Networks Trusted non- Un-trusted non- 3GPP Network 3GPP Network Figure 11.5 3GPP and Non-3GPP access integrated architecture. Reproduced with permission from C 3GPP [7] S4 provides related control and mobility support between GPRS Core and the 3GPP anchor function of Serving GW and is based on a Gn reference point as defined between SGSN and GGSN. S5 provides user plane tunneling and tunnel management between Serving GW and PDN GW. S6a enables transfer of subscription and authentication data for authenticating user access to the evolved system (AAA interface) between MME and HSS. S6c interface is the interface between PDN Gateway in HPLMN (Home PLMN) and 3GPP AAA server for mobility related authentication if needed. S6d is the interface between Serving Gateway in VPLMN (Visited PLMN) and 3GPP AAA Proxy for mobility related authentication if needed. S8 is the roaming PMIP based interface and used in case of roaming with home routed traffic. It provides user and control plane between the Serving GW in the VPLMN and the PDN GW in the HPLMN. S9 provides transfer of (QoS) policy and charging control information between the Home PCRF and the Visited PCRF in order to support local breakout function. S10 serves as a reference point between MMEs for MME relocation and MME to MME information transfer. S11 serves as a reference point between MME and Serving GW. S12 serves as a reference point between UTRAN and Serving GW for user plane tunneling when Direct Tunnel is established. S13 enables UE identity check procedure between MME and EIR (Equipment Identity Register). S14 reference point exists between UE and HANDSF/VANDSF (Home/Visited Access Network Discovery and Selection Function) for direct queries via pull. It enables dynamic provision of information to the UE for access network discovery and selection procedures related to non-3GPP and 3GPP accesses. Gx provides transfer of (QoS) policy and charging rules from PCRF to PCEF in the PDN GW. Gxb provides transfer of (QoS) policy information from PCRF to ePDG. Next Gener