Next Generation Network

1 What Is Next Generation Network (NGN)?
The rapid growth of the Internet with its economical basic transport mechanisms created an expectation of a "one-for-all" network which became the forerunner of NGN. Even though basic pieces of this new network definition have been agreed upon, there is widespread speculation on the complete picture. General direction of converging the PSTN and the packet-based Internet is well understood, however, the ever-changing details and a lack of understanding of "user" behavior prevent a uniform set of objectives and mechanisms in this new network.

  The Internet has evolved this quickly partly because of the new self-organizing transport infrastructure and protocols and its ability to bring the "user" perspective into the domain where only "telco" operators controlled and ruled. This created a set of new opportunities and a fresh outlook on the market conditions and potentials of the NGN.

  The competitive environment has forced an evolution in traditional telecom networks apart from more conventional reasons, i.e. advances in technology at the fundamental level, e.g. photonics, new world economics, service demands and customer behavior of both consumers and business users. The two distinct approaches in network evolution namely Internet and Telco can be summarized as follows:

  (1) The Internet View

• Interconnected networks will mainly serve to provide end-to-end connectivity, carrying packets of data end-to-end between smart terminals, and establishing end-to-end sessions under end user control as required.
• Services will be provided by interaction between end-user equipment (e.g. Yahoo voice+, Web access).
• Legacy carrier-based services will be in decline.

  (2) The "Telco" View

• Services will primarily be provided across interconnected networks operated by multimedia carriers, with a combination of "smart" and "dumb" terminal equipment working with a "smart" network which would control end-to-end services as needed based on user requirements signalled to the network.
• Current telephone networks will develop to support multimedia, forming the basis of NGN.
• Much service development and provision will come from public network operators, supported by end-to-end higher-layer services developed over open interfaces.
  Even though these views are not static and in constant scrutiny and revision, it is safe to say that the combined views will largely influence the eventual evolution of NGN which is in its infancy now. The best way to describe NGN is via its multi-dimensional attributes. The key dimensions to be considered are: network services, technical characteristics, transport and, user, application and network provider benefits. Furthermore, any discussion of NGN has to factor legacy considerations, i.e. PSTN services including Internet access. NGN as we define here is not a single architecture but a set of architectures with a common set of principles and hence varies by service provider history, target applications and assets.

1.1 NGN Functional Requirements
The NGN functional requirements are in constant influx and there is still not an accepted document in standards bodies. However, there are some guidelines that are clearly going to be part of an NGN functional architecture. Some of these are:

• Distributed Control: NGN will provide mechanisms that support distributed processing and computation characteristics of an IP network, and would eliminate some of the fundamental defects of SS7 signaling architecture.
• Management, Control and Transport Functions: Some of the nice features of networks of the past and present will be part of the functional architecture with open network control interfaces that support the service creation, service update, and service logic by other parties.
• Service Provision and Network Operation: Separating service provision and operation processes will encourage a competitive environment with dynamic provisioning of new services.
• Convergence: The NGN will support the converged voice/data services that are flexible and user friendly.
• QoS, Security and Reliability: The NGN will provide mechanisms for QoS, enhanced security and reliability that are part of its architecture.

1.2 NGN Services
The NGN services of a carrier-class and business-class network can be numerous and it is difficult to provide an exhaustive list. Some of the prevalent ones can be classified along the following lines:

  (1) Interactive End-to-End Communication Services

• Diversification in service features, such as security, service level guarantees, and presence information.
• Penetration of easy-to-use terminals is a key issue.
• New means of communication will replace telephony in the future.
  

  (2) Video Delivery Services

• Appropriate business models are being explored, which takes account of copyright issues.
• Amid the convergence between telecommunications and broadcasting, and in light of the soon-to-start digital terrestrial broadcasting, the broadcasting industry is highly paid attention. Potential demand is certain.
  

  (3) Virtual Private Network (VPN) Services
  The diversification of means of network access, and the need for flexible network configuration have made highly value-added VPN a key to differentiation.

  (4) Information Home Appliance Control Services

• Widespread use of cellular phones and PDAs allows users to be always connected.
• Initial targets are remote control of home appliances and home security services.
• Future targets include diverse services using RFID (Radio Frequency Identification) tags and various sensors.
  

