ITU Regional Development Forum 2008:
Bridging the standardization Gap in Developing Countries
Damascus, 20-22 July 2008
NGN Migration scenarios and strategies:
A vision from ITU Specifications
Souheil Marine
Digital Bridge Manager, Alcatel-Lucent
International
Telecommunication
Union
Some Terminology
ƒ Evolution to NGN: A process in which whole or parts of
the existing networks are replaced or upgraded to the
corresponding NGN components providing similar or
better functionality, while attempting to maintain the
services provided by the original network and the
possibility of additional capabilities
¾ From ITU-T specification Y.2261: PSTN/ISDN Evolution to
NGN.
ƒ Migration to NGN synonymous to evolution to NGN
ƒ SoftSwitch and Call Server terms synonymous
ITU Regional Development Forum, Damascus, 20-22 July 2008
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The NGN Migration Problematic
ƒ Developing countries characterized by:
¾
¾
¾
¾
Growth of their voice service market
Dilemma to grow with legacy PSTN/ISDN or with NGN
Inter-working with existing legacy equipment
Seamless continuity of services
ƒ Plus the possibilities offered through NGN migration to
grow new markets (broadband, triple-play) and enrich
infrastructure competition between distinct access
platforms
ƒ Need for a phased approach for operators with existing
legacy equipment
¾ Example scenarios from specification Y.2261
ITU Regional Development Forum, Damascus, 20-22 July 2008
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Migration Scenarios Envisaged by Y.2261
ƒ Call Server (SoftSwitch) based approach of the Core
network with three variants (scenarios):
¾ Scenario 1: Migration starts from Local Exchanges (LE)
¾ Scenario 2: Migration starts from Transit Exchanges (TE)
¾ Scenario 3: One-step approach
ƒ One step evolution of the core network to IP
Multimedia Subsystem (IMS)
ƒ xDSL Access network evolution to NGN
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Core network consolidation before migration
ƒ Reduce number of LE and transfer of affected user access modules (UAM), Private
Automatic Branch Exchanges (PABX) and Access Network to remaining LEs.
UAM
AN
UAM
P S T N /IS D N
LE
PABX
PABX
TE
UAM
AN
AN
LE
TE
TE
UAM
AN
LE
LE
PABX
PABX
UAM
UAM
AN
LE
P S T N /IS D N
PABX
RUAM
LE
AN
PABX
TE
TE
TE
RUAM
AN
AN
PABX
PABX
V o ic e
S ig n a ll in g
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ƒ Step 1
Scenario 1: Migration from LE
¾ Some of the LEs are replaced by Access Gateways (AG) controlled by a
Call Server (CS).
¾ Access elements originally connected to the removed LEs, are now
directly connected to AGs : PABXs and Access Nodes (AN).
¾ User Access Modules Functionality (UAM) assumed by AG and CS.
¾ Trunking Media Gateways (TMG) and Signaling Gateways (SG) are
deployed for interconnection between the PSN and the TEs of the legacy
network as well as other operators' PSTNs/ISDNs.
¾ AGs and TMGs are all controlled by the CS.
ƒ Step 2
¾ Remaining LEs are replaced by the AGs,
¾ Transit Exchanges (TE)s are removed and their control functions are
performed by CS.
¾ TMGs and SGs are deployed for interconnection between PSN and other
operators' PSTNs/ISDNs.
¾ AGs and TMGs are all controlled by the CS.
ITU Regional Development Forum, Damascus, 20-22 July 2008
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UAM
AN
UAM
LE
P S T N /IS D N
AN
LE
PABX
PABX
TE
UAM
AN
TE
TE
UAM
AN
LE
LE
PABX
PABX
P S T N /IS D N
UAM
AN
LE
TE
TE
UAM
TE
LE
PABX
AN
PABX
CS
TM G
SG
P a c k e t S w itc h e d
N e tw o rk
TM G
AN
AN
AG
AG
PABX
AG
PABX
CS
AN
AG
AG
PABX
AN
PABX
PABX
P a c k e t S w itc h e d
N e tw o rk
AG
AG
TM G
SG
AN
PABX
B e a r e r a n d S ig n a llin g t r a f f ic f r o m
o t h e r o p e ra to r ’s P S T N
ITU Regional Development Forum, Damascus, 20-22 July 2008
AN
V o ic e
S ig n a llin g
D a ta
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Scenario 2: Migration from TE
ƒ Step 1
¾ All TE functions are performed by the TMGs and the SGs under the
control of the CS.
¾ LEs are connected to the Packet Switched Network (PSN) via TMGs
and SGs.
¾ TMGs & SGs are deployed for interconnection between PSN and other
operators’ PSTNs/ISDNs.
¾ AGs & TMGs are all controlled by CS.
ƒ Step 2
¾ All LEs are replaced by AG controlled by CS
¾ Access elements originally connected to the removed LEs, are now
directly connected to AGs : PABXs and Access Nodes (AN).
¾ User Access Modules Functionality (UAM) assumed by AG and CS.
¾ TMGs & SGs are deployed for interconnection between PSN and other
operators’ PSTNs/ISDNs.
¾ AGs & TMGs are all controlled by CS.
