S4 Interface

S4 - This is the interface between the P-GW and 2G/3G SGSNs. The interface is based on Gn/GTP (SGSN-GGSN). The user plane interface is based on GTP-U (same as S1-UP and Iu-UP) and the control plane is based on GTP-C (similar to S11).

S4 is a many-to-many interface and is backwards compatible with the Gn interface.