ZyXEL Communications NXC5200 User Manual page 635

An ESSID (ESS IDentification) uniquely identifies each ESS. All access points and
their associated wireless clients within the same ESS must have the same ESSID
in order to communicate.
Figure 259 Infrastructure WLAN
Channel
A channel is the radio frequency(ies) used by wireless devices to transmit and
receive data. Channels available depend on your geographical area. You may have
a choice of channels (for your region) so you should use a channel different from
an adjacent AP (access point) to reduce interference. Interference occurs when
radio signals from different access points overlap causing interference and
degrading performance.
Adjacent channels partially overlap however. To avoid interference due to overlap,
your AP should be on a channel at least five channels away from a channel that an
adjacent AP is using. For example, if your region has 11 channels and an adjacent
AP is using channel 1, then you need to select a channel between 6 or 11.
NXC5200 User's Guide
Appendix E Wireless LANs
635