Bach En Computacion

IrDA Infrared Communications:
An Overview

By
Patrick J. Megowan
David W. Suvak
Charles D. Knutson
Counterpoint Systems Foundry, Inc.
{patm, davesu, knutson}@countersys.com

Biographies:
Patrick Megowan and David Suvak have been involved with the Infrared Data Association
since the beginning. At Hewlett-Packard they created much of the pioneering
HP/Microsoft Windows 95 IrDAsolution. Pat and Dave subsequently founded
Counterpoint Systems Foundry, Inc., to make IrDA software solutions for embedded
systems and non-PC platforms. Counterpoint products are available for major RTOSs and
in stand-alone, DOS, and Windows configurations. Counterpoint is heavily involved in the
ongoing development of standards and technologies. Dr. Charles Knutson is Vice
President of Researchand Development at Counterpoint Systems Foundry.

1.0 Introduction
As infrared data communications, based on standards from the Infrared Data
Association (IrDA), become widely available on personal computers and peripherals, a
timely opportunity exists for effective and inexpensive short range wireless
communications on embedded systems and devices of all types. The IrDA standards weredeveloped rapidly (compared to most standards organizations), and information on the
IrDA protocols has not yet reached every corner of the embedded systems universe. This
paper gives an overview of the IrDA protocols with comments on their use in embedded
environments.
The Infrared Data Association (IrDA) is an industry-based group of over 150
companies that have developed communicationstandards especially suited for low cost,
short range, cross-platform, point-to-point communications at a wide range of speeds.
These standards have been implemented on various computer platforms and more recently
have become available for many embedded applications. Because of their wide acceptance,
the IrDA specifications are now on an accelerated track for adoption as ISO standards.

1.1 What isan IrDA Protocol Stack?
Communications protocols deal with many issues, and so are generally broken into
layers, each of which deals with a manageable set of responsibilities and supplies needed
capabilities to the layers above and below. When you place the layers on top of each other,
you get what is called a protocol stack, rather like a stack of pancakes or a stack of plates.
An IrDAprotocol stack is the layered set of protocols particularly aimed at point-to-point
infrared communications and the applications needed in that environment.

Below is a picture of the IrDA protocol layers. This layering will serve as the
overall structure for much of the remaining discussion.

IAS

IrLAN OBEX

IrCOMM

Tiny TP
IrLMP
IrLAP
Physical Layer
The layers within this stack canbe divided into two groups—required and optional
protocols.

1.2 Required IrDA Protocols
The required layers of an IrDA protocol stack are in unshaded boxes in the
diagram above and include the following:
• Physical Layer: Specifies optical characteristics, encoding of data, and framing
for various speeds.
• IrLAP: Link Access Protocol. Establishes the basic reliable connection.
• IrLMP:Link Management Protocol. Multiplexes services and applications on
the LAP connection.
• IAS: Information Access Service. Provides a “yellow pages” of services on a
device.

1.3 Optional Protocols
The optional protocols are shown above in shaded boxes. The use of the optional
layers depends upon the particular application. The optional protocols are:
•
•
•

TinyTP: Tiny TransportProtocol. Adds per-channel flow control to keep
things moving smoothly. This is a very important function and is required in
many cases.
IrOBEX: The Object Exchange protocol. Easy transfer of files and other data
objects
IrCOMM: Serial and Parallel Port emulation, enabling existing apps that use
serial and parallel communications to use IR without change.

•

IrLAN: Local Area Network...