GPRS Tunnelling Protocol (GTP) is a group of IP-based communications protocols used to carry general packet radio service (GPRS) within GSM, UMTS, LTE and 5G NR radio networks.
Different GTP variants are implemented by RNCs, SGSNs, GGSNs and CGFs within 3GPP networks.
GPRS mobile stations (MSs) are connected to a SGSN without being aware of GTP.
The eGTP-C (or, GTPv2-C) protocol is responsible for creating, maintaining and deleting tunnels on multiple Sx interfaces.
If this random number is of cryptographic quality, then it will provide a measure of security against certain attacks.
Even so, the requirement of the 3GPP standard is that all GTP traffic, including user data should be sent within secure private networks, not directly connected to the Internet.
The GTPv1-U protocol is used to exchange user data over GTP tunnels across the Sx interfaces.
The Charging Gateway Function (CGF) listens to GTP' messages sent from the GSNs on TCP/UDP port 3386.
The core network sends charging information to the CGF, typically including PDP context activation times and the quantity of data which the end user has transferred.
GTP-U is used on the IuPS between the GPRS core network and the RAN, however the GTP-C protocol is not used.
This is due to 3GPP defining enhancements to GTP-C for EPS in version 2 to improve bearer handling.
GTP-U is also used to transport user data from the RNC to the SGSN in UMTS networks.
Fortunately, however the use of different port numbers allows easy blocking of version 0 through simple IP access lists.
GTPv2 (for evolved packet services) went into draft in early 2008 and was released in December of that year.