Restoration and recovery message types

Message type (value)	Description
PGW downlink notification (103)	Also called PGW downlink triggering notification. The PGW Downlink Triggering Notification is sent as part of the PGW triggered SGW restoration procedure if the MME/S4-SGSN, SGW and PGW support this optional feature.
PGW downlink acknowledge (104)	Also called PGW downlink triggering acknowledge. The PGW Downlink Triggering Acknowledge message is sent as a response to a PGW Downlink Triggering Notification message if the MME/S4-SGSN, SGW and PGW support the PGW triggered SGW restoration feature.
PGW restart notification (179)	If both the SGW and the MME/S4-SGSN support the PRN feature, a PGW Restart Notification is sent when the SGW detects that the peer PGW has restarted, and a PGW Restart Notification can also be sent when the SGW detects that the peer PGW has failed and not restarted.
PGW restart acknowledge (180)	The PGW Restart Notification Acknowledge is sent in response to a PGW restart notification.