ZyXEL Communications P-320W v3 User Manual page 237

An ESSID (ESS IDentification) uniquely identifies each ESS. All access points and
their associated wireless stations within the same ESS must have the same ESSID
in order to communicate.
Figure 149 Infrastructure WLAN
Channel
A channel is the radio frequency(ies) used by IEEE 802.11a/b/g wireless devices.
Channels available depend on your geographical area. You may have a choice of
channels (for your region) so you should use a different channel than 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.
Note: To comply with US FCC regulation, the country selection function has been
completely removed from all US models. The above function is for non-US
models only.
P-320W v3 User's Guide
Appendix D Wireless LANs
237