Wireless LAN Network Adapters
A wireless LAN network adapter represents the hardware device that turns a notebook or desktop computer into a participant, or station, on a wireless LAN. The term “station” is commonly used to refer to a computer communicating via a wireless LAN network adapter. The wireless LAN network adaptercan be obtained in one of three basic form factors. First, the wireless LAN adapter can be obtained mounted on a PCI bus-based adapter card designed for insertion into the system unit of a desktop computer.
Access Point
An access point can be considered to represent a bridge between a wired and wireless network. In fact, the access point functions as a LAN bridge, broadcasting frames that flow on the wired LAN on the air while frames received over the air are transmitted on the wired LAN.Wireless Bridge
We previously noted that an access point operates as a gateway between a wireless and wired network. From a technical perspective, an access point actually functions as a bridge; we examine its operation later in this book. Thus, with this fact in mind, you might be a bit perplexed as to how a wirelessbridge differs from an access point.
We can view a wireless bridge as a wireless gateway between LANs. While similar to an access point, the wireless bridge commonly consists of two components: a base station and a directional antenna. The base station can be considered to represent an access point without an antenna that is cabled to a wired LAN. The base unit is also cabled to a directional antenna, with the latter typically mounted on the outside of a building. Through the use of a very sensitive directional antenna, it becomes possible to extend the transmission distance of a wireless LAN. That extension can be from a few thousand feet up to approximately ten miles, with the latter based on obtaining a line of-sight capability between each wireless bridge antenna.
Wireless Routers
Another wireless LAN networking device we briefly discuss in this section isthe wireless router. In actuality, the wireless router represents an access point
that includes a routing capability and may include a built-in Ethernet switch
capability.
Rationale for Wireless LANs
The key advantage associated with the use of wireless LANs is based on the name of this technology. That is, a wireless LAN represents a communications network formed without the use of wires. While the preceding statement is a bit obvious, what may not be as obvious are some of the benefits that canaccrue due to the ability to form a network based on the transmission medium becoming the ether instead of metallic twisted pair wire.
Thus, let’s turn our attention to the advantages associated with being able to form a communications network that uses the air as the transmission medium.
Advantages of Wireless LAN
Economics
One of the key advantages associated with the utilization of wireless LANs is economics. A large portion of economic savings associated with the use of this technology results from the ability to use the air instead of having to cable clients to a hub in a wired LAN environment. By minimizing the need for conventional metallic-based twisted pair wiring, you avoid not only the cost of the wire, but also the cost of installing the wire. The latter can represent a significant expenditure, especially if in an office environment you need toinstall a conduit to run the twisted pair wiring to satisfy building codes.
Adds, Moves, and Changes
Another major advantage associated with the use of wireless LANs is networking flexibility. This flexibility provides the network manager or LAN administrator with the ability to react quicker to client requirements because the installation of a wireless LAN adapter into a desktop or notebook is the only hardware required at the client site. This means the client does not have to wait for the routing of a cable to his work area. This also means the client will not be captive to the availability of a port on a shared-media hub or LAN switch.When a client relocates, a wireless LAN may continue to provide additional flexibility. If the client relocates to and from locations served by the same access point, the relocation can be accomplished without any hardware or software changes.
When a wireless client relocates beyond the range of the access point currently providing service, the client needs to obtain the services of another access point. In a worst-case situation, a new access point must be installed. If the access points are connected to a wired LAN, this will require the installation of a second
access point as well as its cabling to a hub on the wired LAN. Although this action can be more expensive than simply cabling the client to a hub, if several clients are to be relocated, once again the economics associated with the use of wireless LANs over wired LANs will prevail.
Roaming
Each access point has an area of coverage referred to as a basic service area (BSA).Note that each BSA can be considered an isolated island; however, the wired LAN serves as a mechanism to interconnect the separate BSSs. In doing so, the wired LAN represents a distribution system (DS) and the
interconnected BSSs form an extended service set (ESS).
The ability of a wireless client to move from being serviced by one access point to another is referred to as “roaming.” The ability to effect roaming between areas within a building or on a campus depends on the connection of access points to a wired LAN that provides an infrastructure to interconnect access points. By providing organizational employees with the ability to roam throughout an organization, you enhance their productivity.
For example, an employee with a notebook working at her desk could pick up her computer and carry it to a colleague’s office within the building, to the lunchroom, or to another location within the service area of another access point and regain access to the corporate network. Thus, wireless LANs provide a significant advantage based on their support of roaming.
In fact, as we note later in this chapter, you can take your notebook on the road and access your corporate network, check Internet e-mail, or perform other communications functions through the use of public portals in airports and hotels that provide wireless communications access to the Internet.
