Description
The Supplementary Service Control string (SSC) is a user-friendly, dialable string format standardized across 3GPP specifications (e.g., TS 24.526, TS 29.508) for the control of supplementary services. It is the human-machine interface that allows a subscriber to issue commands to the network to manage services like Call Forwarding Unconditional (CFU), Call Barring (BAOC), or Call Waiting (CW). A typical SSC has a structured syntax: a prefix (often '*' or '#'), a service code (a two-digit number identifying the service, e.g., 21 for CFU), an operation code (a single digit for activate, deactivate, register, erase, or interrogate), and optionally, supplementary information such as a target phone number or a password. For example, **21*+123456789# might activate CFU to the number +123456789.
When a user dials an SSC and presses the send/call button, the mobile handset does not treat it as a normal phone call. Instead, it packages the string into a signaling message, specifically a FACILITY or REGISTER message within a call control protocol like DTAP (Direct Transfer Application Part). This message is sent over the radio interface to the MSC (Mobile Switching Centre). The MSC's Call Control function receives the message, parses the SSC according to the standardized syntax, and interprets the requested operation. The MSC then interacts with the relevant network databases—primarily the VLR (Visitor Location Register) and the HLR (Home Location Register)—to execute the command. For registration or interrogation, the MSC may communicate with the HLR via MAP (Mobile Application Part) to update or retrieve the subscriber's service profile.
The SSC mechanism works in conjunction with the network's service logic. For basic services, the MSC can process the SSC directly. For more advanced services or those involving CAMEL control, the MSC may involve the gsmSCF. The standardization of the SSC syntax ensures interoperability between handsets from any manufacturer and networks from any operator, providing a consistent user experience globally. It is a key part of the Man-Machine Interface (MMI) for telecommunications services. While modern smartphones often manage these services through graphical menus or apps, those interfaces ultimately generate the standardized SSC strings for transmission to the network, ensuring backward compatibility.
Purpose & Motivation
The Supplementary Service Control string was created to provide a simple, uniform, and subscriber-empowering method for controlling network-based features. Before its standardization, the activation of services like call forwarding might have required a call to customer service or the use of proprietary, operator-specific codes, leading to a poor user experience and hindering subscriber mobility across different networks. The SSC standard solved this by defining a universal, dialable code language that works on any GSM/UMTS/LTE/5G phone on any compliant network.
Its primary purpose is to enable subscriber self-provisioning and management of supplementary services. This reduces operational costs for network operators by minimizing calls to customer support centers for simple service changes. It also empowers users, giving them immediate control over their telephony features. The structured syntax, with distinct fields for service, operation, and parameters, allows for a wide range of services to be controlled through a consistent and memorable pattern (e.g., *21* for forwarding, *33* for barring).
Historically, the SSC concept was introduced in the early GSM standards (R99) and has been maintained through every subsequent release, including 5G. Its longevity is a testament to its effectiveness as a simple yet powerful user interface mechanism. While new provisioning methods like OMA DM (Open Mobile Alliance Device Management) or HTTP-based interfaces (for 5G) have emerged, the SSC remains a fundamental fallback and a widely understood method for service control, ensuring accessibility and interoperability across decades of mobile technology evolution.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (228 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the specification introduced "SSC Mode Selection" as a new control function, alongside clarifications on the relation between SSC mode 3 and the PDU session type. The release also provided technical corrections regarding the remaining IP address/prefix lifetime specifically for SSC mode 3 operation.
- Updates of QoS Notification Control description and data model TS 29.514CR0028
- Call Control update for PDU sessions TS 31.111CR0683
- Fix implementation error for USIM Call Control procedure and allow updating only the operator specific ePCOs. TS 31.111CR0694
- Remaining IP address/prefix lifetime with SSC mode 3 TS 23.501CR0018
- Relation between the SSC mode 3 and the PDU type TS 23.501CR0028
- Control of the Messages triggering Paging at AMF TS 23.501CR0033
+ 54 more changes
In Release 16, the SSC function was enhanced to support the control of traffic forwarding within a 5G-LAN, allowing for more granular management of user data paths. Additionally, new policy control request triggers were introduced specifically for wireline access and Time-Sensitive Networking (TSN) applications, enabling more dynamic and service-specific policy provisioning. These updates expanded the network's ability to manage supplementary services based on access technology and authorized data network policies.
