Internet Draft J. Soininen,
Document: draft-ietf-v6ops-3gpp-cases-01.txt Editor
Expires: June 2003 Nokia
December 2002
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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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.
Soininen, et al. Expires - June 2003 [Page 1]
Transition Scenarios for 3GPP Networks December 2002
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
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.
Soininen, et al. Expires - June 2003 [Page 2]
Transition Scenarios for 3GPP Networks December 2002
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).
Soininen, et al. Expires - June 2003 [Page 3]
Transition Scenarios for 3GPP Networks December 2002
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
operatorĘs network for all connections destined to a subscriber
of that network operator, or a roaming subscriber currently
located within that network operatorĘs 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.
Soininen, et al. Expires - June 2003 [Page 4]
Transition Scenarios for 3GPP Networks December 2002
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
Soininen, et al. Expires - June 2003 [Page 5]
Transition Scenarios for 3GPP Networks December 2002
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.
Soininen, et al. Expires - June 2003 [Page 6]
Transition Scenarios for 3GPP Networks December 2002
+------+ +------+
| | | | +------+
| 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
Soininen, et al. Expires - June 2003 [Page 7]
Transition Scenarios for 3GPP Networks December 2002
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
Soininen, et al. Expires - June 2003 [Page 8]
Transition Scenarios for 3GPP Networks December 2002
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>
Soininen, et al. Expires - June 2003 [Page 9]
Transition Scenarios for 3GPP Networks December 2002
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
[1] Wasserman, M., "Recommendations for IPv6 in Third Generation
Partnership Project (3GPP) Standards", September 2002, RFC3314.
[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 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
Soininen, et al. Expires - June 2003 [Page 10]