re: The Disruption of a Disruptive Technology: The Once and Never WT4 Waveguide System
Thread,
The following url points to a photocopy of an article in the November 1975 Bell Labs Record which was dug up for me by Mr. Albert La France, a fellow netizen of long standing on the Compuserve Communications Forum.
The article is about a millimeter waveguide technology, known as WT4 waveguide which stands for waveguide at level T4. Actually the WT4 system consisted of many multiples of the T4 rate of 274 Mb/s.
The WT4 was supposed to eventually replace coaxial-based analog "L" carrirs systems, and analog and digital microwave systems for long distance voice, data and video transmission (sound fmailiar?) during the late Seventies, "throughout the Eighties, and beyond."
Fully loaded, a WT4 "system" would have supported fifty-seven (57) independent T4 signals through a single tube, equating, in today's taxonomy, to the payload carrying capacity of an OC-342, or 342 T3s.
Deriv: since a T4 comprises six (6) T3s: 6 T3s/T4 * 57 T4s = 342 T3s.
It almost did what it set out to do, 'cepting for a minor thing that happened along during the Seventies called fiber optics, which had hardly begun field testing at the time that this article was written.
Following the article (url) below, I've reposted some of my reply to Albert. I would suggest that you take some time to read the article [and my postscripts, which provide a retrospective on some of the specifics] if you are interested in:
- the serendipity [which can be inferred] that ultimately affected the evolution of the North American Digital Transmission Hierarchy, from the late 60s through the early 80s;
- how an apparently disruptive technology could get blown away before it's ever had an opportunity to see the "light" of day, by a more compelling disruptive technology (are there any lessons to be learned here?); and,
- how bandwidth utilization perceptions and forecasting of same have changed radically over the past twenty-five years.
Combined with some of my own notes which follow, the article presents some interesting architectural relationships as they existed some twenty-five to thirty years ago, while also providing some instructive insights as to how we may have arrived at the foundation of the digital transmission hierarchy we still use today.
Keep in mind that these technologies preceded any notions of SONET by about six to ten years, depending on whose folklore you wish to believe in.
Enjoy, Frank Coluccio
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"Millimeter Waveguide Scores High in Field Tests"
by William D. Warters, The Bell Laboratories Record, November 1975, pp. 400-408, incl.
bellsystem.homestead.com
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My reply to Albert La France:
That's excellent, Albert. Thanks.
You've brought me back 25 to 30 years. I recall reading this Bell Labs Record article back then. Earlier, I'd read similar accounts in various plant notes when I was with ATT in the late Sixties through '72, prior to liaising to NYTel, but they were much more primitive at that point.
At about the same time of this 1975 printing, there was another attempt at leveraging the T4 (DS4 at 274 Mb/s) over coaxial systems. The one that I recall was a T4 coaxial system between Manhattan and Jersey City, through the Holland Tunnel. T4 was the intended long haul facility at that time, not T3s, and SONET hadn't been thought of yet.
T3s were an after-thought, primarily brought about by increased capacities on microwave radio systems at the time, and later galvanized by fiber systems.
Originally, the DS3 signal (the 44.736 Mb/s line rate of the T3 line) was merely a mux stage in the central office which sat between the T1 access lines, the DS2 mux stage, and the T4 long haul rate. DS3s were used to aggregate metallic T1s (28 of them) into six bundles {of DS3s} which were stepped up through an M3/4 mux to a T4 "line" rate.
Single mode fiber did away with this idea of the WT4 system. Solitons are next.
Frank |
