Specifications

Introduction
Altitude 35x0 Access Point Product Reference Guide22
to another. The bridge forwards packets addressed to unknown systems to the Default Interface
(Ethernet).
The access point internal stack interface handles all messages directed to the access point. Each stores
information on destinations and their interfaces to facilitate forwarding. When a user sends an ARP
(Address Resolution Protocol) request packet, the access point forwards it over all enabled interfaces
except over the interface the ARP request packet was received.
On receiving the ARP response packet, the access point database keeps a record of the destination
address along with the receiving interface. With this information, the access point forwards any directed
packet to the correct destination. Transmitted ARP request packets echo back to other MUs. The access
point removes from its database the destination or interface information that is not used for a specified
time. The AP refreshes its database when it transmits or receives data from these destinations and
interfaces.
Media Types
The access point radio interface conforms to IEEE 802.11a/b/g specifications. The interface operates at a
maximum 54Mbps (802.11a radio) using direct-sequence radio technology. The access point supports
multiple-cell operations with fast roaming between cells. Within a direct-sequence system, each cell can
operate independently. Adding cells to the network provides an increased coverage area and total
system capacity.
The RS-232 serial port provides a Command Line Interface (CLI) connection. The serial link supports a
direct serial connection (assuming a DB9 connector is used). The access point is a Data Terminal
Equipment (DTE) device with male pin connectors for the RS-232 port. Connecting the access point to a
PC requires a null modem serial cable.
MU Association Process
An access point recognizes MUs as they begin the association process. An access point keeps a list of
the MUs it services. MUs associate with an access point based on the following conditions:
● Signal strength between the access point and MU
● Number of MUs currently associated with the access point
● MUs encryption and authentication capabilities
● MUs supported data rate
MUs perform pre-emptive roaming by intermittently scanning for access point’s and associating with
the best available access point. Before roaming and associating, MUs perform full or partial scans to
collect 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 ’s 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 and updates the table.