Two Common Methods of Information Transmission

The first method we will discuss is ISDN (Integrated Service Digital Network) phone lines. This is an actual network that telephone service providers have in place over a large portion of the US and the world. Because of the standards that are used, it is very easy to transfer data from one place to another (e.g., from the USA to Russia or Seattle to Los Angeles). When a connection is made, the telephone service provider actually connects the two sites so that information can be transferred back and forth without interruption. It is very similar to making a phone call. At the present time, ISDN is the preferred communication method for interactive videoconferencing. Government organizations and busineses are currently setting up networks using ISDN protocol, for example @ccess Washington K-20 Network which serves every school district in the state with inexpensive interconnectivity.

Another method that is growing in popularity is IP(Internet Protocol). IP has several advantages over ISDN. One is the cost. Communicating over ISDN lines can be very expensive. Toll charges can range from as little as $.50 a minute to more than $3.00 a minute. IP on the other hand has no toll charges. A connection to the Internet backbone can be obtained via an ISP (Internet service provider) for as little as $20.00 a month. The duration of a connection is immaterial. Another advantage is availability. ISDN is available in most metropolitan areas, but not in most rural areas and availability is not expanding. IP is available in most areas, metropolitan and rural, and is continuing to expand. Additionally, most computers are sold ready to communicate over IP, whereas ISDN requires special equipment to enable communication.

Even with the above mentioned advantages, there are still some drawbacks to using IP. IP is the protocol used to communicate over the Internet. The Internet is like a giant 'party-line.' All of the computers connected to the Internet are able to listen to any other computer, making security a concern. However, as technology continues to improve security is becoming less of a problem.

Additionally, lack of available bandwidth may be a problem when using IP. Think of the Internet as a big highway. The more traffic (computers) on the highway, the slower that traffic moves. This can be a big problem when trying to have an interactive conversation. Because Information (audio/video) is delivered in small chunks, referred to as 'packets,' delays may occur that interfere with the conversation. Each packet contains a portion of the transmission. For example, assume that you asked the question "Hello, how are you?." This could be broken into four packets for transmission, 'Hello' 'how' ' are' you'. These packets are sent over the Internet to a receiving computer. Because of 'traffic jams' the packets may not take the same path to the receiving computer and may arrive out of order; 'how' ' are' ' Hello' ' you.' The receiving computer may play the first, second and fourth packets of information out of order, resulting in the third packet being discarded. On a network with sufficient bandwidth this is not a problem. As the Internet becomes more and more congested, the quality of the transmissions will decrease unless bandwidth continues to increase proportionally. This is not a problem with ISDN as it utilizes a point-to-point connection; you always have a guaranteed amount of bandwidth.

As the Internet continues to grow in bandwidth and security, the transition from ISDN to IP is sure to take place.

Audio/Video Transmission

In most videoconferencing systems the pictures are taken with a camera much like a camcorder and a microphone picks up the audio. Both of these devices use standard analog signals. In order to transmit these analog signals, they must first be converted to digital signals. This is done with a device called a CODEC (coder-decoder). The analog signals (audio and video) are fed into the coder portion of the CODEC and converted to digital and then transmitted to the opposite end. When the opposite end receives the digital signal it is then fed into the decoder portion of the CODEC where it is converted back to analog. The analog signal is then fed into the TV. The audience is then able to hear and see what was sent from the transmitting end.

By putting a camera, microphone, TV, and CODEC on either end it is possible to have a 2-way conversation, hence: IVC (Interactive Video Conferencing)

The digital signal travels on the line at a speed depending on the size (capacity) of the line. If the line is not large enough for full motion then the picture is updated at a slower rate. This causes those jerky motions we often see with low bandwidth systems. However the signal can be distributed over multiple lines. Each line can carry 128 KB/sec of data. In order to get full motion, most systems require three lines or 384 kb/sec of bandwidth. At 384 KB/sec bandwidth we achieve full motion, a better picture and higher quality audio.

Compare image quality by line speed. (33.7 KB - QuickTime Movie - 10 sec) and (670 KB - QuickTime Movie - 10 sec)

Optimal systems have T1 connections, which provide plenty of bandwidth at 1,544 megabits per second for videoconferencing to coexist with other uses of the line (web/data, phone, etc.) Most rural areas have less choice in their connectivity and must settle for an ISDN line (or lines) provided by the local telephone company.