Next generation networks

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A number of terms are being used to describe legacy telecommunication networks as well as NGNs. Following terms are used in this Technical Paper with definitions, mostly based on relevant ITU-T Recommendations.

2.1 IP-based networks [ITU-T Y.1401]: A network in which IP is used as one of the Layer 3 protocols.

2.2 integrated services digital network (ISDN) [ITU-T I.112]: An integrated services network that provides digital connections between user-network interfaces.

2.3 legacy networks [Webopedia]: A network based on older, out-dated protocol that is not based on the IP (TCP/IP) protocol. IPX, SNA, AppleTalk and DECnet are examples of legacy networks.

2.4 next generation network [ITU-T Y.2001]: 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.

2.5 packet switched data network [Wikipedia]: A digital communications network that groups all transmitted data, irrespective of content, type, or structure into suitably sized blocks, called packets. The network over which packets are transmitted is a shared network which routes each packet independently from all others and allocates transmission resources as needed.

2.6 public switched telephone network (PSTN) [ITU-T Q.1290]: A telecommunications network established to perform telephone services for the public subscribers.

2.7 ubiquitous networking [ITU-T Y.2002]: The ability for persons and/or devices to access services and communicate while minimizing technical restrictions regarding where, when and how these services are accessed, in the context of the service(s) subscribed to.


ADF Adaptation Function

ATM Asynchronous Transfer Mode

BICC Bearer Independent Call Control

BRI Basic Rate Interface

DCE Data Circuit-terminating Equipment

DSL Digital Subscriber Line

DTE Data Terminal Equipment

FMC Fixed-Mobile Convergence

IdM Identity Management

IMS IP Multimedia Subsystem

INNI Internal Network-Network Interface

IP Internet Protocol

IPX Internetwork Packet Exchange

LAPB Link Access Procedure-Balanced

LLU Local Loop Unbundling

MDF Main Distribution Frames

MMCF Mobility Management Control Functions

MPLS Multiprotocol Label Switching

MSAN Multi-Service Access Nodes

NACF Network Attachment Control Functions

NAT Network Address Translation

NGA Next Generation Access

NGN Next Generation Networks

NNA Naming, Numbering and Addressing

NNI Network-Network Interface

NT Network Termination

OAM Operation, Administration and Maintenance

OSE Open Service Environment

OTN Optical Transport Network

PAD Packet Assembler-Disassembler

PDH Plesiochronous Digital Hierarchy

PON Passive Optical Network

POTs Plain Old Telephons

PPP Point-to-Point Protocol

PRI Primary Rate Interface

PSDN Public Switched Data Network

PSTN Public Switched Telephone Network

QoS Quality of Service

RACF Resource Admission and Control Function

SDH Synchronous Digital Hierarchy

SNA Systems Network Architecture

SIP Session Initiation Protocol

SLAs Service Level Agreements

TA Terminal Adapter

TCP Transmission Control Protocol

TE Terminal Equipment

URIs Uniform Resource Identifiers

VoD Video on Demand

VPNs Virtual Private Networks

WDM Wavelength Division Multiplexing

4Features of Legacy Telecommunication networks

“Legacy” is a relative term not an absolute term, thus it is importantly recognized that this Technical Paper should set up the concrete scope of “Legacy Networks” in terms of telecommunication networks relatively considering the NGN. This section identifies the scope of legacy telecommunication networks considering migration to NGN and the features of each specific legacy networks are described.

4.1Scope of Legacy Telecommunication Networks

One of general approach to define the legacy networks is the usage of IP. Legacy network defined, normally, a network based on older and out-dated protocol that is not based on the IP (TCP/IP) protocol [1]. Whether set aside IP is old protocol or not (because practically IP has more than 30 years old history), this is one of trend to define legacy networks, for example circuit switched, X.25, IPX, SNA, AppleTalk and DECnet are examples of technologies used in legacy networks. Hence this Technical Paper deals with the migration to NGN of legacy telecommunication networks, so followings are proposed scope of the legacy telecommunication networks taking into account the necessity of migration from public telecommunication networks into NGN:

  • Public Switched Telephone Networks (Circuit Switched networks);

  • Packet Switched Data Networks, and;

  • Integrated Services Digital Networks.

4.2Public Switched Telephone Networks

Public Switched Telephone Network (PSTN) is the oldest and widest popular network in the world which identifies as the most dominant legacy telecommunications network established to perform telephone services for the public users (or subscribers). This network composed mainly based on “Circuit switching” technology establishing a dedicated communications channel (by circuit) between two nodes through the network before the nodes may communicate. The circuit provides the fixed bandwidth according to the channel size (bandwidth) and remains connected for the duration of the communication session. The circuit functions as if the nodes were physically connected as with an electrical circuit.

Critical example of the network using this circuit switching is a telephone network, providing telephone voice-based services. When a call is made from one telephone to another, circuit switches create a constant wire circuit between the two telephones, for as long as the call lasts. Key features of PSTN consequence of circuit technology (e.g., circuit based transmission and switching) are summarized followings:

  • mainly voice-band services (voice and 3.1 kHz Audio-band data services);

  • the channel remains reserved and not allow to use for competing users (even no actual communication is taking place);

  • provides continuous transfer without the overhead;

  • a dedicated path persisting between two communicating parties or nodes can be extended to signal content;

  • the constant bit delay during a connection, and;

  • guaranteed a QoS (Quality of Service) of the circuit (channel), so no circuit can be degraded of QoS by competing users.

Overall configuration model of PSTN is shown in Figure 1. Circuit switching and transmission technology are basement for configuring the PSTN networks. A subscriber cable (a pair of twisted cable) is dedicated to each end user so not allowed to use other users (or terminals) simultaneously. Since the circuit switch is based on 64 kbit channel based switching, all services should be restricted based on this channel capacity. In addition, PSTN uses 3.1 kHz based spectrum, for services as well as signalling information, service capacity in PSTN should be restricted to use this spectrum as well. Because of this, a modem is used for transcoding of digital signal to 3.1 kHz band signal.

Figure 1 – Overall configuration model of PSTN

To provide telephone service to all users in nation-wide and/or international, PSTN normally uses hierarchical structure of the networks. There are several different models, but basic ideas similar such as providing connecting to end user (by Local Exchange, marked  and ), providing connectivity between nodes in the city level (by Tandem Switch, marked  and ), providing connectivity between different regions (by Toll Switch) and, finally between countries (by International Gateways, marked ). Each level of hierarchy has a different role for providing connectivity, relevant systems such as switch and transmission systems have been equipped with different technologies and capabilities. Detailed configuration model of PSTN based on these different roles is shown in Figure 2.

Figure 2 – Detailed configuration model of PSTN
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