Chapter 5 FortiOS Carrier : GTP message type filtering : Configuring message type filtering in FortiOS Carrier : Message Type Fields : GTP-U and Charging Management Messages
  
GTP-U and Charging Management Messages
 
Message Type
Used By
Description
G-PDU
GTP-C, GTP-U
GPRS Packet data unit delivery message.
Node Alive Request/Response
GTP-C, GTP-U
Used to inform rest of network when a node starts service.
Redirection Request/Response
GTP-C, GTP-U
Used to divert the flow of CDRs from the CDFs to another CGF when the sender is being removed, or they are used when the CGF has lost its connection to a downstream system.
Data Record Transfer Request/Response
GTP-C, GTP-U
Used to reliably transport CDRs from the point of generation (SGSN/GGSN) to non-volatile storage in the CGF