ITU-BDT Regional Seminar for Africa on Fixed Mobile Convergence and
Guidelines on the smooth transition of existing mobile networks to
IMT-2000 for Developing Countries
Nairobi, Kenya, 9-12 May
1.4.4: Signalling Protocols and Evolving
Architectures for NGN
Riccardo Passerini,
Passerini, ITUITU-BDT
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Subscriber Growth
1350
1200
1050
(Millions)
900
Fixed
750
600
Mobile
Minute
migration
Fixed Internet
450
300
Mobile Internet
150
0
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
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1
Convergence
Computer &
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Electronics
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Convergence
•The coming together of telecommunications, computing
and broadcasting into information and communications
technologies (ICT)
•Within telecom the convergence of voice and data and
fixed and mobile services
•ICT uses same:
–Technology used to code voice, data and video
–Carrier for voice, data and video
•Expands the range and quality of services
•Requires broadband technologies
•Encourages the use of a single communications regulator
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2
The growing importance of the
telecommunication sector
Telecommunications are a crucial factor of efficiency
for the administrations, public utilities and private
companies.
• Synergy with computers for data processing,
• Faster information and better dialogue
Telecommunications play a crucial role for increasing
the competitivity of entreprises:
• Better productivity and better services
• More jobs with added values with new services
• Less intermediary positions without added values
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Results of convergence of ICT
(Information and Communication Technology)
The telecommunications sector evolves in a broader « ICT » sector
Till 1980
Telecommunications
After 1980
After 1995
Telematics
Informatics
Electronic
media
or
Mediamatics
Electronic
media
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ICT
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3
General overview of NGN: ITU-T Recommendation Y 2001 (12/2004)
The concept of an NGN (Next Generation Network) has been introduced to
take into consideration the new realities in the telecommunications industry,
characterized by factors such as: competition among operators due to ongoing
deregulation of markets, explosion of digital traffic, e.g., increasing use of "the
Internet", increasing demand for new multimedia services, increasing demand
for a general mobility, convergence of networks and services, etc. The NGN
(Next Generation Network) is conceived as a concrete implementation of the
GII (Global Information Infrastructure).
The target of NGN is to ensure that all elements required for interoperability
and network capabilities support applications globally across the NGN while
maintaining the concept of separation between transport, services and
applications.
A major goal of the NGN is to facilitate convergence of networks and
convergence of services. The common understanding is that the NGN has to be
seen as the concrete realization of concepts defined for the GII
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General overview of NGN: ITU-T Recommendation Y 2001 (12/2004)
3.1 Next Generation Network (NGN): A packet-based network able to
provide telecommunication services and able to make use of multiple
broadband, QoS-enabled transport technologies and in which service-related
functions are independent from underlying transport-related technologies. It
enables unfettered access for users to networks and to competing service
providers and/or services of their choice. It supports generalized mobility
which will allow consistent and ubiquitous provision of services to users.
3.2 generalized mobility: The ability for the user or other mobile entities to
communicate and access services irrespective of changes of the location or
technical environment. The degree of service availability may depend on
several factors including the Access Network capabilities, service level
agreements between the user's home network and the visited network (if
applicable), etc. Mobility includes the ability of telecommunication with or
without service continuity.
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4
Objectives of the NGN
NGN should fulfil the requirement of the environment described in ITU-T Recs Y.100 [1], Y.110 [2],
Y.130 [3] and Y.140 [4] or Y.140.1 [5], for example to:
promote fair competition;
encourage private investment;
define a framework for architecture and capabilities to be able to
meet various regulatory requirements;
•
provide open access to networks;
while:
•
ensuring universal provision of and access to services;
•
promoting equality of opportunity to the citizen;
•
promoting diversity of content, including cultural and linguistic diversity;
•
recognizing the necessity of worldwide cooperation with
particular attention to less developed countries.
•
•
•
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Fundamental characteristics of NGN (1)
The term NGN as defined in clause 3 is commonly used to give a name to the
changes to the service provision infrastructures that have already started in the
telecommunication industry. The NGN can be further defined by the following
fundamental characteristics:
• packet-based transfer;
• separation of control functions among bearer capabilities, call/session, and
application/ service;
• decoupling of service provision from transport, and provision of
open interfaces;
• support for a wide range of services, applications and mechanisms based on
service building blocks (including real time/ streaming/ non-real time
and multimedia services);
• broadband capabilities with end-to-end QoS (Quality of Service);
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5
Fundamental characteristics of NGN (2)
• interworking with legacy networks via open interfaces;
• generalized mobility (see 3.2 and 8.7);
• unrestricted access by users to different service providers;
• a variety of identification schemes;
• unified service characteristics for the same service as perceived by the user;
• converged services between fixed/mobile;
• independence of service-related functions from underlying
transport technologies;
• support of multiple last mile technologies;
• compliant with all regulatory requirements, for example concerning
emergency communications, security, privacy, lawful interception, etc.
