Next Generation Networks

The architecture and implementation of the Next Generation Network (NGN) must be based on open, standard-based interfaces and protocols. This is essential to achieve multi-vendor interworking and to accelerate the rate on innovation. It is also well accepted that the NGN must also be based on a distributed architecture that helps greatly to reduce the implementation costs while giving flexibility in the actual deployment. The ITU-T Recommendation Y.2001, “General Overview of NGN”, Dec. 2004, provides a definition of an NGN.

The NGN must be able to support highly customizable services that are easily and rapidly created as well as deployed economically throughout the network. While it is important to enable new services, it is also critical to preserve the existing services provided by the legacy network.

NGN Voice/Data Converged Architecture

Figure 1 describes a NGN architecture of a converged voice/data network that is generally consistent with the vision that most operators have. The architecture can be decomposed into several layers: Core connectivity, Access and Customer Premise Equipment (CPE), Services, and Management.

Figure 1 – Next Generation Network Voice/Data Converged Architecture

Core Connectivity Layer

The core connectivity layer provides the general routing and switching of network traffic from one end of the network to the other. It is based on packet technology, either ATM or IP, providing maximum flexibility. The technology of choice will be dictated by business considerations, but service transparency and quality of service (QoS) have to be ensured in any case since quality disturbances such as delay, jitter and echo must not affect the customer traffic.

At the edge of the packet backbone are the gateways: their main role is to adapt the customer and control traffic to the NGN technology. The gateways interface either with other networks, in which case they are called network gateways, or directly with end-user equipment, in which case they are called access gateways. The gateways interwork with the Service layer components using open protocols to deliver existing and new services.

Access Layer

The access layer includes the various technologies used to reach customers. Access was usually limited in the past to copper lines or DS1/E1. We now see a proliferation of technologies that have emerged to address the need for higher bandwidth and to provide competitive carriers with a means to directly reach customers. Cable, xDSL and wireless are among the most promising solutions that are experiencing rapid growth and innovation.

Customer Premise Equipment, either owned or leased, provides the adaptation between the operator’s network and the customer’s network or equipment. It can be a simple phone, but we see a progressive migration toward intelligent devices supporting both voice and data services.

Service Layer

This layer consists of the equipment that provides available services and applications to the network. Services will be available to the whole network, regardless of the user’s location. These services will be made as independent as possible from whatever access technology is used. The distributed nature of the NGN will make it possible to consolidate much of the equipment that delivers services in centrally located centers where greater efficiencies can be accomplished. In addition, it also makes it possible to distribute the services to the end users equipment rather than to the network. The types of service that will be offered include all of the existing voice services and a range of data and other new multimedia services.

Management Layer

Key to minimizing the operation costs of running an NGN, the management layer provides the network, service and business management functions. It allows end-to-end service provisioning, monitoring, recovery and performance analysis required to run the network.

NGN Service Converged Architecture

While voice/data convergence has enabled new efficiencies, service convergence will enable service providers to deliver innovative new services to any device over any type of access network. Subscribers will define themselves by their network profile and presence rather than by their access line or their handset. At the heart of the converged network there will be a new services infrastructure known as the IP Multimedia Subsystem (IMS). IMS is a product of extensive work done by 3GPP and 3GPP2 to describe core network aspects for mobility standards and is now being used as a basis for converged networks in the NGN standards development of the ITU-T. Next Generation Networks will need to support a wide variety of access technologies and core services, and IMS is designed to satisfy this requirement. As shown in Figure 2, the IP Multimedia Subsystem is one of several possible subsystems envisioned in the evolution of an NGN architecture.

Figure 2: NGN Subsystem Architecture, showing IMS

IMS enables network operators to offer multimedia services based on and built upon Internet applications, services and protocols. Examples of IP multimedia applications include speech communication, real time multimedia applications, and virtual meeting/conferencing applications. IMS enables IP multimedia sessions that support IP multimedia applications. Application of IMS to converged networks necessitates access independence and interoperability. In order to achieve access independence and ensure network interoperability, IMS is based on the widely accepted Internet standards of the Internet Engineering Task Force (IETF), Session Initiation Protocol (SIP) being one such example. IMS is intended to serve as the core network support for the development and delivery of services. IMS enables the convergence of, and access to, voice, video, messaging, data and web-based technologies for the end user.

Standards Definition Challenges

Standards Development Organizations (SDOs) face a number of challenges when specifying Next Generation Networks standards. Some of these are:

• smooth/seamless inter-working between the IP-based network and the PSTN;
• levels of service performance as currently offered by the legacy telephony infrastructure (e.g., call setup delays);
• interoperability across multiple administrative domains taking into account different signaling protocols;
• scalability to support very large number of customers;
• simplicity; and
• the ability to support new services.

It should be kept in mind that many of the standards used for NGN interfaces and applications are evolving/changing rapidly.