Description
The Serving GPRS Support Node (SGSN) is a fundamental core network entity in GSM/GPRS and UMTS networks, dedicated to packet-switched data services. It serves as the central point of control and routing for a mobile subscriber's data session within the network's coverage area. The SGSN's primary roles include mobility management, session management, and user authentication and authorization for packet data access. Physically, it is connected to the Radio Access Network (RAN)—specifically the Base Station Subsystem (BSS) in GSM/GPRS or the Radio Network Controller (RNC) in UMTS—via the Gb or Iu-PS interfaces, respectively. It also connects to the Gateway GPRS Support Node (GGSN) via the Gn interface, which provides the gateway to external packet data networks like the Internet.
From a functional perspective, the SGSN operates by maintaining a context for each attached GPRS/UMTS subscriber. When a mobile station (MS) attaches to the network for packet data services, the SGSN authenticates the user using information from the Home Location Register (HLR) or Authentication Centre (AuC). It then establishes a PDP (Packet Data Protocol) context, which is a logical association between the MS, the SGSN, and the GGSN, defining parameters like the assigned IP address and QoS profile. For mobility, the SGSN tracks the location of the MS at the level of the routing area (a group of cells) and handles routing area updates as the user moves. It routes incoming data packets from the GGSN to the correct RAN element based on the user's current location and routes outgoing packets from the MS towards the GGSN.
The SGSN's architecture includes several key logical components: the mobility management function, which handles attach/detach and location updates; the session management function, which controls PDP context activation, modification, and deactivation; and the packet routing and transfer function. It also performs charging functions, collecting data for billing based on volume or time, and interfaces with charging systems. In UMTS, the SGSN's role expanded to include more sophisticated QoS handling aligned with UMTS bearer services. Throughout its long evolution from Release 99 onwards, the SGSN has been integral to enabling mobile internet access, MMS, and other packet data services before the full migration to LTE/EPC. It represents the core of the packet-switched domain in pre-4G networks, working in tandem with the GGSN to provide a complete data service path.
Purpose & Motivation
The SGSN was created to introduce packet-switched data capabilities into originally voice-centric GSM networks. Before GPRS (General Packet Radio Service), GSM offered only circuit-switched data, which was inefficient for bursty, internet-style traffic. The motivation for the SGSN was to enable efficient, always-on IP-based data services over GSM, leading to mobile email, web browsing, and early mobile applications. It solved the problem of managing mobile subscribers' packet data sessions, including their mobility and authentication, within the cellular network infrastructure.
The historical context is the transition to 2.5G/3G mobile data. The SGSN, alongside the GGSN, formed the GPRS core network, allowing GSM networks to utilize packet switching and share radio resources dynamically among users, dramatically improving data efficiency compared to dedicated circuits. It addressed limitations like the inability to handle IP mobility and session continuity natively. For UMTS, the SGSN evolved to support the new UMTS RAN and enhanced QoS mechanisms, facilitating richer data services. Its enduring presence across many releases underscores its role as the cornerstone of mobile packet data before the clean-slate design of the LTE/EPC, where its functions were redistributed to the MME and S-GW.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (83 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SGSN's function was updated to support the new 5G System (5GS), including new steering of roaming procedures and enhancements for charging over new interfaces. Specific updates included support for Standardized X Interfaces, handling of secondary RAT in offline charging, and the introduction of a Supported Features mechanism. Furthermore, the USIM Service Table was updated for PDU session call control, and there were corrections and updates to QoS and charging AVPs to align with 5GS capabilities.
- new annex to 23.228 for 5GS support TS 23.228CR1174
- Support for identity attestation and verification TS 23.228CR1184
- Updates to 3GPP-GPRS-Negotiated-QoS-Profile AVP TS 29.061CR0505
- Support of 5GS new steering of roaming procedures TS 31.102CR0785
- USIM Service Table update for PDU session call control support TS 31.102CR0786
- Support for secondary RAT in offline charging TS 32.251CR0502
+ 11 more changes
In Release 16, the SGSN's enhancements were not detailed in the provided grounding context, which focuses on legacy GSM LCS architecture. The listed Change Request titles indicate new support areas for the SGSN, including RAN Assisted Codec Adaptation, secondary RAT data usage reporting, and handling SUCI for specific SUPI types. However, the specific technical procedures or interfaces for these SGSN functions within Release 16 are not described in the given text.
