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Infrared Data Association

From Wikipedia, the free encyclopedia

IrDA Logo

IrDA via USB

The Infrared Data Association (IrDA) is an industry-driven interest group that was founded in 1993 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, and the name "IrDA" also refers to that set of protocols. The main reason for using IrDA had been wireless data transfer over the “last one meter” using point-and-shoot principles. Thus, it has been implemented in portable devices such as mobile telephones, laptops, cameras, printers, and medical devices. Main characteristics of this kind of wireless optical communication is physically secure data transfer, line-of-sight (LOS) and very low bit error rate (BER) that makes it very efficient.

Contents

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1Specifications

Specifications

IrDA protocol stack

IrPHY

The mandatory IrPHY (Infrared Physical Layer Specification) is the physical layer of the IrDA specifications. It comprises optical link definitions, modulation, coding, cyclic redundancy check (CRC) and the framer. Different data rates use different modulation/coding schemes:

SIR: 9.6–115.2 kbit/s, asynchronous, RZI, UART-like, 3/16 pulse
MIR: 0.576–1.152 Mbit/s, RZI, 1/4 pulse, HDLC bit stuffing
FIR: 4 Mbit/s, 4PPM
VFIR: 16 Mbit/s, NRZ, HHH(1,13)
UFIR: 96 Mbit/s, NRZI, 8b/10b
GigaIR: 512 Mbit/s – 1 Gbit/s, NRZI, 2-ASK, 4-ASK, 8b/10b

Further characteristics are:

Range:

standard: 1 m;
low-power to low-power: 0.2 m;
standard to low-power: 0.3 m.
The 10 GigaIR also define new usage models that supports higher link distances up to several meters.

Angle: minimum cone ±15°
Speed: 2.4 kbit/s to 1 Gbit/s
Modulation: baseband, no carrier
Infrared window (part of the device body transparent to infrared light beam)
Wavelength: 850–900 nm

The frame size depends on the data rate mostly and varies between 64 B and 64 kB. Additionally, bigger blocks of data can be transferred by sending multiple frames consecutively. This can be adjusted with a parameter called "window size" (1–127). Finally, data blocks up to 8 MB can be sent at once. Combined with a low bit error rate of generally <10⁻⁹, that communication could be very efficient compared to other wireless solutions.

IrDA transceivers communicate with infrared pulses (samples) in a cone that extends at least 15 degrees half angle off center. The IrDA physical specifications require the lower and upper limits of irradiance such that a signal is visible up to one meter away, but a receiver is not overwhelmed with brightness when a device comes close. In practice, there are some devices on the market that do not reach one meter, while other devices may reach up to several meters. There are also devices that do not tolerate extreme closeness. The typical sweet spot for IrDA communications is from 5 to 60 cm (2.0 to 23.6 in) away from a transceiver, in the center of the cone. IrDA data communications operate in half-duplex mode because while transmitting, a device’s receiver is blinded by the light of its own transmitter, and thus full-duplex communication is not feasible. The two devices that communicate simulate full-duplex communication by quickly turning the link around. The primary device controls the timing of the link, but both sides are bound to certain hard constraints and are encouraged to turn the link around as fast as possible.

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
Distribution of the primary/secondary device roles
Negotiation of QoS parameters

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, is it 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 by 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.

OBEX

The optional OBEX (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 OBEX 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: