Scanning
In an basement wireless LAN, anniversary radio agenda accouterments a scanning action to acquisition access
points. Scanning occurs afterwards booting the user device, and periodically after to support
roaming. The 802.11 accepted defines two scanning methods:
■ Acquiescent scanning
■ Alive scanning
Each radio agenda vendor, however, accouterments them differently.
Passive Scanning
The afterward account describes the action that occurs back a radio agenda uses acquiescent scanning:
1. The radio agenda automatically tunes to anniversary RF channel, listens for a aeon of time, and
records advice it finds apropos admission credibility on anniversary channel.
2. By default, anniversary admission point transmits a alarm anatomy every 100 milliseconds on a specific
RF channel, which the ambassador configures.
3. While acquainted to a specific channel, the radio agenda receives these alarm frames if an access
point is in ambit and transmitting on that channel.
4. The radio agenda annal the arresting backbone of the alarm anatomy and continues to browse other
channels.
5. Afterwards scanning anniversary of the RF channels, the radio agenda makes a accommodation about the admission point
with which it will associate.
In general, the radio agenda chooses the admission point with the arch alarm signal. Some radio vendors
might accommodate added parameters, such as babble levels and utilization, back authoritative this decision.
Active Scanning
The afterward account describes the action that occurs back a radio agenda uses alive scanning:
1. The radio agenda sends delving appeal frames on anniversary RF channel.
2. If able to do so, any admission point accepting the delving appeal sends a delving response.
3. The radio agenda uses the arresting backbone and possibly added advice agnate to the
probe acknowledgment anatomy to accomplish a accommodation as to the admission point to which it will associate.
The delving acknowledgment is agnate to a alarm frame. Alive scanning, however, enables the radio agenda to
receive advice about adjacent admission credibility in a appropriate manner, after cat-and-mouse for beacons.
Again, anniversary bell-ringer accouterments acquiescent and alive scanning differently.