HSPA+) are enhanced versions of the
      mobile host.

   Serving Gateway

      Serving Gateway (SGW) WCDMA and
      UTRAN, thus providing more data throughput and lower latencies.

   Home Location Register

      The Home Location Register (HLR) is a gateway function pre-Release-5 database (but
      is also used in Release-5 and later networks in real deployments)
      that contains subscriber data and call routing related
      information.  Every subscriber of an operator including
      subscribers' enabled services are provisioned in EPS, which
      terminates the interface towards E-UTRAN. HLR.

   Home Subscriber Server

      The SGW Home Subscriber Server (HSS) is a database for a given
      subscriber and got introduced in 3GPP Release-5.  It is the entity
      containing the subscription-related information to support the
      network entities actually handling calls/sessions.

   Mobility
      Anchor point Management Entity

      Mobility Management Entity (MME) is a network element that is
      responsible for control plane functionalities, including
      authentication, authorization, bearer management, layer-2 mobility (inter-eNodeB handovers).  For
      each User Equipment connected with the EPS, at any given point of
      time, there is only one SGW.
      mobility, etc.  The SGW MME is essentially the user control plane part of
      the GPRS' SGSN forwarding packets between a PDN-GW.

   Serving Gateway Support Node

      Serving Gateway Support Node (SGSN) is a network element that in GPRS.  The user plane traffic bypasses the MME.

   Mobile Terminal

      The Mobile Terminal (MT) is
      located between the radio access network (RAN) modem and the gateway
      (GGSN).  A per mobile host point to point (p2p) tunnel between radio part of the
      GGSN and SGSN transports the packets between the mobile host and
      the gateway.

   GPRS tunnelling protocol

      GPRS Tunnelling Protocol (GTP) [3GPP.29.060] [3GPP.29.274]
      Mobile Station (MS).

   Public Land Mobile Network

      The Public Land Mobile Network (PLMN) is a
      tunnelling protocol defined by 3GPP.  It network that is
      operated by a network based
      mobility protocol and similar to Proxy Mobile IPv6 (PMIPv6)
      [RFC5213].  However, GTP single administration.  A PLMN (and therefore also provides functionality beyond
      mobility such as inband signaling related to Quality of Service
      (QoS) and charging among others.

   Evolved Packet System

      Evolved Packet System (EPS) is
      an evolution of the 3GPP GPRS
      system characterized operator) is identified by higher-data-rate, lower-latency, packet-
      optimized system that supports multiple Radio Access Technologies
      (RAT).  The EPS comprises the Evolved Packet Core (EPC) together
      with Mobile Country Code (MCC) and
      the evolved radio access network (E-UTRA Mobile Network Code (MNC).  Each (telecommunications) operator
      providing mobile services has its own PLMN.

   Policy and E-UTRAN).

   Mobility Management Entity

      Mobility Management Entity (MME) is a network element that Charging Control

      The Policy and Charging Control (PCC) framework is
      responsible used for control plane functionalities, QoS
      policy and charging control.  It has two main functions: flow
      based charging including
      authentication, authorization, bearer management, layer-2
      mobility, etc.  The MME online credit control, and policy control
      (e.g. gating control, QoS control and QoS signaling).  It is essentially the
      optional to 3GPP EPS but needed if dynamic policy and charging
      control plane part by means of
      the GPRS' SGSN and not located PCC rules based on the user plane data path, i.e. user plane traffic bypasses the MME.

   UMTS Terrestrial Radio Access and services are
      desired.

   Packet Data Network

      UMTS Terrestrial Radio Access

      Packet Data Network (UTRAN) (PDN) is communications
      network, commonly referred a packet based network that either
      belongs to the operator or is an external network such as 3G, and consists of NodeBs (3G
      base station) Internet
      and Radio corporate intranet.  The user eventually accesses services in
      one or more PDNs.  The operator's packet core network are
      separated from packet data networks either by GGSNs or PDN
      Gateways (PDN-GW).

   Packet Data Network Controllers (RNC) Gateway

      Packet Data Network Gateway (PDN-GW) is a gateway function in
      Evolved Packet System (EPS), which make up
      the UMTS radio access network.  The UTRAN allows provides connectivity
      between the mobile host/device and the core network.  UTRAN
      comprises of WCDMA, HSPA and HSPA+ radio technologies.

   Wideband Code Division Multiple Access to
      Internet or other PDNs.  The host attaches to a PDN-GW identified
      by an APN assigned to it by an operator.  The Wideband Code Division Multiple Access (WCDMA) is PDN-GW also serves
      as the radio
      interface used in UMTS networks.

   High Speed topological anchor for addresses/prefixes assigned to the
      mobile host.

   Packet Access

      The High Speed Data Protocol Context

      A Packet Access (HSPA) and Data Protocol (PDP) Context is the Evolved High Speed
      Packet Access (HSPA+) are enhanced versions equivalent of a
      virtual connection between the WCDMA and
      UTRAN, thus providing more data throughput host and lower latencies.

   Evolved UTRAN

      Evolved UTRAN (E-UTRAN) a gateway.

   S4 Serving Gateway Support Node

      S4 Serving Gateway Support Node (S4-SGSN) is communications network, sometimes
      referred a Release-8 (and
      onwards) compliant SGSN that connects 2G/3G radio access network
      to as 4G, EPC via new Release-8 interfaces like S3, S4, and consists of eNodeBs (4G base station) S6d.

   Serving Gateway

      Serving Gateway (SGW) is a gateway function in EPS, which
      make up
      terminates the E-UTRAN radio access network. interface towards E-UTRAN.  The E-UTRAN allows
      connectivity between SGW is the mobile host/device and Mobility
      Anchor point for layer-2 mobility (inter-eNodeB handovers).  For
      each User Equipment connected with the core network.

   eNodeB EPS, at any given point of
      time, there is only one SGW.  The eNodeB SGW is essentially the user
      plane part of the GPRS' SGSN forwarding packets between a base station entity PDN-GW.

   Serving Gateway Support Node

      Serving Gateway Support Node (SGSN) is a network element that supports the Long Term
      Evolution (LTE) air interface.

   GSM EDGE Radio Access Network

      GSM EDGE Radio Access Network (GERAN) is communications network,
      commonly referred to as 2G or 2.5G,
      located between the radio access network (RAN) and consists of base stations the gateway
      (GGSN).  A per mobile host point to point (p2p) tunnel between the
      GGSN and Base Station Controllers (BSC) which make up SGSN transports the GSM EDGE
      radio access network.  The GERAN allows connectivity packets between the mobile host/device host and
      the core network. gateway.

   Terminal Equipment

      The Terminal Equipment (TE) is any device/host connected to the
      Mobile Terminal (MT) offering services to the use.  A TE may
      communicate to a MT, for example, over Point to Point Protocol
      (PPP).

   UE, MS, MN and Mobile

      The terms UE (User Equipment), MS (Mobile Station), MN (Mobile
      Node) and, mobile refer to the devices which are hosts with
      ability to obtain Internet connectivity via a 3GPP network.  A MS
      comprises of a Terminal Equipment (TE) and a Mobile Terminal (MT).
      The terms UE, MS, MN and devices are used interchangeably within
      this document.

   PCC

      The Policy and Charging Control (PCC) framework is used for QoS
      policy and charging control.  It

   UMTS Terrestrial Radio Access Network

      UMTS Terrestrial Radio Access Network (UTRAN) is optional for 3GPP EPS but
      needed if dynamic policy communications
      network, commonly referred to as 3G, and charging control by means consists of PCC
      rules based on user NodeBs (3G
      base station) and services are desired.

