onnection start-up and disconnection, device address discovery and conflict resolution, data rate negotiation and information exchange. On top of the PHY layer specification, IrDA has two mandatory protocols at the MAC level, as well as a number of optional layers that are available for specific usage models. The mandatory protocols are the link access (IrLAP) and link management (IrLMP) protocols (Figure 10-11). IrDA PHY Layer The IrDA infrared physical specification (IrPHY) covers aspects of the infrared beam such as wavelength, minimum and maximum power levels or irradiance in mW/sr (milliwatts per steradian) and beam angle, as well as the physical configuration of the optical components. Infrared wavelengths of 0.85-0.90 um are specified, since light emitting diodes and optical detectors for these wavelengths are readily available and at low-cost. Two power modes are specified - standard and low-power. Link distances of up to 0.2 m are possible in low-power mode, with a maximum power intensity of 28.2 mW/sr or up to 1m in standard mode with 500 mW/sr maximum power intensity. The IrPHY specification also defines the encoding and framing of data for various transmission speeds, as summarised in Table 10-16. SIR is an asynchronous format that uses the same data format as the standard UART (1 start bit, 8 data bits, 1 stop bit). An RZI modulation Network layer Link Management Protocol (IrLMP) Data Link layer Link Access Protocol (IrLAP) Physical layer Physical layer (IrPHY) OSI Model layers IrDA Mandatory protocols Figure 10-11: IrDA Mandatory Protocol Stack and the OSI Model Wireless PAN Standards Table 10-16: IrDA Data Rates and Modulation Methods Transmission type Data rate Modulation SIR (Serial Ir) 9.6-115.2 kbps FIR (Fast Ir) 0.576-1.152 Mbps 4 Mbps VFIR (Very Fast Ir) 16 Mbps method is used (Figure 10-12), with a short Ir pulse being transmitted for each zero data bit. The Ir pulse is shortened to nominally 3/16th of the bit duration in order to reduce the LED power consumption. FIR and VFIR are synchronou