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NGN capabilities (1)
NGN shall provide the capabilities (infrastructure, protocols, etc.) to
make the creation, deployment and management of all kinds of
services (known or not yet known) possible
One of the main characteristics of NGN is the decoupling of services
and transport, allowing them to be offered separately and to evolve
independently.Therefore in the NGN architectures, there shall be a
clear separation between the functions for the services and the
functions for the transport. NGN allows the provisioning of both
existing and new services independently of the network and the access
type used.
Interworking between NGNs of different operators and between NGN
and existing networks such as PSTN (Public Switched Telephone
Network), ISDN (Integrated Services Digital Network) and GSM
(Global System for Mobile communications) is provided by means of
gateways.
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6
NGN capabilities (2)
NGN will support both existing and "NGN aware" end terminal
devices. Hence terminals connected to NGN will include analogue
telephone sets, fax machines, ISDN sets, cellular mobile phones, GPRS
(General Packet Radio Service) terminal devices, SIP [13] (Session
Initiation Protocol) terminals, Ethernet phones through PCs (Personal
Computers), digital set top boxes, cable modems, etc.
Specific issues include the migration of voice services to the NGN
infrastructure, Quality of Service related to real-time voice services
(with guaranteed bandwidth, guaranteed delay, guaranteed packet
loss, etc.) as well as Security. NGN should provide the security
mechanisms to protect the exchange of sensitive information over its
infrastructure, to protect against the fraudulent use of the services
provided by the Service Providers and to protect its own infrastructure
from outside attacks.
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NGN capabilities (3)
A major feature of NGN will be generalized mobility, which will allow
a consistent provision of services to a user, i.e., the user will be
regarded as a unique entity when utilizing different access
technologies, regardless of their types. Generalized mobility means
providing the ability of using different access technologies, at different
locations while the user and/or the terminal equipment itself may be in
movement allowing users to use and manage consistently their
applications/customer services across existing network boundaries.
At present mobility is used in a limited sense such as movement of user
and terminal and with or without service continuity to similar public
accessed networks (such as WLAN, GSM, UMTS, etc.) and service
discontinuity to some wired line accessed networks with strong
limitations (such as UPT). In the future, mobility will be offered in a
broader sense where users may have the ability to use more access
technologies, allowing movement between public wired access points
and public wireless access points of various technologies. This means
that this movement will not necessarily force an interruption of an
application in use or a customer service.
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7
Interactions between NGNs and non-NGN environments
An important aspect of providing seamless operation is the ability of interworking
between NGNs, and between NGNs and other networks, such as PSTN.
……
Other NGNs
IWF
IWF
NGN
IWF
Internet
IWF
IWF
PLMN
PSTN
Figure II.1/Y.2011 – Interworking of NGN with other NGNs and legacy networks
It is envisaged that NGN will interwork with other networks to ensure:
•end-to-end communication capabilities for users of such networks as PSTN are preserved;
•content delivery capabilities for users of Internet, TV networks, etc.;
•step-by-step (transitional) deployment of NGN;
•inheritance of rich services from legacy networks.
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:
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
3.14
3.15
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Definitions
Access Gateway (AG): A unit that provides subscribers with various service access (e.g. PSTN, ISDN, V5.x, xDSL, LAN etc.)
and connects them to the packet node (IP or ATM) of an NGN.
Access Network (AN): See Recommendation G.964[x].
Application: A structured set of capabilities, which provide value-added functionality supported by one or more services,
which may be supported by an API interface.
Application Server (AS): A unit that supports service execution, e.g. to control Call Servers and NGN special resources
(e.g. media server, message server).
Call server (CS): A unit which controls set-up, maintenance, modification and release of a call.
Customer network: A telecommunications network belonging to the customer and located in the customer premise(s). The
customer network is connected to the user side of an access network
Evolution to NGN: A process in which parts of the existing networks are replaced or upgraded to the corresponding NGN
components providing similar or better functionality, while maintaining the services provided by the original network. In
addition,evolution to NGN will provide extra capabilities to the existing networks.
Gateway: A unit that interconnects different networks and performs the necessary translation between the protocols used in
these networks.
Next Generation Network (NGN): See Recommendation Y.2001 [x].
Node: A network element (e.g. switch, router, exchange) providing switching and/or routing capabilities.
