S5 Interface

The S5 interface provides user plane tunnelling and tunnel management between Serving Gateway (SGW) and PDN gateway. It is used for SGW relocation due to UE mobility and if the SGW needs to connect to a non-collocated PDN gateway for the required PDN connectivity.

S5 and S8 Interfaces

Both the S5 and S8 interfaces are used within the Evolved Packet Core (EPC) for LTE and exist between the SGW and PGW. Based on functionality, both the S5 and S8 are same interfaces except that S8 interface is used when roaming between different operators while S5 interface is a internal to the network.