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ROS™  v3.5 

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RS400 

•  RSTP offers edge port recognition, allowing ports at the edge of the network to forward 

frames immediately after activation while at the same time protecting them against loops. 

 

While providing much better performance than STP, IEEE 802.1w RSTP still required up to 
several seconds to restore network connectivity when a topology change occurred. 

A revised and highly optimized RSTP version was defined in the IEEE standard 802.1D-2004 
edition. IEEE 802.1D-2004 RSTP reduces network recovery times to just milliseconds and 
optimizes RSTP operation for various scenarios. 

ROS

TM

 supports IEEE 802.1D-2004 RSTP.  

 

RSTP bridges have roles to play, either root or designated. One bridge, the root bridge, is the 
logical center of the network. All other bridges in the network are designated bridges. 

RSTP also assigns each port of the bridge a state and a role. The RSTP state describes what is 
happening at the port in relation to address learning and frame forwarding. The RSTP role 
basically describes whether the port is facing the center or the edges of the network and 
whether it can currently be used. 

State 

There are three RSTP states: Discarding, Learning and Forwarding. 

The discarding state is entered when the port is first put into service. The port does not learn 
addresses in this state and does not participate in frame transfer. The port looks for RSTP traffic 
in order to determine its role in the network. When it is determined that the port will play an 
active part in the network, the state will change to learning. 

Forwarding

Learning

Discarding

Disabled

Link Down

Forwarding Timer Expires
Or Active RSTP Handshake

Forwarding Timer Expires
Or Active RSTP Handshake has
Occurred

Link rises or falls

RSTP Enabled

BPDUS indicate
port should not
be active

RSTP Disabled in any state