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Re: CASE REPORT: CATV Video Data System
Another case history at the University of Texas at Austin:
To further inform this community about Cable systems support of data, the
very first major interbuilding computer data network at the Univeristy of
Texas at Austin campus was a cable TV system that supported both video and
data. While UT did not utilize modems as most people think of modems, i.e.
a device that provides a dedicated circuit between two points at bandiwdths
of 1200 bps to 1,536,000 bps, it did offer a campus-wide data network for
departments at 10 Mbps full Ethernet speeds. This system operated for
several years just fine. The largest span from the head end was six amps
deep. It connected 72 buildings on the campus. The Ethernet data system
was a bridged system for the first three years and then was converted to a
routed system. After six years of operation the system was completely
replaced with a fiber system.
At the same time UT was utilizing this system, UT was a participant
in the city cable TV system that was a mid-split ( that means there are
about 20 channels reverse and about 60 channels inthe forward direction)
that was separate from the broadcast cable TV system. The Institutional
Network (INET) was a required part of the franchise agreement between the
cable TV company and the city. This system supported both point to point
modems operating at 1200 bps and 19200bps. It also was the test bed for
the test with LANCity equipment. The test bed was between sites that were
connected with cable TV and approx 20 amps to the headend covering 10 miles
of distance. The LAN city test yielded the following results:
>Subject: Re: INET LAN City Bridges
>To: W.Wedemeyer@utexas.edu (Wayne Wedemeyer)
>Date: Mon, 8 Nov 1993 16:51:03 -0600 (CST)
>>Notice of connetion of LAN City bridges on the INET to
>>UT Network Operations Center.....
>> There are two Lan City RF bridges on the INET running to the head-end
>> and back to the NOC. The address of two 8 port 500 CS terminal servers
>> is 220.127.116.11 and 219.
>> These devices are being used for a test of the channel.
>> They seem to ping just fine.
>I tried sending some pings today and I get a fair amount of ping
>failures running 1000 pings of 8192 bytes each. I tried various data
>patterns with no major effect, so it doesn't seem pattern sensitive.
>My first 1K sample had 7 ping failures, the second, third, and fourth
>had 2, 4, and 2 failures each. It may not seem like much but link
>layer drop outs at this rate could stall an FTP file transfer, for
This test result shows that in a data network, as opposed to a
dedicated poinit to point modem connection, the cable TV system was not
error free. The data network people will share with you the fact that any
error rate has expedential ramifications on the bandwidth flow of data.
The small percentage is not indicative of the actual impact on a data
network when congestion goes up.
The error rates indicated by the LAN City equipment are very
indicative of the error rates experienced by the point to point modem uses
on the same system. The INET was a very successful system because it was
installed and maintained by the local cable TV company as part of their
franchise, it allowed public entities (the system did not attach to any
private homes or businesses) to create a video and data system at very low
recurring cost to them, served as a test bed for public entities to test
new technologies between their sites and it was a mechanism for the local
public entities to be able to communicate between themselves. The system
connected the city government sites, the local school district sites, the
local community college sites, the county government sites, the state
government sites and the University of Texas sites.
The result of the INET has been these governmental entities have
joined forces again to create a Great Austin Area Telecommunications
Network (GAATN) that now provides a dedicated fiber optic system among the
exact same entities. The fiber system is made up of fiber paths that
connect each entity's sites together and then all entities merge in a
common site to be able to share voice, video and data. The system is in
the final stages of construction and should be complete by the middle of
March. While GAATN is not a cable TV system any more it is the result of
the success of the INET cable TV system creating demand for more and more
bandwidth. In fact the INET remains a part of the city of Austin's
requirement for renewal of the cable TV franchise in the city.
>Just a comment here amidst the torrent, apropos of Curtis PriestUs
>>If cable modems are a fraud, why is it that LANCity:
>>1. Sold 100,000 frauds to Continental Cablevison
>> 2. And contracted for manufacture of 1,000,000 of these frauds?
>and Wayne WedemeyerUs reference to:
>>R.a Cable TV system that can carry 'data' and videoS,
>thought you might like a case history report:
>I built such a system in 1984 for a planned community in Tucson, Arizona
>called Cobblestone that covered about 5 sq. miles. Our engineer
>was Roy Knappenberger and our company was The Icon Corporation
>and we just did what seemed logical. Solving the analog-digital
>coexistence problems was quite possible even that long ago.
>General Instruments was so proud to participate that they put our system
>plan on the cover of their parts catalog. I managed it until 1989 when I
>sold the company. It purred along well, providing (at that time) 17
>channels of TV, continuous data survey of individual home security
>systems, an interactive database about emergency health concerns and
>security instructions for each individual resident, voice (private phone)
>communication between all homes and the front gate and an upstream-
>downstream community video conferencing system, allowing each
>household to have full voice/video communications with their
>neighbors if they wished.
>For us, a small group of analog-digital pragmatists who didnUt know it
>would take 13 years for the idea to shake kingdoms of capital, it was just
>a logical way to run an information utility. So we did.
>Our heart was really into producing interactive television accompanied
>by interactive digital data information, and once you solve those
>problems, spreading out geographically is mainly a business organization
>issue. I donUt think it is technology that has hindered proliferation of
>these services. It has to do with market turf, capital and vision.
>Computers, Freedom & Privacy Video Project
>cfpvideo@well or email@example.com
>Dendrite Forest, Inc.
>310 455-3915 * P.O. Box 912
>Topanga, CA 90290
FAX (512) 471-2449