Infrared is a special form of radio transmission in which a focused ray of light in the infrared frequency spectrum, measured in terahertz, or trillions of hertz (cycles per second), is modulated with information and sent from a transmitter to a receiver over a relatively short distance. Infrared radiation (IR) is the same technology used to control a TV set with a remote control. Unlike radio-frequency (RF) wireless links, IR wireless cannot pass through walls. It requires line of sight communication.
Infrared data communication is playing an important role in wireless data communication due to the popularity of laptop computers, personal digital assistants, digital cameras, mobile telephones, pagers, and other devices. Among existing uses or likely possibilities are:
• Sending a document from your notebook computer to a printer
• Exchanging business cards between handheld PCs
• Coordinating schedules and telephone books between your desktop and notebook computers
• Sending faxes from your notebook computer to a distant fax machine through a public telephone
• Digital cameras that can beam images into your computer.

Infrared communication involves a transceiver (a combination transmitter and receiver) in both devices that communicate. Special microchips provide this capability. In addition, one or both devices may require special software so that the communication can by synchronized. In the IrDA-1.1 standard, the maximum data size that may be transmitted is 2048 bytes and the maximum transmission rate is 4Mbps.
IR can be also be used for somewhat longer interconnections and is a possibility for interconnections within local area networks. The maximum effective distance is somewhat under 1 kilometer and the maximum projected bandwidth is 16 megabits per second. Since IR is line-of-sight light transmission, it is sensitive to fog and other atmospheric conditions.
Infrared wireless communication standards and specifications are globally developed by the non profit organization Infrared Data Association, often referred to as IrDA. IrDA was formed in 1994. It thrives today due to the hundreds of corporate and individual members who volunteer their time and know-how to the continued development of IrDA applications and specifications. At the core of the Infrared Data Association are Special Interest Groups (SIGs). SIGs are responsible for developing the protocols currently used to define the way IrDA-enabled devices discover, negotiate, and transfer data. Today, there are SIGs defining specifications for making infrared wireless payments at POS terminals and vending machines (IrFM), on the technical and marketing requirements for communicating at data rates exceeding 100 Mbit/s (UFIr), on the transfer of digital content at speeds up to 100 mbps or greater (IrBurst) and on defining common standards with traffic toll collection systems (IrTM).