 Can
I do video conferencing using the campus Ethernet networks? Will I get
good service? Will I interfere with anyone else?
April 17, 2001
The answer is yes, but with some caveats. Missouri State University currently
requires that all video conferencing gear that uses our campus Ethernet network
be connected to a 100Mb, switched network jack. Please see the 100Mb
FAQ for more information on the current availability of 100Mb service in
your area and its cost.
Your video conferencing equipment must support the H.323 protocol and have a
100Mb, full-duplex Ethernet interface available. NetMeeting and Polycom
are among the good choices.
Can't I get good service over 10Mb? I tried it and it appears to work.
Audio and video, unlike most other Internet applications, require a
continuous stream of data between the participants. If a web page or FTP
file download suffers a three second delay, it's no big deal to wait a bit
longer for the information to display or for the download to complete. The
same three second delay in a video conference, however, can be very disruptive to
the conference and even destroy its usability if the delays happen often.
The slower and shared nature of our 10Mb networks leave them prone to
interference where constant data-rates are required such as video or even
pure audio transmissions. A video stream might work just fine until
someone in a lab next door decides to download a large file.
The interference goes both ways. Video over a shared, 10Mb network can
easily interfere with all of the other users on the network causing much
increased contention, retransmissions, and just plain slow network
response. Therefore, for the good of all users on the network, we don't
approve video conferencing on the older, shared, 10Mb networks.
Ok, so what does 100Mb do for be besides being 10 times faster?
Well, it's actually up to 20 times faster. The 100 verses 10 makes it
10 times faster, but it's also full-duplex which means it can transmit and
receive data simultaneously. The switched nature of the connection also
creates a private data path between video conferencing units. As long as
both are on campus, the extra bandwidth is available from point to point
creating a better chance that your video will get though without outside
interference. Also, the video is much less likely to interfere with others
on the network.
100Mb only gives me a better chance? Don't I get a guarantee?
Currently no, but that is changing. Ethernet was designed on a
"best effort" model where the network will do it's best to deliver
your data as fast as possible, but if something gets overloaded somewhere, the
network currently just drops any old packet of data and the originating station
must retransmit it later. This packet could be part of a video
conferencing stream where retransmission might not be possible thus causing
glitches in the picture of voice. It could also be from someone's web page
or a file download where retransmissions are no problem.
The reason that 100Mb works well for video now is because our building feeds
and the core network are unconstrained. This means that there is currently
enough bandwidth to service all of our users. Therefore we're not dropping anyone's packets in the core and
everyone, including video users, are quite happy.
What's changing is that the 100Mb networks are capable of supporting what is
known as "Quality of Service" or simply QoS. This means that the
network can identify video traffic and greatly reduce or even eliminate packet
drops for video streams by giving it a higher priority. Our whole network
is not QoS enabled, meaning that only portions of it recognize and act upon the
priority information, but that is changing with time.
Currently, if we know you're hooking up a video conferencing unit, we can set
some QoS parameters to help your traffic arrive at its campus destination
without drops. These facilities are simply not available on the old, 10Mb
networks.
What about Internet or remote campus destinations?
We can only control the priority on the networks we control. Once the
data leaves Missouri State University's address space and enters MOREnet or the Internet itself, we
have no control as to what happens to the traffic. However, we can and
currently do identify outgoing video traffic and set it to a higher priority as
it leaves campus. We have a special device in place that takes in all
Internet traffic, classifies it, prioritizes it, and performs necessary packet
drops before the normally constrained Internet router even sees the
traffic.
This Internet router would make random packet dropping decisions, but our
flow shaping device insures that lesser priority packets are dropped in an intelligent
fashion and that the data sent to the Internet router is not too much for it to
handle. It also identifies and prioritizes inbound video traffic so our
network will process it as efficiently as possible.
Video to West Plains actually crosses a small portion of MOREnet which currently does not honor these priority settings, but movement in that direction
is currently in progress. MOREnet is also currently unconstrained even
though our Internet connection is at times, but we've already said that video
gets priority on the pipe. West Plains' Internet is currently unconstrained
and video currently poses no problems there.
I have more questions you didn't answer here, who do I call?
The Networking group takes care of the network and they should be contacted
for further information. The people currently dealing with video over the
network are:
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