21. Which method of delta modulation detects changes from the previous value?
a) Modulator
b) Demodulator
c) Encoder
d) Decoder

22. What is the primary advantage of asynchronous serial transmission?
a) High speed
b) Simple implementation
c) Synchronization

d) Low error rate

23. Which network type relies on a fixed path established before data transmission?
a) Circuit-switched network
b) Datagram network
c) Virtual circuit network
d) Packet-switched network

24. Which method of switching treats each packet as a distinct entity?
a) Circuit switching
b) Datagram switching
c) Virtual circuit switching
d) Packet switching

25. What resource reservation method is used in virtual circuits?
a) Dynamic allocation
b) First-Come-First-Serve
c) Static allocation
d) Guaranteed allocation

26. What is the primary advantage of phase shift keying over ASK and FSK?
a) Bandwidth efficiency
b) Power efficiency
c) Speed
d) Error correction

27. How does amplitude shift keying represent binary data?
a) By modifying frequency
b) By modifying phase
c) By modifying amplitude
d) By modifying time duration

28. What resource is primarily conserved in multiplexing?
a) Time
b) Bandwidth
c) Power
d) Voltage

29. What is the primary disadvantage of virtual circuits?
a) High complexity

b) Low reliability
c) High cost
d) Low speed

30. How are data packets handled in datagram networks?
a) Assigned fixed paths
b) Processed sequentially
c) Routed dynamically
d) Guaranteed priority