look at how IP multicasting can be deployed for e-learning
and other media-based applications. by Dr Seamus
most time-strapped enterprises, it is no longer practical
to try to gather hundreds of employees within a single
classroom to train them.
Enter e-learning, which has become an integral part
of any corporate or industrial training program. Besides
allowing distance learning, e-learning also has the
benefit of allowing employees to learn at their own
pace, without conforming to a fixed schedule designed
by traditional classroom training.
One of the most common forms of media broadcasting is
unicasting, where multimedia content is streamed from
one node to another. The most common application of
unicasting is audio and videoconferencing. In the case
of audio and videoconferencing, it is bidirectional
unicasting, since traffic travels from one node to another
in both directions. Unicasting is less bandwidth hungry,
depending on the level of compression for the multimedia
content. The more compression there is in the audio
and video content, the less bandwidth consumption there
On the other hand, multicasting is where multimedia
content is streamed from one node to many downstream
nodes. In multicasting, it is often unidirectional,
where traffic travels from the singular broadcasting
node to the downstream nodes, and usually no traffic
Multicasting and unicasting can be combined in the same
classroom. For example, a trainer can use bidirectional
unicasting to communicate with individual participants
to communicate private or sensitive ideas, while multicasting
is used by the facilitator to communicate pervasive
and generic program content to every participant.
Multicasting used to be exorbitantly expensive, but
not anymore. These days, you can have a full-fledged
broadcasting and production studio for under US$5000,
which will allow you to deliver on-demand video content,
as well as live QuickTime streams. For example, here
is a short breakdown if you are using the Mac platform:
iMac for authoring (US$1399)
iMac for server use (US$1399)
MiniDV camcorder (US$600)
Mac OS X Server (US$999)
Mac OS X Client (US$129)
Sorenson 3 Broadcaster (US$199)
Other incidental expenditure may be necessary if you
want a more professional feel.
For example, you may require a sturdy tripod with lockable
wheels, studio lighting (known as "red heads"
with daylight filter), softbox lights (for diffused
lighting), reflector screens (to soften harsh shadows
cast by lights), bluescreen fabric for chromakey effects,
unidirectional or omnidirectional microphones, lapel
microphones, studio headphones, studio TV monitors,
DVcam recording and playback decks, Steadicam (for stabilising
handheld camera work), and so on.
These professional equipment will obviously push your
initial investment sky high, and may not be necessary
for internal training. But bear in mind though, if you
intend to deliver multicasting to your shareholders
and the media in corporate communication initiatives
as well as internal training audiences, then these additional
equipment may be necessary to deliver more credible
and professional results.
video, the smallest acceptable size these days is
160 by 120 pixels, around 10 frames per second (fps).
The best usable codec is Sorenson 3, which has decent
compression speeds. If you need to scale downwards
for compatibility, you may use Cinepak, one of the
oldest codecs around, although the quality is understandably
If your footage is largely "talking heads",
where the central theme is a person talking with
a half-body (or less) shot, then you can reduce
your frame rate even lower, perhaps to 8 fps.
If you are shooting a panning or zoom shot and
involve several individuals with more movement,
then you may need to retain more frames with a
higher frame rate, but reduce either the dimension
of the video (to a minimum of 160 by 120 pixels),
colour depth, or even compression rate altogether.
Some codecs, such as Sorenson 3 Professional,
offer variable bit rate compression, and will
adjust according to whether there is more movement,
or less movement, and the color diversity and
range within the footage.
In the world of broadcasting, even in the Web-based
environment, the key to success is not so much the visual
quality of video, but the audio quality. Humans pick
up audio defects much more than visual defects, with
a greater inherent tolerance for poorer video than audio.
This means that you have to compensate for bandwidth
utilization and participant tolerance, with a bias towards
audio rather than video. Some of the better audio compression
such as QDesign (www.qdesign.com) works across both
Mac and Windows platforms, and can be highly compressed
while retaining audio quality. If you cannot or choose
not to use QDesign, you may use more basic compression
such as ALaw or µLaw compression, which are more
compatible, but will generate larger file sizes.
You should invest in high-quality microphones, rather
than use cheap US$10 unpowered microphones. Some of
the best microphones are made by Shure (www.shure.com),
and their powered microphones will be able to record
a wider and deeper acoustic range. For discreet recording,
choose the Subminiature Lavalier Microphone, which is
an omnidirectional microphone. If you are narrating
segments, choose the Headworn Microphone, which has
noise canceling features.
Since audio is typically overlaid on video, you should
record all narration as mono tracks. If you cannot record
onto mono physically, you may merge the stereo tracks
into mono via software, or simply delete one of the
stereo tracks. This will then allow you to easily add
audio dubs on your video tracks later.
QuickTime (www.apple.com/ quicktime) has wider audio
response and sound level fidelity, which means that
it more closely approximates what you hear. If you are
using Microsoft Windows Media (www.microsoft.com/windowsmedia),
it will be quite close to QuickTime quality as well,
although the sound may become slightly higher-pitched,
and more "tinny". If you are using RealAudio
(www.real.com), then be aware that the sound level will
be reduced (i.e. the volume becomes lower) and you may
need to compensate via software.
Network good enough?
Of course, any video or audio broadcast can look great
if run across an Intranet on a 100Base-T infrastructure.
However, most learning or corporate broadcast initiatives
must involve remote access employees or participants,
some with only analogue 56k modem access. The idea is
to use the likes of QuickTime Streaming Server, which
can stream simultaneously to audiences with different
access speeds, by sending the rightly-scaled video footage
to them. For example, someone with only 56k modem access
will receive a broadcast stream that is small, while
someone with broadband or Ethernet access will receive
the quarter to full-screen footage.
Even if you do run some of your broadcast streams in-house
on your Ethernet network, you may want to reduce the
video down appropriately so that it does not cannibalize
on other users on your network running their daily network
tasks such as ftp, Web browsing and so on.
Most media streaming servers such as QuickTime Streaming
Server offers error correction so that there is always
some degree of buffer stored before the content is streamed
to downstream users. This will provide a simple "skip
protection" mechanism for viewers. Because of the
buffer, it may compensate for the amount of network
traffic at the time of the multicast. But do note that
no amount of "skip protection" or buffering
can compare to a unicast on a dedicated node-to-node
If you have a dedicated leased line, but running between
64 to 128 kbps, you may want to streamline your multicast
footage to be compatible with analogue 56k modem rates,
since 64 kbps leased lines can be saturated in no time,
and you will bring your own connectivity to a crawl.
For a successful multicast to hundreds of users, you
may want to consider leasing a full T1 line, or at least
dedicate a full-time SDSL for this multicast purpose.
Otherwise, you may have to rent multicasting services
from the likes of Akamai (www.akamai.com).
Multicasting for e-learning or corporate communications
can be very engaging and even addictive. As usual, invest
small first, before progressing to studio environments
with more professional recordings and broadcasts. It
will try your patience, as well as your budget, but
the rewards are often worth the
Seamus Phan is research director at KnowledgeLabs
News Center (www.knowledgelabs.net), an independent
technology news bureau and writes for Network Computing-The
Asian Edition. He can be reached at firstname.lastname@example.org