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)

Technical Specification
Telecommunications and Internet converged Services and
Protocols for Advanced Networking (TISPAN);
IMS-based PSTN/ISDN Emulation Sub-system (PES);
Functional architecture
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
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
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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
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
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]".
ETSI
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).
ETSI
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
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
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 attachment subsystem (NASS) to retrieve line profile information.
ETSI
12 ETSI TS 182 012 V2.1.4 (2008-03)
• Perform signalling interworking between SIP at the Mw/Mx reference point and analog/ISDN signalling. The
analog and ISDN signalling information is conveyed over the P1 reference point.
• Perform signalling interworking between XCAP at the Ut reference point and legacy subscriber line
(e.g. ISDN) signalling via the P1 reference point.
NOTE 1: The main use-case for the interworking between XCAP and legacy subscriber line signalling is
supplementary service control (registration, activation, deactivation, interrogation).
• Act as a SIP User Agent with regard to IMS SIP functional entities.
• Perform functions normally assigned to a P-CSCF on behalf of legacy terminals connected behind the media
gateways (such as managing SIP registration procedures, generating asserted identities, and creating charging
identifiers).
The AGCF appears as a P-CSCF to the other CSCFs. The SIP signalling capabilities available to the AGCF are limited
to those available at the Mw/Mx reference.
Moreover, the AGCF shall provide basic feature logic for:
• delivering the appropriate dialtone pattern;
• processing mid-call events, as described in clause 12.
NOTE 2: A solution based on AGCF will provide similar response time (e.g. dial tone, ring tone) as today in the
PSTN networks.
In case of AGCF failure, stable calls shall be preserved.
Depending on implementation options, the AGCF may or may not be capable of implementing service-independent
feature logic for dealing with register recall events, when it does, it can make certain decisions such as whether or not to
apply dial tone on register recall, whereas in implementations where the AGCF does not implement feature logic, such
decisions must be left for the AS to make.
Further details on the AGCF structure and behaviour are provided in clause 12.
NOTE 3: If desired, a network operator could choose to deploy an MGC that controls a set of media gateways
following most of the AGCF call processing rules defined in the present document, and supports the Gm
interface into an IMS or PES network via a P-CSCF, but this entity would fill the role of "Gateway
(VGW)" depicted in figure 3 and would not be part of the trusted IMS core.
AGCF/VGW shall support a generic solution for calls without dialling information, e.g. fixed destination call or
deferred fixed destination call.
5.2.2 Multimedia Resource Function Controller (MRFC)
The behaviour of the MRFC is identical in the PSTN/ISDN Emulation Subsystem and in the IMS subsystem
ES 282 007 [2].
5.2.3 Media Gateway Control Function (MGCF)
The role of the MGCF is identical in the PSTN/ISDN Emulation Subsystem and in the IMS subsystem ES 282 007 [2].
Signalling procedures for interworking with ISUP signalling are slightly different due to the presence of encapsulated
ISUP information inside the PES and the need to ensure full ISDN transparency in case of ISDN calls transiting through
the PES.
5.2.4 Proxy Call Session Control Function (P-CSCF)
The behaviour of the P-CSCF is identical in the PSTN/ISDN Emulation Subsystem and in the IMS subsystem
ES 282 007 [2]. However, the P-CSCF is not used in configurations where an AGCF is required to control residential or
access media gateways. In such cases, all functions normally provided by the P-CSCF will be provided directly by the
AGCF.
ETSI
13 ETSI TS 182 012 V2.1.4 (2008-03)
5.2.5 Service Call Session Control Function (S-CSCF)
The behaviour of the S-CSCF is identical in the PSTN/ISDN Emulation Subsystem and in the IMS subsystem
ES 282 007 [2].
5.2.6 Interrogating Call Session Control Function (I-CSCF)
The behaviour of the I-CSCF is identical in the PSTN/ISDN Emulation Subsystem and in the IMS subsystem
ES 282 007 [2].
5.2.7 Breakout Gateway Control Function (BGCF)
The behaviour of the BGCF is identical in the PSTN/ISDN Emulation Subsystem and in the IMS subsystem
ES 282 007 [2].
5.3 Internal Reference Points
5.3.1 Reference Point MGCF - CSCF (Mg Reference Point)
The Mg reference point allows the MGCF to forward incoming session signalling (from the PSTN) to the CSCF for the
purpose of interworking with PSTN networks.
The protocol used for the Mg reference point is SIP. SIP messages may contain encapsulated ISUP information.
The role of this reference point is identical in the PES and IMS subsystems.
Details are described in TS 182 006 [3].
5.3.2 Reference Point CSCF - MRFC (Mr Reference Point)
The Mr reference point allows the S-CSCF to relay signalling messages between an application server function and an
MRFC.
The protocol used for the Mr reference point is SIP.
The role of this reference point is identical in the PES and IMS subsystems ES 282 007 [2].
Details are described in TS 182 006 [3].
5.3.3 Reference Point CSCF - CSCF and AGCF - CSCF (Mw Reference
Point)
The Mw reference point allows the communication and forwarding of signalling messaging between CSCFs and
between an AGCF and a CSCF, e.g. during registration and session control.
The protocol used for the Mw reference point is SIP. SIP messages exchanged over the Mw reference point may contain
encapsulated ISUP information, except between the AGCF and a CSCF.
The role of this reference point is identical in the PES and IMS subsystems ES 282 007 [2].
Details are described in TS 182 006 [3].
5.3.4 Reference Point CSCF - BGCF (Mi reference point)
This reference point allows the Serving CSCF to forward the session signalling to the Breakout Gateway Control
Function for the purpose of interworking to the PSTN networks.
The protocol used for the Mi reference point is SIP. SIP messages exchanged over the Mi reference point may contain
encapsulated ISUP information.
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14 ETSI TS 182 012 V2.1.4 (2008-03)
The role of this reference point is identical in the PES and IMS subsystems ES 282 007 [2].
Details are described in TS 182 006 [3].
5.3.5 Reference Point BGCF - MGCF (Mj reference point)
This reference point allows the Breakout Gateway Control Function to forward the session signalling to the Media
Gateway Control Function (and vice-versa) for the purpose of interworking to the PSTN networks. This reference point
may also be used by an MGCF to forward session signalling to the BGCF in case of transit scenarios, if the MGCF
supports transit routeing. The protocol for the Mj reference point is SIP, possibly with encapsulated ISUP information.
The role of this reference point is identical in the PES and IMS subsystems ES 282 007 [2].
Details are described in TS 182 006 [3].
5.3.6 Reference Point BGCF - BGCF (Mk reference point)
This reference point allows the Breakout Gateway Control Function to forward the session signalling to another
Breakout Gateway Control Function.
The Mk reference point is SIP, possibly with encapsulated ISUP information.
The role of this reference point is identical in the PES and IMS subsystems.
Details are described in TS 182 006 [3].
5.3.7 Reference Point AGCF, CSCF or BGCF - IBCF (Mx Reference
Point)
The Mx reference point allows the communication and forwarding of signalling messages between an AGCF, CSCF or
a BGCF and an IBCF.
NOTE: The protocol used for the Mx reference point is SIP.
The role of this reference point is identical in the PES and IMS subsystems.
SIP messages exchanged over the Mx reference point may contain encapsulated ISUP information, except between the
AGCF and the IBCF.
Details are described in TS 182 006 [3].
6 Service Architecture
6.1 Overview
The service architecture for the PES and the IMS subsystems is the same. The generic behaviour of a application server
functions is identical with respect to the PSTN/ISDN Emulation Subsystem and the TISPAN IMS. However, depending
on the type of services to be emulated, certain application servers may need to understand and terminate the ISUP
protocol encapsulated in SIP.
Three types of Application Server Functions (ASF) can be accessed by the IMS-based PES, through the ISC or Ma
reference point (see figure 4).
• SIP Application Servers (SIP AS).
• The IM-SSF Application Server.
• The OSA SCS Application Server.
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15 ETSI TS 182 012 V2.1.4 (2008-03)
A SIP Application Server may contain "Service Capability Interaction Manager" (SCIM) functionality and other
application servers. The SCIM functionality is an application which performs the role of interaction management. The
internal structure of the application server is outside the standards.
The purpose of the IM SSF is to enable access to IN service logic programs hosted in legacy SCPs. The IM-SSF
functionality encompasses the emulation of the IN Call Model (BCSM) on top of SIP signalling, IN triggering and
feature management mechanisms, emulation of the IN Service Switching Finite State Machine and interworking with
INAP.
NOTE 1: The role of the IM-SSF is identical in the PSTN/ISDN Emulation Subsystem and in the IMS subsystem
ES 282 007 [2]. Basic behaviour is also identical. However, in the PES case, mapping procedures may
take into account ISUP information encapsulated in SIP messages.
NOTE 2: The IM SSF is intended to enable access from the PES to IN service logic programs hosted in legacy
SCPs. Access to PES services (i.e. hosted in SIP-based Application Servers) from legacy SSPs in the
PSTN/ISDN is outside the scope of the present document. Appropriate gateway functions (e.g. SPIRITS
gateway as defined in RFC 3136 [9]) have to be implemented in the PSTN/ISDN network for supporting
such scenarios. The purpose of the OSA Service Capability Server is to provide access to OSA
applications, according to the OSA/Parlay framework ES 201 915-1 [8].
Further details can be found in TS 182 006 [3].
