Infrared Networking Basics

By Brien M. Posey | Nov 9, 2000 | Print this Page
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One of the coolest but least understood native Windows 2000 features is infrared networking. Infrared networking allows you to perform such tasks as transferring files between machines and printing to infrared-enabled printers without the need for wires. In spite of this capability, very few of the Windows 2000 books I've read even mention infrared support. In this article series, I'll explain how you can take advantage of Windows 2000's infrared networking capability. I'll begin by discussing how infrared networking works. I'll then explain how to install, configure, and work with Windows 2000's infrared support.

How It Works

Before you can really appreciate Windows 2000's infrared networking support, it's necessary to understand how infrared networking works. Although some aspects of infrared networking are consistent with traditional networking, many aren't. To see why this is the case, let's compare infrared networking with traditional networking.

A traditional network requires a minimum of two PCs that are equipped with network cards and are attached to a communications medium. Each of these PCs must also have a unique computer name for identification purposes and share a common protocol with the other PCs on the network.

In infrared networking, this definition is revised a bit. Whereas traditional networking requires a minimum of two computers, infrared networking is usually limited to only two computers. Actually, they don't both have to be computers--one of the devices could be a pocket PC or a printer. In spite of the fact that there are usually only two devices involved in infrared communications, a computer name and common protocol are still required. The computer name is required in case multiple infrared devices are present in a given area. The computer name allows the devices to determine which devices should be communicating.

In the case of infrared networking, the infrared port takes the place of the network card. (I'll discuss the infrared port in more detail in a future article.) As far as a communications medium goes, whereas traditional networks use copper wire or fiber, infrared networks don't require a physical connection between the two devices. The only requirement from a connection standpoint is that a direct line of sight exists between the two devices.

The Need for a Protocol

A shared protocol is required even in infrared networking because of the nature of infrared communications. To see why this is the case, it's necessary to understand how infrared communications work on a more basic level. At its simplest, infrared communication involves using an infrared emitter to send pulses of infrared light to an infrared receiver. Infrared light is used instead of other types of light that fall into the spectrum of visible light, because it's less susceptible to interference than visible light.

An example of very simple infrared communication is the remote control for your television or stereo. Such a remote contains an infrared emitter. When you press a button on the remote, it emits pulses of infrared light, which the infrared receiver on the television or stereo receives. In the case of a remote control, a chip inside the remote causes the infrared receiver to flash a different pattern of invisible light for each button pressed. If you hold down a button, the flash pattern repeats.

It's possible to watch an infrared remote function; certain types of digital cameras can record infrared light. In Figure 1, you can see a stereo remote. The image on the left shows a remote with the infrared emitter turned off, as would occur during idle times or between pulses of light. However, the image on the right shows what it looks like when the infrared emitter emits a pulse of light.

Figure 1
Figure 1: An infrared remote emits pulses of infrared light.

A comparable chip inside the device you're controlling is set up to look for the various patterns of flashing light. If the device detects a flash pattern that it recognizes, the action associated with that pattern is performed. If the flash pattern is unrecognized, it's ignored. This prevents the device from functioning erratically in the presence of other types of devices remotes.

I've given this long explanation of how your television remote works because PC-based infrared communications work on the same basic principal. Figure 2 shows a portable PC's infrared port. The left image shows the infrared emitter in the off position, and the image on the right shows the infrared emitter emitting a pulse of infrared light. As you can see, computing devices tend to emit much brighter bursts of infrared light than remotes.

Figure 2
Figure 2: A computer's infrared port emits the same type of infrared light as an infrared remote control.

As you can see from the two examples I've provided, infrared communications work by sending and receiving pulses of infrared light. These pulses consist of periods of light and darkness. In the case of a TV or stereo, these pulses are nothing more than recognized patterns. However, in the case of computing devices, the pulses are binary code. When the infrared emitter is on, it's essentially sending a binary one. Likewise, when the infrared emitter is dark, it's considered to be sending a binary zero.

This is where the need for infrared-based protocols comes in. The protocol regulates the timing of the infrared signal. It makes sure that the receiving device is checking the on/off status of the emitter at the same frequency the emitter intends. For example, if the emitter sent pulses at 4-millisecond intervals, but the receiver was expecting 2-millisecond pulses, then a single pulse of light could be mistaken for two pulses.

The protocols must also negotiate things such as packet length (where one segment of binary code ends and the next one begins). For example, suppose the sender sent the following two packets: 10101100 00110010. Without proper timing, the receiver might pick up part of both packets and think it was a single packet. For example, if the receiver picked up the last four bits of the first packet and the first four bits of the second packet, it would receive the code as 11000011. As you can see, this is much different from the intended message.

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Conclusion

In Part 2 ( Installing and Configuring Infrared Support ), I'll continue the discussion by explaining more of the logistics that must be present for infrared communications between two computing devices. I'll then go on to discuss the way that Windows 2000 supports infrared communications. //

Brien M. Posey is an MCSE who works as a freelance writer. His past experience includes working as the director of information systems for a national chain of health care facilities and as a network engineer for the Department of Defense. Because of the extremely high volume of e-mail that Brien receives, it's impossible for him to respond to every message, although he does read them all.