Vnd Migration

8/8/2019 Vnd Migration

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A Step-by-Step Migration ScenarioFrom PSTN to NGN(ETSI Market)

T E C H N I C A L P A P E R


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AbstractThis paper presents a step-by-step migration scenario from

a TDM-based public switched telephone network (PSTN) to

a packet-based next generation network (NGN). From an

economic point of view, it identifies the drivers and benefits

for an established carrier to consolidate its current network

and to migrate to an NGN. From a technology point of view,

the paper focuses on the role of call/session signaling

protocols, and the opportunity to deploy services and

applications through open interfaces.


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A Step-by-Step Migration ScenarioFrom PSTN to NGN

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Step 1: PSTN for Voice and Internet Access . . . . 2

TDM and SS7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Intelligent Network Services . . . . . . . . . . . . . . . . . . . . 2

Internet Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 2: PSTN Consolidation . . . . . . . . . . . . . . . . . 3

Switch Consolidation . . . . . . . . . . . . . . . . . . . . . . . . . 3

Access Consolidation and Voice over DSL . . . . . . . . . . 3

IN-Internet Convergence Services . . . . . . . . . . . . . . . . . 3

Open Service Access . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 3: Voice-Over-Packet Trunking . . . . . . . . . . 4

VoP Trunking through Integrated Gateways . . . . . . . . . . 4

Trunking Gateways with Class 4 Softswitch . . . . . . . . . . 4

Step 4: Voice-Over-Packet Access . . . . . . . . . . . . 5

Class 5 Softswitch . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Residential Gateway . . . . . . . . . . . . . . . . . . . . . . . . . 5

Access Gateway in the DSLAM . . . . . . . . . . . . . . . . . . 5

Distributed Access Gateways . . . . . . . . . . . . . . . . . . . 5

IP Phones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 5: Introduction of Multimedia . . . . . . . . . . . 6

IP Clients with Multimedia Softswitch . . . . . . . . . . . . . . 6

Retailer Portal and Open Interfaces . . . . . . . . . . . . . . . 6

New Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Step 6: Migration to Full NGN . . . . . . . . . . . . . . 7

End-of-Life Replacement of Legacy Equipment . . . . . . . . . 7

Migration to all-IP Signaling . . . . . . . . . . . . . . . . . . . . 7

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8


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IntroductionDriven by liberalization, competition, technological

advances and evolving market demand, many telecom

carriers consider implementing a distributed network

architecture, with a common, packet-based transport

layer for voice and data.

This next generation network is characterized by:

w A clear separation of access, transport, control and

service layers;

w Interoperability through open interfaces between

these layers and all other networks;

w Seamless control of multiple transport technologies

(ATM, IP, TDM, FR, etc.);

w Use of standards-based network elements

(gateways, softswitches, application servers, etc.)

NGNs hold the promise of offering a range of new data

and multimedia services, giving the carrier access to

new revenues.

Depending on the specific market situation (e.g., developing

vs. developed country) and network saturation of a carrier,

different network evolution strategies may be applied:

w Consolidation: optimize the installed PSTN to reduce

capital (CAPEX) and operational expenses (OPEX).

Consolidation can be combined with a selection of

future-safe products to prepare migration to NGN;

w Expansion: keep the existing PSTN infrastructure

and services, but introduce an overlay NGN (based

on broadband access) for addressing new customers

and introducing new services (e.g., multimedia);

w Replacement: replace PSTN components (at their

end-of-life) with equivalent NGN components.

In the remainder of this paper, a six-step consolidation

and expansion scenario is elaborated. It targets established

service providers (ESPs or ILECs) on fixed networks

(although there are many similarities with third generation

(3G) mobile networks). In order to reduce complexity of this

paper, some simplifications have been made at the network

architecture level. Also, quality of service (QoS) on transport

and network management aspects are not addressed.

Although the proposed scenario suggests a step-by-step

migration to NGN, it must be understood that there is no

one size fits all approach, and that depending on the

carriers specific situation the content and sequence of

evolutionary steps may vary, and that some steps may

even be omitted.

A STEP -BY-STEP MIGRATION SCENARIO FROM PSTN TO NGN | TECHNICAL PAPER ALCATEL 1


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Step 1: PSTN for Voice andInternet AccessThe starting point for the migration to NGN is todays

public switched telephone network. (See Figure 1.)

TDM and SS7 [A]

In this network, all voice traffic is transported over TDM,

and controlled by a hierarchy of local (LEX or Class 5) and

transit (TEX/Class 4) circuit switches. The voice-related

signaling network (ISUP and INAP) is handled by the SS7

signaling network.

Intelligent Network Services [B]

Value-added services are provided inside the switches,

or through the intelligent network (IN). Widely spread IN

services include calling card services, number translation

and routing services (such as freephone, premium rate and

universal access number), and enterprise network services

such as virtual private networks (VPNs) and wide area

Centrex.

