- Active scanning:
- In active scanning,
the mobile node takes the
inititive
in finding
a better AP
- When the
signal strength
to the
associated AP drops
below a threshold:
- The moible node will start the active scanning procedure
- In active scanning,
the mobile node takes the
inititive
in finding
a better AP
- The Active Scanning procedure:
- The mobile node
broadcasts a
probe message
to all access points:
- The destination address of the probe frame contains the special "All AP" MAC address
Graphically:
- When an AP receives the probe,
it transmits a response to
the requester to
identify itself:
- The requester node will
associates
itself with the AP
whose signal strength is
the
highest by sending an
Association Request:
The old associated node will also receive the association request:
- This is an indication for the old associated AP to remove the mobile node (and free buffers)
- The mobile node
broadcasts a
probe message
to all access points:
- Fact:
- By default:
- A wireless node will perform both types of scans on all channels allowed by the country of operation
However:
- (While both types of scanning are on by default)
active scanning
is performed only
on channels
on which local government regulations
allow mobile node to
transmit.
- No active scanning on
these channels allowed:
- Channels that are not authorized for unlicensed use
- Channels that require radar detection with dynamic frequency selection (DFS)
- By default: