





Network Working Group                                   J. Soininen, Ed.
Request for Comments: 3574                                         Nokia
Category: Informational                                      August 2003


                Transition Scenarios for 3GPP Networks

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes different scenarios in Third Generation
   Partnership Project (3GPP) defined packet network, i.e., General
   Packet Radio Service (GPRS) that would need IP version 6 and IP
   version 4 transition.  The focus of this document is on the scenarios
   where the User Equipment (UE) connects to nodes in other networks,
   e.g., in the Internet.  GPRS network internal transition scenarios,
   i.e., between different GPRS elements in the network, are out of
   scope.   The purpose of the document is to list the scenarios for
   further discussion and study.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Scope of the Document. . . . . . . . . . . . . . . . . . . . .  2
   3.  Brief Description of the 3GPP Network Environment. . . . . . .  2
       3.1 GPRS Architecture Basics . . . . . . . . . . . . . . . . .  3
       3.2 IP Multimedia Core Network Subsystem (IMS) . . . . . . . .  3
   4.  Transition Scenarios . . . . . . . . . . . . . . . . . . . . .  5
       4.1 GPRS Scenarios . . . . . . . . . . . . . . . . . . . . . .  5
       4.2 IMS Scenarios  . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations. . . . . . . . . . . . . . . . . . . .  9
   6.  Contributing Authors . . . . . . . . . . . . . . . . . . . . . 10
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
       8.1.  Normative References . . . . . . . . . . . . . . . . . . 10
       8.2.  Informative References . . . . . . . . . . . . . . . . . 11
   9.  Editor's Address . . . . . . . . . . . . . . . . . . . . . . . 11
   10. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 12




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1.  Introduction

   This document describes the transition scenarios in 3GPP packet data
   networks that might come up in the deployment phase of IPv6.  The
   main purpose of this document is to identify and to document those
   scenarios for further discussion and study them in the v6ops working
   group.

   Just a brief overview of the 3GPP packet data network, GPRS, is given
   to help the reader to better understand the transition scenarios.  A
   better overview of the 3GPP specified GPRS can be found for example
   from [6].  The GPRS architecture is defined in [1].

2.  Scope of the Document

   The scope is to describe the possible transition scenarios in the
   3GPP defined GPRS network where a UE connects to, or is contacted
   from, the Internet or another UE.  The document describes scenarios
   with and without the usage of the SIP-based (Session Initiation
   Protocol [5]) IP Multimedia Core Network Subsystem (IMS).  The 3GPP
   releases 1999, 4, and 5 are considered as the basis.

   Out of scope are scenarios inside the GPRS network, i.e., on the
   different interfaces of the GPRS network.  This document neither
   changes 3GPP specifications, nor proposes changes to the current
   specifications.

   In addition, the possible transition scenarios are described.  The
   solutions will be documented in a separate document.

   All the possible scenarios are listed here.  Further analysis may
   show that some of the scenarios are not actually relevant in this
   context.

3.  Brief Description of the 3GPP Network Environment

   This section describes the most important concepts of the 3GPP
   environment for understanding the transition scenarios.  The first
   part of the description gives a brief overview to the GPRS network as
   such.  The second part concentrates on the IP Multimedia Core Network
   Subsystem (IMS).










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3.1.  GPRS Architecture Basics

   This section gives an overview to the most important concepts of the
   3GPP packet architecture.  For more detailed description, please see
   [1].

   From the point of view of this document, the most relevant 3GPP
   architectural elements are the User Equipment (UE), and the Gateway
   GPRS Support Node (GGSN).  A simplified picture of the architecture
   is shown in Figure 1.

   The UE is the mobile phone.  It can either be an integrated device
   comprising a combined GPRS part, and the IP stack, or it might be a
   separate GPRS device, and separate equipment with the IP stack, e.g.,
   a laptop.

   The GGSN serves as an anchor-point for the GPRS mobility management.
   It also serves as the default router for the UE.

   The Peer node mentioned in the picture refers to a node with which
   the UE is communicating.

      --         ----       ************       ---------
     |UE|- ... -|GGSN|--+--* IPv4/v6 NW *--+--|Peer node|
      --         ----       ************       ---------

            Figure 1:  Simplified GPRS Architecture

   There is a dedicated link between the UE and the GGSN called the
   Packet Data Protocol (PDP) Context.  This link is created through the
   PDP Context activation process.  During the activation the UE is
   configured with its IP address and other information needed to
   maintain IP access, e.g., DNS server address.  There are three
   different types of PDP Contexts: IPv4, IPv6, and Point-to-Point
   Protocol (PPP).

