S5/S8 Interface

S5/S8 - This is the interface between the S-GW and P-GW. In principle S5 and S8 is the same interface, the difference being that S8 is used when roaming between different operators while S5 is network internal.

The S5 / S8 interface will exist in two flavours one based on Gn/GTP (SGSN-GGSN) and the other will use the IETF specified Proxy Mobile IP (PMIP) for mobility control with additional mechanism to handle QoS.

The motivation for the PMIP flavour of S5/S8 has mainly come from WiMAX/CDMA2000 operators and vendors interested in inter-working with E-UTRAN, GERAN or UTRAN, or re-using the 3GPP EPS specified mechanism also for intra WiMAX / CDMA2000 mobility.

It has been agreed in 3GPP that the usage of PMIP or GTP on S5 and S8 should not impact RAN behaviour or impact the terminals.

The usage of PMIP or GTP on S5/S8 will not be visible over the S1 interface or in the terminal. In the non roaming case, the S-GW and P-GW functions can be performed in one physical node.

S5/S8 is a many-to-many interface.

LTE S5/S8 Interface