Symbol Technologies Spectrum24 AP-4131 - Manual (Page 31)

Introduction
AP-4131 Access Point Product Reference Guide 21
An MU can roam within a coverage area by switching APs. Roaming
occurs when:
•
an unassociated MU attempts to associate or reassociate with an
available AP
• the supported rate changes or the MU finds a better transmit rate with
another AP
• the RSSI (received signal strength indicator) of a potential AP exceeds the
current AP
• the ratio of good-transmitted packets to attempted-transmitted packets
falls below a threshold.
An MU selects the best available AP and adjusts itself to the AP direct-
sequence channel to begin association. Once associated, the AP begins
forwarding any frames it receives addressed to the MU. Each frame contains
fields for the current direct-sequence channel. The MU uses these fields to
resynchronize to the AP.
The scanning and association process continues for active MUs. This process
allows the MUs to find new APs and discard out-of-range or deactivated APs.
By testing the airwaves, the MUs can choose the best network connection
available.
1.3.7 Mobile IP
The Internet Protocol identifies the MU point of attachment to a network
through its IP address. The AP routes packets according to the location
information contained in the IP header. If the MU roams across routers to
another subnet, the following situations occur:
•
The MU changes its point of attachment without changing its IP address,
causing forthcoming packets to become undeliverable.
• The MU changes its IP address when it moves to a new network, causing
it to lose connection.
Mobile IP enables an MU to communicate with other hosts using
only its home IP address after changing its point-of-attachment to the
internet/intranet.