SIP-AS
OSA
IN SCF
AS
INAP
OSA API
Sh
OSA
Si IM-SSF
Sh
SCS
UPSF
Dh
ISC/Ma
SLF
Cx
Dx
S-CSCF
PSTN/ISDN
Emulation Subsystem
Transport Layer
Figure 4: Value Added Services architecture
The Service-CSCF to AS interface is used to forward SIP requests, based on filter criteria associated with the
originating or destination user.
The Interrogating-CSCF to AS interface is used to forward SIP requests destined to a Public Service Identity hosted by
the AS directly to that AS.
The procedures between AGCF and AS (using reference points Mw, Mx, Ic and ISC) shall be standard and open to
allow for interoperability of equipment from different vendors which may be located in different operators' networks.
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16 ETSI TS 182 012 V2.1.4 (2008-03)
6.2 Reference points
6.2.1 Reference Point S-CSCF - ASF (ISC Reference Point)
The role of the ISC reference point is identical with respect to the PSTN/ISDN Emulation Subsystem and the IMS
subsystem.
The information provided over the ISC reference point shall enable an AS to distinguish between access lines receiving
PES services via a VGW and access lines receiving PES services via an AGCF both of which use the same public user
identity.
6.2.2 Reference Point UPSF - SIP AS or OSA SCS (Sh Reference Point)
The role of the Sh reference point with respect to the PSTN/ISDN Emulation Subsystem and the IMS subsystem is
identical.
6.2.3 Reference Point UPSF - IM SSF (Si Reference Point)
The role of the Si reference point with respect to the PSTN/ISDN Emulation Subsystem and the IMS subsystem is
identical.
6.2.4 Reference Point ASF- SLF (Dh Reference Point)
The role of the Dh reference point with respect to the PSTN/ISDN Emulation Subsystem and the IMS subsystem is
identical.
6.2.5 Reference Point ASF - UE and ASF-AGCF (Ut Reference Point)
The role of the Ut reference point with respect to the PSTN/ISDN Emulation Subsystem and the IMS subsystem is
identical.
The Ut reference point enables a A-VGW or R-VGW acting as a UE to manage information related to the services
provided to the legacy equipment (e.g. ISDN terminal, ISDN PBX) it connects.
The Ut reference point enables the AGCF to manage information related to the services provided to the legacy
equipment (e.g. ISDN terminal, ISDN PABX) connected to the Residential or Access Media Gateways it controls.
The Ut reference point applies to SIP Application Servers only.
Details are described in ES 282 007 [2].
6.2.6 Reference Point I-CSCF - AS (Ma Reference Point)
The role of the Ma reference point with respect to the PSTN/ISDN Emulation Subsystem and the IMS subsystem is
identical.
This interface between Interrogating-CSCF and the Application Servers (i.e. SIP Application Server, OSA Service
Capability Server, or CAMEL IM-SSF) is used to forward SIP requests destined to a Public Service Identity hosted by
an Application Server directly to the Application Server.
Details are described in TS 182 006 [3].
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17 ETSI TS 182 012 V2.1.4 (2008-03)
7 External interfaces
7.1 Interfaces with entities in the transfer plane
Transfer plane entities are defined in ES 282 001 [1].
7.1.1 Reference Point MGCF - T-MGF (Mn Reference Point)
The role of this reference point with respect to the PSTN/ISDN Emulation Subsystem and the IMS subsystem is
identical.
7.1.2 Reference Point MGCF - SGF (Ie Reference Point)
The Ie reference point enables the MGCF to exchange SS7 signalling information over IP with the SGF, according to
the SIGTRAN architecture.
7.1.3 Reference Point AS - SGF (P3 Reference Point)
The PES uses the SGF primarily in support of the MGCF signalling to the PSTN, as does the IMS subsystem. In
addition, some Application Servers involved in supporting PES users may use the SGF to support non call related
signalling interactions with the PSTN (e.g. TCAP-based messages for CCBS).
7.1.4 Reference Point MRFC - MRFP (Mp Reference Point)
The role of this reference point with respect to the PSTN/ISDN Emulation Subsystem and the IMS subsystem is
identical.
7.2 Interface with the UE
Conventional SIP UEs do not exist in PES. In PES, the User Equipment comprises one or more analogue/ISDN
terminals and gateway to which they are connected, via either the Z, U, S/T or T reference point.
This gateway may be an Access or Residential Media Gateway or a SIP based Access or Residential Voice over IP
Gateway. When the user equipment is connected to an Access Gateway, this may be via existing V5.x Access Nodes.
A Voice over IP Gateways (A-VGW and R-VGW) plays the role of a UE with regards to the P-CSCF-.
VoIP gateways (A/R-VGW) interact with IMS PES via the Gm and Ut reference points. The protocol used for the Gm
reference point is SIP. Details are described in ES 282 007 [2].
The role of these reference point (Gm and
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