ITU Regional Development Forum, Damascus, 20-22 July 2008
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UAM
UAM
AN
P S T N /IS D N
LE
AN
LE
PABX
PABX
TE
UAM
AN
TE
TE
UAM
AN
LE
LE
PABX
PABX
UAM
UAM
CS
AN
LE
SG
SG
PABX
AN
LE
PABX
P a c k e t S w it c h e d
N e tw o r k
UAM
LE
TM G
TM G
UAM
LE
AN
AN
SG
TM G
PABX
PABX
B e a r e r a n d S ig n a l l i n g t r a f f i c f r o m
o t h e r o p e r a t o r ’s P S T N
CS
AG
PABX
AN
PABX
AG
AG
PABX
AG
P a c k e t S w itc h e d
N e tw o rk
AG
AG
TM G
PABX
SG
B e a r e r a n d S ig n a llin g tr a ff ic f r o m
o th e r o p e r a t o r ’s P S T N
ITU Regional Development Forum, Damascus, 20-22 July 2008
AN
V o ic e
S ig n a llin g
D a ta
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Scenario 3: One-Step Approach
ƒ LEs are replaced by the AGs and their functions are transferred
to the AGs and the CS.
ƒ All access elements such as user access modules (UAMs), remote
user access modules (RUAMs), and private automatic branch
exchanges (PABXs) are connected to access gateways (AGs).
ƒ The access networks (ANs) are either replaced by the access
gateways (AGs) or are connected to packet based network (PBN)
through the AGs.
ƒ Transit gateways (TMGs) under the control of the call server (CS),
and the signalling gateways (SGs), are deployed to replace the TE
functions and provide interconnection between PSN and other
operators’ PSTNs/ISDNs.
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UAM
UAM
AN
P S T N /IS D N
LE
AN
LE
PABX
PABX
TE
UAM
AN
TE
TE
UAM
AN
LE
LE
PABX
PABX
CS
AG
PABX
AN
PABX
AG
AG
AG
P a c k e t S w itc h e d
N e tw o rk
AG
AG
TM G
SG
B e a r e r a n d S ig n a llin g t r a f f ic f r o m
o t h e r o p e r a t o r ’s P S T N
ITU Regional Development Forum, Damascus, 20-22 July 2008
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PABX
AN
PABX
V o ic e
S ig n a llin g
D a ta
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IMS-based evolution to NGN
ƒ PSTN/ISDN evolves directly to a PSN based on the IMS core
ƒ
ƒ
ƒ
ƒ
ƒ
network architecture.
End-users access the network using NGN user equipment or
legacy user equipment connected via an AG.
Transit and signalling gateways (TMGs & SGs) are deployed for
interconnection between the NGN and other operators’
PSTNs/ISDNs.
Concurrent CS-based and IMS-based evolution to NGN
implementations can occur when an existing operator deploys a
separate IMS-based network for new services and supports the
remainder of the services using a CS-based approach.
These two types of network implementations need to interoperate.
Interoperation is possible if SIP is used, but this is beyond the
scope of recommendation Y.2261.
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U AM
U AM
AN
LE
P S T N /IS D N
LE
P AB X
AN
P AB X
TE
U AM
AN
TE
TE
U AM
LE
LE
P AB X
AN
P AB X
AN
IM S
AG
P AB X
AN
AG
P AB X
V o ic e
P a c k e t S w itc h e d
N e tw o rk
TM G
S ig n a llin g
ITU Regional Development Forum, Damascus, 20-22 July 2008
SG
V o IP
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What remains of the PSTN/ISDN services:
Emulation or Simulation ?
ƒ Emulation refers to the Provision of most of the existing
PSTN/ISDN service capabilities and interfaces using
adaptation to an IP infrastructure.
¾ Only a sub-set of PSTN/ISDN could be supported.
ƒ Simulation refers to the same service provision as above
but there is no guarantee that all features are provided.
¾ New features and capabilities may be provided with respect to
legacy PSTN/ISDN.
ƒ Specification Y.2262 specifies two types of adaptation
functions (ADF) for legacy access equipment
¾ ADF1 for simulation
¾ ADF2 for emulation
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ITU Regional Development Forum, Damascus, 20-22 July 2008
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Emulation is complex:
Call Server-based PSTN/ISDN Emulation Service
(CS-PES) Components
ƒ Access Call Server (ACS)
¾ Controls Access Gateways (AG), subscriber registration and call control
ƒ Breakout Call Server (BCS)
¾ Controls Trunking Media Gateways (TMG)to interwork with
PSTN/ISDN
ƒ IMS Call Server (ICS)
¾ Controls interconnection Border Gateway to interwork with Packetbased networks (NGN, IP Multimedia, Internet)
ƒ Gateway Call Server (GCS)
¾ Ensures interoperability between among CS-PESs to provide end-to-end
services
ƒ Routing Call Server (RCS)
¾ Provides routing function between call servers
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Emulation Call Server
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Concluding Remarks
ƒ Y.2261, Y.2262 and Y.2271 provides some functional
guidelines for NGN migration with a focus on
emulating existing PSTN/ISDN network
¾ Scenarios proposed well adapted to the context of legacy
operator willing to move their services as they exist to NGN
¾ But a bit less to new entrants: reality of NGN voice services by
new entrants leans towards simulation rather than emulation
ƒ Developing countries must contribute more effectively
to this standardization effort to take into account their
specific conditions
¾ Legacy PSTN/ISDN infrastructure generally more modern
than in developed countries but…
¾ Growth needs more acute: grow with Emulation, Simulation
or…leapfrog to IMS ?
ƒ The floor is yours: you must contribute !
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Thank you for your attention!
Questions ?
Souheil Marine
Digital Bridge Manager
Alcatel-Lucent
Tel.: +33 1 3077 8192
souheil.marine@alcatel-lucent.fr
http://www.alcatel-lucent.com/digitalbridge
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