Internet Access [C]

With the growing number of Internet users, carriers are

providing connectivity to Internet service providers (ISP)

either through narrowband (PSTN or ISDN) dialup services,

or through introduction of broadband ADSL (with voice

split off as a separate service).

2 ALCATEL A STEP -BY -STEP MIGRATION SCENARIO FROM PSTN TO NGN | TECHNICAL PAPER

STP

Voice

IP, ATMTDMSS7

Concentrator

LEX

Voice

DataSignaling

SCP

INAP[B]

[A]

[C] DSLAM

POTS,ISDN

Dialup

ADSLNT

NAS

TEX

ISUP

LEX

TEX

BAS

WWW Servers

w Figure 1: Current PSTN


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Step 2: PSTN ConsolidationIn the evolutionary move to multimedia and other next

generation applications, the next step is to boost processing

power by consolidating the TDM infrastructure. Network

infrastructure optimization will reduce carriers operational

expenses and allow them to generate additional revenues.

(See Figure 2.)

Switch Consolidation [D]

Deployment of a small number of large exchanges (local

and transit) with increased switching capacity, and high

speed interfaces (SDH, ATM) reduces the operators OPEX

and enables faster deployment of new services. Redundant

switches may be converted to additional remote access

concentrators.

Introduction of new technology with smaller footprint,or packet fabrics inside the exchanges, allows the carrier

to reduce expenses and reuse the switching infrastructure

for new data services.

Access Consolidation [E] and Voice over DSL [F]

Adding new access nodes and upgrading the existing ones

lets the carrier capitalize on his PSTN, while extending

the coverage area and the bandwidth offered to individual

subscribers (fiber closer to the end user). New access

technology provides seamless multiservice access to voice

(POTS, ISDN) and data (ADSL, ATM, IP, FR, etc.) services

and paves the way to NGNs.

Optimization of the ADSL access infrastructure is realized

through introduction of voice over DSL (VoDSL) loop-

emulation services (inverse gateway, with a V5.2/GR303

connection to the LEX).

IN-Internet Convergence Services [G]

Providing an external server to the PSTN and the Internet,

the IN service control point (SCP) may be used as a means

to integrate voice and data into common applications.

Example: IN-Internet convergence applications are click-to-

dial, Internet call waiting, Web-augmented calling, unified

messaging, etc. In order to communicate with the Internet

servers, the SCP has to adopt some IETF protocol suites(e.g., PINT and SPIRITS).

Open Service Access [H]

To prepare for the NGN and to gain extra revenues from

new services, the network operator may deploy application

gateways (ApGW) with open interfaces (e.g., OSA/Parlay,

JAIN, SIP) toward (third party) application servers (AS).


STP

VoDSL

IP, ATMTDMSS7

ApplicationServers

Concentrator

LEX

Voice

DataSignaling

ApGW SCP

INAP

Concentrator

[F]

[E]

[D][H]

[G]

DSLAM

ADSLNT

ATM, IP...POTS,ISDN

NAS

TEX

Parlay, JAIN, SIP

PINT, SPIRITS

SDH

BAS

AN

WWW Servers

V5.2

TEX

w Figure 2: PSTN consolidation


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Step 4: Voice-Over-Packet AccessIn fast growing markets or in markets with aggressive

deployment of broadband access (ADSL, LMDS, cable)

operators may introduce voice-over-packet technology

to capture growth in the access network, or as a means

to offload the local exchanges from DSL.

Class 5 Softswitch [L]

The Class 5 softswitch with local features (e.g., CLASS,

custom calling) will be a shared control element, but several

alternatives for voice gateways (depending on end user

topology, density, service requirements, etc.) may be deployed.

(See Figure 4). Just as in the Class 4 case, the softswitch will

address the gateways using the H.248 or Megaco protocol.

Residential Gateway [M]

ADSL subscribers may install a residential gateway (RGW)or integrated access device (IAD) with VoP coding capability.

Contrary to the ADSL with split-off voice [B] or VoDSL loop

emulation [E] solutions, the RGW provides the broadband

user with end-to-end voice-over-packet.

Access Gateway in the DSLAM [N]

As an alternative to upgrading the CPE of its subscribers,

an ADSL operator may choose to extend the DSLAMs with

VoP gateway functionality.

Distributed Access Gateways [O, P]

Another solution for connecting voice subscribers directly to

the data network is to introduce new access gateways [AGW]

or to upgrade the existing access nodes with AGW

functionality.

IP Phones [Q]

In order to address new generation voice terminals (IP phones),

the Class 5 softswitch can also terminate emerging user-to-

network signaling protocols such as H.323 and SIP.


w Figure 4: Voice-over-Packet in access and terminals

STP

IP, ATM

TDMSS7

ApplicationServers

Concentrator

ApGW SCP

Concentrator

[D][G]

DSLAM

ADSLNTRGW

AN

WWW Servers

Voice

VoPSignaling

LEX

Softswitch

INAP

ISUP, BICC, SIP-T

H.323,SIP

H.248

H.248

H.248

[L]

[M]

[N] [O]

[P]

TGW

TGW

AGW

AGW AGW

TEX


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Step 5: Introduction of MultimediaThere is no doubt that, in the near (and even midterm)

future, voice will be the predominant service, even in

NGNs. The introduction of broadband access in the network,

however, enables the deployment of a new range of data

and multimedia services. These new services will allow

carriers to differentiate and compete with new entrants.

