Site Topography; Site Surveys; Theory Of Operation; Mac Layer Bridging - 3Com AirConnect User Manual

Theory of Operation

17

Site Topography

For optimal performance, place wireless clients and APs away from transformers,
heavy-duty motors, fluorescent lights, microwave ovens, refrigerators and other
industrial equipment.
Signal loss can occur when metal, concrete, brick, walls or floors block transmission.
Locate antennas in open areas or add additional APs as needed to improve coverage.

Site Surveys

A site survey analyzes the installation environment and provides users with
recommendations for the number and placement of APs. 3Com recommends that a
site survey be conducted at any new site prior to installing AirConnect equipment.
Theory of Operation
To improve AP management and performance, you should understand basic AP
functionality and configuration options. The AP includes features for different
interface connections and network management.
The AP provides MAC layer bridging between its interfaces. The AP monitors
traffic from its interfaces and, based on frame address, forwards the frames to the
proper destination. The AP tracks the frames sources and destinations to provide
intelligent bridging as wireless clients roam or network topologies change. The AP
also handles broadcast and multicast message initiations and responds to wireless
client association requests.

MAC Layer Bridging

The AP listens to all packets on all interfaces and builds an address database using
the unique IEEE 48-bit address (MAC address). An address in the database includes
the interface media that the device uses to associates with the AP. (The AP internal
stack interface handles all messages directed to the AP.) The AP uses the database
to forward packets from one interface to another. The bridge forwards packets
addressed to unknown systems to the default interface (either Ethernet or PPP).
Each AP stores information on destinations and their interfaces to facilitate
forwarding. When you send an Address Resolution Protocol (ARP) request packet,
the AP forwards the request over all enabled interfaces (Ethernet, PPP, or radio),
except over the interface on which the ARP request packet was received.
(Radio-received ARP request packets echo back to other APs over radio.) Upon
receiving the ARP response packet, the AP database keeps a record of the
destination address along with the receiving interface. With this information,
the AP forwards any directed packet to the correct destination. The AP forwards
packets for unknown destinations to the Ethernet interface.
The AP removes from its database destinations or interfaces not used for a
specified time. The AP refreshes its database when it transmits or receives data
from these destinations and interfaces.