ETSI TS 182 012 V2.1.4 (2008-03)

Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); IMS-based PSTN/ISDN Emulation Sub-system (PES); Functional architecture

RTS/TISPAN-02044-NGN-R2

General Information

• Status: Published
• Publication Date: 16-Mar-2008
• Technical Committee: TISPAN 2 - TISPAN Architecture
• Current Stage: 12 - Completion
• Due Date: 30-Jun-2008
• Completion Date: 17-Mar-2008

Standards Content (Sample)

ETSI TS 182 012 V2.1.4 (2008-03)
Technical Specification


Telecommunications and Internet converged Services and
Protocols for Advanced Networking (TISPAN);
IMS-based PSTN/ISDN Emulation Sub-system (PES);
Functional architecture

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2 ETSI TS 182 012 V2.1.4 (2008-03)



Reference
RTS/TISPAN-02044-NGN-R2
Keywords
architecture, IMS, ISDN, PSTN
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ETSI

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3 ETSI TS 182 012 V2.1.4 (2008-03)
Contents
Intellectual Property Rights.5
Foreword.5
1 Scope.6
2 References.6
2.1 Normative references.6
2.2 Informative references.7
3 Definitions and abbreviations.7
3.1 Definitions.7
3.2 Abbreviations.8
4 Overview.9
4.1 PSTN/ISDN Emulation subsystem environment.9
4.2 Signalling configurations.9
4.3 Constraints on services.10
4.4 Overlap signalling.10
5 Functional architecture.11
5.1 Overview.11
5.2 Overview of Functional entities of the PES .11
5.2.1 Access Gateway Control Function (AGCF) .11
5.2.2 Multimedia Resource Function Controller (MRFC).12
5.2.3 Media Gateway Control Function (MGCF).12
5.2.4 Proxy Call Session Control Function (P-CSCF).12
5.2.5 Service Call Session Control Function (S-CSCF) .13
5.2.6 Interrogating Call Session Control Function (I-CSCF).13
5.2.7 Breakout Gateway Control Function (BGCF) .13
5.3 Internal Reference Points.13
5.3.1 Reference Point MGCF - CSCF (Mg Reference Point).13
5.3.2 Reference Point CSCF - MRFC (Mr Reference Point).13
5.3.3 Reference Point CSCF - CSCF and AGCF - CSCF (Mw Reference Point) .13
5.3.4 Reference Point CSCF - BGCF (Mi reference point) .13
5.3.5 Reference Point BGCF - MGCF (Mj reference point).14
5.3.6 Reference Point BGCF - BGCF (Mk reference point).14
5.3.7 Reference Point AGCF, CSCF or BGCF - IBCF (Mx Reference Point) .14
6 Service Architecture.14
6.1 Overview.14
6.2 Reference points.16
6.2.1 Reference Point S-CSCF - ASF (ISC Reference Point).16
6.2.2 Reference Point UPSF - SIP AS or OSA SCS (Sh Reference Point).16
6.2.3 Reference Point UPSF - IM SSF (Si Reference Point) .16
6.2.4 Reference Point ASF- SLF (Dh Reference Point) .16
6.2.5 Reference Point ASF - UE and ASF-AGCF (Ut Reference Point).16
7 External interfaces.17
7.1 Interfaces with entities in the transfer plane.17
7.1.1 Reference Point MGCF - T-MGF (Mn Reference Point) .17
7.1.2 Reference Point MGCF - SGF (Ie Reference Point).17
7.1.3 Reference Point AS - SGF (P3 Reference Point).17
7.1.4 Reference Point MRFC - MRFP (Mp Reference Point) .17
7.2 Interface with the UE .17
7.3 Interfaces with the user profile .17
7.3.1 Interface with the SLF (Dx Reference Point) .18
7.3.2 Interface with the UPSF (Cx Reference Point).18
7.4 Interfaces with Charging Functions.18
ETSI

