practice, there are some devices on the market that do not reach one meter, while other devices may reach up to several meters. There are also devices that do not tolerate extreme closeness. The typical sweet spot for IrDA communications is from away from a transceiver, in the center of the cone. IrDA data communications operate in half-duplex mode because while transmitting, a device’s receiver is blinded by the light of its own transmitter, and thus full-duplex communication is not feasible. The two devices that communicate simulate full-duplex communication by quickly turning the link around. The primary device controls the timing of the link, but both sides are bound to certain hard constraints and are encouraged to turn the link around as fast as possible. IrLAP The mandatory IrLAP (Infrared Link Access Protocol) is the second layer of the IrDA specifications. It lies on top of the IrPHY layer and below the IrLMP layer. It represents the data link layer of the OSI model. The most important specifications are: Access control Discovery of potential communication partners Establishing of a reliable bidirectional connection Distribution of the primary/secondary device roles Negotiation of QoS parameters On the IrLAP layer the communicating devices are divided into a "primary device" and one or more "secondary devices". The primary device controls the secondary devices. Only if the primary device requests a secondary device to send, is it allowed to do so. IrLMP The mandatory IrLMP (Infrared Link Management Protocol) is the third layer of the IrDA specifications. It can be broken down into two parts. First, the LM-MUX (Link Management Multiplexer), which lies on top of the IrLAP layer. Its most important achievements are: Provides multiple logical channels Allows change of primary/secondary devices Second, the LM-IAS (Link Management Information Access Service), which provides a list, where service providers can register their services so other devices can access these services by querying the LM-IAS. Tiny TP The optional Tiny TP (Tiny Transport Protocol) lies on top of the IrLMP layer. It provides: Transportation of large messages by SAR (Segmentation and Reassembly) Flow control by giving credits to every logical channel IrCOMM The optional IrCOMM (Infrared Communications Protocol) lets the infrared device act like either a serial or parallel port. It lies on top of the IrLMP layer. OBEX The optional OBEX (Object Exchange) provides the exchange of arbitrary data objects (e.g., vCard, vCalendar or even applications) between