NGN involves three main architectural innovations that are interesting to look at individually:

1. In the core network, NGN implies a consolidation of several transport networks each historically built for a different service into one core transport network. It implies amongst others the migration of voice from a circuit-switched architecture (PSTN) to VoIP, and also migration of legacy services such as X.25, Frame Relay

2. In the wired access network, NGN implies the migration from the “dual” legacy voice next to xDSL setup in the local exchanges to a converged setup in which the DSLAMs integrate voice ports or VoIP, allowing to remove the voice switching infrastructure from the exchange.

3. In cable access network, NGN convergence implies migration of constant bit rate voice to CableLabs PacketCable standards that provide VoIP and SIP services. Both services ride over DOCSIS as the cable data layer standard.

The difference of NGN with previous technologies used in the telecommunication engineering is that there is a more defined separation between the transport portion of the network and the services that run on top of that transport. What this means is that whenever a provider wants to enable a new service, they can do so by defining it directly at the service layer without considering the transport layer.  Or to put it another way, services are more and more independent of transport details. This goes without saying that increasingly, applications, including voice, will tend to be independent of the access network and will reside more on end-user devices.

NGN’s have been implemented in many different countries, some examples are:

1. In the UK,  BT (British Telecom) introduced another popular acronym for NGN – the 21CN (21st Century Networks, sometimes mistakenly quoted as C21N).  This is another loose term for NGN and denotes BT’s initiative to deploy and operate NGN switches and networks in the period 2006-2008 (the aim being by 2008 BT to have only all-IP switches in their network).

2. In Holland, KPN is developing an all-IP, a NGN network in a network transformation program. Next Generation Networks also extends into the messaging domain and in Ireland, Openmind Networks has designed, built and deployed Traffic Control to handle the demands and requirements of all IP networks.

3. In Bulgaria, BTC (Bulgarian Telecommunications Company) NGN has been implemented as part of the underlying network of its telco services, in a large scale project undertaken in 2004. The inherent flexibility and scalability of the new core network approach resulted in an unprecedented rise of classical services deployment as POTS/ISDN, Centrex, ADSL, VPN, as well as implementation of higher bandwidths for the Metro and Long-distance Ethernet / VPN services, cross-national transits and WebTV/IPTV application.