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4 ETSI TS 182 012 V2.1.4 (2008-03)
8 Interconnection with other networks.18
8.1 Interfaces with the PSTN/ISDN .18
8.2 Interfaces with other external IP-based Subsystems .18
9 Interfaces with the Network Attachment Subsystem (NASS).20
10 Interface with the Resource and Admission Control Subsystem (RACS) .20
11 Mode of operation .21
11.1 General Principles .21
11.2 Service Provisioning.22
11.2.1 Provisioning in the UPSF .22
11.2.2 Provisioning in the AGCF .22
11.3 Registration.23
11.4 Service code commands .24
12 AGCF behaviour.24
12.1 AGCF components.24
12.2 Media Gateway Controller .25
12.3 Feature Manager.26
12.4 IMS Agent.27
13 Physical scenarios .27
Annex A (informative): Areas of discussion and potential open items.28
History .29

ETSI

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5 ETSI TS 182 012 V2.1.4 (2008-03)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://webapp.etsi.org/IPR/home.asp).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Telecommunications and Internet
converged Services and Protocols for Advanced Networking (TISPAN).
ETSI

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6 ETSI TS 182 012 V2.1.4 (2008-03)
1 Scope
The present document describes an IMS-based functional architecture for the PSTN/ISDN Emulation Subsystem (PES)
of the ETSI TISPAN NGN overall architecture. The IMS-based PSTN/ISDN Emulation Subsystem described herein
supports the emulation of PSTN services for analog terminals and ISDN services for ISDN terminals and PBXs. These
may be connected directly to residential gateways or access gateways, or via V5 access networks.
The present document provides a framework for an IMS-based functional architecture and is considered to be a
preliminary version. In addition, in order to fulfil the requirements of different operators and national regulatory
requirements, this architecture will need to be enhanced.
See annex A for a list of potential open areas.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• Non-specific reference may be made only to a complete document or a part thereof and only in the following
cases:
- if it is accepted that it will be possible to use all future changes of the referenced document for the
purposes of the referring document;
- for informative references.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
For online referenced documents, information sufficient to identify and locate the source shall be provided. Preferably,
the primary source of the referenced document should be cited, in order to ensure traceability. Furthermore, the
reference should, as far as possible, remain valid for the expected life of the document. The reference shall include the
method of access to the referenced document and the full network address, with the same punctuation and use of upper
case and lower case letters.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
2.1 Normative references
The following referenced documents are indispensable for the application of the present document. For dated
references, only the edition cited applies. For non-specific references, the latest edition of the referenced document
(including any amendments) applies.
[1] ETSI ES 282 001: "Telecommunications and Internet converged Services and Protocols for
Advanced Networking (TISPAN); NGN Functional Architecture Release 1".
[2] ETSI ES 282 007: "Telecommunications and Internet converged Services and Protocols for
Advanced Networking (TISPAN); IP Multimedia Subsystem (IMS) Functional architecture".
[3] ETSI TS 182 006: "Telecommunications and Internet converged Services and Protocols for
Advanced Networking (TISPAN); IP Multimedia Subsystem (IMS); Stage 2 description".
[4] ETSI ES 283 003: "Telecommunications and Internet converged Services and Protocols for
Advanced Networking (TISPAN); IP Multimedia Call Control Protocol based on Session
Initiation Protocol (SIP) and Session Description Protocol (SDP) Stage 3 [3GPP TS 24.229
[Release 7], modified]".
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7 ETSI TS 182 012 V2.1.4 (2008-03)
[5] ETSI TS 183 043: "Telecommunications and Internet converged Services and Protocols for
Advanced Networking (TISPAN); IMS-based PSTN/ISDN Emulation; Stage 3 specification".
[6] ETSI TS 183 021: "Telecommunications and Internet converged Services and Protocols for
Advanced Networking (TISPAN); NGN Release 1; Endorsement of 3GPP TS 29.162 Interworking
between IM CN Sub-system and IP networks".
[7] ETSI ES 282 010: "Telecommunications and Internet converged Services and Protocols for
Advanced Networking (TISPAN); Charging management Endorsement of 3GPP TS 32.240
