Chapter 6 Wireless Settings Screen

6.5.2.3 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.

STP-aware bridges exchange Bridge Protocol Data Units (BPDUs) periodically. 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.

6.5.2.4 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.

Table 16 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.

 

 

Forwarding

All BPDUs are received and processed. All information frames are received and

 

forwarded.

 

 

6.5.3 Additional Wireless Terms

 

Table 17 Additional Wireless Terms

 

 

 

 

TERM

DESCRIPTION

 

Intra-BSS Traffic

This describes direct communication (not through the NWA) between two

 

 

wireless devices within a wireless network. You might disable this kind of

 

 

communication to enhance security within your wireless network.

 

 

 

 

RTS/CTS Threshold

In a wireless network which covers a large area, wireless devices are

 

 

sometimes not aware of each other’s presence. This may cause them to

 

 

send information to the AP at the same time and result in information

 

 

colliding and not getting through.

 

 

By setting this value lower than the default value, the wireless devices must

 

 

sometimes get permission to send information to the NWA. The lower the

 

 

value, the more often the devices must get permission.

 

 

If this value is greater than the fragmentation threshold value (see below),

 

 

then wireless devices never have to get permission to send information to

 

 

the NWA.

 

 

 

 

Preamble

A preamble affects the timing in your wireless network. There are two

 

 

preamble modes: long and short. If a device uses a different preamble

 

 

mode than the NWA does, it cannot communicate with the NWA.

 

 

 

 

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NWA1100-N User’s Guide