You may think you understand video conferencing pretty well until someone who \risn¡¯t at all familiar with it approaches you for a simple definition. When they \rask, ¡°What exactly is video conferencing?¡± you could suddenly realize you¡¯re at \ra loss for words.

The simplest definition of how video conferencing works is simply by the \rintegration of video, audio and peripherals to enable two or more people to \rcommunicate simultaneously over some type of telecommunications lines. In other \rwords, you are transmitting synchronized images and verbal communications \rbetween two or more locations in lieu of them being in the same room. How video \rconferencing works is a little bit harder to explain than answering the \rquestion, ¡°What is video conferencing?¡±

Millions of people use video conferencing every day around the globe, but \rvery few people know just how the technical aspects of the process work. The \rmain ingredients of successful video conferencing are video cameras, \rmicrophones, appropriate computer software and computer equipment and \rperipherals that will integrate with the transmission lines to relay the \rinformation.

The analog information recorded by the microphones and cameras is broken down \rinto discreet units, translating it to ones and zeros. A Codec encodes the \rinformation to a digital signal that can then be transmitted to a codec at the \rother end, which will retranslate these digital signals back into analog video \rimages 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 used \ralmost exclusively but were really only practical for room-based video \rconferencing systems. These dedicated lines were expensive and only large \rcorporations tended to have the facilities and money to invest in this type of \rset-up.

As the Internet became more a part of the everyday lives of all businesses, \rhowever, it changed how video conferencing was conducted. The TCP/IP connections \rof the Internet are much less expensive and can carry large quantities of \rinformation, including video packets for conferencing, relatively easily. \rBecause of this, video conferencing has become much more prevalent in small \rbusinesses and in desktop packages that can be set up with software for \rcomputer-to-computer networking.

Compression makes video transmission practical

The problem that arises when you convert analog to digital for transmission \ris the loss of clarity in an image. Analog signals are a continuous wave of \ramplitudes and frequencies showing shades and ranges of color as well as depth \rand brightness. When you convert to digital, which is strictly 0¡¯s and 1¡¯s, you \rthen need to develop a grid to represent values, intensities and saturations of \rdifferent color values so that the image can be interpreted and reformed at the \rreceiving end.

This vast amount of digital information requires huge bandwidth and means \rthat the time it would take to transmit video images would be impractical for \rmost applications. That¡¯s where compression is crucial. When determining how \rvideo conferencing works, one of the most important elements is the compression \rratio.

The higher the compression ratio, the more quickly the information is capable \rof being transmitted. In many cases, however, this also means some loss in \rclarity or audio/video quality. For instance, a compression ratio of 4:1 would \rbe terribly slow but have a fantastic picture quality. But by the time it was \rtransmitted, everyone at the other end would probably have left the room for a \rcup of coffee. Lossy compression discards unneeded or irrelevant sections of a \rsignal in order to transmit only the essentials, speeding up the transmission \rtime significantly but sometimes resulting in loss of quality.

Compression can either be intra-frame or inter-frame for material that is \rrepetitive or redundant, such as that wall behind the conference participant. \rSince the wall remains static and never changes, this image is redundant and can \rbe eliminated from transmissions to an extent with proper compression. \rIntra-frame compression assumes the redundancy will be present in parts of a \rframe that are close to each other. Inter-frame compression assumes that there \ris redundancy over time (i.e., like that wall). Either of these can achieve a \rfairly high degree of accuracy and reduce the bandwidth needed for transmittal \rof signals.

A newer version of compression/decompression is SightSpeed technology, \rdeveloped by Cornell University. SightSpeed compresses only images considered \ressential and eliminating what is considered ¡®filler,¡¯ relying on the brain to \rfill in the decompression at the other end. Based on an artificial intelligence \rmodel, SightSpeed achieves compression of about 90:1, compared to the typical \r15:1 for video conferencing.

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

Point to point video conferencing

Point to point video conferencing is just what it sounds like ¨C a link \rbetween two different points on the planet, or two different video conferencing \rterminals. It could be between an office in New York City and a conference room \rin Munich. Point to point video conferencing can easily be initiated by someone \ron one end contacting the other end as though making a standard telephone call. \rThere are no special arrangements to be made other than knowing that the \rparticipants will be there.