   HLR

      The Home Location Register (HLR) is a pre-Release-5 database (the
      reality regarding releases is different, though) for a given
      subscriber.  It is Radio Network Controllers (RNC) which make up
      the entity containing UMTS radio access network.  The UTRAN allows connectivity
      between the subscription-related
      information to support mobile host/device and the network entities actually handling
      calls/sessions.

   HSS core network.  UTRAN
      comprises of WCDMA, HSPA and HSPA+ radio technologies.

   Wideband Code Division Multiple Access

      The Home Subscriber Server (HSS) Wideband Code Division Multiple Access (WCDMA) is a database for a given
      subscriber and got introduced the radio
      interface used in 3GPP Release-5.  It UMTS networks.

   eNodeB

      The eNodeB is the a base station entity
      containing the subscription-related information to support that supports the
      network entities actually handling calls/sessions. Long Term
      Evolution (LTE) air interface.

2.2.  The concept of APN

   The Access Point Name (APN) essentially refers to a gateway in the
   3GPP network.  The 'complete' APN is expressed in a form of a Fully
   Qualified Domain Name (FQDN) and also piggybacked on the
   administration of the DNS namespace, thus effectively allowing the
   discovery of gateways using the DNS.  Mobile hosts/devices can choose
   to attach to a specific gateway in the packet core.  The gateway
   provides connectivity to the Packet Data Network (PDN) such as the
   Internet.  An operator may also include gateways which do not provide
   Internet connectivity, rather a connectivity to closed network
   providing a set of operator's own services.  A mobile host/device can
   be attached to one or more gateways simultaneously.  The gateway in a
   3GPP network is the GGSN or PDN-GW.  Figure 1 below illustrates the
   APN-based network connectivity concept.

                                                            .--.
                                                          _(.   `)
                        .--.         +------------+     _(   PDN  `)_
                      _(Core`.       |GW1         |====(  Internet   `)
           +---+     (   NW   )------|APN=internet|   ( `  .        )  )
   [MN]~~~~|RAN|----( `  .  )  )--+  +------------+    `--(_______)---'
    ^      +---+     `--(___.-'   |
    |                             |                       .--.
    |                             |  +----------+       _(.PDN`)
    |                             +--|GW2       |     _(Operator`)_
    |                                |APN=OpServ|====(  Services   `)
   MN is attached                    +----------+   ( `  .        )  )
   to GW1 and GW2                                    `--(_______)---'
   simultaneously

   Figure 1: Mobile host/device attached to multiple APNs simultaneously

3.  IP over 3GPP GPRS

3.1.  Introduction to 3GPP GPRS

   A simplified 2G/3G GPRS architecture is illustrated in Figure 2.
   This architecture basically covers the GPRS core network since R99 to
   Release-7, and radio access technologies such as GSM (2G), EDGE (2G,
   ofter
   often referred as 2.5G), WCDMA (3G) and HSPA(+) (3G, often referred
   as 3.5G).  The architecture shares obvious similarities with the
   Evolved Packet System (EPS) as will be seen in Section 4.  Based on
   Gn/Gp interfaces, the GPRS core network functionality is logically
   implemented on two network nodes, the SGSN and the GGSN.

                    3G                                     .--.
              Uu  +-----+  Iu  +----+      +----+        _(    `.
   [TE]+[MT]~~|~~~|UTRAN|--|---|SGSN|--|---|GGSN|--|----(   PDN  )
                  +-----+      +----+  Gn  +----+  Gi  ( `  .  )  )
                               / |                      `--(___.-'
                     2G    Gb--  |
                    +---+    /   --Gp
     [TE]+[MT]~~|~~~|BSS|___/    |
                Um  +---+       .--.
                              _(.   `)
                            _( [GGSN] `)_
                           (    other    `)
                          ( `  . PLMN   )  )
                           `--(_______)---'

         Figure 2: Overview of the 2G/3G GPRS Logical Architecture

   Gn/Gp:  These interfaces provide a network based mobility service for
           a mobile host and are used between a SGSN and a GGSN.  The Gn
           interface is used when GGSN and SGSN are located inside one
           operator (i.e.  PLMN).  The Gp-interface is used if the GGSN
           and the SGSN are located in different operator domains (i.e.
           'other' PLMN).  GTP protocol is defined for the Gn/Gp
           interfaces (both GTP-C for the control plane and GTP-U for
           the user plane).

   Gb:     Is the Base Station System (BSS) to SGSN interface, which is
           used to carry information concerning packet data transmission
           and layer-2 mobility management.  The Gb-interface is based
           on either on Frame Relay or IP.

   Iu:     Is the Radio Network System (RNS) to SGSN interface, which is
           used to carry information concerning packet data transmission
           and layer-2 mobility management.  The user plane part of the
           Iu-interface (actually the Iu-PS) is based on GTP-U.  The
           control plane part of the Iu-interface is based on Radio
           Access Network Application Protocol (RANAP).

   Gi:     It is the interface between the GGSN and a PDN.  The PDN may
           be an operator external public or private packet data network
           or an intra-operator packet data network.

   Uu/Um:  Are either 2G or 3G radio interfaces between a mobile
           terminal and a respective radio access network.

   The SGSN is responsible for the delivery of data packets from and to
   the mobile hosts within its geographical service area when a direct
   tunnel option is not used.  If the direct tunnel is used, then the
   user plane goes directly between the RNS and the GGSN.  The control
   plane traffic always goes through the SGSN.  For each mobile host
   connected with the GPRS, at any given point of time, there is only
   one SGSN.

3.2.  PDP Context

   A PDP context is an association between a mobile host represented by
   one IPv4 address and/or one /64 IPv6 prefix and a PDN represented by
   an APN.  Each PDN can be accessed via a gateway (typically a GGSN or
   PDN-GW).  On the device/mobile host a PDP context is equivalent to a
   network interface.  A host may hence be attached to one or more
   gateways via separate connections, i.e.  PDP contexts.  Each primary
   PDP context has its own IPv4 address and/or one /64 IPv6 prefix
   assigned to it by the PDN and anchored in the corresponding gateway.
   Applications on the host use the appropriate network interface (PDP
   context) for connectivity to a specific PDN.  Figure 3 represents a
   high level view of what a PDP context implies in 3GPP networks.

   Y
   |                               +---------+       .--.
   |--+ __________________________ | APNx in |     _(    `.
   |  |O______PDPc1_______________)| GGSN /  |----(Internet)
   |MS|                            | PDN-GW  |   ( `  .  )  )
   |/ |                            +---------+    `--(___.-'
   |UE| _______________________ +---------+          .--.
   |  |O______PDPc2____________)| APNy in |        _(Priv`.
   +--+                         | GGSN /  |-------(Network )
                                | PDN-GW  |      ( `  .  )  )
                                +---------+       `--(___.-'

           Figure 3: PDP contexts between the MS/UE and gateway

   In the above figure there are two PDP contexts at the MS/UE (UE=User
   Equipment in 3GPP parlance).  The 'PDPc1' PDP context that is
   connected to APNx provided Internet connectivity and the 'PDPc2' PDP
   context provides connectivity to a private IP network via APNy (as an
   example this network may include operator specific services such as
   MMS (Multi media service).  An application on the host such as a web
   browser would use the PDP context that provides Internet connectivity
   for accessing services on the Internet.  An application such as MMS
   would use APNy in the figure above because the service is provided
   through the private network.

4.  IP over 3GPP EPS
4.1.  Introduction to 3GPP EPS

   In its most basic form, the EPS architecture consists of only two
   nodes on the user plane, a base station and a core network Gateway
   (GW).  The basic EPS architecture is illustrated in Figure 4.  The
   Mobility Management Entity (MME) node performs control-plane
   functionality and is separated from the node(s) that performs bearer-
   plane functionality (GW), with a well-defined open interface between
   them (S11).  The optional interface S5 can be used to split the
   Gateway (GW) into two separate nodes, the Serving Gateway (SGW) and
   the PDN-GW.  This allows independent scaling and growth of traffic
   throughput and control signal processing.  The functional split of
   gateways also allows for operators to choose optimized topological
   locations of nodes within the network and enables various deployment
   models including the sharing of radio networks between different
   operators.

