Editing GPRS core network (section)

==GPRS support nodes (GSN)==
A GSN is a network node that supports the use of GPRS in the GSM core network.  All GSNs should have a ''Gn'' interface and support the GPRS tunneling protocol.  There are two key variants of the GSN, namely gateway GPRS support node and serving GPRS support node.

===Gateway GPRS support node (GGSN)===
The gateway GPRS support node (GGSN)<ref name="3GPP_23.002">{{cite web |title=3GPP TS 23.002 V12.5.0 (2014-10) |url=https://www.etsi.org/deliver/etsi_ts/123000_123099/123002/12.05.00_60/ts_123002v120500p.pdf |publisher=ETSI |access-date=17 October 2019 |ref=RTS/TSGS-0223002vc50 |page=29 |date=October 2014}}</ref> is one of two components of the GPRS PS domain. The GGSN together with the SGSN handle packet transmissions between the GPRS network and external [[packet-switched network]]s, such as the [[Internet]] or an [[X.25]] network.

From an external network's point of view, the GGSN is a router to a "sub-network", because the GGSN ‘hides’ the GPRS infrastructure from the external network. When the GGSN receives data addressed to a specific user, it checks if the user is active. If it is, the GGSN forwards the data to the SGSN serving the mobile user, but if the mobile user is inactive, the data is discarded. In the other direction, mobile-originated packets are routed to the right network by the GGSN.

The GGSN is the anchor point that enables the mobility of the user terminal in the GPRS/[[UMTS]] networks. In essence, it carries out the role in GPRS equivalent to the [[Mobile IP#Operational principles|home agent]] in [[Mobile IP]]. It maintains routing necessary to tunnel the [[protocol data unit]]s (PDUs) to the SGSN that services a particular [[mobile station]] (MS).

The GGSN converts the GPRS packets coming from the SGSN into the appropriate packet data protocol (PDP) format (e.g., IP or X.25) and sends them out on the corresponding packet data network. In the other direction, PDP addresses of incoming data packets are converted to the GSM address of the destination user. The readdressed packets are sent to the responsible SGSN. For this purpose, the GGSN stores the current SGSN address of the user and his or her profile in its location register. The GGSN is responsible for IP address assignment and is the default router for the connected user equipment (UE). The GGSN also performs authentication and charging functions.

Other functions include subscriber screening, [[Address pool|IP pool]] management and [[IP address#Modifications to IP addressing|address mapping]], [[Quality of service|QoS]] and PDP context enforcement.

With [[Long Term Evolution|LTE]] scenario the GGSN functionality moves to [[System Architecture Evolution|SAE]] gateway (with SGSN functionality working in [[Mobility Management Entity|MME]]).

===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)