Chapter 5 FortiOS Carrier : GTP message type filtering : Configuring message type filtering in FortiOS Carrier : Message Type Fields
  
Message Type Fields
Each of the following message types can be allowed or denied by your Carrier-enabled FortiGate unit depending on your carrier network and GTP traffic.
The message types include:
Unknown Message Action
Path Management Messages
Tunnel Management Messages
Location Management Messages
Mobility Management Messages
MBMS messages
GTP-U and Charging Management Messages