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AP-51xx Access Point Product Reference Guide
1.3.1 Cellular 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 point's 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 points makes them part of the same Wireless LAN.
access points with the same ESSID defines 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.
1.3.2 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).
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