Rapid Spanning Tree Protocol (RSTP) is a network protocol that ensures a loop-free topology for Ethernet networks. Nowadays it is a popular solution to implement redundant networks in critical systems for Energy, Aerospace or Factory Automation. This protocol is incorporated into IEEE 802.1Q-2014RSTP provides faster convergence than 802.1D STP when topology changes occur. RSTP defines three port states: discarding, learning, and forwarding and five port roles: root, designated, alternate, backup, and disabled.


A RSTP capable switch  determines what spanning tree will be computed by the algorithm, but the rules as written require knowledge of the entire network.  This information is provided bridges use special data frames called Bridge Protocol Data Units (BPDUs) to exchange information about bridge IDs and root path costs. The switch device needs to manage BPDU in the proper way to ensure that the algorithm running on the CPU it is able to compute the algorithm.

Therefore, RSTP requires hardware and software specific processing. For the hardware processing, SoC-e offers its Managed Ethernet Switch (MES) IP, that supports RSTP.

SoC-e RSTPdstack is a portable C language, POSIX compatible, that implements RSTP processing according to the standard IEEE 802.1D-2004. The integration on Unix or VxWorks OS systems is straightforward. It can be used in combination with SoC-e MES IP or with other switches able to handle BDPU frames.

RSTPdstack implements IEEE 802.1D standard and processes all RSTP related events such as:

  • Reception of a BPDU
  • Physical Link status change
  • 1 second timeout
  • Change in the bridge parameters

As result of any of these events, the RSTP priority vectors and timing vectors are recalculated and the following actions are performed:

  • Transmission of BPDUs
  • Switch’s MAC table clearing
  • Change in switch’s ports status

 For more information, please contact us at: info@soc-e.com