Intermec MobileLAN 21 Series System Manual page 95

Bridging Layer Functions Table
Function Explanation
Network Access points automatically configure into a self-organized network using a spanning tree
Organization topology. As devices are added to or removed from the network, the access points automatically
reconfigure to maintain reliable operation. The spanning tree provides efficient, loop-free
forwarding of frames through the network and allows rapid roaming of end devices.
The root access point initiates the spanning tree. The root coordinates the network and distributes
common system parameters to other access points and wireless end devices. The root is elected
from a group of access points that are designated as root candidates at the time of installation.
The election process also occurs in the event of a root failure. You can configure your network
with overlapping coverage so that the network automatically recovers from any single point of
failure.
End devices can optionally participate in the spanning tree protocol by explicitly attaching to the
network. As a result, operational parameters are easily distributed, unicast flooding is reduced or
eliminated, and roaming hands-off logic is more robust.
Forwarding The access point maintains a forwarding database of all physical station addresses, and it knows
the correct port for each address. The access point updates this database by monitoring source
addresses on each port (backward learning), by receiving explicit attachment messages, and by
examining messages exchanged between access points when wireless end devices roam. The
database also includes the power management status of each end device, which allows the access
point to support the pending message feature of the network. The forwarding database allows the
bridging software to make efficient forwarding decisions.
Switch Support Ethernet switches that do not comply with the 802.1D standard have difficulty handling wireless
end devices that roam between different switched segments. The access point provides data link
tunneling for switches that do not handle roaming. Using data link tunneling, frames for a given
end device always appear on the root access point's switched segment, regardless of roaming,
and the switch's routing tables remain stable.
Flooding When the destination address is unknown, standard LAN bridges flood frames on all ports. Most
Configurations wireless end devices supported by the access point operate at lower speeds than Ethernet;
therefore, indiscriminate flooding from a busy Ethernet backbone to an end device can consume
a substantial portion of the available wireless bandwidth and reduce system performance. The
access point allows you to set flooding control options for both unicast and multicast frames to
free up bandwidth and improve system performance.
Pending Messages Wireless end devices may use power management to maintain battery life. These end devices
wake up periodically to receive frames that arrived while their radio was powered down. The
bridging software in the access point provides a pending message delivery service that allows
frames to be held until the end device is ready to receive them.
Filtering Options The access point incorporates extensive filtering capabilities. Basic filters allow you to filter on
DIX type, protocol port, socket, or SAP. Advanced filters let you create and group filters based
on data patterns that you define.
Configuring the Spanning Tree
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