   A UE can have one or more simultaneous PDP Contexts open to the same
   or to different GGSNs.  The PDP Context can be either of the same or
   different types.

3.2.  IP Multimedia Core Network Subsystem (IMS)

   IP Multimedia Core Network Subsystem (IMS) is an architecture for
   supporting multimedia services via a SIP infrastructure.  It is
   specified in 3GPP Release 5.  This section provides an overview of
   the 3GPP IMS and is not intended to be comprehensive.  A more
   detailed description can be found in [2], [3] and [4].




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   The IMS comprises a set of SIP proxies, servers, and registrars.  In
   addition, there are Media Gateways (MGWs) that offer connections to
   non-IP networks such as the Public Switched Telephony Network (PSTN).
   A simplified overview of the IMS is depicted in figure 2.

             +-------------+  +-------------------------------------+
             |             |  |                           +------+  |
             |             |  |                           |S-CSCF|---
       |     |             |  |                           +------+  |
     +-|+    |             |  |                            /        |
     |  |    |   SIP Sig.  |  |    +------+          +------+       |
     |  |----|------+------|--|----|P-CSCF|----------|I-CSCF|       |
     |  |    |             |  |    +------+          +------+       |
     |  |-----------+------------------------------------------------
     +--+    |  User traf. |  |                                     |
      UE     |             |  |                                     |
             | GPRS access |  |     IP Multimedia CN Subsystem      |
             +-------------+  +-------------------------------------+

              Figure 2: Overview of the 3GPP IMS architecture

   The SIP proxies, servers, and registrars shown in Figure 2 are as
   follows.

     - P-CSCF (Proxy-Call Session Control Function) is the first
       contact point within the IMS for the subscriber.

     - I-CSCF (Interrogating-CSCF) is the contact point within an
       operator's network for all connections destined to a subscriber
       of that network operator, or a roaming subscriber currently
       located within that network operator's service area.

     - S-CSCF (Serving-CSCF) performs the session control services for
       the subscriber.  It also acts as a SIP Registrar.

   IMS capable UEs utilize the GPRS network as an access network for
   accessing the IMS.  Thus, a UE has to have an activated PDP Context
   to the IMS before it can proceed to use the IMS services.  The PDP
   Context activation is explained briefly in section 3.1.

   The IMS is exclusively IPv6.  Thus, the activated PDP Context is of
   PDP Type IPv6.  This means that a 3GPP IP Multimedia terminal uses
   exclusively IPv6 to access the IMS, and the IMS SIP server and proxy
   support exclusively IPv6.  Hence, all the traffic going to the IMS is
   IPv6, even if the UE is dual stack capable - this comprises both
   signaling and user traffic.





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   This, of course, does not prevent the usage of other unrelated
   services (e.g., corporate access) on IPv4.

4.  Transition Scenarios

   This section is divided into two main parts - GPRS scenarios, and
   scenarios with the IP Multimedia Subsystem (IMS).  The first part -
   GPRS scenarios - concentrates on scenarios with a User Equipment (UE)
   connecting to services in the Internet, e.g., mail, web.  The second
   part - IMS scenarios - then describes how an IMS capable UE can
   connect to other SIP-capable nodes in the Internet using the IMS
   services.

4.1.  GPRS Scenarios

   This section describes the scenarios that might occur when a GPRS UE
   contacts services, or nodes outside the GPRS network, e.g., web-
   server in the Internet.

   Transition scenarios of the GPRS internal interfaces are outside of
   the scope of this document.

   The following scenarios are described here.  In all of the scenarios,
   the UE is part of a network where there is at least one router of the
   same IP version, i.e., GGSN, and it is connecting to a node in a
   different network.

   The scenarios here apply also for PDP Context type Point-to-Point
   Protocol (PPP) where PPP is terminated at the GGSN.  On the other
   hand, where the PPP PDP Context is terminated e.g., at an external
   ISP, the environment is the same as for general ISP cases.

      1) Dual Stack UE connecting to IPv4 and IPv6 nodes
      2) IPv6 UE connecting to an IPv6 node through an IPv4 network
      3) IPv4 UE connecting to an IPv4 node through an IPv6 network
      4) IPv6 UE connecting to an IPv4 node
      5) IPv4 UE connecting to an IPv6 node

   1) Dual Stack UE connecting to IPv4 and IPv6 nodes

      The GPRS system has been designed in a manner that there is the
      possibility to have simultaneous IPv4, and IPv6 PDP Contexts open.
      Thus, in cases where the UE is dual stack capable, and in the
      network there is a GGSN (or separate GGSNs) that supports both
      connections to IPv4 and IPv6 networks, it is possible to connect
      to both at the same time.  Figure 3 depicts this scenario.





