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WIRELESS LANS

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Radio frequency connections can add flexibility, scalability and security to your network, cutting overall costs

By J. B. Miles
Special to GCN


Proxim’s RangeLAN2 Series includes a variety of access points and adapters, all with 1.6-Mbps data rates and 1,000-foot optimum ranges. The units operate in the 2.4-GHz frequency.


Now might be the time to consider a wireless LAN for your organization. The industry is hammering out standards and settling interoperability problems. And more products become available every month as the market for wireless LANs, now at $ 1 billion, grows by 40 percent to 60 percent annually.

Wireless LANs use radio frequency or infrared waves to transmit and receive data over the air instead of using copper or fiber-optic cable connections. Users don’t have to search for a place to plug in to a wired network to gain access to shared information. Network managers can make quick network moves and changes without having to disconnect and reinstall a tangle of wiring.

A wireless LAN requires only two components: access points and adapters. Wireless access points are external transmitters and receivers—transceivers—that use an RJ-45, serial or other connection to link to a wired network.

Wireless adapters, equipped with transmit-receive capabilities and antennas, generally come in PC Card formats for notebook computers or as internal ISA/PCI cards for desktop PCs.

Other external adapters use serial or RJ-11 telephone connectors, and still others are fully integrated into handheld computers or scanners.


Lucent Technologies’ WaveLAN series of products includes the WavePoint-II Access Point and several PC Card and ISA adapters, each with a range of 1,800 feet.


Most wireless LANs also come with an array of antenna options that can improve the direction, range or quality of the signal between the access points and adapters. And virtually all manufacturers provide software for setup and configuration.

Access points and adapters commonly used in wireless LANs are remotely manageable via Simple Network Management Protocol remote management software, and Wired Equivalent Privacy encryption is offered as an option with some software.

There are many benefits of wireless LAN technology. In a recent white paper, the Wireless LAN Alliance, a manufacturers’ consortium in Redwood City, Calif., listed five:



Mobility. Wireless LANs give users access to real-time information anywhere in their organization.

Installation speed and simplicity. Installing a wireless LANs can be fast and easy because there’s no need to pull cable through walls and ceilings.

Reduced cost of ownership. The initial investment costs for wireless LAN equipment may be slightly higher than the cost of wired LAN hardware, but overall installation expenses and lifecycle costs can be significantly lower.

Security. By virtue of the spread-spectrum technology that most radio frequency LANs are built around, they are inherently more secure than wired LANs.

Scalability. Wireless LANs can be configured in a variety of topologies to fit changing user needs. The configuration options can take two forms: independent peer-to-peer LANs and infrastructure LANs.

If two or more PCs are connected with wireless adapters, a mobile and flexible on-demand network can be set up in minutes. In an infrastructure LAN, when one or more access points are used to link mobile users to a wired LAN, hundreds of users may be served without the headaches of swapping out wires and cables.


The BreezNet Pro.11 series from Breeze Wireless Communications has optimum ranges of 2,200 feet for the PC Card adapter and 3,000 feet for other products.


Wide area popularity

According to a study commissioned last year by the Wireless LAN Alliance, the average return on investment for a wireless LAN was 8.9 months. And because wireless LANs supply all the benefits of wired LANs with few of the constraints, users love them.

Ninety-seven percent of users said wireless LANs met or exceeded their expectations, 92 percent reported a definite payoff from their use, and 92 percent said plans were under way to deploy more wireless LANs in the future.

Though there are other options (see story, Page 70), wireless LAN products operating in the 2.4-GHz spread-spectrum radio band are best for most users.

The 2.4-GHz band provides more bandwidth than the 900-MHz or 5.7-GHz radio spectrums, which are the only other radio frequency options. The wide 2.4-GHz band allows for relatively fast data throughput, between 1 Mbps and 11 Mbps, for large numbers of users. Because of its Industrial Scientific Medical designation, no license is required to use it.

The 2.4-GHz band also is where most of the IEEE 802.11 and Wireless LAN Interoperability Forum OpenAir standards are being finalized and where interoperability problems between various manufacturers’ products are being solved.