                                                             +--------+
                         S1-MME  +-------+  S11              |   IP   |
                       +----|----|  MME  |---|----+          |Services|
                       |         |       |        |          +--------+
                       |         +-------+        |               |SGi
    +----+ LTE-Uu +-------+ S1-U               +-------+  S5  +-------+
    |MN  |----|---|eNodeB |---|----------------| SGW   |--|---|PDN-GW |
    |    |========|=======|====================|=======|======|       |
    +----+        +-------+DualStack EPS Bearer+-------+      +-------+

                Figure 4: EPS Architecture for 3GPP Access

   S5:      It provides user plane tunnelling and tunnel management
            between SGW and PDN-GW, using GTP or PMIPv6 as the network
            based mobility management protocol.

   S1-U:    Provides user plane tunnelling and inter eNodeB path
            switching during handover between eNodeB and SGW, using the
            GTP-U protocol (GTP user plane).

   S1-MME:  Reference point for the control plane protocol between
            eNodeB and MME.

   SGi:     It is the interface between the PDN-GW and the packet data
            network.  Packet data network may be an operator external
            public or private packet data network or an intra operator
            packet data network.

   The eNodeB is a base station entity that supports the Long Term
   Evolution (LTE) air interface and includes functions for radio
   resource control, user plane ciphering, and other lower layer
   functions.  MME is responsible for control plane functionalities,
   including authentication, authorization, bearer management, layer-2
   mobility, etc.

   The SGW is the Mobility Anchor point for layer-2 mobility.  For each
   MN connected with the EPS, at any given point of time, there is only
   one SGW.

4.2.  PDN Connection

   A PDN connection is an association between a mobile host represented
   by one IPv4 address and/or one /64 IPv6 prefix, and a PDN represented
   by an APN.  The PDN connection is the EPC equivalent of the GPRS PDP
   context.  Each PDN can be accessed via a gateway (a PDN-GW).  PDN is
   responsible for the IP address/prefix allocation to the mobile host.
   On the device/mobile host a PDN connection is equivalent to a network
   interface.  A host may hence be attached to one or more gateways via
   separate connections, i.e.  PDN connections.  Each PDN connection has
   its own IP address/prefix assigned to it by the PDN and anchored in
   the corresponding gateway.  Applications on the host use the
   appropriate network interface (PDN connection) for connectivity.

4.3.  EPS bearer model

   The logical concept of a bearer has been defined to be an aggregate
   of one or more IP flows related to one or more services.  An EPS
   bearer exists between the Mobile Node (MN i.e. a mobile host) and the
   PDN-GW and is used to provide the same level of packet forwarding
   treatment to the aggregated IP flows constituting the bearer.
   Services with IP flows requiring a different packet forwarding
   treatment would therefore require more than one EPS bearer.  The
   mobile host performs the binding of the uplink IP flows to the bearer
   while the PDN-GW performs this function for the downlink packets.

   In order to provide low latency for always on connectivity, a default
   bearer will be provided at the time of startup and an IPv4 address
   and/or IPv6 prefix gets assigned to the mobile host (this is
   different from GPRS, where mobile hosts are not automatically
   assigned with an IP address or prefix).  This default bearer will be
   allowed to carry all traffic which is not associated with a dedicated
   bearer.  Dedicated bearers are used to carry traffic for IP flows
   that have been identified to require a specific packet forwarding
   treatment.  They may be established at the time of startup; for
   example, in the case of services that require always-on connectivity
   and better QoS than that provided by the default bearer.  The default
   bearer and the dedicated bearer(s) associated to it share the same IP
   address(es)/prefix.

   An EPS bearer is referred to as a GBR bearer if dedicated network
   resources related to a Guaranteed Bit Rate (GBR) value that is
   associated with the EPS bearer are permanently allocated (e.g. by an
   admission control function in the eNodeB) at bearer establishment/
   modification.  Otherwise, an EPS bearer is referred to as a non-GBR
   bearer.  The default bearer is always non-GBR, with the resources for
   the IP flows not guaranteed at eNodeB, and with no admission control.
   However, the dedicated bearer can be either GBR or non-GBR.  A GBR
   bearer has a Guaranteed Bit Rate (GBR) and Maximum Bit Rate (MBR)
   while more than one non-GBR bearer belonging to the same UE shares an
   Aggregate Maximum Bit Rate (AMBR).  Non-GBR bearers can suffer packet
   loss under congestion while GBR bearers are immune to such losses.

5.  Address Management

5.1.  IPv4 Address Configuration

   Mobile host's IPv4 address configuration is always performed during
   PDP context/EPS bearer setup procedures (on layer-2).  DHCPv4-based
   [RFC2131] address configuration is supported by the 3GPP
   specifications, but is not used in wide scale.  The mobile host must
   always support layer-2 based address configuration, since DHCPv4 is
   optional for both mobile hosts and networks.

5.2.  IPv6 Address Configuration

   IPv6 Stateless Address Autoconfiguration (SLAAC) as specified in
   [RFC4862] is the only supported address configuration mechanism.
   Stateful DHCPv6-based address configuration is not supported by 3GPP
   specifications [RFC3315].  On the other hand, Stateless DHCPv6-
   service to obtain other configuration information is supported
   [RFC3736].  This implies that the M-bit must always be set to zero
   and the O-bit may be set to one in the Router Advertisement (RA) sent
   to the UE.

   3GPP network allocates each default bearer a unique /64 prefix, and
   uses layer-2 signaling to suggest user equipment an Interface
   Identifier that is guaranteed not to conflict with gateway's
   Interface Identifier.  The UE must configure its link-local address
   using this Interface Identifier.  The UE is allowed to use any
   Interface Identifier it wishes for the other addresses it configures.
   There is no restriction, for example, of using Privacy Extension for
   SLAAC [RFC4941] or other similar types of mechanisms.

   In the 3GPP link model the /64 prefix assigned to the UE is always
   off-link (i.e. the L-bit in the Prefix Information Option (PIO) in
   the RA must be set to zero).  If the advertised prefix is used for
   SLAAC then the A-bit in the PIO must be set to one.  The details of
   the 3GPP link-model and address configuration is described in Section
   11.2.1.3.2a of [3GPP.29.061]. [TS.29061].  More specifically, the GGSN/PDN-GW
   guarantees that the /64 prefix is unique for the mobile host.
   Therefore, there is no need to perform any Duplicate Address
   Detection (DAD) on addresses the mobile host creates (i.e., the
   'DupAddrDetectTransmits' variable in the mobile host should be zero).
   The GGSN/PDN-GW is not allowed to generate any globally unique IPv6
   addresses for itself using the /64 prefix assigned to the mobile host
   in the RA.

   The current 3GPP architecture limits number of prefixes in each
   bearer to a single /64 prefix.  If the mobile host finds more than
   one prefix in the RA, it only considers the first one and silently
   discard
   discards the others [3GPP.29.061]. [TS.29061].  Therefore, multi-homing within a
   single bearer is not possible.  Renumbering without closing layer-2
   connection is also not possible.  The lifetime of /64 prefix is bound
   to lifetime of layer-2 connection even if the advertised prefix
   lifetime would be longer than the layer-2 connection lifetime.

