The four main design requirements for a WLAN solution are as follows:
- High availability is achieved through system redundancy and proper coverage
area design. System redundancy includes redundant APs on separate frequencies.
Proper coverage area design includes accounting for roaming, automatic rate
negotiation when signal strength weakens, proper antenna selection, and
possibly the use of a repeater to extend coverage to areas where an AP cannot
be used.
- Scalability is accomplished by supporting multiple APs per coverage area
using multiple frequencies or hop patterns. APs can also perform load balancing
if desired.
- Diagnostic tools represent a large portion of management within WLANs.
- Interoperability is achieved through adherence to standards such as
802.11a, b, and g, participation in interoperability associations such as
Wireless Ethernet Compatibility Alliance (WECA), and certification such as FCC
certification.
The factors in proper WLAN design will be discussed here and in
subsequent sections.
The type of client that the customer uses will
affect the WLAN design. Some customers may choose to use Personal Computer
Memory Card International Association (PCMCIA) cards in laptops to provide
mobility to their internal staff and easy connectivity for remote users when
they are in the facility. Some may want to use peripherial component interface
(PCI) cards, giving users the freedom to occasionally move desktop personal
computers (PCs) without having to worry about installing cable. Some may use a
repeater or a workgroup bridge to provide connectivity to remote users without
using standard leased lines or having to worry about attempting to run fiber.
Others may want to use data collection terminals. Some customers may use a
combination of these options.
In an environment where the PCs will
remain stationary most of the time, providing wireless connectivity is a fairly
easy task. For installations of this type, users typically need cells of
54-Mbps or 11-Mbps coverage and will not be overly concerned with their link
speed while moving. Many customers do not fully understand the equipment that
will be installed or what to expect. Some question the reliability of the radio
frequency (RF) link and intend to use the wireless link on a limited basis.
Remember that the actual throughput is less than the theoretical
throughput. There are many factors that limit the link speed, including
overhead, operating system, and the number of users. There is more overhead
associated with the RF link than there is on the wired link. Realistically, the
maximum link speed for 802.11b will be around 7 Mbps. File transfer speeds vary
for different operating systems. Speeds for a Microsoft operating system are
about 5.5 Mbps. Linux speeds are closer to 7 Mbps. The 11-Mbps wireless link
can be thought of as a 10-Mbps wired Ethernet segment when deciding how many
users it can handle.