1. Shedding Light on Communications Nanette Halliburton Chapter 26

2. Summary Test engineer Nanette Halliburton explains how information can travel encoded as in a light signal through a communication system Nanette explains the role of reflection and refraction in the transmission of light through a fiber-optic cable as well as the importance of the fiber-optic cable to the country’s communications infrastructure. She then traces an e-mail message from sender to receiver. All the while, Nanette explains the importance of testing.

3. Noise Is anything that interferes with the clarity of a signal. Current traveling through electrical wires creates a magnetic field, which interferes with electrical signals traveling in other wires. Light signals in fiber-optic cables do not have this problem.

4. A message Can be encoded as a light signal. First the signal must be converted from an analog to a digital signal. Then, a laser is turned on and off in sequence with the digital signal. The patter of on-off light pulses travels through a fiber-optic cable at the speed of light.

5. Light Can travel long distances through fiber-optic cables due to the materials used in the cable. Light is reflected as it passes from the core of the optical fiber onto the cladding, which surrounds the core. Refraction is the bending of light that occurs when light moves through one medium to another. The materials of the cladding and core are such that the light is reflected back into the core. It’s as if the light bounces right off of the core wall. This is referred to as Total Internal Reflection.

6. An email message Spends part of its journey encoded as an electrical signal and parts of its journey encoded as a light signal.

7. What does noise refer to in this chapter? Noise is anything that disrupts the signal in a communications system.

8. Why are fiber-optic cables better than telephone wires for transmitting information over long distances? Because the electric signal creates a magnetic field around the wire it travels through. The magnetic field disrupts the current and creates noise in nearby wires. Due to this noise, the electrical signal must be regenerated every mile or so along the wire. With fiber-optic cables the message only has to be regenerated every 50 to 60 miles.

9. Why does the light signal have to be regenerated? The signal must be regenerated because impurities in the glass absorb some of the light and degrade the signal.

10. How can ones and zeros be encoded in a light signal? By flashing the laser light on and off.

11. Nanette is a test engineer. Why is testing a critical part of the development process? Testing is acritical part of the development process because it ensures the product is reliable and well-suited for the real- world market. Examples of the engineers who have tested their designs are Aprille Joy Ericsson (an astronautiacl engineer) and Bob Brown (a design engineer).