How Wireless Networking Works
The wireless network adapter you use to connect a PC to your wireless network transmits data by radio waves. But unlike an FM radio transmitter, your wireless networking equipment sends a signal that can only be picked up for about 300 feet if there are no obstructions (and this kind of performance is usually achieved outside only). As with wired networking technology, such as Ethernet, data is transmitted over a wireless network in pieces, called data packets. Each network adapter has its own unique serial number, called a MAC (media access control) address. You can see the MAC address of your wireless network adapter, as it’s usually printed on the underside of the adapter. The data packet contains the data being sent as well as the address of the sender and recipient. Wi-Fi (802.11b) wireless networks, as well as 802.11g equipment, communicate over the unlicensed 2.4-GHz radio band. They share the band with other home electronics, including cordless phones and microwaves. Wi-Fi5 (or 802.11a) wireless networks use the less crowded 5GHz band, and therefore are less affected by home electronics. While operating at up to five times faster than Wi-Fi (802.11b) equipment, the hardware looks just the same (Figure 2.6).
Other Wireless Networks
Many PDAs, cell phones, and laptops can transmit data at very high frequencies using beams of infrared light. Devices that use an infrared wireless technology called IrDA (Infrared Data Association) can communicate with each other. You could print a document from a laptop to a printer, for instance, or transmit (beam) contact information from one PDA to another. IrDA is a line-of-sight technology, which means that the devices much be lined up in a straight line to communicate. Bluetooth is another technology used to transfer data wirelessly. Bluetooth is found in PDAs and cell phones and can be used to transfer data to laptop and desktop computers and printers. Like 802.11b and HomeRF networking equipment, Bluetooth operates in the 2.4 GHz band, does not require a line of sight between components, and can pass through walls. Bluetooth technology is sometimes referred to as a personal area network (PAN). The technology has a more limited range (about 10 meters) and less speed (720 kilobits per second) than wireless LAN equipment, such as 802.11b.
Wireless network adapters can communicate directly with each other. Each network adapter acts as a transmitter and receiver, and data is broadcast in a cell. As the cells interlock, the network’s range expands. A wireless network in which the network adapters communicate directly with each other is called a peer-to-peer network, or is said to be working in ad-hoc mode. Wireless networks can also work in infrastructure mode, which requires the use of a hardware device that communicates with each network adapter, called an access point (Figure 2.7).
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