Tag Archives: MCI

Remembering Our Microwave Past

Somebody sent me a link to an interesting article posted on 99% Invisible, a website associated with a podcast that looks at “the thought that goes into the things we don’t think about — the unnoticed architecture and design that shape our world” The article covers a book called The Long Lines that documents the abandoned infrastructure of the national microwave network built by AT&T that predated the eventual long-haul fiber networks that now connects us.

The AT&T microwave network was built in the 1950s. The first long-haul microwave route put into service was between New York and Chicago, and went live on September 1, 1950. Over the next few years, microwave routes were established across the country.

The networks were enabled by the high-powered klystrons developed during World War II, plus new microwave technologies that allowed for the simultaneous transmission of multiple channels of data. A klyston is a vacuum tube that amplifies a signal from a low-power level to a higher one. The klystron system enabled the creation of microwave links with enough power to carry not only voice calls, but television signals. The technology was developed at Bell Labs, and the microwave radios were manufactured by Western Electric, the manufacturing arm of AT&T.

The AT&T microwave network enabled the first nationwide broadcasts of television shows and news events. The first television event sent was a speech by President Harry Truman from the San Francisco Peace Conference in September 1951, which was then broadcast by the early television stations in major cities across the country. The first regular TV show that used the microwave network was Edward R. Murrow’s See It Now, broadcast in November 1951.

The AT&T microwave network led to some of the early success of television networks since it allowed for content that people had never seen before, like live Saturday football games from across the country. From the 1950s through the 1970s, practically all national programming was transmitted through the microwave network.

The microwave network wasn’t the only transmission network used by AT&T. The company had built coast-to-coast copper networks, and Alexander Bell made the first transcontinental phone call from New York City to San Francisco on January 25, 1915. This network was eventually enhanced with long-line coaxial networks, but those networks didn’t have the capacity to support television signals.

The microwave network consisted of towers built between thirty and forty miles apart, which accommodated the need for a line-of-sight connection. Interestingly, the core network electronics nodes of the network were built to supposedly withstand a nuclear explosion, since the microwave network also carried military traffic. These core locations included underground bunkers for electronics, staff, and backup power generators.

Anyone of a certain age remembers these towers, which either disappeared or were repurposed for cellular. Each tower had multiple giant horn antennas used to transmit and receive data. I remember in the 1970s that it was always easy to spot the AT&T building as you drove into a city because of the giant antennas on top, like the picture at the top of the blog of the antennas of the AT&T building in Minneapolis.

AT&T isn’t the only company that used a microwave network. MCI got its start as a competitor to AT&T by carrying telephone calls using its own microwave network that was often built along railroad rights-of-way. That network supported the early competition that eventually resulted in a competitive telecom industry.

The microwave towers were eventually replaced by the now-familiar fiber routes that were built starting in the late 1970s, and the greater capacity of fiber quickly made the microwave network obsolete.

The Anniversary of Fiber Optics

Fiber CableI recently saw an article that noted that this month marks the fiftieth anniversary of a scientific paper by Charles Kao in 1966 that kicked off the field of fiber optics communications. That paper eventually won him the Nobel prize for physics in 2009. He was assisted by George Hockman, a British engineer who was awarded the Rank prize for Opto-electronics in 1978.

We are so surrounded by fiber optic technology today that it’s easy to forget what a relatively new technology this is. We’ve gone from theoretical paper to the world covered with fiber optic lines in only fifty years.

As is usual with most modern inventions, Kao and Hockman were not the only ones looking for a way to use lasers for communications. Bell Labs had considered using fiberglass but abandoned the idea due to the huge attenuation they saw in glass – meaning that the laser light signal scattered quickly and wouldn’t travel very far. Bell Labs was instead looking at shooting lasers through hollow metal tubes using focused lenses.

The big breakthrough was when Kao and Hockman found a way to reduce the attenuation within a fiberglass cable to less than 20 decibels per kilometer. At that level of attenuation they could overcome irregularities and impurities in the fiber cable.

It took a decade for the idea to be put to practical use and Corning Glass Works (now Corning Inc.) found ways to lower attenuation even more; they laid the first fiber optic cable in Torino, Italy in 1977.

We didn’t see any wide-spread use of fiber optics in the U.S. until the early 1980s. AT&T and a few other companies like the budding MCI began installing fiber as an alternative to copper for long-haul networks.

We’ve come a very long way since the first generation fiber installations. The glass was expensive to manufacture, and so the early fiber cables generally did not contain very many strands of glass. It was not unusual to see 6 and 8 strand fibers being installed.

Compared to today’s standards, the fiber produced in the 1980s into the early 1990s was dreadful stuff. Early fiber cables degraded over time, mostly due to microscopic cracks introduced into the cable during manufacturing and installation. These cracks grew over time and eventually caused the cables to become cloudy and unusable. Early splicing technologies were also a problem and each splice introduced a significant amount of interference into the fiber run. I doubt that there is much, if any, functional fiber remaining from those early days.

But Corning and other companies have continually improved the quality of fiber optic cable and today’s fiber is lightyears ahead of the early cables. Splicing technology has also improved and modern splices introduce very little interference into the transmission path. In fact, there is no good estimate today of how long a properly-installed fiber cable might last in the field. It’s possible that fiber installed today might still be functional 75 to 100 years from now. The major issues with the life of fiber today is no longer failure of the glass sheath, but rather the damage that is done to fibers over time due to fiber cuts and storm damage.

The speeds achieved in modern fiber optics are incredible. The newly commissioned undersea fiber that Google and others built between Japan and the west coast of the US can pass an incredible 60 Terabits per second of data. Improvements in laser technology have grown probably even faster than the improvements in fiber glass manufacturing. We’ve grown to where fiber optic cable is taken for granted as something that is reliable and relatively easy to install and use. We certainly would be having a very different discussion about broadband today had fiber optic cables not improved quickly over the last several decades.