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.
Figure 5-4. Wireless LANs in Home or Small Offices Have a Simple Configuration
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).
Figure 5-5. Combining a Wireless LAN Access Point and an Ethernet Router Offers the Same Functionality of a Wireless LAN Router
tip
 | 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.
Figure 5-6. Enterprise Wireless LANs Require a Substantial Amount of Cabling to Interconnect Access Points
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. |
Wireless LANs Good for PatientsHealth-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.
note
 | Locate a nearby public wireless LAN hotspot at http://www.wi-fihotspotlist.com/. |
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.
Figure 5-7. Public Wireless LANs Require Components That Fall Outside the Scope of Wireless Networking Technologies
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.
Wireless LANs in HotelsTo 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:
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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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.
Figure 5-8. Ad Hoc Wireless LANs Offer Simple Setup and Operation
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.