5.3.  Prefix Delegation

   IPv6 prefix delegation is a part of Release-10 and is not covered by
   any earlier release.  However, the /64 prefix allocated for each
   default bearer (and to the user equipment) may be shared to local
   area network by user equipment implementing Neighbor Discovery proxy
   (ND proxy) [RFC4389] functionality.

   Release-10 prefix delegation uses the DHCPv6-based prefix delegation
   [RFC3633].  The model defined for Release-10 requires aggregatable
   prefixes, which means the /64 prefix allocated for the default bearer
   (and to the user equipment) must be part of the shorter delegated
   prefix.  DHCPv6 prefix delegation has an explicit limitation
   described in Section 12.1 of [RFC3633] that a prefix delegated to a
   requesting router cannot be used by the delegating router (i.e., the
   PDN-GW in this case).  This implies the shorter 'delegated prefix'
   cannot be given to the requesting router (i.e. the user equipment) as
   such but has to be delivered by the delegating router (i.e. the
   PDN-GW) in such a way the /64 prefix allocated to the default bearer
   is not part of the 'delegated prefix'.  IETF is working on a solution
   for DHCPv6-based prefix delegation to exclude a specific prefix from
   the 'delegated prefix' [I-D.ietf-dhc-pd-exclude].

5.4.  IPv6 Neighbor Discovery Considerations

   3GPP link between the UE and the next hop router (e.g.  GGSN)
   resemble a point to point (p2p) link, which has no link-layer
   addresses [RFC3316] and this has not changed from 2G/3G GPRS to EPS.

   The UE IP stack has to take this into consideration.  When the 3GPP
   PDP Context appears as a PPP interface/link to the UE, the IP stack
   is usually prepared to handle Neighbor Discovery protocol and the
   related Neighbor Cache state machine transitions in an appropriate
   way, even thought though Neighbor Discovery protocol messages contain no link
   layer address information.  However, some operating systems discard
   Router Advertisements on their PPP interface/link as a default
   setting.  This causes the SLAAC to fail when the 3GPP PDP Context
   gets established, thus stalling all IPv6 traffic.

   Currently several operating systems and their network drivers can
   make the 3GPP PDP Context to appear as an IEEE802 interface/link to
   the IP stack.  This has few known issues, especially when the IP
   stack is made to believe the underlying link has link-layer
   addresses.  First, the Neighbor Advertisement sent by a GGSN as a
   response to an address resolution triggered Neighbor Solicitation may
   not contain a Target Link-Layer address option (as suggested in
   [RFC4861] Section 4.4).  Then it is possible that the address
   resolution never completes when the UE tries to resolve the link-
   layer address of the GGSN, thus stalling all IPv6 traffic.

   Second, the GGSN may simply discard all address resolution triggered
   Neighbor Solicitation messages (as hinted in [RFC3316] Section 2.4.1
   that address resolution and next-hop determination are not needed).
   As a result the address resolution never completes when the UE tries
   to resolve the link-layer address of the GGSN, thus stalling all IPv6
   traffic.

6.  3GPP Dual-Stack Approach to IPv6

6.1.  3GPP Networks Prior to Release-8

   3GPP standards prior to Release-8 provide IPv6 access for cellular
   devices with PDP contexts of type IPv6 [3GPP.23.060]. [TS.23060].  For dual-stack
   access, a PDP context of type IPv6 is established in parallel to the
   PDP context of type IPv4, as shown in Figure 5 and Figure 6.  For
   IPv4-only service, connections are created over the PDP context of
   type IPv4 and for IPv6-only service connections are created over the
   PDP context of type IPv6.  The two PDP contexts of different type may
   use the same APN (and the gateway), however, this aspect is not
   explicitly defined in standards.  Therefore, cellular device and
   gateway implementations from different vendors may have varying
   support for this functionality.

   Y                                        .--.
   |                                      _(IPv4`.
   |---+              +---+    +---+     (  PDN   )
   | D |~~~~~~~//-----|   |====|   |====( `  .  )  )
   | S | IPv4 context | S |    | G |     `--(___.-'
   |   |              | G |    | G |        .--.
   | M |              | S |    | S |      _(IPv6`.
   | N | IPv6 context | N |    | N |     (  PDN   )
   |///|~~~~~~~//-----|   |====|(s)|====( `  .  )  )
   +---+              +---+    +---+     `--(___.-'

    Figure 5: A dual-stack mobile host connecting to both IPv4 and IPv6
       Internet using parallel IPv4-only and IPv6-only PDP contexts

   Y
   |
   |---+              +---+    +---+
   | D |~~~~~~~//-----|   |====|   |        .--.
   | S | IPv4 context | S |    | G |      _( DS `.
   |   |              | G |    | G |     (  PDN   )
   | M |              | S |    | S |====( `  .  )  )
   | N | IPv6 context | N |    | N |     `--(___.-'
   |///|~~~~~~~//-----|   |====|   |
   +---+              +---+    +---+

   Figure 6: A dual-stack mobile host connecting to dual-stack Internet
            using parallel IPv4-only and IPv6-only PDP contexts

   The approach of having parallel IPv4 and IPv6 type of PDP contexts
   open is not optimal, because two PDP contexts require double the
   signaling and consume more network resources than a single PDP
   context.  In the figure above the IPv4 and IPv6 PDP contexts are
   attached to the same GGSN.  While this is possible, the DS dual-stack
   (DS) MS may be attached to different GGSNs in the scenario where one
   GGSN supports IPv4 PDN connectivity while another GGSN provides IPv6
   PDN connectivity.

6.2.  3GPP Release-8 and -9 Networks

   Since 3GPP Release-8, the powerful concept of a dual-stack type of
   PDN connection and EPS bearer have been introduced [3GPP.23.401]. [TS.23401].  This
   enables parallel use of both IPv4 and IPv6 on a single bearer
   (IPv4v6), as illustrated in Figure 7, and makes dual stack simpler
   than in earlier 3GPP releases.  As of Release-9, GPRS network nodes
   also support dual-stack type (IPv4v6) PDP contexts.

   Y
   |
   |---+              +---+    +---+
   | D |              |   |    | P |        .--.
   | S |              |   |    | D |      _( DS `.
   |   | IPv4v6 (DS)  | S |    | N |     (  PDN   )
   | M |~~~~~~~//-----| G |====| - |====( `  .  )  )
   | N | bearer       | W |    | G |     `--(___.-'
   |///|              |   |    | W |
   +---+              +---+    +---+

   Figure 7: A dual-stack mobile host connecting to dual-stack Internet
                 using a single IPv4v6 type PDN connection

   The following is a description of the various PDP contexts/PDN bearer
   types that are specified by 3GPP:

   1.  For 2G/3G access to GPRS core (SGSN/GGSN) pre-Release-9 there are
       two IP PDP Types, IPv4 and IPv6.  Two PDP contexts are needed to
       get dual stack connectivity.

   2.  For 2G/3G access to GPRS core (SGSN/GGSN) from Release-9 there
       are three IP PDP Types, IPv4, IPv6 and IPv4v6.  Minimum one PDP
       context is needed to get dual stack connectivity.

   3.  For 2G/3G access to EPC core (PDN-GW via S4 Release-8 SGSN) S4-SGSN) from Release-8
       there are three IP PDP Types, IPv4, IPv6 and IPv4v6 which gets
       mapped to PDN Connection type.  Minimum one PDP Context is needed
       to get dual stack connectivity.

   4.  For LTE (E-UTRAN) access to EPC core from Release-8 there are
       three IP PDN Types, IPv4, IPv6 and IPv4v6.  Minimum one PDN
       Connection is needed to get dual stack connectivity.

6.3.  PDN Connection Establishment Process

   The PDN connection establishment process is specified in detail in
   3GPP specifications.  Figure 8 illustrates the high level process and
   signaling involved in the establishment of a PDN connection.

