Internet Draft                                            J. Soininen,
Document: draft-ietf-v6ops-3gpp-cases-01.txt draft-ietf-v6ops-3gpp-cases-02.txt                    Editor
Expires: June July 2003                                               Nokia
                                                         December 2002
                                                          January 2003

                  Transition Scenarios for 3GPP Networks

Status of this Memo

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

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Copyright Notice

   Copyright (C) The Internet Society (2002).  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
   of this document.

   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..............3
      3.1 GPRS architecture basics...................................3
      3.2 IP Multimedia Core Network Subsystem (IMS).................4
   4. Transition scenarios...........................................5
      4.1 GPRS Scenarios.............................................5
      4.2 Transition scenarios with IMS..............................8
   5. Security Considerations........................................9
   Authors...........................................................9
   References.......................................................10
   Informative references...........................................10
   Normative References.............................................10
   Editor's Address.................................................10

Copyright

   (C) The Internet Society (2002).  All Rights Reserved.

1. Introduction

   This document will describe 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 document those
   scenarios for further discussion, and for study in the v6ops working
   group.

   This document gives neither an overview, nor an explanation of 3GPP
   or the 3GPP packet data network, GPRS. A good overview of the 3GPP
   specified GPRS can be found from [1]. The GPRS architecture
   specification is defined in [2].

2. Scope of the document

   The scope of this document 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 IP Multimedia
   Core Network Subsystem (IMS).

   The scope of this document does not include 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, this document describes the possible transition
   scenarios. The solutions will be documented in a separate document.

   These scenarios may or may not be found feasible, or even likely in
   further study.

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).

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
   [2].

   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
   comprised of a combined GPRS part, and the IP stack, or it might be a
   separate GPRS device, and a 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 a SIP based multimedia
   service architecture. It is specified in Release 5 of 3GPP. This
   section provides an overview of the 3GPP IMS and is not intended to
   be comprehensive. A more detailed description can be found in [3],
   [4] and [5].

   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
        operatorÆs network for all connections destined to a subscriber
        of that network operator, or a roaming subscriber currently
        located within that network operatorÆs service area.

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

   IMS UEs use the GPRS as an access network for 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 an 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.

    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 connection to
   IPv4 and IPv6 networks, it is possible to connect to both at the same
   time. Figure 3 depicts this scenario.

   +-------------+
    |             |
    |     UE      |                                    +------+
    |             |                                    | IPv4 |
    |             |                                   /|      |
    |------|------+                                  / +------+
    | IPv6 | IPv4 |                     +--------+  /
    +-------------+       IPv4          |        | /
        |      |------------------------|        |/
        |                               |        |
        |                 IPv6          |  GGSN  |\
        |-------------------------------|        | \
                        +-----------+   |        |  \  +------+
                        | GPRS Core |   |        |   \ | IPv6 |
                        +-----------+   +--------+     |      |
                                                       +------+
                       Figure 3: Dual-Stack Case

   However, the IPv4 addresses might 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 should 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 first 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 in IPv4 only, but there
   is an IPv6 network deeper in the Internet. This scenario is shown in
   the 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.

   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
   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 Transition scenarios with IMS

   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
   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 does not generate any additional security
   considerations.

Authors

   This is 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>

Acknowledgements

   The authors would like to thank Basavaraj Patil, Tuomo Sipil„, Fred
   Templin, Rod Van Meter, and Jens Staack for good input, and comments
   that helped writing this document.

References

Informative references

    [1] Wasserman, M., "Recommendations for IPv6 in Third Generation
    Partnership Project (3GPP) Standards", September 2002, RFC3314.

Normative References

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

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

    [4] 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.

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

Editor's Address

    Jonne Soininen
    Nokia
    313 Fairchild Dr.           Phone:  +1-650-864-6794
    Mountain View, CA, USA       Email:  jonne.Soininen@nokia.com