SGSNs and GGSNs listen for GTP-U messages on UDP port 2152.
GTP‘ (GTP prime) is used for billing messages. It uses the common GTP messages (GTP Version Not Supported, Echo Request and Echo Response) and adds additional messages related to billing procedures.
|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|