ZyXEL Communications NWA-3160 User Manual
Chapter 8 Wireless Screen
NWA-3160 Series User’s Guide
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8.3.1.3 How STP Works
After a bridge determines the lowest cost-spanning tree with STP, it enables the
root port and the ports that are the designated ports for connected LANs, and
disables all other ports that participate in STP. Network packets are therefore only
forwarded between enabled ports, eliminating any possible network loops.
root port and the ports that are the designated ports for connected LANs, and
disables all other ports that participate in STP. Network packets are therefore only
forwarded between enabled ports, eliminating any possible network loops.
STP-aware bridges exchange Bridge Protocol Data Units (BPDUs) periodically.
When the bridged LAN topology changes, a new spanning tree is constructed.
When the bridged LAN topology changes, a new spanning tree is constructed.
Once a stable network topology has been established, all bridges listen for Hello
BPDUs (Bridge Protocol Data Units) transmitted from the root bridge. If a bridge
does not get a Hello BPDU after a predefined interval (Max Age), the bridge
assumes that the link to the root bridge is down. This bridge then initiates
negotiations with other bridges to reconfigure the network to re-establish a valid
network topology.
BPDUs (Bridge Protocol Data Units) transmitted from the root bridge. If a bridge
does not get a Hello BPDU after a predefined interval (Max Age), the bridge
assumes that the link to the root bridge is down. This bridge then initiates
negotiations with other bridges to reconfigure the network to re-establish a valid
network topology.
8.3.1.4 STP Port States
STP assigns five port states (see next table) to eliminate packet looping. A bridge
port is not allowed to go directly from blocking state to forwarding state so as to
eliminate transient loops.
port is not allowed to go directly from blocking state to forwarding state so as to
eliminate transient loops.
8.3.2 DFS
When you choose 802.11a or 802.11n/a in Access Point mode, the NWA uses
DFS (Dynamic Frequency Selection) to give you a wider choice of wireless
channels.
DFS (Dynamic Frequency Selection) to give you a wider choice of wireless
channels.
DFS allows you to use channels in the frequency range normally reserved for radar
systems. Radar uses radio signals to detect the location of objects for military,
meteorological or air traffic control purposes. As long as your NWA detects no
radar activity on the channel you select, you can use the channel to communicate.
However, a wireless LAN operating on the same frequency as an active radar
system could disrupt the radar system. Therefore, if the NWA detects radar
systems. Radar uses radio signals to detect the location of objects for military,
meteorological or air traffic control purposes. As long as your NWA detects no
radar activity on the channel you select, you can use the channel to communicate.
However, a wireless LAN operating on the same frequency as an active radar
system could disrupt the radar system. Therefore, if the NWA detects radar
Table 28 STP Port States
PORT
STATES
DESCRIPTIONS
Disabled
STP is disabled (default).
Blocking
Only configuration and management BPDUs are received and processed.
Listening
All BPDUs are received and processed.
Learning
All BPDUs are received and processed. Information frames are
submitted to the learning process but not forwarded.
submitted to the learning process but not forwarded.
Forwarding
All BPDUs are received and processed. All information frames are
received and forwarded.
received and forwarded.