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How Video
Conferencing Works
How video conferencing works -- multimedia, interactive communications across miles
October 31, 2004
By: Lori Wilkerson
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 information.
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 set-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 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 computer-to-computer networking.
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 receiving end.
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 ratio.
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 of signals.
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 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 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 signals.
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.
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 chat
rooms, 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 slippers.
Also See:
[ The
new Internet video phone technology from Skype ]
[ The
history of video conferencing -- moving ahead at the speed
of video ]
[ Top 7 video
conferencing tips to ensure effective virtual meetings ]
Home Page:
[ Video-Conferencing-Guide.com ]
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