  (5) Broadband

• Move from selling best-effort pipe to assured services charged per session/time.
• Provide one-way assurance (VoD, Turbo button etc.) and two-way multimedia calling.
• Allow anyone to create services.
  

  (6) Business

• Provide ICT (Information Communication Technology) services, managed desktop, storage and hosted applications.
• Build on IP VPN to have any access, including work at home, cellular and WLAN.
  

  (7) Future Voice

• Derived/replacement where needed.
• Multi-media in both consumer and business.
  

  (8) Mobility

• Support mobile terminals.
• Build on IM/mobile presentation to provide roaming over any access.
• Personal and terminal mobility.

1.3 NGN Architectural Features
Network Architectures for traditional networks and the Internet are quite different due to the primary thrust of their traditional applications. The former is more hierarchical, rigid, robust and time-hardened for voice applications while the latter is of a more recent vintage with its origin in data communication, flat networks with end-to-end control. NGN architectures have tried to exploit the best attributes of the two approaches to enable delivery of network services outlined above.

  The key NGN features enable the above services are:

• Unified packet-based (IP, MPLS, ATM, Ethernet) transport.
• IP and service intelligence, in an IP-managed network.
• Distributed, transport-resource-session-service independent control; End-to-end packet intelligence.
• Using IP-friendly protocols for person-to-person voice or video services.
• Service Rich Platform - Access agnostic.
• Media gateways, call feature servers and signaling gateways are the key building blocks of a multi-service architecture.
• Open standards-based platform.
• Interworking with legacy networks.
  

  The architectural breakdown of NGN consists of access, edge, core and transport network elements. The following are the highlights of some of the attributes and features of these elements.
NGN architectures support a number of wired and wireless access technologies. The dominant ones are:

• DSL: This is one of the fastest growth segments in the industry for broadband access and dominates the US landscape for wireline users.
• Cable: It is growing in importance worldwide and in geographies outside the US. Cable leads the broadband access. The growth in cable anticipates a triple play including voice, data and video over time.
• Private Line (PL): Legacy of traditional networks is taken into consideration. Many enterprises still depend on PL for their networks.
• Ethernet: This technology has grown in scope both geographically and in speed over time to cover metro areas and Gigabits of traffic. It is a mature technology in terms of both standards and affordability.
• Wireless: Support for mobility is essential for success in business. Wireless standards have enabled global evolution in application for both voice and data. 3G wireless is key to NGN.
  

  Major focus in NGN architectures lies at the edge of the network which serves to bridge legacy considerations, multiple access technologies and the high-speed core network. The edge network element has several attributes:

• Scalability
• Feature richness
• Customer control
• Service selection
• Interworking
• High and low speed aggregation
  

  Transport network elements are evolving from TDM (Time Division Multiplexing) copper based architectures to resilient fiber dominated packet based architectures with high speed, granularity and reliability. The primary attributes are:

• Packet-awareness
• Efficient Ethernet support
  

  The core of the network is moving away from traditional TDM switching to high speed ATM switching in the near term and in the long term is expected to be all IP. The overall core attributes are:

• Multiservice
• Smooth scalability
• Capacity and infrastructure
• Quality of service
• Security and protection
• Investment protection
  

2 Why Evolve to NGN?
There are three basic entities that benefit and derive utility from the network: users, application providers and network providers. There might be many of each in a typical NGN. Each of these will benefit if the NGN provides the mechanisms for a joint optimization environment. Here are some of the basic benefits for each:

2.1 NGN User Benefits
The NGN facilitated communications environment will enable its users to:

• Become "interactive," using the abundant bandwidth.
• Be connected by a ubiquitous network "anytime, anywhere and with anyone or anything".
• Enjoy superior usability that is "secure, reliable and simple".
• Enjoy the benefits of a guaranteed and verifiable QoS support.

2.2 NGN Application Provider Benefits
NGN will enable application providers to:

• Be able to create network transport independent services.
• Create new business models.
• Be an independent user of the network resources and a reseller of services to users.