Release 7, 3GPP TS 32.260 Release 7, 3GPP TS 32.297 Release 7, 3GPP TS 32.298 Release 7 and
3GPP TS 32.299 Release 7, modified".
[8] ETSI ES 201 915-1: "Open Service Access (OSA); Application Programming Interface (API);
Part 1: Overview (Parlay 3)".
[9] IETF RFC 3136: "The SPIRITS architecture".
[10] ETSI ETS 300 738: "Human Factors (HF); Minimum Man-Machine Interface (MMI) to public
network based supplementary services".
[11] ITU-T Recommendation H.248: "Gateway control protocol".
[12] ETSI EN 300 659 (all parts): "Access and Terminals (AT); Analogue access to the Public
Switched Telephone Network (PSTN); Subscriber line protocol over the local loop for display
(and related) services".
[13] ETSI ETR 150: "V5 interface; Public Switched Telephone Network (PSTN) mappings".
2.2 Informative references
Not Applicable.
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
Access Gateway (AG): gateway device that interworks a significant number of analogue lines/ISDN accesses (directly
or via an V5 Access Network) to a packet network and is located at the operator's premises
NOTE: An AG can take the form of a Media Gateway (A-MGW) or a Voice over IP Gateway (A-VGW).
Media Gateway (MGW): gateway device acting at the media/transport plane, providing the functions of an MGF as
defined in ES 282 001 [1]
NOTE 1: A MGW may additionally relay signalling traffic, in which case it also provides the functions of an SGF
as defined in ES 282 001 [1].
NOTE 2: In the present document, Media Gateway refers both to Access Gateways and to Residential Gateways, to
form a A-MGW, or a R-MGW, respectively.
Media Gateway Controller (MGC): See ITU-T Recommendation H.248 [11].
Residential Gateway (RG): gateway device that interworks a small number of analogue lines/ISDN accesses
NOTE: A residential gateway typically contains one or two analogue lines/ISDN accesses and is located at the
customer premises. A RG can take the form of a Media Gateway (R-MGW) or a Voice over IP Gateway
(R-VGW).
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8 ETSI TS 182 012 V2.1.4 (2008-03)
Voice over IP Gateway (VGW): SIP-based gateway device that connects legacy equipment to the NGN
NOTE 1: A Voice over IP Gateways (VGW) plays the role of an IMS UE with regards to the P-CSCF.
NOTE 2: A Voice over IP Gateway can be classified as a AG or RG, to form a A-VGW, or a R-VGW, respectively.
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AF Application Function
AG Access Gateway
AGCF Access Gateway Control Function
A-MGF Access Media Gateway Function
A-MGW Access Media GateWay
AN Access Node
AS Application Server
ASF Application Server Function
ATA Analogue Terminal Adaptor
A-VGW Access Voice over IP GateWay
BCSM Basic Call State Model
BGCF Breakout Gateway Control Function
BGF Border Gateway Function
CCBS Call Completion on Busy Subscriber
CSCF Call Session Control Function
DDI Direct Dialling In
DNS Domain Name Server
DSS1 Digital Subscriber Signalling System No.1
GW GateWay
HSS Home Subscriber Server
IBCF Interconnection Border Control Function
I-CSCF Interrogating-Call Session Control Function
IM IP Multimedia
IMS IP Multimedia Subsystem
IM-SSF IP Multimedia-Service Switching Function
ISDN Integrated Services Digital Network
ISUP ISDN User Part
IWF InterWorking Function
MG Media Gateway
MGC Media Gateway Controller
MGCF Media Gateway Control Function
MGF Media Gateway Function
MGW Media Gateway
MRFC Multimedia Resource Function Controller
MRFP Multimedia Resource Function Processor
NAPT Network Address Port Translation
NASS Network Attachment SubSystem
NGN Next Generation Network
OSA Open Service Access
PBX Private Branch Exchange
P-CSCF Proxy-Call Session Control Function
PES PSTN/ISDN Emulation Subsystem
PSTN Public Switched Telephone Network
RACS Resource and Admission Control Subsystem
RG Residential Gateway
R-MGF Residential-MGF
R-MGW Residential Media GateWay
R-VGW Residential Voice over IP GateWay
SCIM Service Capability Interaction Manager
SCS Service Capability Server
S-CSCF Serving-Call Session Control Function
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9 ETSI TS 182 012 V2.1.4 (2008-03)
SIGTRAN SIGnalling TRANsport
SIP Session Initiation Protocol
SLF Subscription Locator Function
SS7 Signalling System n°7
SSF Service Switching Function
TDM Time Division Multiplexing
TGW Trunking Gateway
T-MGF Trunking Media Gateway Function
UE User Equipment
UPSF User Profile Server Function
VGW Voice over IP GateWay
VoIP Voice over IP
4 Overview
4.1 PSTN/ISDN Emulation subsystem environment
Figure 1 shows the PSTN/ISDN Emulation Subsystem and its relationships with other TISPAN NGN subsystem.

