7.1 IrDA in More Detail

There are currently four versions of IrDA; their differences are mainly in the transfer speed. They are:

Serial Infrared (SIR)

This is the original standard with a transfer speed of up to 115 Kbps.

Medium Infrared (MIR)

Improved transfer speed of 1.152 Mbps. Not widely implemented.

Fast Infrared (FIR)

Speed of up to 4 Mbps. Most new computers implement this standard. Windows 2000 and XP support this implementation.

Very Fast Infrared (VFIR)

Speed of up to 16 Mbps. Not widely implemented yet.

Future versions of the IrDA will boost speed up to 50 Mbps.

When two devices with two different IrDA implementations communicate with each other, they will both step down to the lower transfer speed.

In terms of operating range, infrared devices can communicate up to one or two meters. Depending on the implementation, if a device uses a lower power version, the range can be stepped down to a mere 20 to 30 cm. This is crucial for low-power devices.

All data packets exchanged are protected using a Cyclic Redundancy Check (CRC), which uses a number derived from the transmitted data to verify its integrity. CRC-16 is used for speeds up to 1.152 Mbs and CRC-32 is used for speeds up to 4 Mbs. The IrDA also defines a bi-directional communication for infrared communications.