Wireless LAN Systems
A wireless LAN system consists of a set of components and
configurations that satisfy the needs of a particular application. It's possible
to define a general wireless LAN system based on broad application types. Take a
look at some examples.
Home and Small Office Wireless LANs
The use of a wireless LAN in a home or small office avoids the
need to run network cabling to interconnect PCs, laptops, and printers. Just
about anyone can purchase applicable components at an electronics or office
supply store and install a wireless LAN. Installation and configuration of the
wireless LAN is simple.
As shown in Figure 5-4,
a home or small office wireless LAN generally includes a single wireless LAN
router that connects to a broadband Internet connection, such as DSL or cable
modem. The typical range of a wireless LAN router is adequate to cover a house,
apartment, or small office. A router is necessary if there is more than one
network device. For example, a home consisting of one wireless PC, a laptop, and
a printer requires NAT and DHCP to satisfy the addressing needs of all
devices.
An access point alone will also work in a home or small office,
but it will allow only one network device to obtain an IP address and access the
Internet. This occurs because most access points do not implement DHCP and NAT.
The combination of an access point and wired router (see Figure 5-5), however, will suffice for a wireless LAN
router. This might be a less expensive solution than purchasing a wireless LAN
router if you already own an access point or wired router (or both).
tip
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Wireless LAN access points and routers have default security
settings, such as WEP, initially turned off. To prevent someone outside your
home or office from accessing files on your network, activate security controls
when setting up the wireless LAN. |
Enterprise Wireless LANs
A wireless LAN for an enterprise is much more complicated than
for homes and small offices. The main reason is that enterprise wireless LANs
require multiple access points with the need of a substantial distribution
system that interconnects the access points. As show in Figure 5-6, the access points offer overlapping radio
cells that enable users to roam through a facility and access resources on a
wired network. This configuration, often referred to as infrastructure mode, is
the most common for any wireless LAN needing to cover an area greater than
20,000 square feet.
For example, a wireless LAN for a hospital might consist of
hundreds of access points located throughout the hospital. A large array of
Ethernet switches and associated cabling would be necessary to tie everything
together. As with other enterprise wireless LANs, a hospital will likely have
existing hardware that provides DHCP services. As a result, an enterprise
wireless LAN utilizes access points, not wireless LAN routers.
Enterprise wireless LANs also require sophisticated security
mechanisms. More emphasis must be placed on authentication and encryption than
what is necessary for home and small office applications. Read Chapter 8, "Wireless Network Security: Protecting
Information Resources," for more details on wireless LAN security.
tip
|
When deploying an enterprise or public wireless LAN, be certain
to have a wireless LAN specialist perform an RF site survey to assess the
presence of RF interference sources an and determine the optimum placement of
access points and RF channel assignments. |
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Health-care centers, such as hospitals and doctors' offices,
must maintain accurate records to ensure effective patient care. A simple
mistake can cost someone's life. As a result, doctors and nurses must carefully
record test results, physical data, pharmaceutical orders, and surgical
procedures. This paperwork often overwhelms health-care staff, taking 50 to 70
percent of their time. The use of a mobile data collection device that
wirelessly transmits the data to a centralized database significantly increases
accuracy and raises the visibility of the data to those who need the
information. This results in better care given to patients.
Doctors and nurses are also extremely mobile, going from room
to room caring for patients. The use of electronic patient records, with the
ability to input, view, and update patient data from anywhere in the hospital,
increases the accuracy and speed of health care. This improvement is possible by
providing each nurse and doctor with a wireless pen-based computer, such as a
tablet or PDA, coupled with a wireless network to databases that store critical
medical information about the patients.
A doctor caring for someone in the hospital, for example, can
place an order for a blood test by keying the request into a handheld computer.
The laboratory will receive the order electronically and dispatch a lab
technician to draw blood from the patient. The laboratory will run the tests
requested by the doctor and enter the results into the patient's electronic
medical record. The doctor can then check the results through the handheld
appliance from anywhere in the hospital.
Another application for wireless networks in hospitals is the
tracking of pharmaceuticals. The use of mobile handheld bar code printing and
scanning devices dramatically increases the efficiency and accuracy of all drug
transactions, such as receiving, picking, dispensing, inventory taking, and the
tracking of drug expiration dates. Most importantly, however, it ensures that
hospital staff is able to administer the right drug to the right person in a
timely fashion. This would not be possible without the use of wireless networks
to support a centralized database and mobile data collection devices. |
Public Wireless LANs
A public wireless LAN enables anyone
with a wireless LAN NIC-equipped user device to access the Internet. Public
wireless LANs are available from most hotpots, such as airports, convention
centers, hotels, and marinas throughout the world. Good hotspots include those where
people visit regularly on a temporary basis and want access to network
services.
A public wireless LAN is one that anyone can use. This provides
a source of revenue because the hotspot owner can bill subscribers. In some
situations, though, hotspot owners offer free access in order to increase the
use of their establishment.
Wireless LANs for small hotspots are simple. For example, a
coffee shop owner can install a single wireless LAN router that interfaces to a
broadband Internet connection. This configuration is similar to one needed for a
home or small office. Free access encourages patrons to purchase coffee and
other goodies as they surf the web and correspond with e-mail.
In cases where the hotspot owner wants to charge for access,
then the wireless LAN system needs to include an access controller and billing
function as shown in Figure 5-7. When a
user runs her web browser, the access controller automatically redirects her to
a web page that prompts the user to log in or sign up for service. Billing
options include per-minute, per-day, or per-month plans. The billing system
keeps track of usage and automatically charges credit cards.
Large hotspots require multiple access points, comparable to an
enterprise wireless LAN. Public wireless LANs spanning several locations,
however, also requires rather sophisticated access control and billing systems.
A large hotel chain, for example, might deploy public wireless LANs at a hundred
different locations. Users can subscribe for months of access and be able to use
the service from any of the hotels. The access control function in this
situation requires a centralized server that maintains authentication,
authorization, and accounting (AAA) information.
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To offer wireless coverage for their patrons, hotels have been
installing access points in convention centers, ballrooms, meeting rooms,
lobbies, swimming pool areas, and guest rooms.
A hotel wireless LAN can enable guests to do all of the
following during their stay:
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Browse the Web at the pool or in the fitness center.
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Remotely and securely access their corporate networks from
their room.
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Review online schedules and get driving directions.
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Share a high-speed Internet connection with multiple conference
participants.
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Remotely print from guest rooms to printers in the business
center.
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Conduct video conferences with associates or family
members.
The staff and management of hotels can also reap huge benefits
from wireless LANs. For example, the deployment of a wireless LAN makes the
following tasks much easier and efficient:
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Conduct room inspections to see if everything is in order and
no damage was done to the room after guests check out of the hotel. The staff
can check the room and send feedback to the main computer through an
802.11-enabled PDA.
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Perform security and safety inspections to make sure doors are
locked, fire extinguishers are charged, emergency lights are in working order,
and so on. All of the information is updated in real time, saving time and the
possibility of error.
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Keep in contact with maintenance workers by using wireless LAN
phones. Management can contact maintenance whenever needed, resulting in quicker
response times. |
Ad Hoc Wireless LANs
An ad hoc wireless LAN, as Figure 5-8 illustrates, does not utilize access points.
Instead, each individual user device communicates directly with another user
device. The advantage of this configuration is that users can spontaneously form
a wireless LAN quickly. Ad hoc networks are also commonly referred to as
peer-to-peer networks.
For example, an ad hoc wireless LAN makes it easy for someone
to transfer a large file to an associate in a conference room where an
infrastructure wireless LAN is not available. Each user simply configures his
radio NIC to operate in ad hoc mode, and connections are
made automatically. In some cases, the users need to ensure that their IP
addresses are set within the same subnet.
Ad hoc mode is also beneficial for supporting emergency
services where operations might take place in areas where a wired distribution
system for interconnecting access points is not practical. A disaster relief
group, for example, can quickly set up network connections among staff working
in areas afflicted by hurricanes, floods, and terrorist attacks.
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