21. Which of the following communication mode support two-way traffic but in only one direction at a time?
- Simplex
- Half-duplex
- Three-quarters duplex
- Full duplex
Answer : B Explanation: Half-duplex mode support two-way traffic but in only one direction at a time.
22. Unmodulated signal coming from a transmitter is known as:
- Baseband signal
- Primary signal
- Carrier signal
- None of the above
Answer : A Explanation: Unmodulated signal coming from a transmitter is known as: Baseband signal.
23. In TDM, slots are further divided into ________
- Seconds
- Packets
- Bits
- Frames
Answer : D Explanation: Time division multiplexing (TDM) is technique for combining several low rate channels to a single high rate channel. In TDM, slots are further divided into frames.
24. On a simplex data link, which of the following is a possible error recovery technique?
- Backward error correction (BEC)
- The use of hamming codes
- Downward error correction (DEC)
- Automatic Repeat Request (ARQ)
Answer : B Explanation: The hamming codes is an error recovery technique that can be used to detect and correct the errors and on a simplex data link, this is a possible error recovery technique. This technique was developed by R.W. Hamming.
25. A device that connects to a network without the use of cables is said to be
- Centralized
- Distributed
- Wireless
- Open source
Answer : C Explanation: A device that connects to a network without the use of cables is said to be wireless.
26. Which layer is responsible for the delivery of a message from one process to another?
- Transport
- Physical
- Application
- Network
Answer : A Explanation: Transport layer is responsible for the delivery of a message from one process to another. So option A is correct.
27. The geostationary satellite used for communications systems
- Rotates with the earth
- Remains stationery relative to the earth
- Is positioned over equator
- All of the above
Answer : D Explanation: All of the above is correct.
28. In which layer the various services will be provided directly to the users?
- Session layer
- Presentation layer
- Application layer
- Datalink layer
Answer : C Explanation: In application layer the various services will be provided directly to the users.
29. Which of the following statements could be valid with respect to the ICMP (Internet Control Message Protocol)?
- It reports all errors which occur during transmission.
- A redirect message is used when a router notices that a packet seems to have been routed wrongly.
- The “destination unreachable” type message is used when a router cannot locate the destination.
- It informs routers when an incorrect path has been taken.
Answer : B Explanation: A redirect message is used when a router notices that a packet seems to have been routed wrongly is the correct answer.
30. Data communications system depends on four fundamental characteristics:
- Timeliness
- Sender
- Receiver
- Medium
Answer : A Explanation: The data communications system depends on four fundamental characteristics: Delivery, timeliness, accuracy and jitter.
