Brocade Mobility 7131N-FGR Access Point Product Reference Guide (Supporting software release 4.0.0.0-35GRN and later) - Manual (Page 33)

Brocade Mobility 7131N-FGR Product Reference Guide 21
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Theory of operations
1
MUs perform partial scans at programmed intervals, when missing expected beacons or after
excessive transmission retries. In a partial scan, the MU scans access points classified as
proximate on the access point table. For each channel, the MU tests for Clear Channel Assessment
(CCA). The MU broadcasts a probe with the ESSID and broadcast BSS_ID when the channel is
transmission-free. It sends an ACK to a directed probe response from the access point and
updates the table.
An MU can roam within a coverage area by switching access points. Roaming occurs when:
• Unassociated MU attempts to associate or reassociate with an available access point
• Supported rate changes or the MU finds a better transmit rate with another access point
• RSSI (received signal strength indicator) of a potential access point exceeds the current
access point
• Ratio of good-transmitted packets to attempted-transmitted packets that fall below a
threshold.
An MU selects the best available access point and adjusts itself to the access point
direct-sequence channel to begin association. Once associated, the access point begins
forwarding frames addressed to the target MU. Each frame contains fields for the current
direct-sequence channel. The MU uses these fields to resynchronize to the access point.
The scanning and association process continues for active MUs. This process allows MUs to find
new access points and discard out-of-range or deactivated access points. By testing the airwaves,
MUs can choose the best network connection available.
Operating modes
The access point can operate in a couple of configurations.
• Access Point - As an Access Point, the access point functions as a layer 2 bridge. The wired
uplink can operate as a trunk and support multiple VLANs. Up to 16 WLANs can be defined
and mapped to access point WLANs. Each WLAN can be configured to be broadcast by one or
both access point radios. A Brocade Mobility 7131N-FGR Access Point can operate in both an
access point mode and Wireless Gateway/Router mode simultaneously. The network
architecture and access point configuration define how the Access Point and Wireless
Gateway/Router mode are negotiated.
• Wireless Gateway/Router - If operating as a Wireless Gateway/Router, the access point
functions as a router between two layer 2 networks: the WAN uplink (the ethernet port) and the
Wireless side. The following options are available providing a solution for single-cell
deployment:
• PPPoE - The WAN interface can terminate a PPPoE connection, thus enabling the access
point to operate in conjunction with a DSL or Cable modem to provide WAN connectivity.
• NAT - (Network Address Translation) on the Wireless interface. Using NAT, the router is
able to manage a private IP scheme. NAT allows translation of private addresses to the
WAN IP address.
• DHCP - The access point can assign private IP addresses.
• Firewall - A Firewall protects against a number of known attacks.