RadioLinx Configuration Manager
RLXIB-IHN
♦
802.11n
User Manual
Industrial Hotspot
Page 70 of 171
ProSoft Technology, Inc.
May 23, 2011
BPDUs are sent out the port at a rate called the "Hello Time". The accepted
standard value for this is 2 seconds. If a radio (or any other RSTP device) does
not get a BPDU for 2 Hello Times, it assumes the RSTP device that had been
there is no longer available. It can then open an alternate path if one is available.
This process is much like the STP process. If other devices on the network are
not operating in rapid spanning tree mode, the radio will revert to normal
spanning tree operation on a per-port basis.
RSTP provides a performance enhancement over STP operation. By
comparison, the radio using the STP algorithm would revert its port to the
listening state, and then to the learning state, before returning to the forwarding
state. Each of these states takes at least 15 seconds, during which the STP
devices are listening for BPDUs to re-negotiate the network topology. The
advantage of using the RSTP functionality is that is uses active handshaking
between adjacent RSTP devices to re-negotiate the network topology. This
process takes one to two seconds.
Each RLXIB-IHN Radio contains a switch table, which tells it how to forward
Ethernet packets to get them to their proper destination. When the network
topology changes, the RLXIB-IHN Radio flushes its Ethernet switch table
immediately. This allows it to pass traffic immediately over the new network
topology and learn the configuration in the process. Until the learning is
complete, the packets are broadcast to their destination. As each packet is seen
and the switch table rebuilds, the radios return to directing packets to their
destinations.
The primary reason for creating a Spanning Tree is that it allows you to create
fully redundant paths. If any single radio in a redundant path loses its connection,
another path still exists, and the connection will be updated and communication
restored.