PBX: See Recommendation G.100
Public Switched Telephone Network (PSTN): See Recommendation G.100 [x].
Signalling Gateway (SG): A unit that provides signalling conversion between the NGN and the other networks (e.g. STP in SS7).
Telecommunication service: See Recommendation F.700 (xx).
Transit Gateway (TG): A unit that provides an interface between the packet nodes of the NGN and the circuit switched node of
the PSTN for bearer traffic. The TG provides any needed conversion to the bearer traffic.
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8
Evolution principles
Evolution to NGN should allow continuation of the existing network
capabilities and in addition facilitate implementation of new capabilities.
Evolution to NGN should respect the integrity of services provided by the
existing networks and should facilitate introduction of new services.
Considering that provision of NGN is an evolutionary process it is necessary
to define a step-by-step approach leading to the NGN as a target network.
This approach should consider the following objectives:
•
•
•
•
•
•
separation of transport, control, management and service functions.
reduction of cost for the network infrastructure and its maintenance
maximum reuse of the existing resources
achieving comparable QoS level as provided in the existing network
optimum use of the new technologies
rapid implementation of new services and technologies enabling
introduction of new applications
• provision of mechanisms enabling user’s full utilisation of the applications
and network resources.
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Abbreviations
AG
ATM
CS
FR
GII
IN
IP
ISDN
LAN
LL
NGN
PSTN
QoS
SG
SS7
STP
TDM
TG
DSL
Access Gateway
Asynchronous Transfer Mode
Call Server
Frame Relay
Global information infrastructure
Intelligent Network
Internet Protocol
Integrated Services Digital Network
Local Area Network
Leased Line
Next Generation Network
Public Switching Telecommunication Network
Quality of Service
Signalling Gateway
Signalling System number 7
Signalling Transfer Point
Time Division Multiplexing
Transit Gateway
Digital Subscriber Line
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9
Interworking principles
• Deployment of interworking points: During the network planning, the
specified interworking points should be set, via which the inter-domain,
inter-area or inter-network interworking can be accomplished.
• Interworking filtering: Both parties for the interworking should sign an
agreement in advance to decide the interworking scope, authentication and
authorization mode, and execute the operation management layer
commands via policy control to adjust the interworking function.
• Interworking admission control: It is necessary to decide whether to allow
the interworking call access based on the network resource configurations
and the current traffic condition.
• Protocol interworking: It is necessary to ensure the interworking among
different protocols and the completion of interworking calls.
• Interworking charging: The interworking points must have the ability to
provide charging information of the incoming and outgoing interworking
calls to support the settlement between the interworking parties.
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Aspects to consider
Network operators will potentially choose a different evolution path
depending their actual resources. While considering the evolution path
it is essential the following aspects be considered:
•
•
•
•
•
•
•
•
•
•
•
Simplified analysis of the current networks
Management
Signalling
Bearer services
Billing
Leased line provisioning
Security
Services which are required by regulatory bodies
Supplementary services
Technical aspects of naming, numbering, addressing
Access technology evolution
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10
Priorities
Network and service providers may choose different evolution path based on
their existing and forecasted resources. This approach may encompass
different technologies and have different priorities.
Therefore there is a need to prepare a set of documents to help evolution of
the existing networks towards NGN. Taking into consideration that
potentially there are different evolution approaches (at least as many as the
existing networks), it is crucial to consider items provided in clause 8 for each
network and to not violate the evolution and interworking principles
described in clauses 6 and 7. The following provides list of networks or
technologies which may be considered for evolution.
•
•
•
•
•
•
PSTN / ISDN
FR
ATM
IPv4
Mobile Network
Other scenarios
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Security considerations
Evolution of network security should allow continuation of the existing
network security capabilities and in addition provide new resistance
capabilities against new security threats.
Several aspects may be considered:
•Achieving acceptable security level by combination of different layer
security methods
•Similar user security experience while evolving networks to NGN
•No over-provision of security measures.
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11
Evolution of PSTN/ISDN to NGN
NGN (Next Generation Network) is believed to provide new opportunities for
and capabilities to the network and service providers. Considering that
existing networks have different life span and vast amount of capital has been
spent on them, complete replacement of their components is not considered to
be either advisable or possible. So, a phased approach should be considered
for evolution of existing networks to NGN.