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       +-------------+
       |             |
       |     UE      |                                    +------+
       |             |                                    | IPv4 |
       |             |                                   /|      |
       |------|------+                                  / +------+
       | IPv6 | IPv4 |                     +--------+  /
       +-------------+       IPv4          |        | /
           |      |------------------------|        |/
           |                               |        |
           |                 IPv6          |  GGSN  |\
           |-------------------------------|        | \
                           +-----------+   |        |  \  +------+
                           | GPRS Core |   |        |   \ | IPv6 |
                           +-----------+   +--------+    \|      |
                                                          +------+

                          Figure 3: Dual-Stack Case

      However, the IPv4 addresses may be a scarce resource for the
      mobile operator or an ISP.  In that case, it might not be possible
      for the UE to have a globally unique IPv4 address allocated all
      the time.  Hence, the UE could either activate the IPv4 PDP
      Context only when needed, or be allocated an IPv4 address from a
      private address space.

   2) IPv6 UE connecting to an IPv6 node through an IPv4 network

      Especially in the initial stages of IPv6 deployment, there are
      cases where an IPv6 node would need to connect to the IPv6
      Internet through a network that is IPv4.  For instance, this can
      be seen in current fixed networks, where the access is provided
      via IPv4 only, but there is an IPv6 network deeper in the
      Internet.  This scenario is shown in Figure 4.

        +------+                  +------+
        |      |                  |      |                 +------+
        |  UE  |------------------|      |-----------------|      |
        |      |    +-----------+ | GGSN |     +---------+ | IPv6 |
        | IPv6 |    | GPRS Core | |      |     | IPv4 Net| |      |
        +------+    +-----------+ +------+     +---------+ +------+

                Figure 4: IPv6 nodes communicating over IPv4

      In this case, in the GPRS system, the UE would be IPv6 capable,
      and the GPRS network would provide an IPv6 capable GGSN in the
      network.  However, there is an IPv4 network between the GGSN, and
      the peer node.



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   3) IPv4 UE connecting to an IPv4 node through an IPv6 network

      Further in the future, there are cases where the legacy UEs are
      still IPv4 only, capable of connecting only to the legacy IPv4
      Internet.  However, the GPRS operator network has already been
      upgraded to IPv6.  Figure 5 represents this scenario.

       +------+                  +------+
       |      |                  |      |                 +------+
       |  UE  |------------------|      |-----------------|      |
       |      |    +-----------+ | GGSN |     +---------+ | IPv4 |
       | IPv4 |    | GPRS Core | |      |     | IPv6 Net| |      |
       +------+    +-----------+ +------+     +---------+ +------+

               Figure 5: IPv4 nodes communicating over IPv6

      In this case, the operator would still provide an IPv4 capable
      GGSN, and a connection through the IPv6 network to the IPv4
      Internet.

   4) IPv6 UE connecting to an IPv4 node

      In this scenario, an IPv6 UE connects to an IPv4 node in the IPv4
      Internet.  As an example, an IPv6 UE connects to an IPv4 web
      server in the legacy Internet.  In the figure 6, this kind of
      possible installation is described.

       +------+                  +------+
       |      |                  |      |     +---+    +------+
       |  UE  |------------------|      |-----|   |----|      |
       |      |    +-----------+ | GGSN |     | ? |    | IPv4 |
       | IPv6 |    | GPRS Core | |      |     |   |    |      |
       +------+    +-----------+ +------+     +---+    +------+

            Figure 6: IPv6 node communicating with IPv4 node
















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   5) IPv4 UE connecting to an IPv6 node

      This is similar to the case above, but in the opposite direction.
      Here an IPv4 UE connects to an IPv6 node in the IPv6 Internet.  As
      an example, a legacy IPv4 UE is connected to an IPv6 server in the
      IPv6 Internet.  Figure 7 depicts this configuration.