Disadvantages to Wireless LANs
While we note a number of advantages associated with the use of wireless LANs, we would be remiss if we did not mention the other side of the coin and discuss some of the disadvantages associated with the use of this technology. Three basic disadvantages are associated with the use of wireless LANs. Those disadvantages include the time, cost, and effort required to learn a new technology; the proliferation of wireless LAN standards; and security.Learning New Technology
Wireless LAN devices are commonly described as “plug-and-play” products. While this is true to a degree, similar to most technologies the use of wireless LANs requires a learning curve. Even after employees are far along the learning curve, it can require a degree of effort to set up an access point as well as configure wireless routers and wireless clients. Thus, the introduction of wireless LANs can be expected to consume some time and effort.Proliferation of Standards
A few years ago, only one wireless LAN standard existed: the IEEE 802.11 standard. That standard defined three transmission methods that could be used to construct a wireless LAN at data rates of 1 Mbps or 2 Mbps. Transmission methods defined under the IEEE 802.11 standard are infrared, frequencyhopping spread spectrum (FHSS), and direct sequence spread spectrum (DSSS). The latter two methods evolved from military research and spread a signal, which makes it more difficult to jam. In a civilian environment these techniques minimize interference from electrical disturbances, such as electrical
magnetic interference created by machinery, lighting ballasts, and even electric pencil sharpeners.
The basic 802.11 standard was quickly supplemented by the 802.11b specification that defined the use of DSSS at data rates of 1, 2, 5.5, and 11Mbps. While an 11-Mbps data rate may be sufficient for home or small office environments, it is often insufficient if a large number of employees within a given area require wireless connectivity. Thus, another addition to wireless LAN standards was the IEEE 802.11a specification
Security
Unlike a wired LAN where illicit monitoring requires a person to obtain a physical connection to a network, wireless LANs communicate over the air. This means that any person with a notebook or desktop computer, wireless LAN adapter card, and appropriate decoding software represents a threat. If you read one of a series of articles published in 2001 in The New York Times or The Wall Street Journal concerning wireless LAN security, you probably became aware of the saga of two men in a van that roamed the parking lots of Silicon Valley corporations. Without requiring anything but off-the-shelf hardware and software, the parking lot duo was able to easily read the communications of many major corporations. The ease by which these gentlemen were able to read the communications of others is based on the fact that, by default, the encryption capability of wireless LANs is disabled. Even if enabled, the encryption that wireless LANs use has been found by several researches to be weak, providing persons with the ability to decrypt interceptedencrypted communications.
Wireless Applications
The diversity of applications that can be supported through the use of wireless LANs represents another rationale for their use. Although we briefly described the use of wireless LANs on the Microsoft Corporation campus and in Starbucks coffee shops, let’s probe a bit deeper and discuss several additional applicationsthat can provide the rationale for using wireless LANs.
Home Use
At first thought, not many persons use a wired LAN in a home environment, so it might be a bit difficult to believe that the use of wireless LANs can be a valuable asset in the home. However, when we consider the advantages associated with the use of wireless LANs as well as a few of the features built into wireless routers, this technology becomes well suited for use in a home environment.According to many market research organizations, over 35 million homes in the United States have Internet access. Of that population, only eight million homes have either cable modem or digital subscriber line (DSL) modem access to the Internet, with the remainder and vast majority of current usage based on conventional modem dial-up access. However, projections indicate that cable modem and DSL access will triple over the next few years, while the population of dial-up modem users will decrease. Because over half of all
homes with cable or DSL modem access have multiple computers, an economical, easy-to-use mechanism that provides the ability for multiple computers to obtain simultaneous Internet access could find a ready market.
College Campus
As a technical consultant to a local college I was asked a few years ago to recommend new technologies the college should consider and the applications the technologies could support. At the top of my list was wireless LANs, as their use could significantly boost productivity of college employees as well as alleviate some awkward and potentially dangerous situations. Let me explain.A few times each year the local college would have a special event that required computers to be placed in the gym for registration. Such events as Parents’ Day, Alumni Day, and normal semester student registration required cables to be routed from a hub located in the athletic office onto the gym floor. Although the cables were taped to the floor, inevitably someone would trip over a cable.
In addition, when it came time to remove the cable, a bit of residue would remain on the wood floor, which required some old fashioned elbow grease to remove. Thus, the installation of a wireless LAN access point in the athletic office would permit computers with wireless LAN adapter cards to be installed on the gym floor without requiring any cabling or after-use cleanup.
In addition to facilitating registration, the use of wireless LANs provides colleges with the ability to rapidly respond to ad hoc faculty requirements for computer support. For example, assume 20 students register for a course that only 12 were expected to attend. Assuming the course requires hands-on computer access as well as the ability to access the college server or the Internet, the decision criteria might normally be to add cabling to support eight additional computers. However, if a hub does not have eight additional ports, a significant network upgrade might be required to accommodate the additional computers. This could be both costly and time-consuming.
However, if an access point is cabled to the hub, it becomes possible to support not only the eight additional computers, but a significant additional number as well should it become necessary. By stacking several access points and a few dozen wireless LAN adapter cards, it becomes possible for the college to
respond to rapidly evolving networking requirements.