How does it work?
Traditional Video conferencing allows the combination of audio, video, and communications networking technology for real-time interaction, and is often used by groups of people who come together in a specific place (often a conference room) to communicate with other groups of people. Desktop/Multimedia Teleconferencing (DMT) combines personal computing with audio, video, and communications technologies to provide real-time interaction between two or more personal computers. Additionally the system can support a document server which could be used to share documents and applications. In order to deploy DMT you need a videocamera, a screen , an audio-speaker, a microphone and a communications connection. Of course a powerful computer is needed for DMT. Of all these components, many different types exist on the market. There are also many different VC-configurations, in which the elements needed to achieve a videoconferencing session are integrated. The figure below gives a high level overview of the interaction between attendees.
Different means of communication links.
There are various types of communication links available. Each transport has its own characteristics, and some of these characteristics determine if a specific type is more or less suitable for the use of video-conferencing. The most important attributes of a communication link are:
One type of communication link is the Plain Old Telephone System (POTS). It has a relatively low bandwidth transport, but it is the most widely available of any of the transports. Consistently, a user can obtain 28.8 Kbps of bandwidth. However, the maximum acheivable bandwidth is 56kb as this is the most common speed for voice traffic is digital encoded over most telecommunicaitons networks. Unfortunately, this bandwidth is less than is needed to support quality videoconferencing at a level that is necessary for business use. The latency is similar to what you would experience in an ISDN or Switched 56 call and varies depending on the endpoints of your call. POTS lines allow for isochronous data transmission and the user doesn’t have to contend with others once a connection has been established.
Another type is Switched 56. Similar to ISDN, Switched 56 traffic can travel over the same infrastructure that supports ISDN. That’s why the latency and isochronous nature of the transport is the same. Like ISDN, Switched 56 provides a two channel call for video conferencing, but the bandwidth is limited to 56 Kbps per channel. ISDN has a bandwidth of 64 Kbps per channel. Switched 56 is an older technology with decreasing significance.
Another type is the ISDN, the Integrated Services Digital Network. This line has a relatively high bandwidth connection (128 Kbps), very suitable for videoconferencing. It supports isochronous data transmission and bandwidth is guaranteed once a connection has been established. Latency is manageable. ISDN service is becoming more available across the country and the world, but availibility can still be an issue when deciding on this transport for widescale deployment of videoconferencing.
LAN, Local Area Network is nowadays widely available at most corporations, and the existing LAN installations have more than sufficient bandwidth to support videoconferencing connections. Latency, even over several routers for a long distance WAN link, is comparable to ISDN and within the limits for video conferencing needs. Each caller must contend for this shared, asynchrounous resource, so bandwidth is not secured once a connection is established. As you add more video conferencing sessions, bandwidth and the management of its consumption on this medium becomes an issue. Isochronous data transmission can not be guaranteed because packets of information do not necessarily arrive at their destination at regular time intervals.
ATM, Asynchronous Transfer Mode over Frame Relay is a cell switched technology. ATM offers a relatively low latency, high bandwidth solution. ATM support transmission speeds from 45 Mbps (megabits per second) to 622 Mbps now and may be even higher in the future. Intended primarily for use as a network backbone, ATM is expensive and its bandwidth is much higher than needed for videoconferencing. ATM’s biggest hurdle is the cost, and that’s why its availability is not very high.
If we take the specifications of all the types of line in consideration, we can see that bandwidth on POTS is too low and cost of ATM over Frame Relay is too high. Switched 56 is technically feasible, but ISDN offers the same benefits, with greater bandwidth. The LAN has sufficient bandwidth, it is widely available. Its lack of isochronous datatransmission support is a challenge for the future that can be overcome. We can conclude that ISDN and LAN earn the preference to be the transport for videoconferencing-traffic when video quality is an issue.
Conclusion.
Videoconferencing can be a very good replacement for "classic" methods of communicating. Facial expressions are very important in every personal contact, and that's the big advantage of videoconferencing above all existing means of communication. DMT adds the advantage of personal computing to this, so associates can work together on the same document, no matter what the physical distance between their locations. Though this all seems very attractive , some hurdles in the development of this technique still have to be taken. Not all DMT equipment is compatible. Frustration arises if a strongly needed session can't take place because the two machines aren't compatible. A solid communication line that supports videoconferencing-traffic without many errors is still an issue. There are some types that are suitable for the deployment of videoconferencing, but their worldwide availability isn't still achieved.
Security is also an issue. A videoconferencing session is just as safe as an e-mail message, so it isn't suitable to discuss sensitive information by using videoconferencing. If these hurdles can be overcome in the future, desktop multimedia teleconferencing will become another great achievement making the world that much smaller.