Which transmission technology besides radio frequency is specified by IEEE 802.11 according to the material?

• A. Infrared (IR) transmissions
• B. Ultrasound transmissions
• C. Microwave backhaul
• D. Visible light communications

Answer: (A)

IEEE 802.11 is defined mainly for wireless LANs using radio frequency, but the material notes infrared transmissions as another specified PHY option. Infrared uses IR light to carry data, which works over short ranges and typically requires line-of-sight, leading RF to be the dominant method for WLANs today. Including infrared in the standard provides an alternative transmission approach, even though it’s less common due to practical limitations like alignment and lower data rates. The other options—ultrasound, microwave backhaul, and visible light communications—are not described as part of IEEE 802.11’s specified transmission technologies in the material, so infrared is the correct alternative mentioned.