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InternationalTelecommunication
Union
NGN Migration scenarios and strategies:
A vision from ITU Specifications
Souheil MarineDigital Bridge Manager, Alcatel-Lucent
ITU Regional Development Forum 2008:Bridging the standardization Gap in Developing Countries
Damascus, 20-22 July 2008
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Some Terminology
Evolution to NGN: A process in which wholeor partsofthe existing networks are replacedor upgraded to thecorresponding NGN components providing similar orbetter functionality, while attempting to maintain the
services provided by the original network and thepossibility ofadditional capabilities
From ITU-T specification Y.2261: PSTN/ISDN Evolution to
NGN.
Migration to NGN synonymous to evolution to NGN
SoftSwitch and Call Server terms synonymous
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The NGN Migration Problematic
Developing countries characterized by:
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
Plus the possibilities offered through NGN migration togrow new markets (broadband, triple-play) and enrichinfrastructure competition between distinct accessplatforms
Need for a phasedapproach for operators with existinglegacyequipment Example scenarios from specification Y.2261
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Migration Scenarios Envisaged by Y.2261
Call Server (SoftSwitch) based approach of the Core
network with three variants (scenarios):
Scenario 1: Migration starts from Local Exchanges (LE)
Scenario 2: Migration starts from Transit Exchanges (TE)
Scenario 3: One-step approach
One step evolution of the core network to IP
Multimedia Subsystem (IMS) xDSL Access network evolution to NGN
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Core network consolidation before migration Reduce number of LE and transfer of affected user access modules (UAM), Private
Automatic Branch Exchanges (PABX) and Access Network to remaining LEs.
L E
L E
L E
L E
T ET ET E
P A B XP A B X
P A B XP A B X
U A M
U A M
U A M
U A M
A N
A N
A N
A N
L E L E
T ET ET E
P A B XP A B X
P A B XP A B X
U A M
R U A M
U A M
R U A M
A N
A N
A N
A N
V o i c e S ig n a l lin g
P S T N / I S D N
P S T N / I S D N
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Scenario 1: Migration from LE Step 1
Some of the LEs are replaced by Access Gateways (AG) controlled by aCall Server (CS).
Access elements originally connected to the removed LEs, are now
directly connected to AGs : PABXs and Access Nodes (AN). User Access Modules Functionality (UAM) assumed by AG and CS.
Trunking Media Gateways (TMG) and Signaling Gateways (SG) aredeployed for interconnection between the PSN and the TEs of the legacy
network as well as other operators' PSTNs/ISDNs. AGs and TMGs are all controlled by the CS.
Step 2
Remaining LEs are replaced by the AGs,
Transit Exchanges (TE)s are removed and their control functions areperformed by CS.
TMGs and SGs are deployed for interconnection between PSN and otheroperators' PSTNs/ISDNs.
AGs and TMGs are all controlled by the CS.
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L E
L E
T ET ET E
P A B XP A B X
P A B XP A B X
U A M
U A M
U A M
U A M
A NA N
A N
P S T N / I S D N
A NL E
L E
P A B X
A NA N
P a c k e t S w i t c h e d
N e t w o r k
A GP A B X
A G
A G
L E T E
P A B XP A B X
U A MU A M
A NA N
P S T N / I S D N
L ET ET E
T M G
S GC S
P A B XP A B X
P A B X
A N
A N
A N
A N
P a c k e t S w i t c h e dN e t w o r k
A G
C S
A G
P A B X
A G
A G
V o i c e
S i g n a l li n gD a t a
B e a r e r a n d S ig n a l lin g t ra f f ic f ro mo t h e r o p e r a t o r s P S T N
S GT M G
T M G
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Scenario 2: Migration from TE
Step 1 All TE functions are performed by the TMGs and the SGs under the
control of the CS.
LEs are connected to the Packet Switched Network (PSN) via TMGsand SGs.
TMGs & SGs are deployed for interconnection between PSN and otheroperators PSTNs/ISDNs.
AGs & TMGs are all controlled by CS.
Step 2 All LEs are replaced by AG controlled by CS
Access elements originally connected to the removed LEs, are nowdirectly connected to AGs : PABXs and Access Nodes (AN).
User Access Modules Functionality (UAM) assumed by AG and CS.
TMGs & SGs are deployed for interconnection between PSN and otheroperators PSTNs/ISDNs.
AGs & TMGs are all controlled by CS.
