Hirschmann RS20 Programming Manual page 96

Rapid Spanning Tree
Alternate port
This is a blocked port that takes over the task of the bridge port if the
connection to the root bridge fails. The alternate port guarantees the
connection of the bridge to the root bridge.
Backup port
This is a blocked port that serves as a backup in case the connection to
the designated port of this network segment (without RSTP bridge) fails.
Disabled port
This is the port that does not play any role with the Spanning Tree
Operation, and is therefore switched off or does not have any connection.
P-BID = 16 384
Bridge 1
P-BID = 20 480
Bridge 2
P-BID = 40 960
Bridge 7
P-BID = 28 672
Bridge 4
Figure 50: Port role assignment
96
P-BID = 24 576
Bridge 3
P-BID = 32 768
Port 2
Port 1
Bridge 5
6.6 The Rapid Spanning Tree Protocol
Priority of the bridge identifikation (BID)
P-BID
= BID without MAC Address
Root path
Interrupted path
Root port
Designated port
Alternate port
Backup port
Edge port
Redundanz L2P
Release 5.0 04/09