Multipoint conferencing is more complex

Multipoint conferencing is more complicated because it has to coordinate \rseveral different locations simultaneously. Since you can¡¯t be in direct contact \rwith several places at once while they are all in contact with others, you need \rone source that will tie them all together. In video conferencing, this is \rcalled a multipoint bridge or multipoint conferencing unit (MCU).

An MCU enables multi-location video conferencing by providing a sort of \r¡°central processing center¡± for all of the locations through which all the \rinformation flows. The MCU receives all information from the various locations \rand then sends it out to each location. In some cases the MCU is located on a \rparticular PC, and in other cases it is located on a remote server (the most \rcommon structure, particularly for more powerful MCU networks).

Audio is usually sent and received simultaneously in all locations with an \rMCU with no problem because of the relatively small bandwidth needed for \rtransmittal. It is broadcast in what is called ¡°full duplex¡± mode, meaning \reveryone can talk and hear at the same time with no cutting off when one person \ror another speaks.

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

\r
• Continuous Presence video conferencing, which allows up to four \r conference sites to be seen simultaneously on split screens. This is usually \r used if you have a small group or individuals in separate locations and will \r primarily be seeing close-up shots.
\r
• Universal Control video conferencing is controlled by the \r initiating conference site. The primary site determines who sees what at all \r other sites.
\r
• Voice Activated video conferencing is by far the most common type \r used today. The image with these systems shifts to the site that is currently \r activating the microphone so that you can always see whoever is speaking. \r However, if there is a good deal of background noise participants should mute \r their microphones when they aren¡¯t talking in order to avoid the image jumping \r about needlessly.
\r

Overcoming the language barrier

Obviously, communicating through video conferencing can¡¯t be achieved unless \rboth ends of the conference are ¡°speaking the same language.¡± That is, whatever \ris being transmitted electronically will need to be reassembled properly and \rheard and seen clearly at the other end. The Codec system (Coder-Decoder) is \ruseless if both ends aren¡¯t using the same virtual language to interpret the \rsignals.

The International Telecommunications Union (ITU) developed a set of standards \rin 1996 dubbed H.323 to outline specific guidelines for Video Conferencing \rstandards and protocols so that compliance and support across networks would be \reasier to achieve and maintain. Since then, many manufacturers and developers of \rvideo conferencing tools have adopted the H.323 guidelines as their own.

Web conferencing solutions such as Click to Meet, Lotus¡¯s SameTime, and WebEx \ralso offer corporate solutions that are based on Internet video conferencing. \rThese systems have shared protocols that can be downloaded and used anywhere at \rany location for subscribers through the Internet. These are becoming more \rpopular with companies who like the convenience and user-friendliness. They will \rno doubt become more and more refined over time, vying with and perhaps \rsurpassing the H.323 standards.

Overcoming firewall issues

There are, of course, obstacles to overcome when you take a look at how video \rconferencing works. After all, you¡¯re sending vast amounts of translated data \reither directly or through a gatekeeper system (the MCU) that is switching and \rtransferring information between a variety of computers. Just about any business \rthese days has a firewall system to provide security and protect the system from \rpotential viruses. Trouble is, many firewalls also block the transmission of \rdata for video conferencing.

Recent innovations have largely circumvented these problems by designing \rfirewall solutions that recognize video conferencing signaling requests and allow \rthe information packets to bypass the firewall or router without disabling the \rfirewall protection for other traffic. Even with this, however, there may be \roccasions when packets are dropped because of heavy traffic on the system, so \rinvesting in a firewall system that can handle substantial traffic is essential \rto quality video conferencing performance.

How video conferencing works will certainly evolve over time and improve in \rthe coming years, but a basic understanding of what it is and how it works now \rwill help you make the best choice for you when you¡¯re ready to begin using \rvideo conferencing yourself.

This article on the "How Video Conferencing Works" reprinted with \rpermission.\rCopyright ? 2004 Evaluseek Publishing.

About the Author\rLori Wilkerson is a full-time freelance writer who loves her job because it \rgives her the opportunity to learn more about the world every day. Right now, \rshe knows a little bit about almost everything, and a lot about\rvideo conferencing,\r\rvideo teleconferencing, and\r\rdesktop video conferencing. She has two dogs who are spoiled \rand one teenager who is not. She does her video conferencing in pink bunny \rslippers.