by December 31, 2001 0 comments



WLAN (wireless LAN) is a data-transmission system designed to provide location-independent network access between computing devices by using radio waves rather than a cable infrastructure. In the corporate enterprise, WLANs are usually implemented as the final link between the existing wired network and a group of client computers, giving these users wireless access to the full resources and services of the corporate network across a building or campus setting.

WLANs offer a variety of benefits over traditional wired networks, including productivity, convenience, and cost advantages. These highly mobile, simple, fast and easy-to-install networks, provide access to real time information anywhere in the building and eliminate the need to pull cable through walls. While the initial cost of installation of hardware for WLANs may be higher than wired LAN, the total cost ownership is significantly lower because WLANs eliminate the direct costs of cabling and labor associated with installing and repairing it. WLANs are scaleable and can be implemented in a variety of topologies from peer-to-peer networks suitable for a small number of users, to full infrastructure LANs capable of supporting thousands of users.



WLANs use various types of technology for data transmission. The appropriate technology for a given situation depends on the specific needs of the client. The most common technology is spread-spectrum that consumes more bandwidth but assures high reliability, integrity and security. Between the two spread-spectrum technologies, DSSS (Direct Sequencing Spread Spectrum) and FHSS (Frequency Hopping Spread Spectrum), DSSS is more popular. It generates redundant bit pattern for each bit to be transmitted using broadband carrier that provides higher throughput and makes the connection faster and clearer.

Other technologies used for Wireless data transmission are narrowband technology that uses radio-transmission systems to transmit and receive user information on one specific radio frequency. The radio signal frequency is kept as narrow as possible to minimize cost through simple radio design. Narrowband technology has limited range, reliability, and security. The infrared technology systems use very high frequencies in the electromagnetic spectrum to carry data. Like light, infrared cannot penetrate opaque objects. Infrared technology also has limited range and lower throughput. It is used as directed (or line-of-sight) infrared or diffuse (or reflective) infrared that does not require line-of-sight, but is limited to individual rooms.

Infrared is used mainly for Personal Area Networks. The microwave technology uses low microwave frequencies that allow for range and throughput rates in between those of infrared and spread-spectrum technologies. Microwave works best with a clear line of sight. Licensing is required for Microwave WLANs operating at 18.8 GHz to 19.2 GHz. Line of sight and licensing limitations, coupled with high costs and safety concerns, have inhibited the growth of microwave 
technology.

A radio signal can take multiple paths from a transmitter to a receiver, an attribute called multipath. The number of reflective surfaces, distance from the transmitter to the receiver, product design, the radio technology and antenna being used can cause the transmission to be weakened.

WLAN configurations can be simple or complex. At the most basic level, two PCs with wireless adapter cards can set up an independent network, peer-to-peer wireless LAN, whenever they are in range of one another.

NICs (Network Interface Cards) connect the computer to the WLAN. These are available for both desktop and Laptop use.

The network-management software configures wireless connections, checks their performance and allows the network manager to change them when required.

The first step towards setting up a wireless infrastructure LAN is site survey. A site survey helps determine how and where access points can be placed, to create a seamless WLAN. Each access point has an area of coverage, called microcell, associated with it. At any point in time, a mobile PC equipped with a WLAN adapter, or NIC, must be associated with a single access point and its microcell. Site survey should ensure that individual microcells overlap to allow continuous communication within a wired network.

Access points serve as transmitters/receivers connecting the wireless clients to the wired network. The number of clients an access point can serve can vary. A good thumb rule is 1-50. They extend the range of peer-to-peer WLAN by working as a repeater, doubling the distance between wireless clients and usually have a finite range of 500 feet indoor and 1000 feet outdoor. The access point is connected through a single cable to the wired network that allows it access to the information and resources available on the wired network. All PCs that are equipped with a wireless NIC and within the microsell of the access point get connected to the wired network without the use of cable thus creating a WLAN. A number of access points can be connected to the wired network to allow clients to roam through the network. The client is handed off from one access point to another in a way that is invisible to the client, ensuring unbroken connectivity as long as roaming users stay in range of at least one access point. Network managers can also use extension points that are like access points but are not tethered to the network. They relay signals from the clients to access points or other extension points, giving them the ability to extend the range between two clients. Directional antennas are used when the distance between two WLANs is a mile or more. A directional antenna is placed at each location targeting the other location. The antenna is tethered to an access point allowing each location to share the information and resources of the other.

While WLANs provide installation and configuration flexibility and the freedom inherent in network mobility, customers may have some concerns when considering WLAN systems, including: throughput, security, ease of use, and power source issues.

Whether or not throughput is fast, reliable, and maintains its integrity can depend on a variety of factors like number of users.

More users can cause air-wave congestion which can lead to slower throughput. Throughput improves whenever there is less interference, whether from internal user or external sources. Throughput also improves when mobile users are closer to the access points, hence range is also important. The type of WLAN systems determines the type of throughput. For example throughput and speed for infrared wireless system is different from spread spectrum. Latency and bottlenecks are issues for both wired and WLANs. These have to be addressed by using appropriate management tools to improve throughput. Data rates for most WLANs is with 1-10 Mbps range. This is generally sufficient for most LAN-based office applications. Note that as in the wired Ethernet actual throughput will always be less than maximum. Signal degradation or interference can happen through radio waves, microwave ovens and/ or wireless devices operating at the same frequency.

WLANs have their roots in military technology, so, from their inception, security has been an important priority. In fact, it is extremely difficult for unintended receivers (eavesdroppers) to listen in on WLAN traffic. A WLAN solution can support multiple layers of security. To gain access to the network, you must know the network ID of an access point. Once a user is associated with an access point, they have the same security as provided on the wired network: authentication with login ID and password, and so on. In addition, WEP (Wired Equivalent Privacy), a standards-based security protocol for wireless networks, may be enabled, providing further security. Some WLAN products offer multiple layers of security, like access point locking, user authentication, domain identification and option to scramble wireless data transmissions using encryption.

End user wireless products are designed to run off the AC or battery power from their host notebook or hand-held computer.

WLAN vendors typically employ special design techniques to maximize the host computer’s energy usage and battery life.

In infrastructure WLANs, the WLAN is linked to the wired network, allowing users to efficiently share network resources.

However, wireless devices do not interoperate if they use different technologies. Systems using different frequency bands do not interoperate, even if they both employ the same technology and systems from different vendors may not interoperate even if they both employ the same technology and the same frequency band, because of differences in implementation by each vendor. To counter these issues, an interoperability alliance organization, WECA (Wireless Ethernet Compatibility Alliance), is formed by WLAN providers. WECA’s mission is to certify interoperability of IEEE 802.11 High Rate products and promote that standard for the enterprises, small businesses and homes. Products bearing the WECA logo will interoperate with products from other manufacturers also bearing the WECA logo.

With the recent adoption of new standards for high-rate WLANs, mobile users can realize levels of performance, throughput, and availability comparable to those of traditional wired Ethernet. As a result, WLANs are on the verge of becoming a mainstream connectivity solution for a broad range of business customers. According to Frost and Sullivan, the wireless LAN industry exceeded $300 million in 1998 and will grow to $1.6 billion in 2005. To date, wireless LANs have been primarily implemented in vertical applications such as manufacturing facilities, warehouses, and retail stores and the future will see business segments like healthcare facilities, educational institutions, and corporate enterprise office spaces benefit with the growth of WLANs.

Angie Alfred works for 3Com

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