The serving gateway is a network element that manages the user data path (SAE bearers) within EPC. It therefore connects via the S1-U interface towards eNB and receives uplink packet data from here and transmits downlink packet data on it. Thus the serving gateway is some kind of distribution and packet data anchoring function within EPC. It relays the packet data within EPC via the S5/S8 interface to or from the PDN gateway. A serving gateway is controlled by one or more MMEs via S11 interface.
The main function of SGW are :
- In visited network in case of roaming
- Local mobility anchor point : Switching the user plane path to a new eNB in case of Handover
- IRAT mobility anchor point :Mobility anchoring for inter-3GPP mobility. This is sometimes referred to as the 3GPP Anchor function
- Packet routing & forwarding between eNB, PDN GW and SGSN
- Lawful intercept
- LTE idle mode Packet buffering and notification to MME
- Charging per UE, PDN and QCI
- Bearer bindings for PMIP S5/S8
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