What exactly is Internet telephony? Generally speaking, it is any technology providing voice telephony services over Internet Protocol (IP) connections.

Traditionally, telephony relied on a century-old technology called circuit switching, which, though old, is very reliable. This technology has been replaced in certain situations by packet switching technology that the Internet is built on. This technology is variously called Internet telephony or IP telephony or voice over IP (VoIP) or voice over network (VoN).

At the heart of Internet telephony is the switchover of telephonic transmissions from the analogue mode to the digital mode (see box).

As said earlier, a major lure for IP telephony is the potential to save a lot on the long-distance costs, though there are also other considerations like transmission of images and video. At the same time, the down side is erratic quality.

VocalTec, a New Jersey, USA-based company is credited with launching the VoIP industry with the introduction of Internet Phone in 1995. It let two multimedia PCs with microphones, speakers, sound cards, modems or network interface cards serve as a kind of telephone. This new kind of telephone required an Internet network connection instead of the traditional public switched telephone network (PSTN). This PC-to-PC Internet telephony let people communicate inexpensively (no per-minute charges). At that time, it was necessary to specify that this could only work on multimedia computers, though it is no longer necessary to say so because all new computers are multi-media enabled.

There were, however, certain drawbacks. These systems were not as convenient or of the same sound quality as conventional telephone calls. Many of these issues are being resolved with newer technology and the use of private networks with stricter quality of service controls.

The next logical progression was making PC-to-telephone calls. It allowed one person to use a multimedia PC as an IP-based telephone (either connected to a LAN or to an Internet service provider via a modem) to dial up to a person with a conventional telephone. This involved the Internet telephony gateway to be in the geographical region of the person with the conventional telephone. This gateway changes the conventional telephone voice transmission to an IP telephony format.

The most recent step in the development of IP telephony services is the placement of gateways in a large number of geographic areas. This removes the need of a PC on either end of a conversation. Which means you can make a call using a conventional telephone to call another phone, only you go over the Internet rather than through the regular phone companies. The unfortunate part is that it is not possible in India—yet.

The use of private networks instead of the public Internet as well as specialised equipment to reduce some of the sound quality problems associated with Internet telephony makes telephone-to-telephone communications a viable alternative to traditional telephone calls.

Actually, it is not too difficult to deliver good quality of sound and even pictures over private networks, but due to the inherent inconsistencies and weaknesses of the Internet’s infrastructure, the quality of voice can vary considerably, though this issue is being addressed by protocols that support quality of service.

Internet telephony means rather low cost voice calls as long as sending and receiving users have identical software that uses proprietary techniques or compatible software that uses the common (H.323) standard. They must also be willing to talk from their PCs and to prearrange the times to talk. Using ITSPs, users can make PC-to-phone or phone-to-phone calls, using the Internet as the network backbone.

The Internet protocol is either being used or being considered for future network backbones by all major telecom carriers. Another IP telephony application that is expected to take off is with call centres that can answer a question sent to them directly from a Web site. This voice integration is desired by user and vendor alike and is expected to flourish in the 2001-2003 timeframe.

You might well ask which are the main programs used for Internet telephony? As far as chatting is concerned, both Yahoo Messenger (http://messenger.yahoo.com) and ICQ (http://web.icq.com) work, as do Microsoft Netmeeting (http://www.microsoft.com/windows/netmeeting/), Media Ring Talk (http://www.mediaring.com/), Net2Phone(http://www.net2phone.com) and others. This software can be downloaded from the Net, though there are some charges for certain services. According to people who use the software, overall, connectivity to the USA is not too bad, though packet losses make the lag time (see box) noticeable and, at times, data loss results in snatches of conversation missing and delays. Unlike voice networks data networks aren’t designed to facilitate immediate transmission and on data networks, there is the problem of prioritising the data, making voice data speed up and using low-priority e-mails to fill up the spare bandwidth. Of course, you have to remember that Internet telephony is not legal in India — yet.

This is a problem that has been the bugbear of Internet telephony and it is largely due to bandwidth issues. A voice signal needs connectivity of up to about 8 kb per second. Most of the users on dial-up use 28.8 k modems that can’t do much better than 3 kb per second. Even if you use a modem with a higher rating, it is not of much use because of the general bandwidth squeeze in India.

Another major issue is that an Internet telephone call is generally half-duplex. This means that one person talks at a time. This is because most of the multi-media cards are half-duplex and unless there are full-duplex sound cards at both ends, the experience of Net telephony is more akin to radio transmission (the Hindi movie over-and-out style) than that of a regular phone conversation.

Convergence issues were discussed in pre-Budget Economic Survey which recommended that the government open up Internet telephony and bundle together Internet access and telephone to bring about the information communication revolution to rural areas.

However, contrary to expectations, the Budget did not address the Internet telephony issue. Thus we can’t expect any real improvement in voice services, though the lure of virtually free calls will continue to make Internet telephony attractive to many users.

Transmissions, analogue and digital

IN understanding Internet telephony, it is important to understanding the difference between analogue and digital transmissions.

The term analogue is used to describe the waveform nature of voices and other sounds. The term is intended to express the concept that voices and other sounds are infinitely variable. For example, sounds may vary in their loudness and softness. They may also vary in their pitch. Until recently, telecommunications systems were invariably analogue. This means that the analogue voice waveform of a person having a conversation on a telephone is converted by his telephone into an analogue electrical signal with almost exactly the same waveform. The electrical signal has the same characteristics, in electrical form, as the voice had in the form of sound waves. The telephone of the party called converts this electrical signal back into sound through a speaker in the telephone handset.

On the other hand, digital transmissions transmit sounds in the form of a series of electrical pulses along the transmission medium. These pulses are called digits, giving the term digital. This is as opposed to an electrical signal whose characteristics mirror the characteristics of a sound wave. If the transmission medium is fibre optic cable, the numbers are transmitted as a series of light pulses.

The conversion of an electrical waveform representing the sound into a series of digits is called quantisation. The conversion process occurs by periodically sampling the electrical wave for the purpose of generating the numbers that form part of the wave representing the sound. Each digit is called a "bit". Satisfactory quantisation of sound can occur if the sound wave in the range of 300 to 3,400 Hertz is sampled at a rate which generates 64,000 bits per second, although sometimes lower rates are used. Any wire, fibre optic cable, radio system or other transmission medium which has the capacity of carrying 64,000 bits per second (equivalent to 64,000 electrical pulses or light pulses per second) will, therefore, be able to carry the digital transmission which represents sound. The digital transmission can be reconstructed by equipment at the receiving end into an electrical waveform, and then into a sound wave that is the same as that which generated the stream of bits. A speed of 64,000 bits per second, or 64 kilobits per second, is often denoted as 64 kbps.

The transmission of sound in digital form brings several significant advantages. They are:

a. Unlike an analogue signal which degrades in strength and quality with the length of the transmission path, it is possible to transmit a digital signal over any distance with extremely low degradation.

b. Digital multiplexing and demultiplexing is a more stable and adaptable process than analogue multiplexing. It suffers from less degradation and is easier to maintain than analogue multiplexing systems.

c. It permits the use of techniques known as digital compression which effectively increase the capacity of a single transmission medium by a factor of 4 or more (these techniques are principally used for international transmissions).

d. It more readily allows for transmission of computer data (because computer data is invariably in digital form), thereby enabling computers and other digital devices to communicate with each other across the network.

e. It permits the use of more sophisticated signalling systems.

Source: Gilbert & Tobin, Australia.