Charging functions
Network Management
Functions
Core
Applications/ IMS
User Profiles
Residential
and Access
MGW
Other MM
TISPAN
Subsystems
PSTN/ISDN Emulation
Residential
Subsystem
and Access
VGW
PSTN/ISDN
(TDM based)
Resource and
Network Attachment
Admission Control
Subsystem
Subsystem

Figure 1: PSTN/ISDN Emulation Subsystem and its environment
4.2 Signalling configurations
Figure 2 illustrates the signalling configurations supported by the PSTN/ISDN Emulation Subsystem (PES) described in
the present document.

MGW/ MGW/
analog access analog access
VGW VGW
ISDN access ISDN access
V5.x V5.x
AN AN
PSTN/ISDN Emulation
Subsystem
T-MGF T-MGF
ISDN/PSTN ISDN/PSTN
Trunk
Trunk

Figure 2: Signalling Configurations
ETSI

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10 ETSI TS 182 012 V2.1.4 (2008-03)
Legacy terminals, i.e. analog phones and ISDN phones may be connected to R-VGW, R-MGW, A-VGW and A-MGW,
using the interfaces based on the Z, S/T and U reference point, respectively.
ISDN PBXs may be connected to an A-VGW or A-MGW using the interfaces based on the T reference point.
When connected to an AG (A-VGW or A-MGW) a legacy terminal or ISDN PBX may be connected directly to the
AG or indirectly via a V5.xAccess Node.
The R-VGW and A-VGW are connected to the IMS PES via the Gm reference point.
The R-MGW and A-MGW are connected to the IMS PES via the P1 reference point.
PSTN/ISDN islands may also be connected via trunking media gateway function (T-MGF), controlled via the Mn
reference point. Transit network functionality is supported as provided by the IMS ES 282 007 [2].
4.3 Constraints on services
The range of services that can be emulated in TISPAN NGN Release 1 is constrained by the functional architecture and
the IMS SIP profile defined in ES 283 003 [4] on the Mw/Mx and ISC reference points, and of the Gm reference points
in case of VGW.
4.4 Overlap signalling
Overlap sending is a mechanism that is used for dialling over analogue and ISDN accesses, and is inbuilt in the inter-
exchange signalling systems of the PSTN/ISDN networks. As such, it is a mechanism that the IMS-based PSTN/ISDN
emulation subsystem architecture shall support, in a similar manner as for the PSTN.
To support overlap signalling the PES shall support the following functionality:
• at the originating side, the VGW and the AGCF shall support the ability to collect digits sent by the user to the
extent of its knowledge of the dialling plan in use. As a result, the completeness of the number may be
unknown, and the VGW and AGCF may, dependent on operator policy, use overlap sending;
• Networks supporting overlap sending should provide a B2BUA function that has the ability to collect digits,
before routeing to another network that does not support overlap sending, such that the address information is
provided in a single message;
• at the terminating side, e.g. when connected to a legacy PBX, the VGW and the AGCF should support based
on operator policy the ability to transfer digits to the user using overlap sending;
• at the terminating side, e.g. when connected to a legacy PBX, an AS may support the ability to transfer digits
to the user dependent on operator policy, using overlap sending;
• In case of an incoming call (from another network), the I-CSCF or TrRF or O-MGCF, possibly in combination
with HSS/DNS/ENUM, will forward the call only when a sufficient number of digits have been received:
- for terminating cases to access the service profile assigned to a user. Only for cases additional digits not
relevant for the IMS service profile lookup are received as overlap signalling, e.g. for DDI towards a
PBX, based on network options this additional overlap signalling should be sent towards the terminating
user;
- for transit cases when the number received points towards another network to select and forward the call
to an appropriate network egress point (e.g. IBCF or I-MGCF). the solution shall interoperate with IMS
networks not supporting overlap signalling without requiring any changes in those networks.
NOTE 1: A terminating IMS network not supporting overlap signalling will perform a database lookup to assign a
S-CSCF for an incoming call and will return a 404 error response to an INVITE with an incomplete
number.
• in interconnection scenarios, as a network option, it shall be possible to support overlap signalling.
NOTE 2: In the PES network the service level provided to the user should not be dependent on using overlap or
en-bloc sending.
ETSI

