Defining the WLAN Requirements
When designing any network, the first step is to determine user
needs. For a WLAN, this includes defining the coverage area. Before you can
determine what you need, you have to decide why you need it. Mobility is most often the reason for
implementing a wireless network, although mobility should not be confused with
providing uninterrupted connectivity with the LAN. So, early in the planning
stage, you must determine the key points at which users will reside, as well as
the most common paths between the primary gathering locations, such as
conference rooms, the offices of key personnel, development labs, and so forth.
Critical to this process is a good diagram of the facility showing what the WLAN
needs to cover.
You also need to determine the minimum speeds users require.
Toward this end, you must have a description of the applications that the users
run. Of course, every network engineer will say that each user needs 100 Mbps,
just as in a wired switched network. However, wireless is not a switched medium.
It is a shared medium. Therefore, not all applications will truly fit well into
a WLAN system. Based on most networks analyzed, network use is in fact very
"peaky"a user requests a download (low speed required), followed by the actual
download (greater speed required). The opposite can be true when uploading
documents. Because traffic loads tend to vary to a great extent, most network
designs require a fraction of the available bandwidth thought of as mission
critical. This does not mean that high-speed networks of 100 Mbps and even
gigabit rates are never needed; after all, the minimum amount of speed required
generally increases over time as more users access a LAN.
It is unlikely that all users in a
LAN will use the same client device. Therefore, you need to determine whether
users need specialty devices on the wireless system, such as bar code readers,
PCI cards, PCMCIA cards, wireless IP phones, or perhaps even wireless print
servers. If so, you need to decide whether it is possible to procure all the end
devices from the same vendor or whether there will be different-vendor products
in the mix. This decision could be very important because of some
vendor-interoperability issues with proprietary features
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