Understanding the wireless landscape, part 1

Wireless Personal Area Networks

WPANs are "cable replacement" technologies designed to connect individual devices to nearby peripherals. For example, WPANs may use wireless to connect PDAs to printers, headsets to cellphones, and PCs to wireless mice and keyboards. WPANs reach up to 33 feet, delivering kilobits per second, depending upon technology and product. Common WPAN technologies include:

Technology	Frequency	Reach	Capacity	Usage Examples
Infrared (IrDA)	850-950 nm	1-2 meters	115 Kbps	Peer-to-peer beaming between PDAs, wireless printing
Bluetooth 1.1 (802.15)	2.4 GHz FHSS	10 meters	780 Kbps	Piconets composed of nearby wireless headsets, Keyboards, MP3 players, and other PC or audio/video peripherals

IrDA ports were once common on PDAs and laptops, but are now being phased out in favor of technologies like Bluetooth that offer greater speed and reach. Bluetooth is well suited for connecting no more than half-a-dozen peripherals to a master device located in the same room. Vendors hope that the recently approved Bluetooth 1.2 specification will increase adoption by adding adaptive frequency hopping to improve peaceful coexistence with other devices sharing the 2.4 GHz band (like cordless phones and Wi-Fi).

Wireless Local Area Networks

WLANs are designed to connect stations to each other and nearby wired networks. For example, WLANs connect home PCs to a residential broadband gateway, traveler laptops to a public Internet hot spot, and business devices (PCs, scanners, cash registers) to a wireless Access Point (AP or WAP). WLANs extend wired networks by untethering LAN stations, giving users wireless access to the public Internet or company intranets. Distance and speed are inversely related, but WLANs usually deliver megabits per second to devices within a few hundred feet. Common WLAN technologies include:

Technology	Frequency	Reach	Capacity	Usage Examples
802.11a	5 GHz DSSS	300 feet	54 Mbps	Hot spots in high user density areas, supporting high bitrate audio-video applications
802.11b	2.4 GHz DSSS	300 feet	11 Mbps	Public wireless hot spots in hotels, convention centers, cafes, and airports, entry-level residential broadband gateways for wireless home networking
802.11g	2.4 GHz DSSS	300 feet	54 Mbps	Fast replacing 802.11b as wireless technology of choice in enterprise LANs, will eventually dominate public and home WLANs as well. Interoperates with 802.11b, but not a.

Products implementing all three 802.11 standards are certified by the Wi-Fi Alliance, but only 802.11b and 802.11g interoperate with each other. Because 802.11a uses a different frequency, an 802.11b station cannot talk to an 802.11a AP. Situations where interoperability is top priority, like wireless Internet in hotels and airports, often use 802.11b. Newer 802.11g products will gradually replace 802.11b, especially in larger WLANs that can benefit from 802.11g's higher capacity.

On the other hand, the frequency range used by 802.11b and 802.11g is relatively crowded, subject to more interference in just three non-overlapping channels. Because it uses the 5GHz band, 802.11a can be a better choice for corporate WLANs that support hundreds of users in one spot, or for wireless links that require higher sustained throughput without interference.

802.11a and 802.11g are both capable of reaching 54 Mbps, but a mixed-mode 802.11b/g WLAN falls far short of this rate. On the other hand, 802.11a data rates drop faster than 802.11g as distance increases. To maximize your options, consider using dual-band, tri-mode A+B+G products -- for example, business users who roam between 802.11a office WLANs and 802.11b/g home WLANs may find tri-mode products worth the extra cost.

Click here to read part 2 of this tip.

About the author: Lisa Phifer is vice president of Core Competence, Inc., a consulting firm specializing in network security and management technology. She is also a site expert to SearchMobileComputing.com and SearchNetworking.com.

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