You may think you understand video conferencing pretty well until someone whoisn't at all familiar with it approaches you for a simple definition. When theyask, "What exactly is video conferencing?" you could suddenly realize you're ata loss for words.

The simplest definition of how video conferencing works is simply by theintegration of video, audio and peripherals to enable two or more people tocommunicate simultaneously over some type of telecommunications lines. In otherwords, you are transmitting synchronized images and verbal communicationsbetween two or more locations in lieu of them being in the same room. How videoconferencing works is a little bit harder to explain than answering thequestion, "What is video conferencing?"

Millions of people use video conferencing every day around the globe, butvery few people know just how the technical aspects of the process work. Themain ingredients of successful video conferencing are video cameras,microphones, appropriate computer software and computer equipment andperipherals that will integrate with the transmission lines to relay theinformation.

The analog information recorded by the microphones and cameras is broken downinto discreet units, translating it to ones and zeros. A Codec encodes theinformation to a digital signal that can then be transmitted to a codec at theother end, which will retranslate these digital signals back into analog videoimages and audio sounds.

The theory's the same, the transmission has changed

In the earlier days of video conferencing, T1, ATM and ISDN lines were usedalmost exclusively but were really only practical for room-based videoconferencing systems. These dedicated lines were expensive and only largecorporations tended to have the facilities and money to invest in this type ofset-up.

As the Internet became more a part of the everyday lives of all businesses,however, it changed how video conferencing was conducted. The TCP/IP connectionsof the Internet are much less expensive and can carry large quantities ofinformation, including video packets for conferencing, relatively easily.Because of this, video conferencing has become much more prevalent in smallbusinesses and in desktop packages that can be set up with software forcomputer-to-computer networking.

Compression makes video transmission practical

The problem that arises when you convert analog to digital for transmissionis the loss of clarity in an image. Analog signals are a continuous wave ofamplitudes and frequencies showing shades and ranges of color as well as depthand brightness. When you convert to digital, which is strictly 0's and 1's, youthen need to develop a grid to represent values, intensities and saturations ofdifferent color values so that the image can be interpreted and reformed at thereceiving end.

This vast amount of digital information requires huge bandwidth and meansthat the time it would take to transmit video images would be impractical formost applications. That's where compression is crucial. When determining howvideo conferencing works, one of the most important elements is the compressionratio.

The higher the compression ratio, the more quickly the information is capableof being transmitted. In many cases, however, this also means some loss inclarity or audio/video quality. For instance, a compression ratio of 4:1 wouldbe terribly slow but have a fantastic picture quality. But by the time it wastransmitted, everyone at the other end would probably have left the room for acup of coffee. Lossy compression discards unneeded or irrelevant sections of asignal in order to transmit only the essentials, speeding up the transmissiontime significantly but sometimes resulting in loss of quality.

Compression can either be intra-frame or inter-frame for material that isrepetitive or redundant, such as that wall behind the conference participant.Since the wall remains static and never changes, this image is redundant and canbe eliminated from transmissions to an extent with proper compression.Intra-frame compression assumes the redundancy will be present in parts of aframe that are close to each other. Inter-frame compression assumes that thereis redundancy over time (i.e., like that wall). Either of these can achieve afairly high degree of accuracy and reduce the bandwidth needed for transmittalof signals.

A newer version of compression/decompression is SightSpeed technology,developed by Cornell University. SightSpeed compresses only images consideredessential and eliminating what is considered 'filler,' relying on the brain tofill in the decompression at the other end. Based on an artificial intelligencemodel, SightSpeed achieves compression of about 90:1, compared to the typical15:1 for video conferencing.

Any video conferencing session you use will provide compression of thetransmission signal. The key is determining the balance between speed and videopicture quality that is right for your needs.

Point to point video conferencing

Point to point video conferencing is just what it sounds like - a linkbetween two different points on the planet, or two different video conferencingterminals. It could be between an office in New York City and a conference roomin Munich. Point to point video conferencing can easily be initiated by someoneon one end contacting the other end as though making a standard telephone call.There are no special arrangements to be made other than knowing that theparticipants will be there.