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L E
L E
T ET ET E
P A B XP A B X
P A B XP A B X
U A M
U A M
U A M
U A M
A NA N
A N
P A B XP A B X
P A B X
U A M
U A MU A M
A N
A N
A N
A N
P S T N / I S D N
P a c k e t S w i t c h e d
N e t w o r k
P A B X
A NL E
L E
S G
B e a r e r a n d S i g n a l lin g t ra f f ic f r o mo t h e r o p e r a t o r s P S T N
S G
L E
L E L E
L E S G
U A M
P A B XP A B X
P A B X
A NA N
P a c k e t S w i t c h e dN e t w o r k
A G
P A B X
A G
V o i c eS i g n a l l i n g
D a t a
B e a r e r a n d S i g n a l li n g t r a ff ic f r o m
o t h e r o p e r a t o r s P S T N
S G
A G A G
A G
A G
T M G
C S
C S
T M G
T M G T M G
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Scenario 3: One-Step Approach
LEs are replaced by the AGs and their functions are transferredto the AGs and the CS.
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).
The access networks (ANs) are either replaced by the access
gateways (AGs) or are connected to packet based network (PBN)
through the AGs.
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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L E
L E
T ET ET E
P A B XP A B X
P A B XP A B X
U A M
U A M
U A M
U A M
A NA N
A N
P S T N / I S D N
A NL E
L E
P A B XP A B X
P A B X
A NA N
P a c k e t S w i t c h e dN e t w o r k
A G
P A B X
A G
V o i c eS ig n a l lin gD a t a
B e a r e r a n d S ig n a l lin g t r a f f ic f r o mo t h e r o p e r a t o r s P S T N
S G
A G A G
A G
A G
T M G
C S
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IMS-based evolution to NGN
PSTN/ISDN evolves directly to a PSN based on the IMS corenetwork architecture.
End-users access the network using NGN user equipment orlegacy user equipment connected via an AG.
Transit and signalling gateways (TMGs & SGs) are deployed for
interconnection between the NGN and other operatorsPSTNs/ISDNs.
Concurrent CS-based and IMS-based evolution to NGNimplementations can occur when an existing operator deploys aseparate IMS-based network for new servicesand 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 thescope of recommendation Y.2261.
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L E
L E
L E
L E
T ET ET E
P A B XP A B X
P A B XP A B X
U A M
U A M
U A M
U A M
A N
A N
A N
A N
A G
P A B X
P A B X
A N
A N
P S T N / I S D N
P a c k e t S w i t c h e d
N e t w o r k
T M G S G
V o i c e V o I PS ig n a l l i n g
I M S
A G
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What remains of the PSTN/ISDN services:
Emulation or Simulation ?
Emulation refers to the Provision ofmost ofthe existing
PSTN/ISDN service capabilities and interfaces usingadaptation to an IP infrastructure.
Only a sub-setof PSTN/ISDN could be supported.
Simulation refers to the same service provision as above
but there is no guaranteethat all features are provided. New features and capabilitiesmay be provided with respect to
legacy PSTN/ISDN.
Specification Y.2262 specifies two types of adaptation
functions (ADF) for legacy access equipment ADF1 for simulation
ADF2 for emulation
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Emulation is complex:
Call Server-based PSTN/ISDN Emulation Service(CS-PES) Components
Access Call Server (ACS)
Controls Access Gateways (AG), subscriber registration and call control
Breakout Call Server (BCS)
Controls Trunking Media Gateways (TMG)to interwork withPSTN/ISDN
IMS Call Server (ICS) Controls interconnection Border Gateway to interwork with Packet-
based networks (NGN, IP Multimedia, Internet)
Gateway Call Server (GCS)
Ensures interoperability between among CS-PESs to provide end-to-endservices
Routing Call Server (RCS)
Provides routing function between call servers
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Emulation Call Server
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Concluding Remarks
Y.2261, Y.2262 and Y.2271 provides some functionalguidelines for NGN migration with a focus onemulating existing PSTN/ISDN network
Scenarios proposed well adapted to the context of legacyoperator willing to move their services as they exist to NGN
But a bit less to new entrants: reality of NGN voice services bynew entrants leans towards simulation rather than emulation
Developing countries must contribute more effectivelyto this standardization effort to take into account theirspecific conditions
Legacy PSTN/ISDN infrastructure generally more modern
than in developed countries but Growth needs more acute: grow with Emulation, Simulation
orleapfrog to IMS ?
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 [email protected]
http://www.alcatel-lucent.com/digitalbridge
