deployment of broadband networks. Widespread use of real-time, high-speed data networks will develop, whose performance will offer economic advantages to high-volume users (Dvorak, 1987; Langseth, 1987).

But the changes in network architecture and operation brought about by these powerful new technologies will have unintended side effects which, if no adjustments are made, could seriously impair the ability of the public networks to provide the mix of services required to meet national security emergency preparedness (NSEP) goals. The sections that follow present a more detailed picture of how transmission, switching, integrated circuit technology, and network technologies are being deployed in the public networks and will briefly assess the implications of each of these technological trends for NSEP.

TRANSMISSION

Optical Fiber

Background

As copper-based systems become obsolete, the media that will provide transmission in the public networks will be optical fiber, satellite radio, and terrestrial radio. Increasingly, the dominant domestic transmission medium will be optical fiber (Henry, 1988; Solomon, 1988).

Optical fibers, first tested less than 20 years ago, are strands of ultrapure “glass,” usually fabricated from a silica-based compound, which guide lightwaves along a transmission path. Transmission is accomplished by modulating the light from a light source (either a light-emitting diode or a laser) and coupling the resulting optical beam into the fiber. At the receiving end, a photo-detector typically performs the first level of demodulation to provide multiplexed electrical output signals. Lasers are the preferred light source, since their narrower light beam and purer spectrum couples more efficiently into the fiber and results in higher overall transmission efficiency.

Fiber transmission provides unequalled channel capacity (bandwidth) and signal quality. Already, commercially available fiber systems can transmit at 1.7 Gbit/s rates, thus supporting over 24,000 voice conversations; systems with twice that capacity are forecast to be operational soon. Fiber has an inherent transmission capacity estimated at 20 THz, or more than 10,000 times existing systems; roughly the capacity of all the voice traffic in the United States at



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