Before you purchase components for a wireless LAN, make sure you specify what the system should do. Surprisingly, many businesses overlook this crucial step. Incomplete and missing requirements are the major reason such LANs fail, leading to time-consuming and expensive attempts to correct the inadequacies of the installed system.
Be certain to first define the following requirements:
- Coverage and mobility. Specifying the coverage, or
area where the end-users will operate the wireless devices, helps the designer
determine the number and location of wireless LAN access points. Mobility
requirements derive from the movement of users through the coverage areas. For example,
a wireless network in a hospital may need to provide continuous connectivity in
specific wards and clinics, but not within operating rooms and office areas.
It's generally best to illustrate the coverage areas on drawings of the facility or building.
- Application requirements. These specify the transmission needs of the software that will operate over the wireless LAN. For example, warehouse management system software requires the transmission of relatively low-bandwidth bar-code information between wireless handheld bar-code scanners and a host computer. A desktop video application, however, requires the transmission of realtime video signals. How frequently you expect to use these different information types helps determine the design specifications for your data transmission rate and throughput.
- Number of users. Simply put, this is the number of devices that require access to the wireless LAN. Be sure to allow for future expansion.
- End-user device types. Included in this category are laptop computers, bar-code data collectors, and mobile patient monitors. You should identify the available physical interfaces -- such as PC Card, PCI, ISA, or USB -- for each device.
- Battery longevity. For mobile and portable applications, specify the length of time the end-user devices need to operate on a set of batteries. A mobile patient-monitoring device, for example, may need to operate for at least 72 hours, the typical length of an inpatient hospital stay. This information indicates whether wireless LAN components need to support power-management functions.
- System interfaces. Most likely, the wireless LAN will have to interface with existing systems such as Ethernet networks, applications, and databases. The system interface requirements describe the architectures and communications protocols of these systems.
- Information security requirements, or the level of protection your data needs from particular threats. The degree of needed security depends on the severity of the consequences the organization faces if data is lost. Military and law enforcement agencies require high-level security. Other organizations probably require much lower levels. These requirements determine whether you should include mechanisms such as encryption.
- Environment. Conditions such as the room temperature and humidity, construction materials, floor space, and presence and intensity of electromagnetic waves could affect the operation of the system. In most cases, you should perform a site survey to inspect the facility and evaluate the presence of potential radio-frequency interference.
- Schedule. Identify any circumstances that will affect the schedule, such as the availability of funds, an urgency to see a return on investment, the availability of project team members, and the interdependency between this project and others. Spell out the schedule requirements so the team knows the time frames it must work within.
- Budget. An organization may have a limited amount of money to spend on the wireless LAN. If you know the budget constraints, it's best to identify them in the requirements.
By defining these requirements, you'll have made a solid foundation for designing a wireless LAN. Next time I'll cover your next step: determining the components and configurations that meet specific requirements.