Infrared data-link transmission occurs between two infrared devices. All transmissions over the link go from the primary (commanding) device to the secondary (receiving) device. The primary role is determined dynamically when a link is established and continues until the connection is closed. Any station that is capable can assume the primary role. When two computers are in range, either one can assume the primary role, so a user can initiate a data transfer on either computer. Some devices may only be capable of assuming the secondary role.
A device creates a link by automatically detecting the other or by a user request. The commanding station sends a connection request at 9,600 bits per second (bps) to the other device (including information such as an address, data rate, and other capabilities). The responding device assumes the secondary role and returns information that contains its address and capabilities. The primary and secondary stations then change the data rate and link parameters to the common set defined by the initial information transfer. Finally, the primary station sends data to the secondary station confirming the connection. The devices are then connected and begin data transfer under control of the primary device.
The Winsock API supports multiple simultaneous connections over a single IrDA link. This feature allows several different programs to use a single infrared device simultaneously. For example, you might place a portable computer within range of a desktop computer to simultaneously send and receive mail, update your calendar and contacts, and print deferred documents. Each activity can be controlled by a separate program on the laptop computer that locates and connects to its corresponding program on the desktop computer.
A single infrared device cannot link simultaneously with more than one other infrared device. However, you can install multiple infrared devices on a computer to provide simultaneous links to multiple infrared devices. For example, using separate infrared devices, a desktop computer can simultaneously print to an infrared port, communicate with a portable computer, and dial a network connection.