4G LTE Interfaces, Gx(or S7) & Gxc Interfaces, Rx Interfaces , SGi Interfaces

Gxc
•Interface between Serving GW (S-GW) and PCRF (Policy and Charging Rule Function)
•This interface is only needed in case the S5/S8 interface is based on PMIP (IETF candidate)
•The reason is that only in this case the S-GW will perform the mapping between IP service flows in S5/S8 and GTP tunnels in the S1-U interface. The information to do the mapping comes from directly from the PCRF

Gx(Also referred as S7)
•Interface between PDN GW and PCRF (Policy and Charging Rule Function)
•It allows:
•the PCRF to request the setup of a SAE bearer with appropriate QoS
•the PDN GW to ask for the QoSof an SAE bearer to setup
•to indicate EPC status changes to the PCRF to apply a new policy rule.

Rx
•Interface between PCRF (Policy & Charging Rules Function) and the external PDN network/operators IMS (in general, towards the Service Domain)
•Standardized in 3GPP TS 29.214: “ Policy and Charging Control over the Rx reference point (release 8)”

SGi
•Interface used by the PDN GW to send and receive data to and from the external data network or Service Platform
•It is either IPv4 or IPv6 based
•Downlink data coming from the external PDN must be assigned to the right SAE bearer of the right user by analysis of the incoming packet’s IP addresses, port numbers, etc.
•This interface corresponds to the Giinterface in 2G/3G networks
•Standardized in 3GPP TS 29.061: “Interworking between the Public Land Mobile Network (PLMN) supporting packet based services and Packet Data Networks (PDN)