Specifications

Introduction
Altitude 3500 Series Access Point Product Reference Guide
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● MUs encryption and authentication capabilities
● MUs supported data rate
MUs perform pre-emptive roaming by intermittently scanning for access points and associating with the
best available access point. Before roaming and associating, MUs perform full or partial scans to collect
Altitude 35xx statistics and determine the direct-sequence channel used by the access point.
Scanning is a periodic process where the MU sends out probe messages on all channels defined by the
country code. The statistics enable an MU to reassociate by synchronizing its channel to the access
point. The MU continues communicating with that access point until it needs to switch cells or roam.
MUs perform partial scans at programmed intervals, when missing expected beacons or after excessive
transmission retries. In a partial scan, the MU scans Altitude 35xxs 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 Altitude 35xx 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 falls 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 the MUs to find
new access points and discard out-of-range or deactivated access points. By testing the airwaves, the
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. Each WLAN can
be configured to be broadcast by one or both Altitude 35xx radios. An Altitude 3510 or Altitude 3550
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: