GTPv1-C is used on Gn and Gp interfaces of the Universal
Mobile Telecommunication System (UMTS) and GPRS.
GTPv2-C is used across various Evolved Packet Core (EPC) signaling
interfaces, such as S5, S8, and S11.
GTP-U is used across various EPC signaling interfaces, such
as S1-U, S5, and S8, and on Gn and Gp interfaces of the UMTS and
GPRS.