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.
This article on the "How Video Conferencing Works" reprinted with
permission.
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
conferencing,
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.
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