Specifications

Functions
112
4.4 Spanning Tree Algorithm
RS2-4R
Release 1.0 03/04
U Fast reconfiguration
Why can RSTP react faster to an interruption of the root path?
D Introduction of edge ports
When reconfiguring RSTP switches to forwarding mode at the end of
"Hello Time" immediately
(see Table 12 on page 162). RSTP waits for
the end of "Hello Time" to be sure, that no BPDU sending bridge is
connected.
If the user is sure, that an DTE is connected to this port and still
remains, he can switch off STP on this port. Thus there will be no
latency at this port in the case of reconfiguration.
D Introduction of alternate ports
Since the port roles are already distributed in regular operation, a brid-
ge can switch over immediately from the root port to the alternative
port after having lost the connection to the root bridge.
D Communicating with neighboring bridges
The decentralized, direct communication between neighboring brid-
ges permits immediate reaction to changes in state of the Spanning
Tree architecture.
D Filter table
When STP is used, the age of the entries in the table determines what
is to be updated. The RSTP deletes the entries of the ports immedia
-
tely and specifically that are affected by reconfiguration.
D Reaction to an event
Without having to adhere to any time specifications, RSTP reacts im-
mediately to events such as connection interruption, connection
established, etc.
Note: The price for this fast reconfiguration is the risk that data packets may
be duplicated or misplaced during the reconfiguration phase. If you cannot
accept such a risk in your application, switch back to the slower Spanning
Tree Protocol or select one of the other redundancy procedures described in
this manual.