- Introducing Rate Control for 5G CIoT TS 23.501CR0752
- Introduction of data transfer in Control Plane CIoT 5GS Optimisation TS 23.501CR0889
- CIoT Introduction of Overload Control TS 23.501CR0894
- Introduction of Service Gap Control TS 23.501CR1014
- UL CL/BP controlled by I-SMF TS 23.501CR0848
- Control of traffic forwarding in 5G-LAN TS 23.501CR0909
+ 64 more changes
In Release 17, the changes to the Supplementary Service Control (SSC) string function are not directly addressed in the provided grounding context or the listed Change Request titles. The CR titles focus on enhancements in areas such as Network Slice Admission Control, congestion control analytics, and policy control for various services, but none specify modifications to the SSC string or its related procedures. Therefore, based solely on the given materials, there is no identified new feature or update for the SSC function in this release.
- TS23.501 KI#1 Network Slice Admission Control Function (NSACF) definition TS 23.501CR2679
- TS23.501 KI#2 Network Slice Admission Control Function (NSACF) definition TS 23.501CR2680
- Adding the usage of Session Management Congestion Control Experience analytics TS 23.501CR2708
- Network access control by Credential Holder TS 23.501CR2717
- Support of Emergency and Priority Services in Network Slice Admission Control TS 23.501CR2837
- Network Slice Admission Control in EPC TS 23.501CR2924
+ 35 more changes
In Release 18, the SSC function was enhanced to provide more granular network control over slice usage and data flows, including new policy controls for multi-modal services and mechanisms for latency requirements. These updates introduced explicit network control of slice usage and clarified inputs for UE policy control, such as the Configured NSSAI. Furthermore, the enhancements extended policy control to support Low Latency, Low Loss, Scalable Throughput (L4S) traffic and to manage both uplink and downlink based on round-trip latency requirements for specific data flows.
- Policy control enhancements to support multi-modal flows TS 23.501CR3864
- Improved network control of the UE beahviour for a network slice TS 23.501CR3939
- Network access control when the UE accesse an SNPN that provides access for Localized Services TS 23.501CR4270
- Network control of the slice usage TS 23.501CR4443
- Update to Support Network Controlled Repeater TS 23.501CR5273
- Group related data rate policy control TS 29.512CR1056
+ 29 more changes
In Release 19, the SSC function saw updates primarily focused on QoS notification control, including support for PDU Set QoS and notification control in both UL and DL directions. Enhancements were made to the policy control framework, correcting and clarifying procedures for traffic steering controls, DDN event policy control, and congestion control. Additionally, corrections were applied to specifications regarding SSC modes 2 and 3 in the context of I-SMF insertion.
- Control Plane and User Plane Protocol stacks involving the MWAB node TS 23.501CR5561
- KI#2: UE subscription and policy control for energy efficiency and energy saving TS 23.501CR5739
- Functional Description of Energy Efficiency Control Functionality TS 23.501CR5740
- Control of UE access to MWAB TS 23.501CR5468
- Support Alternative QoS profile with PDU Set QoS and Notification Control TS 23.501CR5524
- QoS notification control in UL and DL direction information TS 29.512CR1376
+ 14 more changes
In Release 20, the SSC function was updated to support policy control for network energy saving, as indicated by the Change Request titles. This involved an update to the architecture and the Exposure Interface Function (EIF) to enable this new policy control capability. The enhancement allows the network's energy consumption information to be exposed and used within the supplementary service control framework.
Explore further
Broader topics and technologies where SSC plays a role.
Defining Specifications
3GPP specifications that define or reference SSC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 24.526 vj30 | UE Policies for 5GS; Stage 3 | Rel-19 |
| TS 25.211 vj00 | UTRA FDD Layer 1: Transport & Physical Channels | Rel-19 |
| TS 25.213 vj00 | UTRA FDD Spreading and Modulation | Rel-19 |
| TR 26.803 vh00 | 5G Media Streaming Extensions for Edge Processing | Rel-17 |
| TS 26.891 vg00 | Media Distribution Services in 5G System | Rel-16 |
| TR 28.844 vi00 | Technical Report on Charging Aspects of Satellite in 5GS | Rel-18 |
| TS 29.109 vj00 | GAA Bootstrapping Interfaces (Zh, Dz, Zn, Zpn) | Rel-19 |
| TS 29.508 vj40 | 5G Session Management Event Exposure Service | Rel-19 |
| TS 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.514 vj40 | 5G System; Policy Authorization Service; Stage 3 | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |
| TS 29.525 vj40 | 5G UE Policy Control Service Stage 3 | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 31.111 vj30 | USIM Application Toolkit (USAT) Specification | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.291 vj40 | Charging Management: Service-Based Interface Protocol | Rel-19 |
| TS 32.899 vf10 | 5G Charging Architecture Study | Rel-15 |
| TR 33.919 vj00 | GAA Overview TR | Rel-19 |