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+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
+
+
+
+
+Soininen                     Informational                      [Page 1]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+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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+
+Soininen                     Informational                      [Page 2]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+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].
+
+
+
+
+Soininen                     Informational                      [Page 3]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
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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.
+
+
+
+
+
+Soininen                     Informational                      [Page 4]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+   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.
+
+
+
+
+
+Soininen                     Informational                      [Page 5]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+       +-------------+
+       |             |
+       |     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.
+
+
+
+Soininen                     Informational                      [Page 6]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+   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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+Soininen                     Informational                      [Page 7]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+   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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+
+Soininen                     Informational                      [Page 8]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+   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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+Soininen                     Informational                      [Page 9]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
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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.
+
+
+
+
+
+
+Soininen                     Informational                     [Page 10]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
+
+   [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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+Soininen                     Informational                     [Page 11]
+
+RFC 3574         Transition Scenarios for 3GPP Networks      August 2003
+
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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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+Soininen                     Informational                     [Page 12]
+