   UE         eNb/        MME         SGW       PDN-GW       HSS/
   |           BS          |           |           |         AAA
   |           |           |           |           |           |
   |---------->|(1)        |           |           |           |
   |           |---------->|(1)        |           |           |
   |           |           |           |           |           |
   |/---------------------------------------------------------\|
   |             Authentication and Authorization              |(2)
   |\---------------------------------------------------------/|
   |           |           |           |           |           |
   |           |           |---------->|(3)        |           |
   |           |           |           |---------->|(3)        |
   |           |           |           |           |           |
   |           |           |           |<----------|(4)        |
   |           |           |<----------|(4)        |           |
   |           |<----------|(5)        |           |           |
   |/---------\|           |           |           |           |
   | RB setup  |(6)        |           |           |           |
   |\---------/|           |           |           |           |
   |           |---------->|(7)        |           |           |
   |---------->|(8)        |           |           |           |
   |           |---------->|(9)        |           |           |
   |           |           |           |           |           |
   |============= UL Uplink Data =============>==========>|(10) =========>==========>|(10)       |
   |           |           |           |           |           |
   |           |           |---------->|(11)       |           |
   |           |           |           |           |           |
   |           |           |<----------|(12)       |           |
   |           |           |           |           |           |
   |<============ DL Downlink Data =============<===========|(13) =======<===========|(13)       |
   |           |           |           |           |           |

     Figure 8: Simplified PDN connection setup procedure in Release-8

   1.   The UE (i.e the MS) requires a data connection and hence decides
        to establish a PDN connection with a PDN-GW.  The UE sends an
        "Attach Request" (layer-2) to the BS.  The BS forwards this
        attach request to the MME.

   2.   Authentication of the UE with the AAA server/HSS follows.  If
        the UE is authorized for establishing a data connection, the
        following steps continue

   3.   The MME sends a "Create Session Request" message to the
        Serving-GW.  The SGW forwards the create session request to the
        PDN-GW.  The SGW knows the address of the PDN-GW to forward the
        create session request to as a result of this information having
        been obtained by the MME during the authentication/authorization
        phase.

        The UE IPv4 address and/or IPv6 prefix get assigned during this
        step.  If a subscribed IPv4 address and/or IPv6 prefix is
        statically allocated for the UE for this APN, then the MME
        already passes the address information to the SGW and eventually
        to the PDN-GW in the "Create Session Request" message.
        Otherwise, the PDN-GW manages the address assignment to the UE
        (there is another variation to this where IPv4 address
        allocation is delayed until the UE initiates a DHCPv4 exchange
        but this is not discussed here).

   4.   The PDN-GW creates a PDN connection for the UE and sends "Create
        Session Response" message to the SGW from which the session
        request message was received from.  The SGW forwards the
        response to the corresponding MME which originated the request.

   5.   The MME sends the "Attach Accept/Initial Context Setup request"
        message to the eNodeB/BS.

   6.   The radio bearer between the UE and the eNb is reconfigured
        based on the parameters received from the MME MME.  (See note 1
        below)

   7.   The eNb sends "Initial Context Response" message to the MME.

   8.   The UE sends a "Direct Transfer" message to the eNodeB which
        includes the Attach complete signal.

   9.   The eNodeB forwards the Attach complete message to the MME.

   10.  The UE can now start sending uplink packets to the PDN GW.

   11.  The MME sends a "Modify Bearer Request" message to the SGW.

   12.  The SGW responds with a "Modify Bearer Response" message.  At
        this time the downlink connection is also ready ready.

   13.  The UE can now start receiving downlink packets packets, including
        possible SLAAC related IPv6 packets.

   The type of PDN connection established between the UE and the PDN-GW
   can be any of the types described in the previous section.  The DS dual-
   stack (DS) PDN connection, i.e the one which supports both IPv4 and
   IPv6 packets is the default one that will be established if no
   specific PDN connection type is specified by the UE in Release-8
   networks.

      Note 1: The UE receives the PDN Address Information Element
      [TS.24301] at the end of radio bearer setup messaging.  This
      Information Element contains only the Interface Identifier of the
      IPv6 address.  In a case of GPRS the PDP Address Information
      Element [TS.24008] would contain a complete IPv6 address.
      However, the UE must ignore the IPv6 prefix if it receives one in
      the message (see Section 11.2.1.3.2a of [TS.29061]).

6.4.  Mobility of 3GPP IPv4v6 Type of Bearers

   3GPP discussed at length various approaches to support mobility
   between a Release-8 LTE network and pre-Release-8 networks a pre-Release-9 2G/3G network
   without a S4-SGSN for the new dual-stack type of bearers.  The chosen
   approach for mobility is as follows, in short: if a mobile is known to be at risk allowed
   for doing handovers between a Release-8 LTE network and a pre-
   Release-8 networks,
   Release-9 2G/3G network without a S4-SGSN while having open PDN
   connections, only single stack bearers are used.  Essentially
   meaning: this
   means following deployment options:

   1.  If a network knows a mobile may do handovers between a Release-8
       LTE network and pre-Release-8 networks (segment), a pre-Release-9 2G/3G network will only without a S4-SGSN,
       then the network is configured to provide only single stack
       bearers, even if the mobile host requests dual-stack bearers.  This can happen e.g. if an operator is using pre-
       Release-8 SGSNs in some parts of the network.  The single stack
       bearers of Release-8 are easy to map one-to-one to pre-Release-8
       bearers.

   2.  If a the network knows a the mobile will not be able to do handover to
       pre-Release-8 does handovers only between a
       Release-8 LTE network (segment), it will and a Release-9 2G/3G network or a pre-
       Release-9 network with a S4-SGSN, then the network is configured
       to provide the mobile with dual-stack bearers on request.  This can happen e.g. if an
       operator has upgraded their SGSNs to support dual-stack bearers,
       or if an operator is running  The
       same also applies for LTE-only network. deployments.

   When a network operator and their roaming partners have upgraded
   their networks to Release-8, it is possible to use the new IPv4v6
   dual-stack type of bearers.  A Release-8 mobile device always
   requests for a dual-stack bearer, but accepts what is assigned by the
   network.

7.  Dual-Stack Approach to IPv6 Transition in 3GPP Networks

   3GPP networks can natively transport IPv4 and IPv6 packets between
   the mobile station/UE and the gateway (GGSN or PDN-GW) as a result of
   establishing either a dual-stack PDP context or parallel IPv4 and
   IPv6 PDP contexts.

   Current deployments of 3GPP networks primarily support IPv4 only. IPv4-only.
   These networks can be upgraded to also support IPv6 PDP contexts.  By
   doing so devices and applications that are IPv6 capable can start
   utilizing the IPv6 connectivity.  This will also ensure that legacy
   devices and applications continue to work with no impact.  As newer
   devices start using IPv6 connectivity, the demand for actively used
   IPv4 connections is expected to slowly decrease, helping operators
   with a transition to IPv6.  With a dual-stack approach, there is
   always the potential to fallback to IPv4.  A device which may be
   roaming in a network wherein IPv6 is not supported by the visited
   network could fall back to using IPv4 PDP contexts and hence the end
   user would at least get some connectivity.  Unfortunately, dual-stack
   approach as such does not lower the number of used IPv4 addresses.
   Every dual-stack bearer still needs to be given an IPv4 address,
   private or public.  This is a major concern with dual-stack bearers
   concerning IPv6 transition.  However, if the majority of active IP
   communication has moved over to IPv6, then in case of NAT44 [RFC1918]
   IPv4 connections the number of active IPv4 connections can still be
   expected to gradually decrease and thus giving some level of relief
   regarding NAT44 function scalability.

