WLAN Modes of Operation

WLANs can function in two primary modes of operation—“ad-hoc mode” (also
referred to as “peer-to-peer mode”) and “AP mode.” Each one functions in a
slightly different way and each has advantages within specific situations. Some
networks actually make use of both modes and are thus called “hybrid mode”
networks.
The first mode for WLANs is ad-hoc mode.This is the easiest WLAN mode
to configure and requires the least hardware. An ad-hoc mode WLAN is comprised
of two or more computers communicating directly with each other using
wireless network cards.There is no hardware or software AP used in this type of
WLAN; each computer simply joins the network on an ad-hoc basis. Figure 1.12
shows the design of an ad-hoc mode WLAN.
The second WLAN mode is AP mode. In this WLAN mode, a hardware or
software AP is configured as part of the WLAN design.This AP then provides
connectivity for all of the systems on the WLAN.The wireless network card on
each computer is configured to use a specific AP to connect to a specific WLAN
and all traffic to other computers on the WLAN is brokered through the AP.  Figure 1.13 shows the design of an AP WLAN with both software and a hardware
APs on the network.
Each of these WLAN modes offers benefits and detriments depending on the
WLAN environment that you are trying to configure.Ad-hoc mode WLANs are
very easy to configure and do not require a great deal of effort to set up.There is
no real administrative management required for the network and additional systems
can be added in or removed with almost no effort. While this works well for small
home networks or very small offices, this mode of WLAN does not work well in
most business environments, as there is no ability to centrally manage the WLAN
or supply security for the WLAN. In an ad-hoc network, each computer is responsible
for its own security and the WLAN itself is unmanaged.
AP mode WLANs are slightly more difficult to set up than ad-hoc mode
WLANs, but provide a single point of control and security for the WLAN.This
helps a great deal in keeping the network safe and controlled. Using an AP mode
WLAN does also require either a hardware or software AP in the WLAN design. This adds cost over an ad-hoc WLAN, but is usually the best way to go for most
WLAN designs.
A hybrid mode WLAN makes use of both ad-hoc mode and AP mode.This
configuration is fairly rare because once an AP is added to the WLAN, most
administrators reconfigure all of the systems to use the AP.The design for this
type of WLAN is shown in Figure 1.14.Typically the only time you will run
into this type of configuration is when a WLAN is being switched from ad-hoc
mode to AP mode, and the transition is not yet complete.This certainly is not a
design that an administrator should intentionally introduce to a network.