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11 ETSI TS 182 012 V2.1.4 (2008-03)
5 Functional architecture
5.1 Overview
The functional architecture described in the preent document is one of the possible architectural options for structuring
the TISPAN PSTN/ISDN Emulation Subsystem (PES) identified in the TISPAN NGN overall architecture ES 282 001
[1]. This functional architecture uses the same architecture as the IMS defined in ES 282 007 [2] with extensions
defined in the present document. Figure 3 provides an overview of the functional entities that make up this architecture
and shows their relationships to the other components of the NGN architecture.

Rf /Ro
Application
Ut

Servers Rf /Ro
Other types of service logic
Charging
Ut
Functions
PSTN/ISDN Emulation logic
Sh Rf /Ro
Network
ISC Dh
Attachment Iw
UPSF
Cx SLF
Dx
Subsyste IWF
Ib
P3
m
e2
Mw
PES
e2 Mx
Ic
IBCF
I/S- CSCF
Mx Mx
Mw
Mi
Mx
AGCF Mk
BGCF
P1
Mr
Mw
Other
Gq '
Mj

Gm Mx
Mg
IP
P- CSCF
MRFC MGCF

Ie
Net-
Gq ' Gq ' SGF

PSTN/
works
Mp Mn
ISDN
Resource and Admission Control Subsystem
A/R-
VGW
analog acc.
MRFP
T- MGF
ISDN acc.
A/R-
I -BG F
IP Transport (Access and Core)
MGW

Figure 3: PSTN/ISDN Emulation Subsystem - Functional Architecture
Most of the functional entities inside the PSTN/ISDN Emulation Subsystem are identical or derived from their IMS
counterpart 282 007 [2], with the noticeable exception of an Access Gateway Control Function (AGCF) that has the
responsibility of controlling residential and access media gateways. For the other functional entities, any differences are
noted in the following clause.
A physical entity can house functional entities supporting both PES and IMS, that can be supported by a common
addressing scheme.
5.2 Overview of Functional entities of the PES
5.2.1 Access Gateway Control Function (AGCF)
This functional entity is the first point of contact for Residential Media Gateway (R-MGW) and Access Media
Gateways (A-MGW). This entity is specific to the PSTN/ISDN emulation subsystem. It performs the following
functions:
• Act as an MGC for controlling media gateways functions (R-MGF and A-MGF) located in residential and
access gateways.
• Interact with the resource and admission control subsystem (RACS).
• Interact with the network attachm
...