   As the networks evolve to support Release-8 EPS architecture and the
   dual-stack PDP contexts, newer devices will be able to leverage such
   capability and have a single bearer which supports both IPv4 and
   IPv6.  Since IPv4 and IPv6 packets are carried as payload within GTP
   between the MS and the gateway (GGSN/PDN-GW) the transport network
   capability in terms of whether it supports IPv4 or IPv6 on the
   interfaces between the eNodeB and SGW or, SGW and PDN-GW is
   immaterial.

8.  Deployment issues

8.1.  Overlapping IPv4 Addresses

   Given the shortage of globally routable public IPv4 addresses,
   operators tend to assign private IPv4 addresses [RFC1918] to hosts
   when they establish an IPv4 only IPv4-only PDP context or an IPv4v6 type PDN
   context.  About 16 million hosts can be assigned a private IPv4
   address that is unique within a domain.  However, in case of many
   operators the number of subscribers is greater than 16 million.  The
   issue can be dealt with by assigning overlapping RFC 1918 IPv4
   addresses to hosts.  As a result the IPv4 address assigned to a host
   within the context of a single operator realm would no longer be
   unique.  This has the obvious and know known issues of NATed IP connection
   in the Internet.  Direct host to host connectivity becomes
   complicated, unless the hosts are within the same private address
   range pool and/or anchored to the same gateway, referrals using IP
   addresses will have issues and so forth.  These are generic issues
   and not only a concern of the EPS.  However, 3GPP as such does not
   have any mandatory language concerning NAT44 functionality in EPC.
   Obvious deployment choices apply also to EPC:

   1.  Very large network deployments are partitioned, for example,
       based on a geographical areas.  This partitioning allows for
       overlapping IPv4 addresses ranges to be assigned to hosts that
       are in different areas.  Each area has its own pool of gateways
       that are dedicated for a certain overlapping IPv4 address range
       (referred here later as a zone).  Standard NAT44 functionality
       enables the
       allows for communication between hosts that are assigned from the
       same IPv4 address but belong [RFC1918] private zone to different zones, yet are part of the same operator domain.
       Internet.  Communication between zones require special
       arrangement, such as using intermediate gateways (e.g.  Back to
       Back User Agent (B2BUA) in case of SIP).

   2.  A mobile host/device attaches to a gateway as part of the attach
       process.  The number of hosts that a gateway supports is in the
       order of 1 to 10 million.  Hence all the hosts assigned to a
       single gateway can be assigned private IPv4 addresses.  Operators
       with large subscriber bases have multiple gateways and hence the
       same [RFC1918] IPv4 address space can be reused across gateways.
       The IPv4 address assigned to a host is unique within the scope of
       a single gateway.

   3.  New services requiring direct connectivity between hosts should
       be build on IPv6.  Possible existing IPv4-only services and
       applications requiring direct connectivity can be ported to IPv6.

8.2.  IPv6 for transport

   The various reference points of the 3GPP architecture such as S1-U,
   S5 and S8 are based on either GTP or PMIPv6.  The underlying
   transport for these reference points can be IPv4 or IPv6.  GTP has
   been able to operate over IPv6 transport (optionally) since R99 and
   PMIPv6 has supported IPv6 transport starting from its introduction in
   Release-8.  The user plane traffic between the mobile host and the
   gateway can use either IPv4 or IPv6.  These packets are essentially
   treated as payload by GTP/PMIPv6 and transported accordingly with no
   real attention paid to the information (at least from a routing
   perspective) contained in the IPv4 or IPv6 headers.  The transport
   links between the eNodeB and the SGW, and the link between the SGW
   and PDN-GW can be migrated to IPv6 without any direct implications to
   the architecture.

   Currently, the inter-operator (for 3GPP technology) roaming networks
   are all IPv4 only IPv4-only (see Inter-PLMN Backbone Guidelines [GSMA.IR.34]).
   Eventually these roaming networks will also get migrated to IPv6, if
   there is a business reason for that.  The migration period can be
   prolonged considerably because the 3GPP protocols always tunnel user
   plane traffic in the core network and as described earlier the
   transport network IP version is not in any way tied to user plane IP
   version.  Furthermore, the design of the inter-operator roaming
   networks is such that the user plane and transport network IP
   addressing is completely separated from each other.  The inter-
   operator roaming network itself is also completely separated from the
   Internet.  Only those core network nodes that must be connected to
   the inter-operator roaming networks are actually visible there, and
   be able to send and receive (tunneled) traffic within the inter-
   operator roaming networks.  Obviously, in order the roaming to work
   properly, the operators have to agree on supported protocol versions
   so that the visited network does not, for example, unnecessarily drop
   user plane IPv6 traffic.

8.3.  Operational Aspects of Running Dual-Stack Networks

   Operating dual-stack networks does imply cost and complexity to a
   certain extent.  However these factors are mitigated by the assurance
   that legacy devices and services are unaffected and there is always a
   fallback to IPv4 in case of issues with the IPv6 deployment or
   network elements.  The model also enables operators to develop
   operational experience and expertise in an incremental manner.

   Running dual-stack networks requires the management of multiple IP
   address spaces.  Tracking of hosts needs to be expanded since it can
   be identified by either an IPv4 address or IPv6 prefix.  Network
   elements will also need to be dual-stack capable in order to support
   the dual-stack deployment model.

   Deployment and migration cases described in Section 6.1 for providing
   dual-stack like capability may mean doubled resource usage in
   operator's network.  This is a major concern against providing dual-
   stack like connectivity using techniques discussed in Section 6.1.
   Also handovers between networks with different capabilities in terms
   of networks being dual-stack like service capable or not, may turn
   out hard to comprehend for users and for application/services to cope
   with.  These facts may add other than just technical concerns for
   operators when planning to roll out dual-stack service offerings.

8.4.  Operational Aspects of Running a Network with IPv6 Only IPv6-only Bearers

   It is possible to allocate IPv6 only IPv6-only type bearers to mobile hosts in
   3GPP networks.  IPv6 only  IPv6-only bearer type has been part of the 3GPP
   specification since the beginning.  In 3GPP Release-8 (and later) it
   was defined that a dual-stack mobile host (or when the radio
   equipment has no knowledge of the host IP stack capabilities) must
   first attempt to establish a dual-stack bearer and then possibly fall
   back to single IP version bearer.  A Release-8 (or later) mobile host
   with IPv6 only IPv6-only stack can directly attempt to establish an IPv6 only IPv6-only
   bearer.  The IPv6 only behavior IPv6-only behaviour is up to a subscription provisioning
   or a PDN-GW configuration, and the fallback scenarios do not
   necessarily cause additional signaling.

   Although the bullets below introduce IPv6 to IPv4 address translation
   and specifically discuss NAT64 technology [RFC6144], the current 3GPP
   Release-8 architecture does not describe the use of address
   translation or NAT64.  It is up to a specific deployment whether
   address translation is part of the network or not.  Some operational
   aspects to consider for running a network with IPv6 only IPv6-only bearers:

   o  The mobile hosts must have an IPv6 capable stack and a radio
      interface capable of establishing an IPv6 PDP context or PDN
      connection.

   o  The GGSN/PDN-GW must be IPv6 capable in order to support IPv6
      bearers.  Furthermore, the SGSN/MME must allow the creation of PDP
      Type or PDN Type of IPv6.

   o  Many of the common applications are IP version agnostic and hence
      would work using an IPv6 bearer.  However, applications that are
      IPv4 specific would not work.

   o  Inter-operator roaming is another aspect which causes issues, at
      least during the ramp up phase of the IPv6 deployment.  If the
      visited network to which outbound roamers attach to does not
      support PDP/PDN Type IPv6, then there needs to be a fallback
      option.  The fallback option in this specific case is mostly up to
      the mobile host to implement.  Several cases are discussed in the
      following sections.

   o  If and when a mobile host using IPv6 only IPv6-only bearer needs to access
      to IPv4 Internet/network, a translation of some type from IPv6 to
      IPv4 has to be deployed in the network.  NAT64 (and DNS64) is one
      solution that can be used for this purpose and works for a certain
      set of protocols (read TCP TCP, UDP and UDP, ICMP, and when applications
      actually use DNS for resolving name to IP addresses).

