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Content for  TR 23.981  Word version:  17.0.0

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0  Introductionp. 5

3GPP specifications design the IMS to use exclusively IPv6, however early IMS implementations and deployments may use IPv4, as specified in clause 5.1 of TS 23.221. Therefore it is understood that there will exist IPv4 based IMS implementations, namely initial IMS implementations and IMS implementations based on 3GPP2 specifications. This is the motivation to study interworking and migration scenarios related to IPv4 based IMS implementations.
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1  Scopep. 6

The present document studies study interworking and migration scenarios related to IPv4 based IMS implementations. The study provides guidelines for operators and vendors on interworking aspects of IPv4 based IMS implementations, and provides guidelines on migrating to 3GPP IMS using IPv6.

2  Referencesp. 6

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1]  Void.
[2]
TS 21.905: "Vocabulary for 3GPP Specifications".
[3]
TS 23.221: "Architectural Requirements".
[4]
TS 23.228: "IP Multimedia (IM) Subsystem - Stage 2".
[5]
TS 23.141: "Presence Service; Architecture and Functional Description".
[6]
TS 23.060: "General Packet Radio Service (GPRS); Service description; Stage 2".
[7]
TS 33.203: "3G security; Access security for IP-based services".
[7a]
TS 23.002: "Network Architecture".
[8]
draft-ietf-ngtrans-isatap-21.txt   (April 2004)"Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)", work in progress.
[9]
TS 24.008: "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3".
[10]
RFC 2373:  "IP Version 6 Addressing Architecture".
[11]
OMA DM WG: "OMA Device Management 1.1.2".
[12]
OMA "OMA Client Provisioning 1.1".
[13]
TS 24.167: "3GPP IMS Management Objects (MO); Stage 3".
[14]
TS 27.060: "Mobile Station (MS) supporting Packet Switched Services".
[15]
RFC 2507:  "IP Header Compression".
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3  Definitions, symbols and abbreviationsp. 7

3.1  Definitionsp. 7

For the purposes of the present document, the terms and definitions given in TS 21.905 and the following apply.
Dual stack IM CN subsystem:
For the purpose of this technical report, a dual stack IM CN subsystem is an IM CN subsystem implementation in which all network entities support IPv4 and IPv6 for IMS communication. It is an IM CN subsystem implementation that supports both IPv6 as per 3GPP Release 5 or later standards, and an IPv4 IM CN subsystem.
IPv4 based IM CN subsystem implementation, IPv4 IM CN subsystem:
For the purpose of this technical report, an IPv4 based IM CN subsystem implementation (or short: IPv4 IM CN subsystem) means an IM CN subsystem implementation, which is based on 3GPP Release 5 or later standards, but uses IPv4 rather than IPv6.
IPv4 based UE implementation, IPv4 UE:
For the purpose of this technical report, an IPv4 based UE implementation (or short: IPv4 UE) means a UE implementation, which is based on 3GPP Release 5 or later IMS standards, but uses IPv4 rather than IPv6 to access an IM CN subsystem.
IPv6 based IM CN subsystem implementation, IPv6 IM CN subsystem:
For the purpose of this technical report, an IPv6 based IM CN subsystem implementation (or short: IPv6 IM CN subsystem) means the IM CN subsystem implementation according to 3GPP Release 5 or later standards that uses IPv6.
IPv6 UE:
For the purpose of this technical report, an IPv6 UE means a UE implementation, which is based on 3GPP Release 5 or later IMS standards and uses only IPv6 to access IM CN subsystem even though the IP stack in the UE as such may be a dual IPv4 and IPv6 stack.
IMS dual stack UE:
For the purpose of this technical report, an IMS dual stack UE means a UE implementation, which is based on 3GPP Release 5 or later IMS standards, but in addition to IPv6 can use IPv4 to access an IPv4 IM CN subsystem.
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3.2  Symbolsp. 7

For the purposes of the present document, the following symbols apply:
Gi
Reference point between GPRS and a packet data network.
Gm
Reference Point between a UE and a P-CSCF.
Gn
Interface between two GSNs within the same PLMN.
Mb
Reference point to network services.

