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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]
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+RFC 3574 Transition Scenarios for 3GPP Networks August 2003
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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].
+
+
+
+
+Soininen Informational [Page 3]
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+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.
+
+
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+Soininen Informational [Page 4]
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+RFC 3574 Transition Scenarios for 3GPP Networks August 2003
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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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+Soininen Informational [Page 5]
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+RFC 3574 Transition Scenarios for 3GPP Networks August 2003
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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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+Soininen Informational [Page 6]
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+RFC 3574 Transition Scenarios for 3GPP Networks August 2003
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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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+RFC 3574 Transition Scenarios for 3GPP Networks August 2003
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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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+RFC 3574 Transition Scenarios for 3GPP Networks August 2003
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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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+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.
+
+
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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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