One or more MTP primary (MTPPRIMARY) indications are delivered to the application when the ISUP layer receives a primary indication from the MTP 3 layer. This can occur when the application binds to an ISUP user SAP.
The MTP backup status indicates that the run state of MTP is currently backup on this board in a redundant board pair, monitoring the status of the primary. No active traffic passes through this SAP until the board becomes the primary member of the pair.