2.3 NGN Network Provider Benefits
From a network provider perspective NGN enables:

  (1) The creation of a rich variety of new services and business opportunities that capitalize on NGN features to generate new revenue streams

  (2) The future infrastructure of telephony services

• Shared with multimedia services
• To face the need for renewing PSTN infrastructure (when obsolete)
• Securing voice revenue stream
  

  (3) Ability to serve several kinds of access networks
  Furthermore, NGN fuses the best properties of today´s networks onto a common lowest cost infrastructure and eliminates the need for multiple dedicated networks for different applications. In the case of a large carrier this will reduce CAPEX (Capital Expenditure) and OPEX (Operating Expenditure) over the long run. The Internet aspects of NGN gives rise to greater flexibility and operational ease similar to Ethernet. The properties that are key to success of NGN are:

• Latency Control of an ATM Network
• Bandwidth of an Optical Network
• Ubiquity/Reliability of the PSTN
• Mobility of the GSM Network
• Security of Financial Funds Transfers
• Content Richness of Cable/Television
• Security of a Private Network
• Verifiable QoS support
• Uniform and Cross Layer Reliability
  

  NGN results in greater cost reduction potential which is larger for optics than for electronics, leading to increased network efficiency and utilisation. There is increased flexibility and responsiveness to dynamic traffic demands/changes. Optical networks are in line with the MPLS (Multiprotocol Label Switching) concept (simplified core, complex and intelligent edge). In the present competitive environment it is important to keep network costs as low as possible, seek faster return on investment to fend strong pressure to tariff reduction. Additional derived benefits are:

  (1) Make it easier to create new services

• Faster
• More people can create
  

  (2) Make it easier to buy and use services

• Enable customers
  

  (3) Make it simpler to deliver and maintain service

• Process automation
  

  (4) 30%-40% cost reduction

  (5) New services

• Open APIs and applications platforms
• Mobile enabled
• Re-usable components/capabilities
• Build on broadband
  

  (6) Cost reduction

• Not enough to do efficiencies and automation
• Radical network convergence to fewer networks and systems carrying more services
• Converge in from the edge
  

3 When NGN Targeted?
Network evolution towards NGN has been taking place in recent time with varying degrees of success driven by market pull (e.g. access) and technology push (e.g. transport - optical in particular). Some of the building blocks of NGN have therefore taken firm roots while others are currently in varying degrees of development - some in standards bodies, some undergoing trials and others in research labs. Here are some observations on the evolution to NGN:

  (1) Some (pre-NGN) pieces are already there:

• PSTN (VoIP, VoATM) trunking (some VoIP offers)
• Private/corporate network solutions (Centrex IP, IP VPN etc.)
  

  (2) A long way to NGN. Convergence of Telephony and Data (IT, Internet) approaches:

• PSTN/ISDN evolving towards NGN oriented platforms (Replacement of obsolete PSTN/ISDN network elements: Year 2005 onwards)
• Packet data networks evolving from the current high speed Internet access (ADSL, WLAN, etc.) platforms (To offer new generation services: Year 2005 onwards)
• Mobile convergence: Year 2006 onwards
  

  (3) Current phone network is stable and works well 

  (4) Network consolidation is happening, but equipment, though some of it old, will be upgraded and running for a few years

Figure 1 shows the view of an NGN roadmap for the first decade of the new century. This roadmap depicts evolution at the different levels of the network, i.e. from CPE to service applications.

Figure 1 also suggests there are many general characteristics with few details. The major building blocks are already in place and in the foreseeable future and we expect greater convergence of wireline and wireless technologies. In addition, at the user level we expect true multimedia experience to emerge in the marketplace. This trend will eventually lead to more simplified architectures to support anytime, anywhere communication at a global level between users and machines in an interchangeable fashion. A major stumbling block on the faster development and deployment of NGN networks and services is the inability to forecast the user attitudes. With the introduction of new service mechanisms and verification mechanisms with the QoS support, this problem will be alleviated and the developments will accelerate.

4 NGN Trends

4.1 NGN Market Trends
In recent times the broadband access market growth has laid the foundation for NGN growth in the industry. The access has been dominated by DSL, cable and wireless technologies. Table 1 summarizes recent studies by Point Topic Ltd., showing that as the broadband access market gathers steam, value-added services has grown to a $3.3 billion market for service providers. This amounts to 10% of overall worldwide consumer broadband access revenues.

