The S-GW is the anchor point in the user plane between different 3GPP access networks. It can shield interfaces within the 3GPP network towards different access networks. The S-GW functions as a gateway for the EPC and terminates the interface towards E-UTRAN. The S-GW provides the following functions:
- Local mobility anchor point for inter-eNodeB handovers
- Assistance of the eNodeB reordering function during inter-eNodeB handovers by sending one or more "end marker" packets to the source eNodeB immediately after switching the path
- ECM-IDLE mode downlink packet buffering and initiation of paging triggered on the E-UTRAN
- Packet routing and forwarding
- Transport level packet marking in the uplink and the downlink (DSCP)
- Accounting based on the user and QCI granularity for inter-operator charging
