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By Root 1582 0

—they can’t talk and listen at the same time. IrDA has a mode that emulates full-duplex communication, but it’s really half-duplex. The IrDA protocol offers exactly nothing in the way of encryption or authentication. Infrared’s main security feature is the fact that you have to be literally within arm’s reach to establish a link. Clearly, infrared is not the best solution for a dedicated network connection, but for a quick file transfer or print job without getting your hands dirty, it’ll do in a pinch.

Table 24-2 lists infrared’s important specifications.

Table 24-2 Infrared Specs

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NOTE Many modern laptops still come with a little infrared window, but don’t let that fool you into thinking the laptop has IrDA networking. These IR receivers are for use with remotes so you can use the laptop just like a TV or DVD player.

Bluetooth

Bluetooth wireless technology (named for ninth-century Danish king Harald Bluetooth) is designed to create small wireless networks preconfigured to do very specific jobs. Some great examples are audio devices such as headsets that connect to your smartphones, personal area networks (PANs) that link two PCs for a quick-and-dirty wireless network, and input devices such as keyboards and mice. Bluetooth is not designed to be a full-function networking solution, nor is it meant to compete with Wi-Fi. If anything, Bluetooth has replaced infrared as a means to connect PCs to peripherals.

Bluetooth, like any technology, has been upgraded over the years to make it faster and more secure. Two major versions of Bluetooth are widespread today. The first generation (versions 1.1 and 1.2) supports speeds around 1Mbps. The second generation (2.0 and 2.1) is backward compatible with its first-generation cousins and adds support for more speed by introducing Enhanced Data Rate (EDR), which pushes top speeds to around 3Mbps.

The IEEE organization has made first-generation Bluetooth the basis for its 802.15 standard for wireless PANs. Bluetooth uses the FHSS spread-spectrum broadcasting method, switching between any of the 79 frequencies available in the 2.45-GHz range. Bluetooth hops frequencies some 1600 times per second, making it highly resistant to interference.

Generally, the faster and further a device sends data, the more power it needs to do so, and the Bluetooth designers understood a long time ago that some devices (such as a Bluetooth headset) could save power by not sending data as quickly or as far as other Bluetooth devices may need. To address this, all Bluetooth devices are configured for one of three classes that define maximum power usage in milliwatts (mW) and maximum distance.

Bluetooth is not designed to be a full-fledged wireless networking solution. Bluetooth is made to replace the snake’s nest of cables that currently connects most PCs to their various peripheral devices—keyboard, mouse, printer, speakers, scanner, and the like—but you won’t be swapping out your 802.11-based networking devices with Bluetooth-based replacements anytime soon.

Having said that, Bluetooth-enabled wireless networking is comparable to other wireless technologies in a few ways:

Like infrared, Bluetooth is acceptable for quick file transfers where a wired connection (or a faster wireless connection) is unavailable.

Almost all wireless headsets are now Bluetooth.

Bluetooth’s speed and range make it a good match for wireless print server solutions.

Bluetooth hardware comes either integrated into many newer portable electronic gadgets such as PDAs and cell phones or as an adapter added to an internal or external expansion bus. Bluetooth networking is enabled through ad hoc-styled PC-to-PC (or PDA, handheld computer, or cell phone-to-PC) connections, or in an infrastructurelike mode through Bluetooth access points. Bluetooth access points are very similar to 802.11-based access points, bridging wireless Bluetooth PAN segments to wired LAN segments.

Cellular

A cellular wireless network enables you to connect to the Internet through a network-aware PDA, cell phone, or smartphone.