A WLAN designer must be aware of the different 802.11 standards. A designer
must also be aware of the limitations of 802.11 while designing a WLAN. Because
the standard does not cover communication between APs across the wired
backbone, it is recommended that the WLAN backbone consist of a single product
from a manufacturer. Many applications require features not defined by the
Institute of Electrical and Electronic Engineers (IEEE) such as roaming, load
balancing, and wireless repeaters.
Just as with wired networks, the
topology of WLANs may take many forms
. But in
reference to a WLAN, the term ‘topology’ does not refer to architectures such
as bus or ring. Instead, it refers to the Basic Service Area (BSA), which is
comprised of microcells. Each AP has an area of coverage referred to as a
microcell or cell. In an installation consisting of a single AP this is a very
simple concept. When multiple APs are installed, the cells must overlap so that
the wireless connection is never interrupted while roaming from AP to AP. The
main purpose of a site survey is to locate the proper placement for the APs and
survey the cells to allow for proper overlap. Too much or too little overlap
can cause disruption of the wireless connection to the client.
Sometimes
the topology of the WLAN will be dictated by the layout of the wired LAN to
which the WLAN will be connected
. For
example, if wired connectivity is only available along one side of a 9290 sq m
(100,000 sq ft) warehouse, the distance limitations of a 100 m (328 ft)
Category 5 cable run may not be sufficient to reach the recommended location of
the AP. This is where the site survey engineer will have to be creative. There
are many possible solutions, including the following:
- Wireless hop using a repeater talking back to a wired AP
- A repeater or a hub to extend the Category 5 cable run
- A fiber link to provide connectivity on the other side of the warehouse
A site survey engineer is responsible for not only finding the best
locations for the APs, but also for finding ways to connect the APs to the
wired network. Therefore, it is crucial that the engineer have an understanding
of wired networks. This understanding should cover wired LAN topologies,
standards, and components.