Specifications

Introduction
Altitude 3500 Series Access Point Product Reference Guide
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● Direct-Sequence Spread Spectrum on page 31
● MU Association Process on page 31
● Operating Modes on page 32
● Management Access Options on page 33
● Altitude 35xx MAC Address Assignment on page 33
Wireless Coverage
An access point establishes an average communication range with MUs called a Basic Service Set (BSS)
or cell. When in a particular cell, the MU associates and communicates with the access point supporting
the radio coverage area of that cell. Adding access points to a single LAN establishes more cells to
extend the range of the network. Configuring the same ESSID (Extended Service Set Identifier) on all
access point makes them part of the same Wireless LAN.
Access points with the same ESSID define a coverage area. A valid ESSID is an alphanumeric, case-
sensitive identifier up to 32 characters. An MU searches for an access point with a matching ESSID and
synchronizes (associates) to establish communications. This device association allows MUs within the
coverage area to move about or roam. As the MU roams from cell to cell, it associates with a different
access point. The roam occurs when the MU analyzes the reception quality at a location and determines
a different access point provides better signal strength and lower MU load distribution.
If the MU does not find an access point with a workable signal, it can perform a scan to find any AP. As
MUs switch APs, the AP updates its association statistics.
The user can configure the ESSID to correspond to up to 16 WLANs on each 802.11a or 802.11b/g radio.
A Wireless Local Area Network (WLAN) is a data-communications system that flexibly extends the
functionalities of a wired LAN. A WLAN does not require lining up devices for line-of-sight
transmission, and are thus, desirable. Within the WLAN, roaming users can be handed off from one
access point to another like a cellular phone system. WLANs can therefore be configured around the
needs of specific groups of users, even when they are not in physical proximity.
MAC Layer Bridging
The access point provides MAC layer bridging between its interfaces. The access point monitors traffic
from its interfaces and, based on frame address, forwards the frames to the proper destination. The
access point tracks source and destination addresses to provide intelligent bridging as MUs roam or
network topologies change. The access point also handles broadcast and multicast messages and
responds to MU association requests.
The access point listens to all packets on its LAN and WAN interfaces and builds an address database
using MAC addresses. An address in the database includes the interface media that the device uses to
associate with the access point. The access point uses the database to forward packets from one interface
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 Altitude
35xx 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