Editing GPRS core network (section)

===Serving GPRS support node (SGSN)===
The Serving GPRS Support Node (SGSN)<ref name="3GPP_23.002" /> is the node that is serving the [[Mobile station|MS]]/[[User equipment|UE]]. The SGSN supports [[GPRS]] and/or [[UMTS]].<ref>3G TS 23.060 version 3.1.0, p.23</ref> The SGSN keeps track of the location of an individual [[Mobile station|MS]]/[[User equipment|UE]] and performs security functions and access control. The SGSN is connected to the [[GERAN]] base station system through the Gb or Iu interface and/or to the [[UTRAN]] through the Iu interface.<ref name="3GPP TS 23.060 V14.3.0 (2017-03), p.23">3GPP TS 23.060 V14.3.0 (2017-03), p.23</ref>
A SGSN is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The location register of the SGSN stores location information (e.g., current cell, current [[Visitor Location Register|VLR]]) and user profiles (e.g., [[International mobile subscriber identity|IMSI]], address(es) used in the packet data network) of all GPRS users registered with it.

====Common SGSN functions====
* Detunnel GTP packets from the GGSN (downlink)
* Tunnel IP packets toward the GGSN (uplink)
* Carry out mobility management when a standby mode mobile moves from one routing area to another routing area
* Billing a user according to data used.
* Mobile Equipment Identity Check Procedure (Gf/S13' interfaces).
* The SMS GMSCs and SMS IWMSCs support SMS transmission via the SGSN.<ref>3GPP TS 23.060 V14.3.0 (2017-03), p.24</ref>
* The Offline Charging System (OFCS) collects charging records from SGSNs.<ref name="3GPP TS 23.060 V14.3.0 (2017-03), p.23" />
* The SGSN contains mechanisms for avoiding and handling overload situations. <ref>3GPP TS 23.060 V14.3.0 (2017-03), p.35</ref>
* The SGSN communicate with other SGSN(s) and/or MME(s) ([[Mobility Management Entity]]) (Gn/S16/S3 interfaces)

====GSM/EDGE specific SGSN functions====
[[Enhanced Data Rates for GSM Evolution]] (EDGE) specific SGSN functions and characteristics are:
* Maximum data rate of approx. 60&nbsp;kbit/s (150&nbsp;kbit/s for EDGE) per subscriber
* Connect via [[Frame Relay]] or IP to the [[Base Station Subsystem#Packet control unit|packet control unit]] using the Gb protocol stack
* Accept uplink data to form IP packets
* Encrypt downlink data, decrypt uplink data
* Carry out mobility management to the level of a [[radio cell|cell]] for connected mode mobiles

====WCDMA specific SGSN functions====
* Carry up to about 42&nbsp;Mbit/s traffic downlink and 5.8&nbsp;Mbit/s traffic uplink (HSPA+)
* Tunnel/detunnel downlink/uplink packets toward the [[Radio Network Controller|radio network controller]] (RNC)