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| This material is for those wishing to understand how H.323
works. Not required reading, this tutorial will help you to know
why our
network design recommendations and codec recommendations exist and
why you should follow them. Let's start with some basics as they
relate to K-20 sites. |
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| What is IP or H.323 Videoconferencing? |
- ITU H.323 is an internationally agreed upon recommendation
(standard) for voice and video communications over IP networks.
|
- The International Telecommunications Union (ITU) is the standards
setting entity that gave us H.323.
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- Like H.320 for communications over ISDN, H.323 defines basic
parameters that, when followed by manufacturers, allow their
codecs to connect with codecs by another manufacturer.
|
- Using a camera, microphone, monitor, and an endpoint (codec
or compressor - decompressor), H.323 video allows you to
participate in live, interactive videoconferences with other
sites on K-20,
Internet and Internet2.
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|
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| H.323 Suite: |
| H.323 is actually a collection of standards. Each one is responsible
for a selected function or feature. For example, H.261, H.263 and
H.264 are video codecs. They are software algorithms that do the
compressing/encoding and the decompressing/decoding of the video.
More detail about these can be found in the tutorials below.
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 |
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| Bandwidth: |
Bandwidth with your LAN is probably 10 or 100Mb. Washington
school districts, Community Technical Colleges, and Bacalaureate
Colleges have at least a T-1 connection to K-20.
From the
diagram below,
you
can
see that
the
connection
to K-20
can
be
a bottleneck
if data is saturating the pipe.
|
 |
| |
| Videoconferencing data is real time data. That means the data packets
need to arrive quickly and in the same sequence as they were sent.
Thus, it's important that the data can traverse the network with
minimal latency (delay caused by queuing or excessive number of hops),
little packet loss and low jitter (variation in latency). Frozen,
blurry or pixilated video is the result of too many packets lost,
excessive queuing and too much jitter. Audio can also be affected,
becoming distorted or nonexistent altogether. |
| |
| Why Use H.323? |
| In Washington, we are seeing fewer new installations of ISDN codecs
and more IP-based codecs using H.323. The Internet has become an
integral part of telecommunications that is still having new applications
and better transmission methods developed. Development for ISDN apllications
is dwindling, as is deployment of ISDN to rural areas of Washington. |
| |
| The World is moving towards IP-based communications systems with
convergence of the telecommunications and information technologies
industries. IP-based application development is growing much faster
than applications using the traditional analog transmission systems. |
| |
| K-20 multipoint bridging services will continue to support legacy
H.320 (ISDN-based) systems. However, we have a fast growing user
base that are either using or plan to use H.323. |
| |
| Recommended Reading: |
- Technical
Primer on H.323
 ,
by DataBeam (now part of IBM). Note this covers up to H.323 Version
2. The standard is up to Version
4 now.
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| Additional Reading: |
- A long list of links to other web sites you might useful.
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