PSTN/ISDN ( Public Switched Telephone Network/Integrated Services
Digital Network) being one of the first networks, is considered to be prime
candidate for evolution. For PSTN/ISDN evolution to NGN a phased
approach is considered
Different evolutionary Scenarios with PSTN/ISDN emulation (adaptation to
IP infrastructure) and with PSDN/ISDN simulation (session control over IP
interfaces and infrastructure) are presently under consideration in ITU in
order to providereference for the evolution to NGN
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Evolution Architecture
PSTN
LEX
IP
GW
IP
IP can be considered as a “ Data NGN ”
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12
Signalling Requirements to Support "IP telephony"
PSTN
STP
Transit
Exchange
PSTN
CA
MGC
MG
MGC
IP Network
STP
MG
Local
Exchange
Transit
Exchange
Local
Exchange
Phone (E.164)
Phone (E.164)
Network configuration A (phone to phone communication)
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Configuration A: Phone to Phone Communication (with IP
Transit Network)
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In the IWF (such as MG, MGC, SG function) between the PSTN and
IP network at the originating and terminating sides, control signalling
(ISUP - H.323 / SIP conversion) and information signalling (64-kbps
bearer - IP packet conversion) are converted. In the IP network, a call
is controlled by the H.323 / SIP protocol. A user dials a phone number
to identify the terminating phone terminal and also, in some cases,
additional information (e.g. through the use of prefix dialling) to select
an IP transit network.
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PSTN
STP
Transit
Exchange
CA
MGC
MG
IP Network
Local
Exchange
IP Phone
Phone (E.164)
Network configuration B1 (IP phone to phone communication)
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Configuration B-1: IP Phone to Phone communication
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In the IWF (such as MGC, MG, SG functions) between a PSTN
and an IP network at the terminating side, the signalling protocol
(ISUP - H.323 / SIP conversion) and the user information (64-kbps
bearer - IP packet conversion) are converted. In the IP network, a
call is controlled by the H.323 / SIP protocol. The originating IP
phone user dials a phone number to identify the terminating
phone terminal.
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PSTN
CA
STP
Transit
Exchange
MGC
MG
IP Network
Local
Exchange
IP Phone
Phone (E.164)
Network configuration B2 (phone to IP phone communication)
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Configuration B-2: Phone to IP Phone communication
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CA
IP P h on e (ID )
IP P h on e (ID )
Configuration C: IP Phone to IP Phone communication
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Configuration C: IP Phone to IP Phone communication
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Network capabilities to support “IP telephony”
interworking between the PSTN and the IP network
Carrier A
Carrier B
PSTN
STP
Transit
Exchange
CA
MGC
MG
H323,SIP,etc
IP Network
CA
IP Network
RTP
Local
Exchange
Phone (E.164)
IP Phone
Network configuration connecting carriers (NNI between IP-IP network
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Carrier B
ISUP(SS7)
SDH
MGC
MG
CA
IP Network
Local
Exchange
IP Phone
Phone (E.164)
Network configuration connecting carriers (NNI between PSTN-IP network
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17
Control Protocols for support of “IP telephony”
PSTN
STP
MGC
SG
Transit
Exchange
MG
H.248/
MEGACO
H.323/SIP
CA
IP Network
H.323/SIP
RTP/RTCP
Local
Exchange
Phone (E.164)
IP Phone
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TERMS AND DEFINITIONS
Media Gateway (MG): A media gateway converts the media provided by one type of network
to the format required by another type of network. Terminates voice calls on inter-switch
trunks from the PSTN, compresses and packetizes the voice data, and delivers compressed
voice packets to the IP network. For voice calls originating in an IP network, the media
gateway performs these functions in reverse order.
Media Gateway Controller (MGC): Controller that controls the parts of the call state that
pertain to connection control for the media channels within a media gateway. A media
gateway controller handles the registration and management of resources at the media
gateway(s). A media gateway controller exchanges ISUP messages with central-office
switches via a signaling gateway (described below). Because vendors of media gateway
controllers often use off-the-shelf computer platforms, a media gateway controller is
sometimes called a softswitch.
Signalling Gateway (SG): A signalling gateway provides transparent interworking of
signalling between switched-circuit and IP networks. The signalling gateway may terminate
PSTN/SS7 signalling or relay messages over an IP network to a media gateway controller or
another signalling gateway. Because of its critical role in integrated voice networks,
signalling gateways are often deployed in groups of two or more to ensure high availability
Call Agent (CA): Function that controls the provision of services to users.
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18
1
TERMS AND DEFINITIONS
Telephone Number Mapping (ENUM): Protocols for mapping telephone numbers to IP phone
identifiers (i.e. E.164 numbers to URIs).
IP Network:An IP network is a network that uses IP technologies to transport information. It
may be a Private IP network, or a Carrier’s network.
Phone: Phone refers to a PSTN terminal.
IP Phone: IP phone refers to a terminal (e.g. dedicated voice terminal or multipurpose personal
computer) that is connected directly (e.g. Through an Ethernet interface or an xDSL line) to an
IP network.
IP telephony:“IP telephony” is a service that enables the exchange of voice information,
primarily in the form of packets, using IP protocols.
Internet Telephony: The combination of the term ‘Internet’ with the term ‘telephony’ is
regarded as a specific use of the Internet, rather than a service. The Internet offers many
capabilities to users, including the ability to carry bi-directional speech in real time or near
real time. This is considered to be an Intrinsic capability of the Internet and not
a telecommunications service.
(Note) Internet telephony is a particular application of the Internet and therefore falls outside of
the scope of this document.
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CONTROL PROTOCOLS FOR SUPPORT OF “IP TELEPHONY”
This section describes the protocol stacks used for the call control and
media transport in “IP telephony”.
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Protocol Stacks (1)
1)
IP phone
/MGC
CA
2)
MGC
H.323/SIP
H.248/MEGACO/
SCTP/TCP/UDP
TCP/UDP
IP
IP
Layer 2
Layer 2
Layer 1
Layer 1
MG
Protocol stack (example for configurations B-1 and B-2)
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Protocol Stacks (2)
MG
3)
IP phone
SG
4)
MGC
SS7 Upper Layer
RTP/RTCP
SCTP
UDP
Adaptation Layer
IP
IP
Layer 2
Layer 2
Layer 1
Layer 1
Protocol stack (example for configurations B-1 and B-2)
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General Framework for migrating Telephony networks
towards Next Generation Networks (NGN)
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General Framework for migration to NGN
(The Essential Report on IP telephony – ITU-D
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Step 1: use of today’s TDM based network for voice telephony and Internet
access
Step 2: consolidation of switching and access equipment;
Step 3: introduction of Voice-over-Packet technology for trunking;
Step 4: introduction of Voice-over-Packet technology in access and CPE
Step 5: multimedia services and new applications;
Step 6: end-of-life replacement of legacy infrastructure and migration to all-IP
signalling.
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B
SCP
WWW
INAP
ISUP
STP
SS7
TEX
TEX
TDM
A
IP, ATM
NAS
LEX
Voice
LEX
BAS
Conc.
DSLAM
Dial-up
ADSL
NT
C
POTS, ISDN
Voice
Data
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Step 1: PSTN for Voice and Internet
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TDM
D
TEX
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C on c.
C on c.
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IP , A T M
NAS
LEX
SL
BAS
F
AN
D SLA M
NT
P O T S , IS D N , A T M , IP , ...
V o ic e
D a ta
S ig n a llin g
Step 2 : PSTN Consolidation
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K
INAP
AS
ApGW
SCP
WWW
J
TGW
LEX/TEX
TDM
Class 4
Softswitch
H.248
STP
SS7
ISUP, BICC, SIP-T
BICC
I
IP, ATM
TGW
V oD
LEX
Conc.
Conc.
SL
AN
DSLAM
NT
Voice
Data
VoP
Signalling
Step 3: Voice over Packet for Trunking
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IN AP
AS
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TGW
H .248
H.248
IP, ATM
TGW
H.248
LEX
N
A GW
C onc.
H .248
AN
P M
O
A GW
RGW
DSLAM
NT
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H .323
SIP
IP
Voice
D ata
VoP
Q
IP
Signalling
Step 4: Voice over Packets in access and CPE
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S IP ,
P a rla y ,
J A IN
AS
S
C la s s 4
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C la s s 5
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WWW
STP
SS7
TG W
L E X /T E X
TDM
S IP , H .3 2 3
IP , A T M
TG W
LEX
C onc.
AGW
Conc.
AN
DSLA M
NT
AGW
R
IP
V o ic e
D a ta
IP
VoP
S ig n a llin g
Step 5 : Multimedia
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TGW
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IP, ATM
V
AGW
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AGW
AN
DSLAM
RGW
NT
IP
Voice
IP
Data
AGW
VoP
IP
Signalling
Step 6 : The full NGN
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24
Protocols: Status of studies being undertaken by
international standards organizations
Call control
Protocol
Media control
H.323
ITU-T SG16
H.323
SIP
IETF SIP-WG
RFC3261
H.248/MEGACO
RTP/RTCP
IETF MEGACO-WG
RFC3015
ITU-T SG16
H.248
IETF MMUSIC-WG
RFC1889
RFC3398
Note : For the latest draft document, see
URL of SIPPING-WG
IETF SIPPING-WG
Interwork
SIP-ISUP inter-working
ITU SG11
TRQ.2815 supplement 45
ITU SG11
Q.1912.5
Note: http://www.ietf.org/html.charters/sipping-charter.html
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ANNEX:
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