Infrared Data Association
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The Infrared Data Association (IrDA) defines physical specifications communications protocol standards for the short range exchange of data over infrared light, for uses such as personal area networks (PANs).
- IrDA is a very short-range example of free-space optical communication.
- IrDA interfaces are used in palmtop computers and mobile phones.
- IrDA specifications include IrPHY, IrLAP, IrLMP, IrCOMM, Tiny TP, IrOBEX, and IrLAN. IrDA has now produced another standard, IrFM, for Infrared financial messaging also known as "Point & Pay".
For the devices to communicate via IrDA they must have a direct line of sight.
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IrPHY
The mandatory IrPHY (Infrared Physical Layer Specification) is the lowest layer of the IrDA specifications. The most important specifications are:
- range (1.0m, low-power 0.1m)
- angle
- speed (2.4kbit/s - 16Mbit/s)
- modulation
- Infrared window
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
- Negotiation of the Primary/Secondary device roles
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 it is 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 via 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.
IrOBEX
The optional IrOBEX (Infrared Object Exchange) provides the exchange of arbitrary data objects (e.g. vCard, vCalendar or even applications) between infrared devices. It lies on top of the Tiny TP protocol, so Tiny TP is mandatory for IrOBEX to work.
IrLAN
The optional IrLAN (Infrared Local Area Network) provides the possibility to connect an infrared device to a local area network. There are three possible methods:
- Access Point
- Peer to Peer
- Hosted
As IrLAN lies on top of the Tiny TP protocol, the Tiny TP protocol must be implemented for IrLAN to work.
See also
External links
- Infrared Data Association website with the original specifications available for free (http://www.irda.org/)
- Linux Infrared HOWTO (http://www.tldp.org/HOWTO/Infrared-HOWTO/)
- Linux Infrared Remote Control (http://www.lirc.org)
- Linux status of infrared devices (IrDA, ConsumerIR, Remote Control) (http://tuxmobil.org/ir_misc.html)de:IrDA
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