When using standalone ERP, all devices have a role, and all devices participate at least as ERP members.
Ring-APS (R-APS) messages are sent at initial start-up of a configuration and periodically when link or node failures or recoveries occur. Each ERN applies the information received in the R-APS messages and forwards the received RAPS messages if both ports are in the forwarding state.
The sending ERN terminates the message when it receives a message originally sent from itself.
Configurable timers prevent ERNs from receiving outdated messages and decrease failure reporting time to allow increased stability within the topology.
To properly configure and troubleshoot ERP, an understanding of the messaging, operational states, and timers is essential. For more information about the ERP protocol, see ITU-T G.8032.