(See Figure 5.)

IP Clients [R] with Multimedia Softswitch [S]

A prerequisite for the deployment of multimedia services

is the general availability of appropriate terminals. Todays

personal computers are a good starting point, but it is

expected that the convergence of computer, consumer

and communications technology will result in a number

of new multimedia devices.

These new terminals will communicate with the softswitch

through emerging multimedia signaling protocols such as

H.323 and SIP.

In order to fully support the new network and terminal

capabilities, the softswitch is extended with mixed-media

session and QoS control.

Retailer Portal and Open Interfaces [T]

With the introduction of new business models and

new players (e.g., virtual network operators, third party

application providers, content providers), there is a need

for application access (for authentication, authorization,

accounting, roaming, subscriber profiles, etc.) and service

brokering platforms (terminal capabilities negotiation,

bandwidth brokering, content aggregation, etc.).

Such portals not only provider the network operator with

new business opportunities as a service retailer, but also

clearly separate network control from services functionality.

In a full-fledged NGN architecture, applications and network

will interface through standardized protocols (e.g., SIP) and

APIs (e.g., JAIN, OSA/Parlay).

New Applications [U]

From an applications viewpoint, plain vanilla voice-over-

packet is not considered a differentiator. It is even assumed

that voice services offered on VoP networks will have fewer

features than the ones on circuit networks (especially in an

H.323 environment).


AGW

ADSL-NT

STP

DSLAM

WWW ServersSIP, Parlay, JAIN

SIP

IP, ATM

SIP,H.323

SIP,H.323

TDMSS7

ApplicationServers

Concentrator

LEX

VoiceDataVoPSignaling

SCP TEX

Softswitch

Portal

NAS

Concentrator

[T]

[U][S]

[R]

BAS

AN

ApGW

w Figure 5: Multimedia


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Therefore evolution of the applications portfolio toward

data and multimedia is considered an absolute prerequisite

for telecom service providers to differentiate, grow and

generate new revenues. Typical examples of multimedia

applications include:

w Mixed-media calls/conferences

w Real-time data streaming

w Instant messaging, presence and location services

w Etc.

Massive deployment of innovative new applications

will be enabled by the availability of application servers

and terminals, with easy-to-use service creation tools.

Step 6: Migration to Full NGNAs a final migration step toward the full NGN, the remaining

legacy PSTN equipment is transformed to or replaced by

NGN compliant network components. (See Figure 6.) The

aim of this ultimate (though optional) transformation, is

to capitalize on existing CAPEX (e.g., access concentrators

connected to local exchanges) while further reducing the

OPEX (packet-only network for transport and signaling).

End-of-Life Replacement of Legacy Equipment [V]

At the end of their life, remaining TDM exchanges and access

nodes are gracefully transformed to or replaced by trunking

gateways, access gateways and softswitches as outlined in

the previous sections.

Migration to all-IP Signaling [W]

While keeping the upper layers (SCCP, ISUP, TCAP, INAP)intact, the lower layers of the SS7 signaling network are

replaced by a packet-based equivalent, as defined by the

IETF SIGTRAN working groups.


AGW

TGW

AGW

AN ADSL-NT

STP

DSLAM

WWWServers

IP, ATM

SS7

ApplicationServers

BAS

Concentrator

SS7/IP

LEX

AGW

Voice

DataVoPSignaling

ApGW

TEX

SCP

Softswitch

Portal

AGW

RGW

[W]

[V]

TDM

w Figure 6: The full NGN


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ConclusionNext generation networks do not replace existing networks,

but will gradually expand their capabilities to generate new

revenues thanks to voice-data convergence.

Alcatels NGN value proposition toward established carriers

is to help them capitalize on their installed base, expand

switch capacity and boost transmission speeds (consolidation),

while smoothly introducing NGN technology and new

services (expansion and replacement).

Although there is no one size fits all solution, and operator

requirements have to be considered on an individual basis,

this approach allows operators to get new revenues from

multimedia and other next generation applications while

maintaining income from voice services and holding costs

down.

Alcatels offer covers the full spectrum of solutions presented

in this paper. It includes a wide range of products in the

transport, access, media, control, services and management

layers, complemented by professional services for economic

modeling, network planning, integration and operation.



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w w w . a l c a t e l . c o m

Alcatel and the Alcatel logo are registeredtrademarks of Alcatel. All other trademarksare the property of their respective owners.Alcatel assumes no responsibility for theaccuracy of the information presented,which is subject to change without notice.

12 2001 Alcatel. All rights reserved.

3CL 00352 0012 TQZZA Ed.01 11501

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