2. Voice over IP and the move to NGNs

The advent of the Internet as a backbone network for transporting multimedia flows rendered the circuit-switching technology used in conventional telephony unsuitable. This led manufacturers to focus on recovering the "intelligence" of the telephone network (notably call processing functions and service platforms) and placing it on servers. The switching units (or switching matrices) of the old telephone switches were replaced by IP routers, in the case of all-IP communications, or by "transcoding" gateways, in the case of communications between the Internet and the PSTN. These transcoding gateways, which can be remotely controlled from a call server via a protocol such as MGCP or MEGACO/H.248, are one of the techniques known as NGN (Next Generation Networks). In these approaches, call control is placed at the level of functions called Media Gateway Controler (MGC). Transcoding functions...