GE ML1200 Switch User Manual

Multilink ML1200
Managed Field Switch
Chapter 13: Rapid Spanning Tree
Digital Energy
Rapid Spanning Tree Protocol
13.1 Overview
13.1.1 Description
The Rapid Spanning Tree Protocol (RTSP), like STP, was designed to avoid loops in an
Ethernet network. Rapid Spanning Tree Protocol (RSTP) (IEEE 802.1w) is an evolution of the
Spanning Tree Protocol (STP) (802.1d standard) and provides for faster spanning tree
convergence after a topology change.
13.1.2 RSTP concepts
The IEEE 802.1d Spanning Tree Protocol (STP) was developed to allow the construction of
robust networks that incorporate redundancy while pruning the active topology of the
network to prevent loops. While STP is effective, it requires that frame transfer must halt
after a link outage until all bridges in the network are sure to be aware of the new topology.
Using STP (IEEE 802.1d) recommended values, this period lasts 30 seconds.
The Rapid Spanning Tree Protocol (IEEE 802.1w) is a further evolution of the 802.1d
Spanning Tree Protocol. It replaces the settling period with an active handshake between
switches (bridges) that guarantees topology information to be rapidly propagated through
the network. RSTP converges in less than one second. RSTP also offers a number of other
significant innovations. These include
Topology changes in STP must be passed to the root bridge before they can be
propagated to the network. Topology changes in RSTP can be originated from and
acted upon by any designated switch (bridge), leading to more rapid propagation
of address information
STP recognizes one state - blocking for ports that should not forward any data or
information. RSTP explicitly recognizes two states or blocking roles - alternate and
backup port including them in computations of when to learn and forward and
when to block