Solution

The correct answer is Option 4.

Key Points

• Statement A: ALOHA is used for multiple access on a shared medium.
  • ALOHA is a simple communication scheme in which each source in a network sends data whenever there is a frame to send. If the frame collides with another frame, the sender waits for a random amount of time before resending the frame.
• Statement D: CDMA codes are sequences of numbers generated by orthogonal codes.
  • CDMA (Code Division Multiple Access) uses orthogonal codes to separate different users. These codes are unique and enable multiple users to share the same frequency without interference.

Additional Information

• Statement B: TDMA (Time Division Multiple Access) does not use WALSH TABLES for time slot allocation. TDMA allocates distinct time slots to different users, but the allocation is not managed by Walsh tables, which are used in CDMA for spreading codes.
• Statement C: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) was not invented for wireless networks. It was designed for wired Ethernet networks. Wireless networks typically use CSMA/CA (Collision Avoidance) due to the hidden node problem.