- Support for RLOS in IMS TS 23.228CR1193
- Support for RAN Assisted Codec Adaptation TS 23.228CR1194
- Support for USIM configuration of RLOS PLMN list TS 31.102CR0847
- Support for Trusted non-3GPP access networks list by USIM TS 31.102CR0891
- Support of SUCI for SUPI Type GLI and GCI TS 31.102CR0896
- Support for eCall over IMS over NR TS 31.102CR0892
+ 3 more changes
In Release 17, updates to the SGSN function primarily focused on enhancing Control and User Plane Separation (CUPS) support, specifically through updates to enable L2TP in both RADIUS and Diameter message flows. Furthermore, support was added for confirming UE supported algorithms in the Path Switch procedure. These updates continued the evolution of the SGSN's role within the broader network architecture.
- Support for Attestation for IMS priority sessions TS 23.228CR1241
- KI#3: Support for IMC for SNPN TS 23.228CR1239
- [TEI17, AE_enTV-S4] Support of ETSI TS 103 720 second version TS 26.346CR0668
- Updates to support CUPS TS 29.061CR0535
- Updates to support L2TP for CUPS TS 29.061CR0536
- Updates to support L2TP in RADIUS message flow TS 29.061CR0537
+ 12 more changes
In Release 18, there were no new specifications or Change Requests introduced for the SGSN (Serving GPRS Support Node) function itself. The provided CR titles and grounding context exclusively detail enhancements for other network functions like the NWDAF, IMS Data Channel, NRF, and charging systems. Consequently, Release 18 did not define any updates to SGSN-specific procedures, interfaces such as Gs, or its role in LCS positioning for GPRS.
- Support of PSAP resolution with NWDAF TS 23.228CR1258
- Architecture of IMS supporting data channel TS 23.228CR1263
- KI#4 Describe option to support MRF registration and discovery using NRF TS 23.228CR1265
- Supporting UE centric AR Telephony Communication TS 23.228CR1284
- Update of DCMF service to support media processing TS 23.228CR1303
- Support DC in 3GPP PS Data Off exempt services TS 31.102CR1054
+ 7 more changes
In Release 19, the SGSN function saw no specific new features or updates detailed in the provided context. The Change Request titles and the grounding specification text focus entirely on enhancements for IMS services, charging, and satellite communication, with no mention of the SGSN. The technical details provided continue to describe the SGSN's existing role in LCS procedures, such as using the Gs interface to check a mobile station's GPRS attachment status.
- Support of IMS data channel interworking between DCMTSI UE and MTSI UE TS 23.228CR1418
- Support of MPS priority for IMS Immediate Messaging and IMS Session-based Messaging TS 23.228CR1419
- KI#6: Support of Standalone IMS Data Channel feature TS 23.228CR1422
- Supporting of network initiated IMS Data Channel TS 23.228CR1425
- KI#5: Support of Data off feature for data channel TS 23.228CR1421
- Support of UE-Satellite-UE communication in IMS - Functionality TS 23.228CR1428
+ 20 more changes
Explore further
Broader topics and technologies where SGSN plays a role.
Defining Specifications
3GPP specifications that define or reference SGSN, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 03.071 v7b0 | Location Services (LCS) Stage 2 Description | Rel-7 |
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TR 21.978 v1300 | CAMEL Control of VoIP Services Feasibility Study | Rel-4 |
| TR 22.945 v1300 | Fax Services Guidance for GSM/UMTS | Rel-4 |
| TR 22.980 vj00 | Network Composition Feasibility Study | Rel-19 |
| TS 23.018 vj00 | Basic call handling in 3GPP CS domain | Rel-19 |
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 23.078 vj00 | CAMEL Phase 4 Stage 2 Specification | Rel-19 |
| TS 23.107 vj00 | UMTS QoS Framework | Rel-19 |
| TS 23.119 vj00 | Gateway Location Register (GLR) Stage 2 Description | Rel-19 |
| TS 23.125 v1700 | Flow Based Charging Architecture | Rel-7 |
| TS 23.141 vj00 | Presence Service Stage 2 Architecture | Rel-19 |
| TS 23.171 v1300 | LCS Stage 2 Specification for UMTS | Rel-4 |
| TS 23.207 vj00 | End-to-End QoS Framework for GPRS | Rel-19 |
| TS 23.221 vj00 | 3GPP System Architectural Requirements | Rel-19 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TS 23.251 vj00 | Network Sharing Stage 2 Specification | Rel-19 |
| TS 23.271 vj00 | LCS Stage 2 Specification | Rel-19 |
| TS 23.327 vd10 | 3GPP-WLAN Mobility Stage 2 Description | Rel-13 |
| TS 23.815 v1500 | IMS Charging Implications | Rel-5 |
| TS 23.851 v1600 | Network Sharing Architecture for 3G Systems | Rel-6 |
| TR 23.923 v1300 | Mobile IP+ Feasibility Study for UMTS/GPRS | Rel-4 |
| TR 23.976 vj00 | Push Service Requirements Analysis | Rel-19 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TR 23.981 vj00 | IPv4 IMS Interworking and Migration Study | Rel-19 |
| TS 24.065 v1310 | GPRS Subnetwork Dependent Convergence Protocol | Rel-4 |
| TS 24.161 vj00 | Network-Based IP Flow Mobility (NBIFOM) | Rel-19 |
| TS 24.228 v1500 | IP Multimedia Call Control Signaling Flows | Rel-5 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 25.305 vj00 | UTRAN UE Positioning Stage 2 | Rel-19 |
| TS 25.412 vj00 | Iu Interface Signalling Transport Specification | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TS 26.346 vj20 | MBMS User Services Media Codecs & Protocols | Rel-19 |
| TS 27.060 vj00 | TE-MT Interworking for Packet Domain | Rel-19 |
| TS 28.702 vj00 | Core Network NRM IRP Information Service | Rel-19 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.119 vj00 | GTP for GLR in 3GPP Networks | Rel-19 |
| TS 29.199 v1900 | Multimedia Messaging Web Services | Rel-9 |
| TS 29.281 vj20 | GTPv1-U Protocol Specification | Rel-19 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TR 31.900 vj00 | 3GPP TS 31.900: Security Interworking Guidance | Rel-19 |
| TS 32.102 vj00 | Telecom Management Physical Architecture Framework | Rel-19 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 32.252 vc00 | 3GPP WLAN Interworking Charging | Rel-12 |
| TS 32.254 vj21 | Charging for Northbound APIs | Rel-19 |
| TS 32.271 vj20 | 3GPP LCS Charging Management Spec | Rel-19 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TS 32.278 vj00 | Monitoring Events Offline Charging Specification | Rel-19 |
| TS 32.296 vj00 | Online Charging System (OCS) Architecture | Rel-19 |
| TS 32.401 vj00 | Performance Management Concept & Requirements | Rel-19 |
| TS 32.622 vb10 | Generic Network Resources IRP NRM | Rel-11 |
| TS 32.632 vb00 | Core Network Resources IRP: Network Resource Model | Rel-11 |
| TS 32.732 vb00 | IMS Network Resource Model IRP: Information Service | Rel-11 |
| TS 32.808 v1800 | Common User Profile Storage Framework | Rel-8 |
| TS 32.833 vb00 | Converged OSS End-to-End Management Study | Rel-11 |
| TS 33.102 vj10 | 3G Security Architecture Specification | Rel-19 |
| TS 33.107 vj00 | Lawful Interception Architecture & Functions | Rel-19 |
| TS 33.108 vj00 | LI Handover Interface Specification | Rel-19 |
| TS 33.320 vj00 | H(e)NB Subsystem Security Architecture | Rel-19 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 33.805 vc00 | 3GPP Network Product Security Assurance Methodology | Rel-12 |
| TS 33.822 v1800 | Security Architecture for Inter-Access Mobility | Rel-8 |
| TS 33.859 vb10 | UTRAN Key Hierarchy Enhancement Study | Rel-11 |
| TS 33.863 ve20 | Security for Battery-Efficient IoT Device to Enterprise | Rel-14 |
| TR 33.978 v1800 | Interim Security for Early IMS | Rel-8 |
| TS 43.064 vj00 | GPRS Radio Interface Lower-Layer Functions | Rel-19 |
| TS 43.129 vj00 | PS Handover in GERAN A/Gb and GAN Modes | Rel-19 |
| TS 43.130 vj00 | Iur-g Interface Overview | Rel-19 |
| TS 43.318 vj00 | Generic Access Network (GAN) Stage 2 | Rel-19 |
| TR 43.901 vj00 | Generic Access to A/Gb Interface Feasibility Study | Rel-19 |
| TR 43.902 vj00 | GAN Enhancements Feasibility Study | Rel-19 |
| TS 44.065 vj00 | GPRS SNDCP Specification | Rel-19 |
| TS 44.160 vg00 | GERAN Iu Mode RLC/MAC Protocol Specification | Rel-16 |
| TS 44.318 vj00 | Generic Access Network (GAN) Interface Procedures | Rel-19 |
| TS 48.016 vj00 | Gb Interface Network Service Specification | Rel-19 |
| TS 52.402 vj00 | GSM Performance Management Measurements | Rel-19 |