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Next Generation Networks (NGN)

Next Generation Networks (NGN) are being implemented globally as a means to radically change the cost base, agility and service capabilities of telecoms providers: key enabling technologies include IP, MPLS, ADSL, Metro-Ethernet, SIP and H.248...


The ITU-T working definition of an NGN is as follows: "A Next Generation Network (NGN) is a packet-based network able to provide services including 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 offers unrestricted access by users to different service providers. It supports generalized mobility which will allow consistent and ubiquitous provision of services to users."

An NGN could be defined as having the following key characteristics:

  • Packet-based transfer...NGNs remove the circuit switching of traditional PSTN/ISDN networks, and unify all switching using a combination of connectionless layer 2 switching (for example carrier Ethernet), connection-oriented layer 2 switching (MPLS, or in some cases ATM or 802.3ag), and layer 3 routing (using the IP protocol)
  • Separation of control functions among bearer capabilities, call/session, and application/ service...traditional services such as PSTN or Frame Relay implemented all elements of the service on all nodes; a PSTN switch had to transport the caller's voice (the bearer part), control the establishment and release of calls (the call/session control part) and either implement or trigger advanced services (such as number translation or portability). In an NGN, these functions are separate; transport of the voice and signalling is across a common packet-switched network dedicated to multi-service transport, call/session control is carried out by centralised servers (perhaps IMS-based), and advanced services are triggered from the call/session control servers and implemented on separate application servers which can be remote from the other elements.
  • Decoupling of service provision from network, and provision of open interfaces...in an NGN, the network must be capable of supporting a range of applications in terms of bandwidth and QoS; however the network need not be aware of the specific applications, just the bandwidth and QoS requirements they place upon the network. By the same reasoning, applications can be developed and deployed across this common infrastructure, provided they can request bandwidth and QoS from the transport network by some means, without requiring any new capability from the transport network.
  • Support for a wide range of services, applications and mechanisms based on service building blocks (including real time/ streaming/ non-real time services and multi-media)...NGNs will carry not just traditional "conversational" services (such as voice calls), but also transactional services (such as purchasing an item), streaming services (such as watching video-on-demand or IPTV), and real-time interactive services (such as video-conferencing)
  • Broadband capabilities with end-to-end QoS and transparency...NGNs must support the QoS demands of the application types mentioned above, and must also provide adequate end-to-end bandwidth to consumers, typically several Mbit/s minimum.
  • Interworking with legacy networks via open interfaces...the existing telecommunications networks will be required for several years at least, both to support legacy services and CPE for consumers, and to facilitate a measured transition to NGN at interconnect points. NGNs typically adopt a backwards-compatibility model, using traditional SS7 signalling and TDM bearers at interconnect points, interworking functions at the access points where customers connect legacy services to the NHN (often called Multi-Service Access Nodes), and backhaul of legacy traffic across NGN core networks using techniques such as MPLS pseudowires and IPv4overIPv6 tunnelling.
  • Generalized mobility...as access to core network services becomes more generalised (see next point), it is necessary to manage mobility between service providers and between access points into the service provider network.
  • Unrestricted access by users to different service providers...NGNs will increasingly allow services to be accessed from different access networks, including fixed line, traditional mobile, and fixed wireless such as WiMAX). This is consistent with the concept of transport and service separation discussed earlier.
  • A variety of identification schemes which can be resolved to IP addresses for the purposes of routing in IP networks...traditional addressing schemes such as E.164 are unsuitable for NGNs, where the basic addressing of endpoints will be an IPv4 or IPv6 address. Therefore methods to translate legacy addressing, including X.121 and E.164 into IP addresses on a large scale is required. The ENUM initiative of the IETF/ITU-T is one such approach.
  • Unified service characteristics for the same service as perceived by the user...see above
  • Converged services between Fixed/Mobile...see above
  • Independence of service-related functions from underlying transport technologies...see above
  • Compliant with all Regulatory requirements, for example concerning emergency communications and security/privacy, etc...the regulatory bodies around the world, such as Ofcom, the FCC and the EU have traditionally placed strict requirements on the functionality and performance of telecoms networks and services. In NGNs, some of these requirements either cannot be met, or are extremely expensive to meet. the response of regulators after several years of consultation has generally been to relax certain conditions which are most problematic for NGNs, and to phase in the obligation to comply with oters whcih can be achieved. See for example this article for more details of the regulatory approach to voice and VoIP. For more information on Next Generation Access (NGA), see this article.

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