Samsung MagicLAN SWL-2000P User Manual page 9

• Roaming
Roaming is a service that allows wireless clients to use the network in motion by automatically moving the
connection to an old Access Point into a new Access Point when the clients enter into a new cell.
• Scanning, Beaconing & ESS ID
When a wireless client is initialized, it is necessary for it to find and communicate with the correct group for
wireless devices, including Access Point (AP). At this point, it may search for all the frequency channels and
this process is called "scanning."
There may be multiple APs and network operating at the same time. It may be necessary to ensure that the
station joins with the correct network during the scanning process. To achieve this, each AP is assigned to
be part of a logical group called the Extended Service Set (ESS). The name of this logical group is the ESS
ID. When roaming is operating, there may be several Access Points as part of the same ESS.
After powering up, the wireless client will listen on its default frequency channel. It will be listening for
"beacons" sent by another wireless station or AP. Here, a beacon is a short message containing the ESS ID
that will be broadcast roughly ten times a second.
When the wireless station hears a beacon, if the ESS ID in the beacon matches its own, the client knows that
it is on the correct channel and can communicate with its group. If no beacons are seen, or if the ESS ID
does not match, the wireless client may move to the next frequency channel and repeat this listening
procedure. If all frequency channels have been searched with no matched ESS ID found, it will assume that
it is the first client in the group to wake up and will return to its default channel and start to issue beacons
itself.
In DSSS, this scanning process occurs at start up and may also occur when the client roams between APs.
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