1. Introduction

A Wireless LAN (WLAN) is an on-site network system that removes or reduces the need for wired connections, thereby adding new flexibility to networking. Mobile users can access information and network resources as they attend meetings, collaborate with other users, or move to other locations without the need to find network socket points to plug into. But the benefits of WLANs extend beyond user mobility and productivity. With WLANs, the network itself is movable. WLANs allow a network administrator to set up ad-hoc networks of selected users without the need to install cabling. A conference room of users can be set-up such that they can access a peer-to-peer network of themselves to the exclusion of other users. WLANs are now experiencing broader applicability in a wide range of business settings. Hotspots are being established in the courts for WLANs and this is an opportune moment for law offices to consider WLAN.

This article explains the basic components and technologies of WLANs and how they work together. It explores the factors that law offices must consider when evaluating WLANs for their business needs.

2. Overview

A WLAN (WLAN) is a flexible network system implemented as an extension to, or as an alternative for, a wired local area network within a building or office. Using electromagnetic (radio) waves, WLANs transmit and receive data over the air, minimising the need for wired connections. Thus, WLANs combine data connectivity with user mobility.

Over the last few years, WLANs have gained strong popularity in a number of industries, including health-care, retail, manufacturing, warehousing, and academic institutions. These industries have profited from the productivity gains of using hand-held terminals and notebook computers to transmit real-time information to centralised hosts. WLANs are becoming more widely accepted for general-purpose connectivity in many businesses.

3. Uses of Wireless LANs

Wireless LANs frequently augment rather than replace wired LAN networks – often providing the final few meters of connectivity between a backbone network and the mobile user. The following list describes some of the uses made possible through WLANs:

• Doctors and nurses in hospitals use hand-held or notebook computers with WLAN capability deliver patient information instantly to the hospitals’ central servers.
• Consulting or accounting audit teams or small workgroups can quickly set-up a peer-to-peer network without the need to run unsightly cables in a client’s office.
• Network managers in dynamic environments minimise the cost having to re-run cables when changes are made to sitting arrangements or office layout.
• Training sites at corporations and students at universities use wireless connectivity to facilitate access to information, information exchanges, and learning.
• Network managers installing networked computers in older buildings find that WLANs are a cost-effective network infrastructure solution since older buildings seldom have the needed basic infrastructure for any network cabling.
• Retail store owners use wireless networks to simply frequent network reconfiguration.
• Trade show and branch office workers minimise setup requirements by installing preconfigured WLANs needing no local MIS support.
• Warehouse workers use WLANs to exchange information with central databases and increase their productivity.
• Network managers implement WLANs to provide a quick backup for mission-critical applications running on wired networks.
• Senior executives in conference rooms they have access to real-time information at their fingertips.

4. Benefits of WLANs

The widespread reliance on a local area network among businesses and the meteoric growth of the Internet and online services are strong testimonies to the benefits of shared data and shared resources. With WLANs, users can access shared information without looking for a place to plug in, and network managers can set up or augment networks without installing or moving cables. WLANs offer the following advantages over traditional wired LANs:

1. Mobility
   WLAN systems can provide users with access to real-time information anywhere in their office using their laptops. This mobility supports productivity and service opportunities not possible with wired LANs.
2. Installation Speed and Simplicity
   Installing a WLAN system can be fast and easy and can eliminate the need to pull cable through walls and ceilings.
3. Installation Flexibility
   Wireless technology allows the network to go where cables cannot go.
4. Reduced Cost-of-Ownership
   While the initial investment required for WLAN hardware can be higher than the cost of wired LAN hardware, overall installation expenses over the life span of the equipment can be significantly lower. Long-term cost benefits are greatest in dynamic environments requiring frequent changes to the office layout.
5. Scalability
   Wireless LAN systems can be configured in a variety of topologies to meet the needs of specific applications and installations. Configurations are easily changed and range from peer-to-peer networks suitable for a small number of users to full infrastructure networks of thousands of users that allows roaming over a broad area.

5. Wireless LAN Technology Options

Manufacturers of WLANs have a range of technologies to choose from when designing a WLAN solution. Each technology comes with its own set of advantages and limitations.

1. Spread Spectrum
   Most WLAN systems use spread-spectrum technology, a wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. Spread-spectrum is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission, but the tradeoff produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum signal looks like background noise. There are two types of spread spectrum radio: frequency hopping and direct sequence.
   
2. Narrowband Technology
   A narrowband radio system transmits and receives user information on a specific radio frequency. Narrowband radio keeps the radio signal frequency as narrow as possible just to pass the information. Undesirable crosstalk between communications channels is avoided by carefully coordinating different users on different channel frequencies.
   
3. Frequency-Hopping Spread Spectrum Technology
   Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.
   
4. Direct-Sequence Spread Spectrum Technology
   Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered (and, of course, the more bandwidth required). Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low-power wideband noise and is rejected (ignored) by most narrowband receivers.
   
5. Infrared Technology
   Infrared (IR) systems use very high frequencies, just below visible light in the electromagnetic spectrum, to carry data. Like light, IR cannot penetrate opaque objects; it is either directed (line-of-sight) or diffuse technology. Inexpensive directed systems provide very limited range (3 ft) and typically are used for Personal Area Networks (PANs) but occasionally are used in specific WLAN applications. High performance directed IR is impractical for mobile users and is therefore used only to implement fixed subnetworks. Diffuse (or reflective) IR WLAN systems do not require line-of-sight, but cells are limited to individual rooms.

6. How WLANs Work

Wireless LANs use electromagnetic airwaves (radio and infrared) to communicate information from one point to another without relying on any physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. This is generally referred to as modulation of the carrier by the information being transmitted. Once data is superimposed (modulated) onto the radio carrier, the radio signal occupies more than a single frequency, since the frequency or bit rate of the modulating information adds to the carrier.

Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies. To extract data, a radio receiver tunes in (or selects) one radio frequency while rejecting all other radio signals on different frequencies.

In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an access point, connects to the wired network from a fixed location using standard Ethernet cable. At a minimum, the access point receives, buffers, and transmits data between the WLAN and the wired network infrastructure. A single access point can support a small group of users and can function within a range of less than one hundred to several hundred feet. The access point (or the antenna attached to the access point) is usually mounted high but may be mounted essentially anywhere that is practical as long as the desired radio coverage is obtained.

End users access the WLAN through WLAN adapters, which are implemented as PC cards in notebook computers, or use ISA or PCI adapters in desktop computers, or fully integrated devices within hand-held computers. WLAN adapters provide an interface between the client network operating system (NOS) and the airwaves (via an antenna). The nature of the wireless connection is transparent to the NOS.

Bluetooth technology is a forthcoming wireless personal area networking (WPAN) technology that has gained significant industry support and will coexist with most WLAN solutions. The Bluetooth specification is for a 1 Mbps, small form-factor, low-cost radio solution that can provide links between mobile phones, mobile computers and other portable handheld devices and connectivity to the internet. This technology, embedded in a wide range of devices to enable simple, spontaneous wireless connectivity is a complement to WLANs – which are designed to provide continuous connectivity via standard wired LAN features and functionality.

7. WLAN Configurations

1. Independent WLANs
   1. The simplest WLAN configuration is an independent (or peer-to-peer) WLAN that connects a set of PCs with wireless adapters. Any time two or more wireless adapters are within range of each other, they can set up an independent network. These on-demand networks typically require no administration or preconfiguration and are often used in conference room situations or during trade shows.
   2. Access points can extend the range of independent WLANs by acting as a repeater (see Figure 2), effectively doubling the distance between wireless PCs.
2. Infrastructure WLANs
   In infrastructure WLANs (see Figure 3), multiple access points link the WLAN to the wired network and allow users to efficiently share network resources. The access points not only provide communication with the wired network but also mediate wireless network traffic in the immediate neighborhood. Multiple access points can provide wireless coverage for an entire building or office.
3. Microcells and Roaming
   Wireless communication is limited by how far signals carry for given power output. WLANs use cells, called microcells (see Figure 4), similar to the cellular mobile telephone system to extend the range of wireless connectivity. At any point in time, a mobile PC equipped with a WLAN adapter is associated with a single access point and its microcell, or area of coverage. Individual microcells overlap to allow continuous communication within wired network. They handle low-power signals and hand-off users as they roam through a given geographic area.

