Editing GPRS core network (section)

===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]]).