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Fiber Optic Network Development Begins

Fiber Optic Network Development Begins

By Michael A. Saginaw
Associate News Editor

Lincoln Laboratories, Digital Equipment Corporation, and AT&T Bell Laboratories are pooling their expertise to complete a fiber optic test-bed for research in high speed and high volume network communication.

Fiber optic cables have the capacity to carry vast quantities of information at ultra-high speeds.

"There's the vision of the time when people will transmit images and multimedia things by computers and [fiber optic] networks," said Robert G. Gallager ScD '57, a professor of electrical engineering and computer science here who is researching the architecture of the network.

Although they are now used extensively in telephone lines, fiber optics are not used to their full capacity because the light signals which propagate through them are created electronically at one end with lasers and detected electronically at the other end. Thus the electronics create a bottleneck and obscure the full capabilities of fiber optics.

In the test-bed, however, all information traveling between the nodes, places that send and receive fiber optic data, is in the form of light. In this network, a node is typically an entire center like Lincoln Laboratories. When finished, the test-bed will only have 10 to 15 nodes, but the knowledge gained from managing this network is crucial for the national information highway. Therefore, a key research issue in the test-bed is its architecture.

Expandable architecture needed

"You want to make sure you can enlarge it to arbitrarily large sizes, nationally and internationally," said Gallager. "If you build a lovely test-bed and it only works for 10 or 20 nodes, it's not going to go very far."

As millions of light-encoded messages travel over the test-bed simultaneously, one message is distinguished from the others by its frequency, according to Professor of Electrical Engineering and Computer Science Robert S. Kennedy ScD '59, who is heavily involved in the project. This is known as frequency division.

Another common technique for distinguishing messages is time division, where a message from the sender is transmitted as a series of incredibly short pulses. These pulses are sent periodically, and the receiver only looks for pulses at the appropriate time. Time division is not currently used in the test-bed because the technology for optical time division is not as advanced as that for frequency division, according to Kennedy.

The test-bed will also test the effectiveness of consortia in bringing technology from the laboratory to the marketplace.

All three parties in the consortium have overlapping knowledge and experience in optical and communications technology, yet each party has its own specialty, according to Kennedy. Bell Laboratories brings to the project its competence in optical devices technology. DEC is very experienced with computer networks. Lincoln Laboratories is known for its ability as a system integrator. Finally, MIT professors view the project in terms of its long range effects and possibilities, Kennedy said.

The three party consortium has received $8.4 million in funding from the Defense Advanced Research Projects Agency, a government agency which has been supporting computer science and network research for many years.

Fiber hard to connect

Lincoln Laboratories will soon be connected to the test-bed, but it may take longer for MIT to become connected. There is already fiber optic cable underground from MIT to Lincoln Laboratories. But MIT is still negotiating with the New York and New England Telephone Company to try to use this cable.

As it is, the cable has termination equipment on it. Just like other conventional communication lines, this cannot take advantage of the full capabilities of the fiber optic cable. The Institute wants permission to get at the fiber optic cable itself.

"The phone companies feel that those lines are there for commercial use and to make money, not for research," Kennedy said.

If the Institute is not able to get directly at the fiber optic cable, it will still be connected to Lincoln Laboratories electronically.

Meanwhile, Columbia University in New York City and Bellcore are working on a smaller fiber optic network which also has applications for a national information highway.