  Aside from security services, which Point Topic assumes every customer is using in some way, there are 49 million value-added service accounts on 90 million broadband lines worldwide. Of these, home networks and online gaming currently attract the most users and annual revenues; they accounted for a total of 25.8 million users and $1.6 billion by early this year.

  Service providers looking to develop products with potential for the highest monthly revenue per user are more likely to focus on video-on-demand services and IP telephony, which bring in Average Revenue per User (ARPU) of $29.21 and $10.58 per month, respectively.

  Since adoption of these services is still in the early stages, the problem for providers is guessing which ones will generate the most cash down the line. Of course, they also want to avoid those that don´t. File transfers and teleworking, for example, account for a combined 14.4 million users, but contribute nothing to revenues.

  General market trends include:
  (1) Consumers want business like services.
  (2) Ubiquitous Communication Services (Any Access/Transport) will be prevalent.
  (3) New differentiated value-added services would evolve with the deployment of high quality secure broadband services.
  (4) End-to-end service enablement will be delivered thru packet intelligence.
  (5) Customer "self-management" of network and services using "Web technology".
  (6) Value shifts from core to user, and from network to services.

• New business opportunities with network and service integration caused by deregulation
• Unbundling network resources and functions and then rebundling them on demand in a multi-carrier environment
• Emerging "dynamic collaboration" in enterprise systems through the integration of IT and network technologies
• Versatile service support in a ubiquitous network environment

4.2 NGN Technology Trends
Some of the key technologies for NGN would have to include:

• Middleware and distributed systems (to enable Service Provider-Network Provider separation).
• IP, including IPv6, broadband, QoS, security, mobile and wireless.
• Multi-domain network management (for seamless roaming and QoS support).
• Seamless interworking between core and access networks.
• Micro and opto-electronics.
• Cross-media content.
• Multi-modal and adaptive interfaces.
• Multi-lingual dialogue mode.
• Embedded intelligence.
• QoS parameters have to be agreed between network providers.
• The same service used on a different terminal, or transmitted over a different access network, will require different QoS values.
• QoS on IP has been a research topic for several years. The solution usually proposed in the literature is the use of integrated services in the access network and differentiated services and/or MPLS in the core. The deployment of integrated services is difficult, since that the solution is proving to be not scalable for large-scale networks. Figure 2 shows some growth trends on network resources.

4.3 User Behavior and Usage Trends
There are many types of functionality that future users will demand. These generally have implications throughout all parts of the network. This therefore represents the top-down view.

  Business models, societal and economic/political factors determine the rate at which networks evolve, since they influence the financial resources that are available, the incentive for introducing new services, and the level of governmental support/pressure.

  The general trends taking place in the core and access networks pay special attention to the optical (core) and mobile (access) environments.

  The following behavior and usage trends impact NGN architectures and features:
  (1) Increasing use of Internet-based services, but demanding more than just Internet access
  (2) Increasing emphasis on mobility and roaming
  (3) Increasing use of peer-to-peer applications and group communication
  (4) End-user content creation
  (5) Less-obtrusive hardware that exploits the existence of more embedded sensors and communication between embedded devices
  (6) Flexibility:

• Same data to be available on different networks
• Terminals and services to be transported between networks
• A "one-stop shop" for billing
  

  (7) Services that are integrated, interactive, cost effective, easy to use and with filtering features
  (8) Higher bandwidths (e.g. for entertainment services, gaming, etc.)
  (9) QoS (availability, reliability, speed, synchronization etc.)
  (10) Security
  (11) Verification and conformance to contracts by all providers and users

  Figure 3 provides a mechanism that would facilitate end-to-end conformance in addition to conformance and verification at network adjacencies. The figure also shows possible layering at each network termination. Since there are no verifiable service creation mechanisms on the current infrastructures, especially covering multiple administrative domains, this mechanism will be proposed to ITU by ZTE Corporation.

