What is IP Telephony

What is Internet Telephony Good For?

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 WWW. Deployment of new IP telephony services requires significantly lower investment in terms of time and money than in the traditional PSTN environment.

But: The wide business deployment is still hindered by lower quality of voice over IP, particularly by higher delay and jitter. Also many technical aspects of accounting, billing, charging , roaming etc. remain open yet.

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.
 

Caller's Terminal	Callee's Terminal	Notes	Costs Paid By Caller
PC	PC	This class is attractive especially for private users who already have an Internet access and an audio-capable PC. Necessary software is available for free . This pure-IP scenario is likely to take advantage of integration with other Internet services, such as WWW, instant messaging, E-mail, etc.	Costs of ownership and maintenance of the hardware (PC with modem and sound or a dedicated device) and software (IPT software is often provided for free). Costs of Internet access (incl. the local call).
PC	telephone  (POTS/ISDN/GSM...)	This is an extension of the previous class in that the PC-callers may reach also the PSTN callees. A gateway converting the Internet call into a PSTN call has to be used and located as near to the callee as possible to minimize the price for the gateway-to-callee connection. This scenario is commercially provided  by  gateway operators like iConnect.	Costs of ownership and maintenance of the hardware (PC with modem/dedicated device) and software (IPT software is often provided for free). Costs of Internet access (incl. the local call). Costs charged by the gateway operator. (~ 5-12 cents per minute to the U.S. in August 98) The costs charged by the  operator are determined mainly by the costs of the call placed from the gateway to the callee.
telephone  (POTS/ISDN/GSM...)	telephone  (POTS/ISDN/GSM...)	This class is attractive for those who want to save on long-distance call and do not have/want to use a PC. For example, mobile phone users certainly prefer to carry only the mobile phone without any additional boxes. The call has to pass two gateways: GSTN-to-Internet and Internet-to-GSTN. This solution has been comercialy provided by gateway operators like AccessPower, DeltaThree.	Costs charged by both  gateway operators.(~ 7-17 cents per minute to the U.S. in August 98) The costs charged by the destination gateway are determined mainly by the costs of the call placed from the gateway to the callee. Local Call Costs
telephone  (POTS/ISDN/GSM...)	PC	This class is useful for those who want to reach Internet users with an ordinary telephone. Telenor provides this service commercially in Norway under the name "Interfon".	Costs charged by a gateway operator. Local Call Costs

Architecture

Architecture: the Internet telephony systems are composed of these elements:

• end devices; these may be either traditional telephones (analog/GSM/ISDN/...), audio-equipped personal computers, or single use appliances
• 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

They communicate with each other over signaling and voice-transporting protocols. To ensure interoperability between products of different vendors, standardization bodies have elaborated  standards for both classes of protocols. See the section "Players and ..." for more details.

Future

Making predictions is difficult and it belongs to the competence area of oracles, magicians and marketing managers. But let us at least summarize some important factors.

The law of supply and demand works also in the Internet telephony. An article has been published by Communications Industry Researchers, which claimed the prices of the traditional and the Internet telephony will equalize as soon as the quality of the both standards will do so. We believe, that the most significant obstacles in reaching the equilibrium are the still unsatisfactory voice quality  and the lack of means of commercial deployments. Both of them are under investigation. The voice quality will increase with special QoS means and generic increasing bandwidth. The means of commercial deployments are being designed by both, commercial and academic world. For example, the gateway discovery architecture which enables open market of gateway operators is being proposed by IETF.

IPT may also become a subject to government regulations. Such efforts are very welcome to traditional telcos - a good example is the action brought by Czech Telecom against Paegas' "Internet call" service.  According to Bruce Jacobs,  some governments intend to regulate even the PC-based telephony (India, Pakistan), other have indicated they will treat IPT as simple resale (Canada) and others have recognized that action is premature (see the decision by EU and FCC). Look at the VON Coalition's pages for additional information on the regulations.

Another legal issue is wiretapping. A pretty contraversial discussion about the justification and standardization of wiretapping took place on the Raven mailing list of IETF. Eventually, IAB and IESG issued a RFC 2804 which justifies why IETF does not include such a functionality in its standards-track.