8. Setting Up WLANs

The following factors have to be considered when setting up a WLAN:

1. Range/Coverage
   The distance over which radio frequency (RF) waves can communicate is dependant on the product design (including transmitted power and receiver design) and the environment in which the WLAN has to work, especially in indoor environments. Interaction with typical building objects, including walls, metal, and even people, can affect the range and coverage of a particular system. Most WLAN systems use RF because radio waves can penetrate many indoor walls and surfaces. The range (or radius of coverage) for typical WLAN systems varies from under 100 feet to more than 500 feet. Coverage can be extended and true freedom of mobility be achieved via roaming through microcells.
2. Data Throughput
   As with wired LAN systems, actual rate of data throughput in WLANs is dependent upon the product and how it is configured. Factors that affect throughput include airwave congestion (number of users), propagation factors such as range and multipath, the type of WLAN system used, as well as bottlenecks on the wired portions of the WLAN. Typical data rates range from 1 to 11 Mbps, much slower than in wired LANs of 100Mbps.
   
   
3. Mulitpath Effects
   A radio signal can take multiple paths from a transmitter to a receiver, an effect called multipath. Reflections of the signals can cause them to become stronger or weaker, which can affect data throughput. The effect of multipath depends on the number of reflective surfaces in the environment, the distance from the transmitter to the receiver, the product design and the radio technology used.
4. Interoperability with Wired Infrastructure
   Most WLAN systems provide industry standard interconnection with wired systems including Ethernet (802.3) and Token Ring (802.5). Standards based interoperability makes the wireless portion of the network completely transparent to the rest of the network. WLAN nodes are supported by network operating systems (NOS) in the same way any other LAN node. Once installed, the NOS treats the wireless nodes like any other component of the network.
5. Interoperability with Wireless Infrastructure
   There are several types of interoperability that are possible between different WLANs. This will depend both on technology choice and on the specific vendor’s implementation. Products from different vendors employing the same technology and the same implementation typically allow for the interchange of adapters and access points. An eventual goal of standardisation of WLAN specifications is to allow compliant products to interoperate without explicit collaboration between vendors.
6. Interference and Coexistence
   The unlicensed nature of radio-based WLANs means that other products that transmit energy in the same frequency spectrum can potentially provide some measure of interference to a WLAN system. Micro-wave ovens are a potential concern, but most WLAN manufacturers design their products to account for microwave interference. Another concern is the co-location of multiple WLAN systems. While co-located WLANs from different vendors may interfere with each other, others coexist without interference. This issue is best addressed directly with the appropriate vendors.
7. Simplicity/Ease of Use
   Users need very little new information to take advantage of WLANs. Because the wireless nature of a WLAN is transparent to a user’s NOS, applications work the same as they do on wired LANs. WLAN products incorporate a variety of diagnostic tools to address issues associated with the wireless elements of the system; however, products are designed so that most users rarely need these tools. WLANs simplify many of the installation and configuration issues that plague network managers. Since only the access points of WLANs require cabling, network managers are freed from pulling cables for WLAN end users. Lack of cabling also makes moves, adds, and changes trivial operations on WLANs. Finally, the portable nature of WLANs lets network managers pre-configure and troubleshoot entire networks before installing them at remote locations. Once configured, WLANs can be moved from place to place with little or no modification.
8. Security
   Because wireless technology has roots in military applications, security has long been a design criterion for wireless devices. Security provisions are typically built into WLANs, making them more secure than most wired LANs. It is extremely difficult for unintended receivers (eavesdroppers) to listen in on WLAN traffic. Complex encryption techniques make it impossible for all but the most sophisticated to gain unauthorised access to network traffic. In general, individual nodes must be security-enabled before they are allowed to participate in network traffic.However, stories that we hear in the media about the vulnerability of WLANs is often due to improper setting up and configuration of the WLAN system. Users often install a WLAN system “out-of-the-box” without any security features enabled. While the may be alright in a testing environment, once the WLAN system is intended for actual use, it is prudent to consult your vendor about the type of security features to implement. 
9. Cost
   A WLAN implementation includes both infrastructure costs for the wireless access points and user costs for the WLAN adapters. Infrastructure costs depend primarily on the number of access points deployed. The number of access points typically depends on the required coverage region and/or the number and types of users to be serviced. Wireless LAN adapters are required for standard computer platforms. The cost of installing and maintaining a WLAN is generally lower than the cost of installing and maintaining a wired LAN for two reasons. First, a WLAN eliminates the direct costs of cabling and the labor associated with installing and repairing it. Second, because WLANs simplify moves, adds, and changes, they reduce the indirect costs of user downtime and administrative overhead.
10. Scalability
    WLANs can be designed to be extremely simple or quite complex. WLANs can support large numbers of nodes and/or large physical areas by adding access points to boost or extend coverage.
11. Battery Life for Mobile Platforms
    End-user wireless products are capable of being completely untethered, and run off the battery power from their host notebook or hand-held computer. WLAN vendors typically employ special design techniques to maximise the host computer’s battery life.
12. Safety
    The output power of WLAN systems is very low, much less than that of a hand-held cellular phone. Since radio waves fade rapidly over distance, very little exposure to RF energy is provided to those in the area of a WLAN system. WLANs must meet stringent government and industry regulations for safety. No adverse health affects have ever been attributed to WLANs.

