21. Which transmission mode is used for data communication along telephone lines?

A. Parallel
B. Serial
C. Synchronous
D. Asynchronous
E. None of the above

22. Who invented the modem?

A. Wang Laboratories Ltd.
B. AT & T Information Systems, USA
C. Apple Computers Inc.
D. Digital Equipment Corpn.
E. None of the above

23. With an IP address starting at 200, you currently have 10 subnets. What subnet mask should you use to maximize the number of available hosts?

A. 192
B. 224
C. 240
D. 248
E. 252

24. Which of the following communications modes support two-way traffic but in only one direction of a time?

A. simplex
B. half-duplex
C. three-quarters duplex
D. full-of the above
E. None of the above

25. Which of the following TCP/IP internet protocol a diskless machine uses to obtain its IP address from a server?

A. RDP
B. RARP
C. RIP
D. X.25
E. None of the above