       +------+                  +------+
       |      |                  |      |     +---+    +------+
       |  UE  |------------------|      |-----|   |----|      |
       |      |    +-----------+ | GGSN |     | ? |    | IPv6 |
       | IPv4 |    | GPRS Core | |      |     |   |    |      |
       +------+    +-----------+ +------+     +---+    +------+

           Figure 7: IPv4 node communicating with IPv6 node

4.2.  IMS Scenarios

   As described in section 3.2, IMS is exclusively IPv6.  Thus, the
   number of possible transition scenarios is reduced dramatically.  In
   the following, the possible transition scenarios are listed.

      1) UE connecting to a node in an IPv4 network through IMS
      2) Two IPv6 IMS connected via an IPv4 network

   1) UE connecting to a node in an IPv4 network through IMS

      This scenario occurs when an IMS UE (IPv6) connects to a node in
      the IPv4 Internet through the IMS, or vice versa.  This happens
      when the other node is a part of a different system than 3GPP,
      e.g., a fixed PC, with only IPv4 capabilities.  This scenario is
      shown in the Figure 8.

       +------+     +------+     +-----+
       |      |     |      |     |     |  +---+  +------+
       |  UE  |-...-|      |-----| IMS |--|   |--|      |
       |      |     | GGSN |     |     |  | ? |  | IPv4 |
       | IPv6 |     |      |     |     |  |   |  |      |
       +------+     +------+     +-----+  +---+  +------+

           Figure 8: IMS UE connecting to an IPv4 node










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   2) Two IPv6 IMS connected via an IPv4 network

      At the early stages of IMS deployment, there may be cases where
      two IMS islands are only connected via an IPv4 network such as the
      legacy Internet.  See Figure 9 for illustration.

       +------+     +------+     +-----+          +-----+
       |      |     |      |     |     |          |     |
       |  UE  |-...-|      |-----| IMS |----------|     |
       |      |     | GGSN |     |     | +------+ | IMS |
       | IPv6 |     |      |     |     | | IPv4 | |     |
       +------+     +------+     +-----+ +------+ +-----+

          Figure 9: Two IMS islands connected over IPv4

5.  Security Considerations

   This document describes possible transition scenarios for 3GPP
   networks for future study.  Solutions and mechanism are explored in
   other documents.  The description of the 3GPP network scenarios does
   not have any security issues.






























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6.  Contributing Authors

   This document is a result of a joint effort of a design team.  The
   members of the design team are listed in the following.

      Alain Durand, Sun Microsystems
      <Alain.Durand@sun.com>

      Karim El-Malki, Ericsson Radio Systems
      <Karim.El-Malki@era.ericsson.se>

      Niall Richard Murphy, Enigma Consulting Limited
      <niallm@enigma.ie>

      Hugh Shieh, AT&T Wireless
      <hugh.shieh@attws.com>

      Jonne Soininen, Nokia
      <jonne.soininen@nokia.com>

      Hesham Soliman, Ericsson Radio Systems
      <hesham.soliman@era.ericsson.se>

      Margaret Wasserman, Wind River
      <mrw@windriver.com>

      Juha Wiljakka, Nokia
      <juha.wiljakka@nokia.com>

7.  Acknowledgements

   The authors would like to thank Basavaraj Patil, Tuomo Sipila, Fred
   Templin, Rod Van Meter, Pekka Savola, Francis Dupont, Christine
   Fisher, Alain Baudot, Rod Walsh, and Jens Staack for good input, and
   comments that helped writing this document.

8.  References

8.1.  Normative References

   [1] 3GPP TS 23.060 v 5.2.0, "General Packet Radio Service (GPRS);
       Service description; Stage 2(Release 5)", June 2002.

   [2] 3GPP TS 23.228 v 5.3.0, " IP Multimedia Subsystem (IMS); Stage
       2(Release 5)", January 2002.






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   [3] 3GPP TS 24.228 V5.0.0, "Signalling flows for the IP multimedia
       call control based on SIP and SDP; Stage 3 (Release 5)", March
       2002.

   [4] 3GPP TS 24.229 V5.0.0, "IP Multimedia Call Control Protocol based
       on SIP and SDP; Stage 3 (Release 5)", March 2002.

   [5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
       Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
       Session Initiation Protocol", RFC 3261, June 2002.

8.2.  Informative References

   [6] Wasserman, M., "Recommendations for IPv6 in Third Generation
       Partnership Project (3GPP) Standards", RFC 3314, September 2002.

9.  Editor's Address

   Jonne Soininen
   Nokia
   313 Fairchild Dr.
   Mountain View, CA, USA

   Phone:  +1-650-864-6794
   EMail:  jonne.soininen@nokia.com


























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10.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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