IrLAP

IrLAP, or Infrared Link Access Protocol, is the data link layer protocol in the Infrared Data Association (IrDA) protocol stack. It provides reliable, connection-oriented communication between infrared-enabled devices over the IrDA physical layer (IrPHY). The protocol handles link establishment and teardown, framing and sequencing of data, flow control, and error detection, enabling point-to-point infrared data transfer between devices such as phones, laptops, and printers. IrLAP frames are HDLC-like and typically fall into Information (I) frames, Supervisory (S) frames, and Unnumbered (U) frames. A sliding window mechanism with sequence numbering supports reliable delivery and in-order reception; a CRC is used for error detection.

IrLAP operates on top of the IrPHY and serves as the basis for higher-layer protocols. It is designed to work with IrLMP, the Link Management Protocol, which handles device discovery, connection management, and support for IrDA profiles and services. The combination of IrLAP and IrLMP enables interoperable infrared communications across a range of devices.

The IrLAP specification covers operation over multiple physical layer speeds defined by IrDA, including SIR (Serial Infrared), MIR (Medium Infrared), and FIR (Fast Infrared). Historically standardized in the IrDA specifications, IrLAP has been largely superseded in modern devices by newer wireless technologies but remains a foundational element in older IrDA implementations.