8.5.  Restricting Outbound IPv6 Roaming

   Roaming was briefly touched upon in Sections 8.2 and 8.4.  While
   there is interest in offering roaming service for IPv6 enabled mobile
   hosts and subscriptions, not all visited networks are prepared for
   IPv6 outbound roamers.  There are basically two issues.  First, the
   visited network (S4-)SGSN SGSN does not support the IPv6 PDP Context or IPv4v6
   PDP Context types.  These should mostly concern pre-Release-8 pre-Release-9 2G/3G
   networks without S4-SGSN but there is no definitive rule as the
   deployed feature sets vary depending on implementations and licenses.
   Second, the visited network might not be commercially ready for IPv6
   outbound roamers, while everything might work technically at the user
   plane level.  This would lead to "revenue leakage" especially from
   the visited operator point of view (note that the use of visited
   network GGSN/
   PDN-GW GGSN/PDN-GW does not really exist in real deployments today).
   Therefore, it might be in the interest of operators to prohibit
   roaming selectively within specific visited networks.

   Unfortunately, it is not mandatory to implement/deploy 3GPP standards
   based solution to selectively prohibit IPv6 roaming without also
   prohibiting other packet services (such as IPv4 roaming).  However,
   there are few possibilities how this can be done in real deployments.
   The examples given below are either optional and/or vendor specific
   features to the 3GPP EPC:

   o  Using Policy and Charging Control (PCC) [3GPP.23.203] [TS.23203] functionality
      and its rules to fail, for example, the bearer authorization when
      a desired criteria is met.  In this case that would be PDN/PDP
      Type IPv6/IPv4v6 and a specific visited network.  The rules can be
      provisioned either in the home network or locally in the visited
      network.

   o  Some Home Location Register (HLR) and Home Subscriber Server (HSS)
      subscriber databases allow prohibiting roaming in a specific
      (visited) network for a specified PDN/PDP Type.

   The obvious problems are that these solutions are not mandatory, are
   not unified across networks, and therefore also lack well-specified
   fall back mechanism from the mobile host point of view.

8.6.  Inter-rat  Inter-RAT Handovers and IP Versions

   It is obvious that when operators start to incrementally deploy EPS
   (and E-UTRAN) along
   with the existing UTRAN/GERAN, handovers between different radio
   technologies (inter-rat (inter-RAT handovers) become inevitable.  In case of inter-rat
   inter-RAT handovers 3GPP supports the following IP addressing
   scenarios:

   o  E-UTRAN IPv4v6 bearer has to map one to one to UTRAN/GERAN IPv4v6
      bearer.

   o  E-UTRAN IPv6 bearer has to map one to one to UTRAN/GERAN IPv6
      bearer.

   o  E-UTRAN IPv4 bearer has to map one to one to UTRAN/GERAN IPv4
      bearer.

   Other types of configurations are considered network planning
   mistakes.  What the above rules essentially imply is that the network
   migration has to be planned and subscriptions provisioned based on
   the lowest common nominator, if inter-rat inter-RAT handovers are desired.  For
   example, if some part of the UTRAN network cannot serve anything but
   IPv4 bearers, then the E-UTRAN is also forced to provide only IPv4
   bearers.  Various combinations of subscriber provisioning regarding
   IP versions are discussed further in Section 8.7.

8.7.  Provisioning of IPv6 Subscribers and Various Combinations During
      Initial Network Attachment

   Subscribers' provisioned PDP/PDN Types have multiple configurations.
   The supported PDP/PDN Type is provisioned per each APN for every
   subscriber.  The following PDN Types are possible in the HSS for a
   Release-8 subscription [3GPP.23.401]: [TS.23401]:

   o  IPv4v6 PDN Type (note that IPv4v6 PDP Type does not exist in HLR). a HLR
      and Mobile Applicatio Part (MAP) [TS.29002] signaling prior
      Release-9).

   o  IPv6 only  IPv6-only PDN Type

   o  IPv4 only  IPv4-only PDN Type.

   o  IPv4_or_IPv6 PDN Type (note that IPv4_or_IPv6 PDP Type does not
      exist in HLR). a HLR or MAP signaling.  However, a HLR may have multiple
      APN configurations of different PDN Types, which effectively
      achieves the same functionality).

   A Release-8 dual-stack mobile host must always attempt to establish a
   PDP/PDN Type IPv4v6 bearer.  The same also applies when the modem
   part of the mobile host does not have exact knowledge whether the
   host operating system IP stack is a dual-stack capable or not.  A
   mobile host that is IPv6 only IPv6-only capable must attempt to establish a
   PDP/PDN Type IPv6 bearer.  Last, a mobile host that is IPv4 only IPv4-only
   capable must attempt to establish a PDN/PDP Type IPv4 bearer.

   In a case the PDP/PDN Type requested by a mobile host does not match
   what has been provisioned for the subscriber in the HSS (or HLR), the
   mobile host possibly falls back to a different PDP/PDN Type.  The
   network (i.e. the MME or the SGSN) S4-SGSN) is able to inform the mobile
   host during the network attachment signaling why it did not get the
   requested PDP/PDN Type.  These response/cause codes are documented in
   [3GPP.24.008][3GPP.24.301]:
   [TS.24008] for requested PDP Types and [TS.24301] for requested PDN
   Types:

   o  ESM  (E)SM cause #50 "PDN "PDN/PDP type IPv4 only IPv4-only allowed".

   o  ESM  (E)SM cause #51 "PDN "PDN/PDP type IPv6 only IPv6-only allowed".

   o  ESM  (E)SM cause #52 "single address bearers only allowed".

   The above respone/cause response/cause codes apply to Release-8 and onwards.  In
   pre-Release-8 networks used response/cause codes vary depending on
   the vendor, unfortunately.

   Possible fall back cases when the network deploys MMEs and/or S4-
   SGSNs include (as documented in [3GPP.23.401]): [TS.23401]):

   o  Requested & and provisioned PDP/PDN Types match -> => requested.

   o  Requested IPv4v6 & and provisioned IPv6 -> => IPv6 and a mobile host
      receives indication that IPv6-only bearer is allowed.

   o  Requested IPv4v6 & and provisioned IPv4 -> => IPv4 and the mobile host
      receives indication that IPv4-only bearer is allowed.

   o  Requested IPv4v6 & and provisioned IPv4_or_IPv6 -> => IPv4 or IPv6 is
      selected by the MME MME/S4-SGSN based on an unspecified criteria.  The
      mobile host may then attempt to establish, based on the mobile
      host implementation, a parallel bearer of a different PDP/PDN
      Type.

   o  Other combinations cause the bearer establishment to fail.

   In addition to PDP/PDN Types provisioned in the HSS, it is also
   possible for a PDN-GW (and a MME) MME/S4-SGSN) to affect the final
   selected PDP/
   PDN PDP/PDN Type:

   o  Requested IPv4v6 & and configured IPv4 or IPv6 in the PDN-GW -> => IPv4
      or IPv6.  If the MME operator had included the "Dual Address
      Bearer Flag" into the bearer establishment signaling, then the
      mobile host receives an indication that IPv6-only or IPv4-only
      bearer is allowed.

   o  Requested IPv4v6 & and configured IPv4 or IPv6 in the PDN-GW -> => IPv4
      or IPv6.  If the MME operator had not included the "Dual Address
      Bearer Flag" into the bearer establishment signaling, then the
      mobile host may attempt to establish, based on the mobile host
      implementation, a parallel bearer of different PDP/PDN Type.

