When a network administrator installs an AP, the administrator assigns a oneor
two-word Service Set Identifier (SSID) to the access point. (When you “view
available networks” in Microsoft Windows XP, for example, a list is displayed
showing the SSID of each AP in range.) The administrator must also assign a channel
number to the AP. To understand channel numbers, recall that 802.11 operates in
the frequency range of 2.4 GHz to 2.485 GHz. Within this 85 MHz band, 802.11
defines 11 partially overlapping channels. Any two channels are non-overlapping if
and only if they are separated by four or more channels. In particular, the set of
channels 1, 6, and 11 is the only set of three non-overlapping channels. This means
that an administrator could create a wireless LAN with an aggregate maximum
transmission rate of 33 Mbps by installing three 802.11b APs at the same physical
location, assigning channels 1, 6, and 11 to the APs, and interconnecting each of the
APs with a switch.