How Video Conferencing Works – Multimedia, Interactive Communication Across the Miles
By Lucy P. Roberts
You may think you understand video conferencing pretty well until someone who
isn’t at all familiar with it approaches you for a simple definition. When they
ask, “What exactly is video conferencing?” you could suddenly realize you’re at
a loss for words.
The simplest definition of how video conferencing works is simply by the
integration of video, audio and peripherals to enable two or more people to
communicate simultaneously over some type of telecommunications lines. In other
words, you are transmitting synchronized images and verbal communications
between two or more locations in lieu of them being in the same room. How video
conferencing works is a little bit harder to explain than answering the
question, “What is video conferencing?”
Millions of people use video conferencing every day around the globe, but
very few people know just how the technical aspects of the process work. The
main ingredients of successful video conferencing are video cameras,
microphones, appropriate computer software and computer equipment and
peripherals that will integrate with the transmission lines to relay the
The analog information recorded by the microphones and cameras is broken down
into discreet units, translating it to ones and zeros. A Codec encodes the
information to a digital signal that can then be transmitted to a codec at the
other end, which will retranslate these digital signals back into analog video
images 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
almost exclusively but were really only practical for room-based video
conferencing systems. These dedicated lines were expensive and only large
corporations tended to have the facilities and money to invest in this type of
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 connections
of the Internet are much less expensive and can carry large quantities of
information, including video packets for conferencing, relatively easily.
Because of this, video conferencing has become much more prevalent in small
businesses and in desktop packages that can be set up with software for
Compression makes video transmission practical
The problem that arises when you convert analog to digital for transmission
is the loss of clarity in an image. Analog signals are a continuous wave of
amplitudes and frequencies showing shades and ranges of color as well as depth
and brightness. When you convert to digital, which is strictly 0’s and 1’s, you
then need to develop a grid to represent values, intensities and saturations of
different color values so that the image can be interpreted and reformed at the
This vast amount of digital information requires huge bandwidth and means
that the time it would take to transmit video images would be impractical for
most applications. That’s where compression is crucial. When determining how
video conferencing works, one of the most important elements is the compression
The higher the compression ratio, the more quickly the information is capable
of being transmitted. In many cases, however, this also means some loss in
clarity or audio/video quality. For instance, a compression ratio of 4:1 would
be terribly slow but have a fantastic picture quality. But by the time it was
transmitted, everyone at the other end would probably have left the room for a
cup of coffee. Lossy compression discards unneeded or irrelevant sections of a
signal in order to transmit only the essentials, speeding up the transmission
time significantly but sometimes resulting in loss of quality.
Compression can either be intra-frame or inter-frame for material that is
repetitive or redundant, such as that wall behind the conference participant.
Since the wall remains static and never changes, this image is redundant and can
be eliminated from transmissions to an extent with proper compression.
Intra-frame compression assumes the redundancy will be present in parts of a
frame that are close to each other. Inter-frame compression assumes that there
is redundancy over time (i.e., like that wall). Either of these can achieve a
fairly high degree of accuracy and reduce the bandwidth needed for transmittal
A newer version of compression/decompression is SightSpeed technology,
developed by Cornell University. SightSpeed compresses only images considered
essential and eliminating what is considered ‘filler,’ relying on the brain to
fill in the decompression at the other end. Based on an artificial intelligence
model, SightSpeed achieves compression of about 90:1, compared to the typical
15:1 for video conferencing.
Any video conferencing session you use will provide compression of the
transmission signal. The key is determining the balance between speed and video
picture quality that is right for your needs.
Point to point video conferencing
Point to point video conferencing is just what it sounds like – a link
between two different points on the planet, or two different video conferencing
terminals. It could be between an office in New York City and a conference room
in Munich. Point to point video conferencing can easily be initiated by someone
on 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 the
participants will be there.
Multipoint conferencing is more complex
Multipoint conferencing is more complicated because it has to coordinate
several different locations simultaneously. Since you can’t be in direct contact
with several places at once while they are all in contact with others, you need
one source that will tie them all together. In video conferencing, this is
called 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 the
information flows. The MCU receives all information from the various locations
and then sends it out to each location. In some cases the MCU is located on a
particular PC, and in other cases it is located on a remote server (the most
common structure, particularly for more powerful MCU networks).
Audio is usually sent and received simultaneously in all locations with an
MCU with no problem because of the relatively small bandwidth needed for
transmittal. It is broadcast in what is called “full duplex” mode, meaning
everyone can talk and hear at the same time with no cutting off when one person
or another speaks.
Video transmission, however, can be broadcast in a number of ways with an MCU
depending 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
- 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
Overcoming the language barrier
Obviously, communicating through video conferencing can’t be achieved unless
both ends of the conference are “speaking the same language.” That is, whatever
is being transmitted electronically will need to be reassembled properly and
heard and seen clearly at the other end. The Codec system (Coder-Decoder) is
useless if both ends aren’t using the same virtual language to interpret the
The International Telecommunications Union (ITU) developed a set of standards
in 1996 dubbed H.323 to outline specific guidelines for Video Conferencing
standards and protocols so that compliance and support across networks would be
easier to achieve and maintain. Since then, many manufacturers and developers of
video conferencing tools have adopted the H.323 guidelines as their own.
Web conferencing solutions such as Click to Meet, Lotus’s SameTime, and WebEx
also offer corporate solutions that are based on Internet video conferencing.
These systems have shared protocols that can be downloaded and used anywhere at
any location for subscribers through the Internet. These are becoming more
popular with companies who like the convenience and user-friendliness. They will
no doubt become more and more refined over time, vying with and perhaps
surpassing the H.323 standards.
Overcoming firewall issues
There are, of course, obstacles to overcome when you take a look at how video
conferencing works. After all, you’re sending vast amounts of translated data
either directly or through a gatekeeper system (the MCU) that is switching and
transferring information between a variety of computers. Just about any business
these days has a firewall system to provide security and protect the system from
potential viruses. Trouble is, many firewalls also block the transmission of
data for video conferencing.
Recent innovations have largely circumvented these problems by designing
firewall solutions that recognize video conferencing signaling requests and allow
the information packets to bypass the firewall or router without disabling the
firewall protection for other traffic. Even with this, however, there may be
occasions when packets are dropped because of heavy traffic on the system, so
investing in a firewall system that can handle substantial traffic is essential
to quality video conferencing performance.
How video conferencing works will certainly evolve over time and improve in
the coming years, but a basic understanding of what it is and how it works now
will help you make the best choice for you when you’re ready to begin using
video conferencing yourself.
This article on the "How Video Conferencing Works" reprinted with
Copyright © 2004 Evaluseek Publishing.
About the Author
Lori Wilkerson is a full-time freelance writer who loves her job because it
gives 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 teleconferencing, and
desktop video conferencing. She has two dogs who are spoiled
and one teenager who is not. She does her video conferencing in pink bunny
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