Telephony Common Questions, Part 1
  By Todd Ogasawara

General Questions

I know how to use a telephone, so what kinds of questions should I ask about telephony?

If you're like most people, you probably don't think about your telephone and telephone service too much unless something goes wrong. Telephone service in the U.S. is over a hundred years old in some places. What's there to think about? You pick up a handset, push a couple of buttons, and talk to a person or get a busy signal. But computer telephony brings up all sorts of new questions, including the ones answered below.

How is telephony pronounced?

Telephony is pronounced teh-le'-fuh-ny. You often hear it mispronounced as tele-phoney.

What is Computer Telephony (CT)?

CT is pretty much what it sounds like: The melding of computers and telephone systems. The range of CT topics range from inexpensive desktop solutions for your personal computer to multimillion dollar telephone company systems.

Who uses CT?

You have probably used a CT system many times without realizing it! If you've ever called a business and heard a multi-choice recorded message like, "If you wish to speak to customer service, press 1. If you wish to speak to technical support, press 2," then you have used a CT system. If you've called a bank and used an automated system to check your bank balance, then you have used a CT system. CT technology is used in nearly every facet of business and personal communications today.

Can I try CT technology without spending a lot of money?

If you bought your desktop personal computer in the last two years, you may already have everything you need to get started. PCs often are sold with devices called voice modems. These devices can work with voices on the telephone as well as with data and fax. Check the documentation that came with your system to learn whether you have a voice modem. Single-line voice modems sell for $150 to $300 and can serve as sophisticated answering machines, speakerphones, or phone number databases with autodialing. There are also simpler devices for less than $100 that let you use telephone company services like three-way calling, call screening, and caller-ID without having to remember any touchtone keystrokes.

Do I need to notify my telephone company when I use CT technology?

No, not in the sense that you need their permission to attach a CT device or system to the telephone lines. You may need to contact your telephone company, however, if you want to use features like caller-ID (having the telephone number of the person calling you delivered between the first and second rings) or forward-on-busy (having a call to you automatically rerouted somewhere else, like to your voice mail, if your telephone line is busy). And, you certainly need to discuss your needs with your telephone company if you are installing a mission-critical business phone system for your home office or small business.

Internet Telephony Primer

For most of us the telephone is an unremarkable instrument. It might sit on your desk or table. Or, it might hang on a wall. You probably pick up a handset at least once a day, press in a phone number on a touchpad and speak to someone across the hall or halfway around the world using a century old technology called circuit switching. The remarkably unremarkable thing about telephones and circuit switching technology is that they are possibly the most reliable tools in our business and personal lives.

More recently you may have heard of a new kind of telephony based on the packet switching technology that the Internet is built on. You may have heard the term Internet Telephony or IP Telephony or Voice over IP (VoIP) or Voice over Network (VON). For our purposes we can consider these terms synonymous (although there are some subtle differences). The purpose of this primer is to explain the basic concepts and types of Internet Telephony.

Why IP Telephony?
The long distance cost savings is, perhaps, the first thing that attracts people to the possibility of using some form of IP Telephony. However, there are even more intriguing features. IP Telephony brings the possibility of transmitting images or video. It also allows the potential for collaboration via electronic white boards or shared applications. In short, it makes rich telecommunications practical and economical.

PC to PC
PC-to-PC Internet Telephony
Vocaltec developed the first Internet Telephony application just a few years ago. It let two multimedia PCs (microphone, speaker, sound card, modem or Network Interface Card) 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 cheaply (no per minute charges). However, these early 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 (QoS) controls.

PC to Telephone
PC-to-PC Internet Telephony
The next step allowed one person to use a multimedia PC as a IP based telephone (either connected to a LAN or to an Internet Service Provider via a modem) to dial a person with a conventional telephone. This involved the an Internet Telephony Gateway to be in the geographical region of the person with the conventional telephone. This gateway translates the conventional telephone voice transmission to an IP Telephony format.

Telephone to Telephone
Phone-to-Phone Internet Telephony
The most recent step in the development of IP Telephony services is the placement of gateways in multiple geographic areas. This removes the need of a PC on either end of a conversation. The use of private networks instead of the public Internet as well as specialized equipment to reduce some of the sound quality problems associated with IP Telephony makes telephone-to-telephone communications a viable alternative to traditional telephone calls.

Is That All There is to It?
Not at all! This primer describes IP Telephony in a highly simplified manner. It barely does justice to the promise and potential of this technology. And, we did not even describe the kinds of services made possible by IP Telephony. Some examples?

  • Line doubling services that let you receive or reroute incoming voice calls from your web browser.
  • Push-to-talk services that let you speak to a human customer service representative while looking at a firm's product on a web page.
  • Telecommuting services that lets companies maximize their work-at-home staff.

Join us in the Telephony Forum Newsgroups to further discuss IP Telephony in its various forms. And, check out the information below to learn even more about this amazing technology.

IP Telephony Alphabet Soup

Protocol Description
G.723 Algorithm for compressed digital audio over POTS lines. It is used with H.324.
G.729 Voice algorithm (CS-ACELP: Conjugate Structure Algebraic Code Excited Linear Predictive) for coding speech signals in telecommunications networks.
ITU-T T.120 Standards Document conferencing (data sharing) portion of a multimedia teleconference. This is a set of recommendations that specifies how to efficiently and reliably distribute files and graphical information in real-time during a multipoint multimedia meeting.
H.320 ISDN (Integrated Services Digital Network) video conferencing
H.323 LAN based video conferencing
H.324 POTS (Plain Old Telephone Service) modem based video conferencing
Where to Go to Get More Information