Internet protocol (IP) telephony, originally viewed as the most "disruptive" of new technologies, has now gone mainstream. It is already being deployed in access and backbone, in business and home. And it's being promoted to play its part in just about every type of voice application: from voice-enabled Web surfing, through corporate voice services, to the expansion of traditional carrier voice networks.
The six-stage evolution of IP telephony started in 1995. In stage one, the IP Telephony industry introduced personal computer (PC) software that allowed users to make telephone callsover the Internet. Both ends of the connection needed the same software. It was an economical way to make long-distance international calls. The cost was several hundred dollars upfront but allowed unlimited free telephone calls over the Internet.
Stage two allowed phone calls over the local enterprise companies intranet network.
Stage three connected intranets to the Internet for low-cost voice-over IP (VoIP) between enterprise intranet networks. In 1998, we also began to see common nomenclature as well as interoperable standard products. The media gateway (MG) and media gateway controller (MGC) were introduced as IP elements that we considered separate from the underlying PSTN.
Stage four began the integration at the transport level between the underlying private IP network and the PSTN. Because there was no Signaling System 7 (SS7) connectivity betweenthe two networks, this required a two-step dialing process where users had to dial an 800number to access the IP Telephony MGC. Then after they dialed the 800 number, they woulddial the called party phone number. The rates offered were significantly lower than thoseoffered in the traditional interexchange carrier (IXC) market.
Stage five commenced when companies began deploying softswitch-based architectures aspart of the public network. The softswitch-based architectures were not quite yet part of the PSTN. By contrast, a competitive local-exchange carrier (CLEC) that puts in a traditional Class 5 switch is considered part of the PSTN. The difference is merely conceptual. Stage fivehad PSTN interoperability but not integration. Stage five is in its infancy at the time of thispublication.
Stage six will finally introduce PSTN/IP network integration, with full SS7 connectivity andcomplete interoperability between the IP telephony network and the traditional PSTN service switching point (SSP)-based network. These two networks will coexist and inter-operateat the transport and services levels for a long time. The industry is entering stage six today. Carriers are beginning to deploy softswitch-based architectures and taking advantage of theeconomics of packet networks.