Voice Over IP or IP Telephony?
<<<...Instead of a trunk card, say, connecting to a dedicated circuit, or to the PSTN, it plugs into a gateway that encapsulates the voice traffic into IP (or frame relay or ATM) sends it across your WAN and pops it out at the far end. You use one circuit instead of two and save yourself carrier costs. Time Division Multiplexers (remember GDC, Newbridge and the like?) did this well over a decade ago, but you had to dedicate timeslots to the voice, whether anyone was making a call or not. The difference with the VoIP setup is that the bandwidth can be used by your data traffic if there’s no voice. Of course it is a bit more complicated than this, since you have to configure your network for the prioritisation, low delays and minimal jitter that voice traffic requires but that’s only on a couple of devices. To be honest, if you’re not doing it, you probably should be.
IP telephony is a much bigger concept. If you embrace it completely (and you don’t have to as we’ll see), it’s goodbye to your exiting PBXs, key systems and handsets. The IP part of the equation is no longer just gateway to gateway but right from the handset on your desk. PBXs are replaced with softswitches—servers that handle all call routing, management and reporting functions. Gateways manage connections to other sites, and to the PSTN, and the handsets are now fully functioning IP stations that can almost take the place of a PC, for some users. Circuit vs Packet Switching Where traditional voice calls involved the connection-oriented setting up of a circuit end-to-end for the duration of the call, IP calls are packet-based.... more >>>