Finally, it gives high levels of data security along with encryption options.

Glossary
Access point. A wireless device that transports data between a wireless network and a wired network.

Adapter. A wireless device that provides an interface between client hardware and the airwaves.

DSSS. Direct Sequence Spread Spectrum, one of two technologies used in 2.4-GHz radio frequency wireless LANs.

FHSS. Frequency Hopping Spread Spectrum, the other technology used in 2.4-GHz radio frequency wireless LANs.

IEEE 802.11. An Institute of Electrical and Electronic Engineers set of standards for wireless LANs.

Independent network. A wireless network that provides temporary peer-to-peer connectivity without relying on a complete network infrastructure.

IR. Infrared systems use high frequencies to carry data and are limited to short distances because IR cannot pass through opaque objects.

Industrial Scientific Medical. Unregulated 900-MHz, 2.4-GHz and 5.7-GHz bands that require no licensing fee.

 Narrowband. Narrowband radio systems transmit and receive information on a specific and narrow radio frequency.

OpenAir. A standard developed by the Wireless LAN Interoperability Forum for 2.4-GHz wireless LANs that focuses on interoperability.

Packet radio network. Often used by state and local law enforcement agencies. Provides relatively slow 19.2-Kbps throughput.

PAN. Personal area network, a short-range point-to point wireless system for personal and small office, home office use that often uses infrared technology.

Radio frequency terms. Hertz is the international standard for measuring frequency in cycles per second. Megahertz is 1 million hertz. Gigahertz is 1 billion hertz.

Wireless node. A user computer with a wireless network adapter.

WMAN. Wireless metropolitan area network, usually developed by a third-party provider that charges fees based on bandwidth use or time.

WWAN. Wireless WAN, often developed by using wireless bridges between LANs.



 Basic 2.4-GHz access points with an RJ-45 Ethernet connector cost between $1,000 and $2,000, depending on options. Client adapters tend to cost between $295 and $695, depending on configurations.

Most of them operate at 100-milliwatt power levels, though some operate at 500 milliwatts.

The range for most 2.4-GHz LAN components running at 1 Mbps or 2 Mbps is from 500 feet indoors to 1,000 feet outdoors, but other factors such as interference sources, number of users and topography must also be entered into the equation.

Site monitoring and link surveying software bundled with many wireless products can help users determine their optimum configurations.

Along with 900-MHz and 5.7-GHz radio frequency systems, 2.4-GHz wireless LANs use spread-spectrum technology that was developed years ago by the military.

Simply stated, spread spectrum trades off bandwidth efficiency for security and reliability.



If the receiver knows the parameters of the spread spectrum signal, the signal itself comes in loud and clear. If it doesn’t, the message looks like background noise to an unintended receiver.

But to further confuse the uninitiated, there are two types of spread-spectrum techniques: Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS).

FHSS uses a narrowband carrier that hops, or changes frequencies, in a pattern known to both the transmitter and receiver. If synchronized, the signal occurs clearly as if it were on a single, logical channel. If not synchronized, the signal appears as indecipherable short-duration noise.

DSSS produces a redundant bit pattern called a chip or chipping code for each bit to be transmitted.

The longer the chip, the easier it is to recover original data if contaminated. DSSS appears as low-power wideband noise to unintended receivers.

Proponents of each technology continue to argue their respective merits, and the systems listed in this guide are evenly split when it comes to the use of FHSS and DSSS.

DSSS’ proponents claim it is the logical pathway to the 11-Mbps throughputs of the future.

That point is supported by the fact that 3Com Corp.’s new 11-Mbps AirConnect and Aironet Wireless Communications Inc.’s Aironet 11-Mbps 4800 Series are both based on DSSS technology.

FHSS is less expensive to implement than DSSS, but it requires more access points to gain 11-Mbps throughput. DSSS transceivers are more expensive, but operate at longer ranges, thus requiring fewer access points.

J.B. Miles, of Pahoa, Hawaii, writes about communications and computers.
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