Wireless networks allow data transmission without help of cable or fiber. However, typically, device that is capable of wireless transmission is connected to core network through fiber or copper cable. Even thought wired solutions are cheaper and offer higher bandwidth, some installations are incapable of accommodating the cable. Usually it is true for horizontal installations.
Infrared transmission relies on infrared radiation. It is popular for data transmission between TV remote and TV. Infrared signal is sent by laser diode. The signal is not visible by human eye (however it is easily spottable by camera). Receiver part consists of the photo-diode which is capable of converting signal into digital signal. Traditional infrared transmission has very short travel distance compared to cable or fiber solutions. For longer distances higher powered infrared lasers are used. They can rely either on point-to-point or broadcast transmission type.
Point-to-point transmission uses focused high powered infrared laser beams. Both transmitter and receiver should be pointed directly at each other with no obstruction in the view between them. Weather can easily affect transmission if signal travels outside. It is difficult to intercept the signal, since it would require connection break between transmitter and receiver.
Broadcast transmission does not require precise calibration, since the transmitter sends data signal in every direction. However, throughput of such transmission is much lower than the point-to-point one. Also it is not secure, since any receiver could pick up signal without knowledge of the transmitter.
Infrared is advantageous for the LAN/WAN applications due to its low cost and high bandwidth. Compared to other wireless solutions infrared is relatively inexpensive. Most of modern mobile phones has infrared transmitter in order to control TVs and other electronics. Also it offers relatively high bandwidth of up to 2.5 Gbps.
Infrared transmitters are fairly easy to install. The device needs to be plugged in and pointed at the direction of receiver (broadcast device does not need to be pointed). Short range solutions are very portable and have low power requirements.
Disadvantages include need for direct line of sight, and weather attenuation.