3.3  Abbreviationsp. 7

For the purposes of the present document, the following abbreviations apply:
ALG
Application Level Gateway
CN
Core Network
CSCF
Call/Session Control Function
DHCP
Dynamic Host Configuration Protocol
DNS
Domain Name System
GGSN
Gateway GPRS Support Node
GPRS
General Packet Radio Service
GSN
GPRS Support Note
I-CSCF
Interrogating CSCF
IM
IP Multimedia
IMS
IP Multimedia Subsystem
IM-MGW
IP Multimedia - Media GateWay
IP
Internet Protocol
IPSec
IP Security protocol
MRFP
Multimedia Resource Function Processor
NAT
Network Address Translation
NA(P)T-PT
Network Address (Port-Multiplexing) Translation-Protocol Translation
OMA
Open Mobile Alliance
OTA
Over the Air Activation
PCO
Protocol Configuration Options
P-CSCF
Proxy-CSCF
PDP
Packet Data Protocol
QoS
Quality of Service
S-CSCF
Serving-CSCF
SGSN
Serving GPRS Support Node
SIP
Session Initiation Protocol
SMS
Short Message Service
TrGW
Transition Gateway
UE
User Equipment
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4  Architectural Requirementsp. 8

4.1  Generalp. 8

An IMS dual stack UE shall be able to determine whether to use IPv4 or IPv6 when accessing the IMS.
A dual stack IMS shall be able to determine whether to use IPv4 or IPv6.
IMS security shall be possible for both IPv4 and IPv6 IMS networks and UEs accessing these networks.
SIP Compression shall be possible for both IPv4 and IPv6 IMS networks and UEs accessing these networks.
P-CSCF discovery mechanisms shall be possible for both IPv4 and IPv6 IMS networks and UEs accessing these networks.
An IPv4 IM CN Subsystem shall be able to interwork with an IPv4 IM CN Subsystem.
An IPv4 IM CN Subsystem shall be able to interwork with an IPv6 IM CN Subsystem.
A dual stack IM CN Subsystem shall be able to interwork with an IPv4 IM CN Subsystem.
A dual stack IM CN Subsystem shall be able to interwork with an IPv6 IM CN Subsystem.
A dual stack IM CN Subsystem shall be able to interwork with a dual stack IM CN Subsystem.
A dual stack IM CN Subsystem may support IPv4 UEs.
An IPv4 IM CN Subsystem and a dual stack IM CN Subsystem may support IPv4 private addressing - i.e. the IMS elements shall support the case in which both the IMS network and the user are within (the same) IPv4 private address domain.
The mechanisms described in this TR shall not limit the flexibility with respect to APN usage for IMS.
It is desirable to avoid media tromboning e.g. in case a call traverses a NAT and then is routed back into the same network.
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4.2  Operational aspects for GPRS systemp. 8

4.2.1  Support of PDP type IPv6p. 8

If GPRS Roaming is used, i.e. the GGSN and P-CSCF are in the home network, then the support of IMS using IPv6 requires the support of PDP contexts of PDP type IPv6 in both the visited and the home network.
Clause 5.2.2.3 discusses a possible work-around for the case where this requirement is not met because the visited network does not support PDP type IPv6.

4.2.2  GPRS network/nodesp. 9

Current deployed GPRS systems are known to be IPv4 only. For early IMS deployment using IPv4, it is expected that GPRS systems as early as Release 1999 would be used and it should be possible to run early IPv4 IMS system without requiring upgrades to GPRS and its support system (i.e. DNS, Gi reference etc.). In order to achieve this, certain assumptions must be made on the deployed networks and also some guidelines must be provided on expected impacts on GPRS system to move towards IPv6 IMS deployment.
Levels of migration and interworking aspects are described below:
  • The working principle in this TR is that the deployment of IPv6 networks interworking with IPv4 networks on the application layer does not impose any new requirements on the transport layer;
  • The most efficient and transparent way of supporting access to IPv6 services over GPRS is to ensure that GGSN is dual stack;
  • It is expected that connection scenarios with a change of PDP Type between SGSN and GGSN are not practical deployment cases and as such are not even considered as part of the scenarios analysis as shown in Annex A.
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