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                                   CHAPTER FIVE ANSWERS TO REVIEW QUESTIONS
 

1. Data is protected because guardbands are frequencies used to separate individual signals in an FDM to prevent interference with each other.

2. A modem is built into a frequency division multiplexer to allow the FDM to be connected directly to an analog telephone line.

3. Time slot, wavelength.

4. STDM eliminates wasted time slots when a terminal has nothing to transmit.

5. The devices in a communication network always used in pairs are multiplexers and modems.

6. Cascading multiplexers are used to connect communication lines to another multiplexer.

7. An inverse multiplexer takes high-speed lines and divides the data on them to lower-speed lines. This is the opposite of what occurs with multiplexers. An example of where an inverse multiplexer can be found is in an organization where it is necessary for two host computers to communicate with each other.

8. The functions of both a multiplexer and a concentrator are similar; however, multiplexers must be used in pairs, whereas concentrators are not.

9. A concentrator is used as a switch when it connects multiple terminals to multiple computers.

10. Concentrator.

11. Changes are made to the network control program by adding, deleting, or changing the information about the terminals, generating the NCP listing down the network, and loading the new version of the NCP into the FEP and then bringing the network backup.

12. Network control program is the name of the program that runs in an IBM FEP.

13. The maximum number of terminals that can be connected to a controller is 32.

14. Local controllers are placed near the host computers. Remote controllers are located some distance from the computer.

15. A protocol converter allows communication to occur between terminals and computers that use different protocols.

16. A personal computer equipped with an adapter board that performs protocol conversion makes the computer appear as a specific terminal (an IBM 3270 terminal) wired to an IBM mainframe.

17. Encryption.

18. The two problems a call back unit represents are: the user gets charged for the phone call if a charge back system is in place, and portable terminals cannot be used.

19. A network technician would use a line monitor to look at data as it is transmitted on a line to determine if errors are occurring.

20. Port.