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rfc:rfc3574

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).

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.
  1. - —- ———

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

  1. - —- ———
          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

 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.
  1. P-CSCF (Proxy-Call Session Control Function) is the first

contact point within the IMS for the subscriber.

  1. 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.
  1. 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

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

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.

Soininen Informational [Page 9] RFC 3574 Transition Scenarios for 3GPP Networks August 2003

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

Soininen Informational [Page 11] RFC 3574 Transition Scenarios for 3GPP Networks August 2003

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.

Soininen Informational [Page 12]

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