IP Telephony

What is Internet Protocol (IP) Telephony?

Definition: Internet telephony (IPT) is transport of telephone calls internally over the data network or externally over the Internet, no matter whether traditional telephony devices, multimedia PCs or dedicated terminals take part in the calls and no matter whether the calls are entirely or only partially transmitted over the Internet.

Benefits of Internet Telephony

The most significant benefit of IPT and driver of its evolution is money-saving and easy implementation of innovative services:

• In the future, Internet Telephony Service Providers (ITSP) may use a single infrastructure for providing both, Internet access and Internet telephony. Only data-oriented switches could  be deployed for switching data as well as packetized voice. Multiplexing data and voice could also result in better bandwidth utilization than in today's over-engineered voice-or-nothing links.  Not only the providers, but also their clients will profit of lower costs eventually.

• Now, customers may take advantage of flat Internet rating vs. hierarchical PSTN rating and save money while letting their long-distance calls be routed over Internet. This is especially true in Europe, where the prices of long-distance calls are still higher than in US. But: according to some estimations, the prices of the traditional and the Internet telephony will equalize together with the convergence of quality of services provided by them.

• The IPT users may also profit of its software-oriented nature: software solutions may be easily extended and integrated with other services and applications, e.g. whiteboarding, electronic calendar, or video conferencing.  Deployment of new IP telephony services usually requires lower investment in terms of time and money than in the traditional PSTN environment.

Internet Telephony Scenarios

The IPT usage scenarios are commonly  classified by  the type of devices terminating an Internet call. Because there may be either a PSTN device or a data-oriented terminal on each side of a call, there are 4 generic classes. Note, that although "PC" is a well established term, any device capable of transmitting voice over data network may apply in this context. See for example the dedicated device Aplio/phone.

Architecture

      Internet telephony systems are composed of these elements:

• End devices; these may be either traditional telephones (analog/GSM/ISDN/), audio-equipped personal computers (soft phones), or single use appliances such as SIP devices
• Gateways; if a traditional telephone is used at either calling side the call (i.e. its transmission format, signaling procedures, audio codecs) has to be translated to/from the format for transport over Internet; this is the task of the gateways
• Gatekeepers/proxies; the gatekeepers/proxies provide centralized call management functions; they may provide call admission control, bandwidth management, address translation, authentication, user location, etc.
• Multipoint conference units; these manage multiparty conferences