5 Summary of NGN  Requirements
NGN should comply with the following requirements:

• Use open system protocols and open service architecture.
• Support secure multimedia services using ubiquitous broadband packet networks.
• Allow evolution of circuit switched networks to packet switched networks.
• Promote reduction of OPEX and CAPEX, providing increased revenue opportunities through new services and products thus bringing faster return on investments. This will be partly accomplished by the auto provisioning systems developed.
• Bring convergence between fixed and mobile networks and multimedia and across all layers of network transport.
• Exploit new services for "intelligent" homes.
• Provide communication, by a ubiquitous network, anytime, anywhere using any medium.
• Optimize use of existing networks through network consolidation.
• Provide voice, audio and video simultaneously, sharing telephony services with multimedia services.
• Eliminate notion of core, transit and local switches and exchanges through seamless interworking between core and access networks.
• Support multitude of access networks such as fixed copper, fibre, wireless, etc.
• Provide management functions shared between different technologies and services.
• Provide seamless service continuity in mobile and multi-network environments.
• Support common API for accepting application requests and network control interfaces for network resources.
• Be application agnostic.
• Provide capability for exchanging network and service attributes between network operators.
• Allow future network evolutions.
• Provide flexibility, accessibility and availability and reduced complexity for the end users
• Allow provision of customer premises integrated devices (e.g., one device supporting audio, video and data applications).
• Allow separation of functionalities between user, control and management planes.
• Be controllable, maintainable and manageable.
  

6 NGN Migration and Deployment
Today´s PSTN presents an enormous challenge for evolution. Although parts of this network architecture is approaching obsolescence, the key issue is the lack of flexibility in the current network to enable NGN services without fundamental changes, e.g. TDM to packet. Voice services tend to be significantly carried forward from PSTN, which still dominate the revenues for service providers globally.

  The deployment plans vary based on incumbents versus new greenfield operators. There are different obvious considerations for the two scenarios that impact existing users, cost and new services. Some of the considerations are highlighted below:

  (1) Replacing legacy PSTN elements/areas progressively

• Only when becoming obsolete (too little OPEX/CAPEX gain, particularly in Core)
• Migration of PSTN to NGN might accelerate after 2010
  

  (2) Greenfield deployment

  (3) Overlay deployment, building over xDSL and fiber-based access to the Internet

• ADSL is being deployed fast, with huge investments
• Opportunity to provide new (audio-data-video) services
  

  (4) Convergence between fixed-mobile and Internet services/applications

  (5) Nomadicity (Mobility Management for Roaming)

  (6) Mobility through fixed WLAN

  (7) Harmonizing/Converging with mobile IMS and IP-cable

  As per ITU documentation, there are two major policy domains which are shown pictorially in Figure 4: "raw" transport and content - they are separate and independent of each other. The purpose of the transport architecture is to carry all types of content. This separation has both technical and business context. In a competitive market, it is likely that the transport provider will provide delivery services, and a separate content service provider will provide the contents transported. Even if one organization has business in both transport and content, it is extremely unlikely that all contents would be provided by either a transporter or a content provider.

  Migration is intended to help the operating companies to evolve their existing networks. An earlier step in migration consists of redeploying existing resources in TDM networks which are under utilized for the purpose of enhanced TDM services, e.g. higher voice quality. Similarly and simultaneously there are other possible applications of resource utilization still within the TDM domain.

  To reduce the complexity of migration, it will be useful to distill the current diversity of networks to a select few as a starting point. Further, there is in essence a class of target networks that share a set of core principles of NGN. The target NGN does not have to be identical for they have different historical origins and different driving factors in time and space. The common feature of these networks is conformity with the general concept and requirements for NGN.

  ITU documents suggests a stepwise approach in which operating companies can migrate based on decomposition of their exiting networks into sub-networks  to ease migration. One strategy could be to select certain pieces of a technology from each technology itself as a way of migration towards NGN as shown in Figure 5.

  One example of this decomposition can be choosing parts of each of the technologies listed below to make an NGN:

• PSTN network (TDM technology)
• IN network
• Management network
• SS7 signalling network
• Leased line network
• IP network
• ATM/FR network
  

  The migration should consider access, transport, control, management and services as a whole.

7 Conclusions
Although the road to NGN is different based on the starting points of different carriers, the need for NGN based on market, technology and economic considerations form a common denominator. It is no longer a case whether NGN is needed but rather when and at what speed of evolution. The basic building blocks for NGN already exist thanks to standards, innovation and commitment from several vendors and service providers.

  Challenges still remain in the evolution methodology, timing and cost. Due to the recent changes in the economic climate for telecommunications companies, this has been simultaneously a problem and an opportunity to move forward towards a target NGN.

Manuscript received: 2004-04-23