How Video Conferencing Works - Multimedia, Interactive Communication Across the Miles
You may think you understand video conferencing pretty well until someone who \r\nisnt at all familiar with it approaches you for a simple definition. When they \r\nask, What exactly is video conferencing? you could suddenly realize youre at \r\na loss for words.
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The simplest definition of how video conferencing works is simply by the \r\nintegration of video, audio and peripherals to enable two or more people to \r\ncommunicate simultaneously over some type of telecommunications lines. In other \r\nwords, you are transmitting synchronized images and verbal communications \r\nbetween two or more locations in lieu of them being in the same room. How video \r\nconferencing works is a little bit harder to explain than answering the \r\nquestion, What is video conferencing?
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Millions of people use video conferencing every day around the globe, but \r\nvery few people know just how the technical aspects of the process work. The \r\nmain ingredients of successful video conferencing are video cameras, \r\nmicrophones, appropriate computer software and computer equipment and \r\nperipherals that will integrate with the transmission lines to relay the \r\ninformation.
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The analog information recorded by the microphones and cameras is broken down \r\ninto discreet units, translating it to ones and zeros. A Codec encodes the \r\ninformation to a digital signal that can then be transmitted to a codec at the \r\nother end, which will retranslate these digital signals back into analog video \r\nimages and audio sounds.
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The theorys the same, the transmission has changed
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In the earlier days of video conferencing, T1, ATM and ISDN lines were used \r\nalmost exclusively but were really only practical for room-based video \r\nconferencing systems. These dedicated lines were expensive and only large \r\ncorporations tended to have the facilities and money to invest in this type of \r\nset-up.
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As the Internet became more a part of the everyday lives of all businesses, \r\nhowever, it changed how video conferencing was conducted. The TCP/IP connections \r\nof the Internet are much less expensive and can carry large quantities of \r\ninformation, including video packets for conferencing, relatively easily. \r\nBecause of this, video conferencing has become much more prevalent in small \r\nbusinesses and in desktop packages that can be set up with software for \r\ncomputer-to-computer networking.
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Compression makes video transmission practical
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The problem that arises when you convert analog to digital for transmission \r\nis the loss of clarity in an image. Analog signals are a continuous wave of \r\namplitudes and frequencies showing shades and ranges of color as well as depth \r\nand brightness. When you convert to digital, which is strictly 0s and 1s, you \r\nthen need to develop a grid to represent values, intensities and saturations of \r\ndifferent color values so that the image can be interpreted and reformed at the \r\nreceiving end.
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This vast amount of digital information requires huge bandwidth and means \r\nthat the time it would take to transmit video images would be impractical for \r\nmost applications. Thats where compression is crucial. When determining how \r\nvideo conferencing works, one of the most important elements is the compression \r\nratio.
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The higher the compression ratio, the more quickly the information is capable \r\nof being transmitted. In many cases, however, this also means some loss in \r\nclarity or audio/video quality. For instance, a compression ratio of 4:1 would \r\nbe terribly slow but have a fantastic picture quality. But by the time it was \r\ntransmitted, everyone at the other end would probably have left the room for a \r\ncup of coffee. Lossy compression discards unneeded or irrelevant sections of a \r\nsignal in order to transmit only the essentials, speeding up the transmission \r\ntime significantly but sometimes resulting in loss of quality.
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Compression can either be intra-frame or inter-frame for material that is \r\nrepetitive or redundant, such as that wall behind the conference participant. \r\nSince the wall remains static and never changes, this image is redundant and can \r\nbe eliminated from transmissions to an extent with proper compression. \r\nIntra-frame compression assumes the redundancy will be present in parts of a \r\nframe that are close to each other. Inter-frame compression assumes that there \r\nis redundancy over time (i.e., like that wall). Either of these can achieve a \r\nfairly high degree of accuracy and reduce the bandwidth needed for transmittal \r\nof signals.
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A newer version of compression/decompression is SightSpeed technology, \r\ndeveloped by Cornell University. SightSpeed compresses only images considered \r\nessential and eliminating what is considered filler, relying on the brain to \r\nfill in the decompression at the other end. Based on an artificial intelligence \r\nmodel, SightSpeed achieves compression of about 90:1, compared to the typical \r\n15:1 for video conferencing.
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Any video conferencing session you use will provide compression of the \r\ntransmission signal. The key is determining the balance between speed and video \r\npicture quality that is right for your needs.
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Point to point video conferencing
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Point to point video conferencing is just what it sounds like a link \r\nbetween two different points on the planet, or two different video conferencing \r\nterminals. It could be between an office in New York City and a conference room \r\nin Munich. Point to point video conferencing can easily be initiated by someone \r\non one end contacting the other end as though making a standard telephone call. \r\nThere are no special arrangements to be made other than knowing that the \r\nparticipants will be there.
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Multipoint conferencing is more complex
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Multipoint conferencing is more complicated because it has to coordinate \r\nseveral different locations simultaneously. Since you cant be in direct contact \r\nwith several places at once while they are all in contact with others, you need \r\none source that will tie them all together. In video conferencing, this is \r\ncalled a multipoint bridge or multipoint conferencing unit (MCU).
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An MCU enables multi-location video conferencing by providing a sort of \r\ncentral processing center for all of the locations through which all the \r\ninformation flows. The MCU receives all information from the various locations \r\nand then sends it out to each location. In some cases the MCU is located on a \r\nparticular PC, and in other cases it is located on a remote server (the most \r\ncommon structure, particularly for more powerful MCU networks).
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Audio is usually sent and received simultaneously in all locations with an \r\nMCU with no problem because of the relatively small bandwidth needed for \r\ntransmittal. It is broadcast in what is called full duplex mode, meaning \r\neveryone can talk and hear at the same time with no cutting off when one person \r\nor another speaks.
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Video transmission, however, can be broadcast in a number of ways with an MCU \r\ndepending upon the quality of the software and the complexity of the system. \r\nSome common types of video transmission for video conferencing include:
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- Continuous Presence video conferencing, which allows up to four \r\n conference sites to be seen simultaneously on split screens. This is usually \r\n used if you have a small group or individuals in separate locations and will \r\n primarily be seeing close-up shots.
- Universal Control video conferencing is controlled by the \r\n initiating conference site. The primary site determines who sees what at all \r\n other sites.
- Voice Activated video conferencing is by far the most common type \r\n used today. The image with these systems shifts to the site that is currently \r\n activating the microphone so that you can always see whoever is speaking. \r\n However, if there is a good deal of background noise participants should mute \r\n their microphones when they arent talking in order to avoid the image jumping \r\n about needlessly.
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Overcoming the language barrier
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Obviously, communicating through video conferencing cant be achieved unless \r\nboth ends of the conference are speaking the same language. That is, whatever \r\nis being transmitted electronically will need to be reassembled properly and \r\nheard and seen clearly at the other end. The Codec system (Coder-Decoder) is \r\nuseless if both ends arent using the same virtual language to interpret the \r\nsignals.
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The International Telecommunications Union (ITU) developed a set of standards \r\nin 1996 dubbed H.323 to outline specific guidelines for Video Conferencing \r\nstandards and protocols so that compliance and support across networks would be \r\neasier to achieve and maintain. Since then, many manufacturers and developers of \r\nvideo conferencing tools have adopted the H.323 guidelines as their own.
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Web conferencing solutions such as Click to Meet, Lotuss SameTime, and WebEx \r\nalso offer corporate solutions that are based on Internet video conferencing. \r\nThese systems have shared protocols that can be downloaded and used anywhere at \r\nany location for subscribers through the Internet. These are becoming more \r\npopular with companies who like the convenience and user-friendliness. They will \r\nno doubt become more and more refined over time, vying with and perhaps \r\nsurpassing the H.323 standards.
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Overcoming firewall issues
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There are, of course, obstacles to overcome when you take a look at how video \r\nconferencing works. After all, youre sending vast amounts of translated data \r\neither directly or through a gatekeeper system (the MCU) that is switching and \r\ntransferring information between a variety of computers. Just about any business \r\nthese days has a firewall system to provide security and protect the system from \r\npotential viruses. Trouble is, many firewalls also block the transmission of \r\ndata for video conferencing.
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Recent innovations have largely circumvented these problems by designing \r\nfirewall solutions that recognize video conferencing signaling requests and allow \r\nthe information packets to bypass the firewall or router without disabling the \r\nfirewall protection for other traffic. Even with this, however, there may be \r\noccasions when packets are dropped because of heavy traffic on the system, so \r\ninvesting in a firewall system that can handle substantial traffic is essential \r\nto quality video conferencing performance.
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How video conferencing works will certainly evolve over time and improve in \r\nthe coming years, but a basic understanding of what it is and how it works now \r\nwill help you make the best choice for you when youre ready to begin using \r\nvideo conferencing yourself.
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This article on the \”How Video Conferencing Works\” reprinted with \r\npermission.
\r\nCopyright 2004 Evaluseek Publishing.
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About the Author
\r Lori Wilkerson is a full-time freelance writer who loves her job because it \r gives her the opportunity to learn more about the world every day. Right now, \r she knows a little bit about almost everything, and a lot about\r video conferencing,\r \r video teleconferencing, and\r \r desktop video conferencing. She has two dogs who are spoiled \r and one teenager who is not. She does her video conferencing in pink bunny \r slippers.
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