9. Conclusion

WLANs are extremely simple and convenient to use in law offices. Many lawyers are already using laptops at their desk as their primary computer. With a WLAN, this laptop can be moved, without any need to reconfigure, to the conference room for meetings with clients where notes can be taken directly onto the laptop or information found in the officer servers can be accessed immediately.

However like all new technologies, implementation must be thought through carefully, especially where security is concerned since access to WLANs are not subject to physical limitations like the walls of the office.

WLAN Glossary

Access Point: A device that transports data between a wireless network and a wired network (infrastructure).

IEEE 802.X: A set of specifications for Local Area Networks (LAN) from The Institute of Electrical and Electronic Engineers (IEEE). Most wired networks conform to 802.3, the specification for CSMA/CD based Ethernet networks. The 802.11 committee completed a standard for 1 and 2 Mbps WLANs in 1997 that has a single MAC layer for the following physical-layer technologies: Frequency Hopping Spread Spectrum, Direct Sequence Spread Spectrum, and Infrared.

Independent network: A network that provides (usually temporarily) peer-to-peer connectivity without relying on a complete network infrastructure.

Infrastructure network: A wireless network centered about an access point. In this environment, the access point not only provides communication with the wired network but also mediates wireless network traffic in the immediate neighborhood.

Microcell: A bounded physical space in which a number of wireless devices can communicate. Because it is possible to have overlapping cells as well as isolated cells, the boundaries of the cell are established by some rule or convention.

Multipath: The signal variation caused when radio signals take multiple paths from transmitter to receiver.

Radio Frequency (RF) Terms: GHz, MHz, Hz: The international unit for measuring frequency is Hertz (Hz), which is equivalent to the older unit of cycles per second. One Mega-Hertz (MHz) is one million Hertz. One Giga-Hertz (GHz) is one billion Hertz. For reference: the standard electrical power frequency is 60 Hz, the AM broadcast radio frequency band is 0.55 -1.6 MHz, the FM broadcast radio frequency band is 88-108 MHz, and microwave ovens typically operate at 2.45 GHz.

Roaming: Movement of a wireless node between two microcells. Roaming usually occurs in infrastructure networks built around multiple access points.

Wireless Node: A user computer with a wireless network interface card (adapter).