S-GW
Serving Gateway
The S-GW is the user data plane ingress and egress point of the E-UTRAN side of the EPC. As such, when the subscriber moves around the E-UTRAN, their point of attachment to the EPC remains fixed at the S-GW (unless the network decides that a S-GW relocation is required). Additional responsibilities include lawful interception of subscriber traffic, as well as downlink data buffering whilst the subscriber is paged.