   If for some reason a

   A SGSN that does not understand the requested PDP Type,
   then Type is supposed to
   handle the requested PDP Type is handled as IPv4.  If for some reason a MME does
   not understand the requested PDN Type, then the PDN Type is handled
   as IPv6.

9.  IANA Considerations

   This document has no requests to IANA.

10.  Security Considerations

   This document does not introduce any security related concerns.

11.  Summary and Conclusion

   The 3GPP network architecture and specifications enable the
   establishment of IPv4 and IPv6 connections through the use of
   appropriate PDP context types.  The current generation of deployed
   networks can support dual-stack connectivity if the packet core
   network elements such as the SGSN and GGSN have the capability.  With
   Release-8, 3GPP has specified a more optimal PDP context type which
   enables the transport of IPv4 and IPv6 packets within a single PDP
   context between the mobile station and the gateway.

   As devices and applications are upgraded to support IPv6 they can
   start leveraging the IPv6 connectivity provided by the networks while
   maintaining the fall back to IPv4 capability.  Enabling IPv6
   connectivity in the 3GPP networks by itself will provide some degree
   of relief to the IPv4 address space as many of the applications and
   services can start to work over IPv6.  However without comprehensive
   testing of different applications and solutions that exist today and
   are widely used, for their ability to operate over IPv6 PDN
   connections, an IPv6 only access would cause disruptions.

12.  Acknowledgements

   The authors thank Shabnam Sultana, Sri Gundavelli, Hui Deng, and
   Zhenqiang Li, Mikael Abrahamsson, James Woodyatt and Cameron Byrne
   for their reviews and comments on this document.

13.  Informative References

   [3GPP.23.060]
              3GPP, "General Packet Radio Service (GPRS); Service
              description; Stage 2", 3GPP TS 23.060 8.8.0, March 2010.

   [3GPP.23.203]
              3GPP, "Policy and charging control architecture (PCC)",
              3GPP TS 23.203 8.11.0, September 2010.

   [3GPP.23.401]
              3GPP, "General Packet Radio Service (GPRS) enhancements
              for Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN) access", 3GPP TS 23.401 10.3.0, March 2011.

   [3GPP.23.975]
              3GPP, "IPv6 Migration Guidelines", 3GPP TR 23.975 1.1.1,
              June 2010.

   [3GPP.24.008]
              3GPP, "Mobile radio interface Layer 3 specification", 3GPP
              TS 24.008 8.12.0, December 2010.

   [3GPP.24.301]
              3GPP, "Non-Access-Stratum (NAS) protocol for Evolved
              Packet System (EPS)", 3GPP TS 24.301 8.8.0, December 2010.

   [3GPP.29.060]
              3GPP, "General Packet Radio Service (GPRS); GPRS
              Tunnelling Protocol (GTP) across the Gn
   connections, an IPv6-only access would cause disruptions.

12.  Acknowledgements

   The authors thank Shabnam Sultana, Sri Gundavelli, Hui Deng, and Gp interface",
              3GPP TS 29.274 8.8.0, April 2010.

   [3GPP.29.061]
              3GPP, "Interworking between the Public Land Mobile Network
              (PLMN) supporting packet based services
   Zhenqiang Li, Mikael Abrahamsson, James Woodyatt, Cameron Byrne, Ales
   Vizdal and Packet Data
              Networks (PDN)", 3GPP TS 29.061 8.5.0, April 2010.

   [3GPP.29.274]
              3GPP, "3GPP Evolved Packet System (EPS);  Evolved General
              Packet Radio Service (GPRS)  Tunnelling Protocol Frank Brockners for
              Control plane (GTPv2-C)", 3GPP TS 29.060 8.11.0,
              December 2010. their reviews and comments on this
   document.

13.  Informative References

   [GSMA.IR.34]
              GSMA, "Inter-PLMN Backbone Guidelines", GSMA
              PRD IR.34.4.9, March 2010.

   [I-D.ietf-dhc-pd-exclude]
              Korhonen, J., Savolainen, T., Krishnan, S., and O. Troan,
              "Prefix Exclude Option for DHCPv6-based Prefix
              Delegation", draft-ietf-dhc-pd-exclude-01 draft-ietf-dhc-pd-exclude-02 (work in
              progress), January June 2011.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3316]  Arkko, J., Kuijpers, G., Soliman, H., Loughney, J., and J.
              Wiljakka, "Internet Protocol Version 6 (IPv6) for Some
              Second and Third Generation Cellular Hosts", RFC 3316,
              April 2003.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
              (DHCP) Service for IPv6", RFC 3736, April 2004.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, April 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, April 2011.

   [TR.23975]
              3GPP, "IPv6 Migration Guidelines", 3GPP TR 23.975 1.1.1,
              June 2010.

   [TS.23060]
              3GPP, "General Packet Radio Service (GPRS); Service
              description; Stage 2", 3GPP TS 23.060 8.8.0, March 2010.

   [TS.23203]
              3GPP, "Policy and charging control architecture (PCC)",
              3GPP TS 23.203 8.11.0, September 2010.

   [TS.23401]
              3GPP, "General Packet Radio Service (GPRS) enhancements
              for Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN) access", 3GPP TS 23.401 10.4.0, June 2011.

   [TS.24008]
              3GPP, "Mobile radio interface Layer 3 specification", 3GPP
              TS 24.008 8.12.0, December 2010.

   [TS.24301]
              3GPP, "Non-Access-Stratum (NAS) protocol for Evolved
              Packet System (EPS)", 3GPP TS 24.301 8.8.0, December 2010.

   [TS.29002]
              3GPP, "Mobile Application Part (MAP) specification", 3GPP
              TS 29.002 9.5.0, June 2011.

   [TS.29060]
              3GPP, "General Packet Radio Service (GPRS); GPRS
              Tunnelling Protocol (GTP) across the Gn and Gp interface",
              3GPP TS 29.274 8.8.0, April 2010.

   [TS.29061]
              3GPP, "Interworking between the Public Land Mobile Network
              (PLMN) supporting packet based services and Packet Data
              Networks (PDN)", 3GPP TS 29.061 8.5.0, April 2010.

   [TS.29274]
              3GPP, "3GPP Evolved Packet System (EPS);  Evolved General
              Packet Radio Service (GPRS)  Tunnelling Protocol for
              Control plane (GTPv2-C)", 3GPP TS 29.060 8.11.0,
              December 2010.

Authors' Addresses

   Jouni Korhonen (editor)
   Nokia Siemens Networks
   Linnoitustie 6
   FI-02600 Espoo
   FINLAND

   Email: jouni.nospam@gmail.com

   Jonne Soininen
   Renesas Mobile
   Porkkalankatu 24
   FI-00180 Helsinki
   FINLAND

   Email: jonne.soininen@renesasmobile.com

   Basavaraj Patil
   Nokia
   6021 Connection drive
   Irving, TX  75039
   USA

   Email: basavaraj.patil@nokia.com

   Teemu Savolainen
   Nokia
   Hermiankatu 12 D
   FI-33720 Tampere
   FINLAND

   Email: teemu.savolainen@nokia.com

   Gabor Bajko
   Nokia
   323 Fairchild drive 6
   Mountain view, CA  94043
   USA

   Email: gabor.bajko@nokia.com
   Kaisu Iisakkila
   Renesas Mobile
   Porkkalankatu 24
   FI-00180 Helsinki
   FINLAND

   Email: kaisu.iisakkila@renesasmobile.com