Multipoint conferencing is more complex

Multipoint conferencing is more complicated because it has to coordinateseveral different locations simultaneously. Since you can't be in direct contactwith several places at once while they are all in contact with others, you needone source that will tie them all together. In video conferencing, this iscalled a multipoint bridge or multipoint conferencing unit (MCU).

An MCU enables multi-location video conferencing by providing a sort of"central processing center" for all of the locations through which all theinformation flows. The MCU receives all information from the various locationsand then sends it out to each location. In some cases the MCU is located on aparticular PC, and in other cases it is located on a remote server (the mostcommon structure, particularly for more powerful MCU networks).

Audio is usually sent and received simultaneously in all locations with anMCU with no problem because of the relatively small bandwidth needed fortransmittal. It is broadcast in what is called "full duplex" mode, meaningeveryone can talk and hear at the same time with no cutting off when one personor another speaks.

Video transmission, however, can be broadcast in a number of ways with an MCUdepending upon the quality of the software and the complexity of the system.Some common types of video transmission for video conferencing include:

* Continuous Presence video conferencing, which allows up to four conference sites to be seen simultaneously on split screens. This is usually used if you have a small group or individuals in separate locations and will primarily be seeing close-up shots.
* Universal Control video conferencing is controlled by the initiating conference site. The primary site determines who sees what at all other sites.
* Voice Activated video conferencing is by far the most common type used today. The image with these systems shifts to the site that is currently activating the microphone so that you can always see whoever is speaking. However, if there is a good deal of background noise participants should mute their microphones when they aren't talking in order to avoid the image jumping about needlessly.

Overcoming the language barrier

Obviously, communicating through video conferencing can't be achieved unlessboth ends of the conference are "speaking the same language." That is, whateveris being transmitted electronically will need to be reassembled properly andheard and seen clearly at the other end. The Codec system (Coder-Decoder) isuseless if both ends aren't using the same virtual language to interpret thesignals.

The International Telecommunications Union (ITU) developed a set of standardsin 1996 dubbed H.323 to outline specific guidelines for Video Conferencingstandards and protocols so that compliance and support across networks would beeasier to achieve and maintain. Since then, many manufacturers and developers ofvideo conferencing tools have adopted the H.323 guidelines as their own.

Web conferencing solutions such as Click to Meet, Lotus's SameTime, and WebExalso offer corporate solutions that are based on Internet video conferencing.These systems have shared protocols that can be downloaded and used anywhere atany location for subscribers through the Internet. These are becoming morepopular with companies who like the convenience and user-friendliness. They willno doubt become more and more refined over time, vying with and perhapssurpassing the H.323 standards.

Overcoming firewall issues

There are, of course, obstacles to overcome when you take a look at how videoconferencing works. After all, you're sending vast amounts of translated dataeither directly or through a gatekeeper system (the MCU) that is switching andtransferring information between a variety of computers. Just about any businessthese days has a firewall system to provide security and protect the system frompotential viruses. Trouble is, many firewalls also block the transmission ofdata for video conferencing.

Recent innovations have largely circumvented these problems by designingfirewall solutions that recognize video conferencing signaling requests and allowthe information packets to bypass the firewall or router without disabling thefirewall protection for other traffic. Even with this, however, there may beoccasions when packets are dropped because of heavy traffic on the system, soinvesting in a firewall system that can handle substantial traffic is essentialto quality video conferencing performance.

How video conferencing works will certainly evolve over time and improve inthe coming years, but a basic understanding of what it is and how it works nowwill help you make the best choice for you when you're ready to begin usingvideo conferencing yourself.

This article on the "How Video Conferencing Works" reprinted withpermission.
Copyright © 2004 Evaluseek Publishing.

About the Author
Lori Wilkerson is a full-time freelance writer who loves her job because itgives her the opportunity to learn more about the world every day. Right now,she knows a little bit about almost everything, and a lot about video conferencing, video teleconferencing, and desktop video conferencing. She has two dogs who are spoiledand one teenager who is not. She does her video conferencing in pink bunnyslippers.