Description
The Global Cable Identifier (GCI) is a standardized identifier defined in 3GPP specifications to uniquely identify a cable modem or a cable network termination point within a cable broadband infrastructure. It is used in scenarios involving fixed-mobile convergence, particularly when a mobile core network needs to authenticate and manage User Equipment (UE) that is accessing services through a trusted non-3GPP access network, such as a cable network based on DOCSIS or other standards. The GCI is structured to provide global uniqueness and is typically used within authentication and authorization protocols. For example, in the context of the 3GPP Evolved Packet Core (EPC) and 5G Core (5GC), when a UE attaches via a trusted non-3GPP access, the network may use identifiers like the GCI (along with others) to determine the specific access point and apply appropriate policies. The GCI may be conveyed within authentication exchanges, such as in Extensible Authentication Protocol (EAP) methods, or within policy control interfaces. Specifications like 3GPP TS 23.003 (Numbering, addressing and identification), TS 29.561 (5G System; Interworking between 5G Network and external Data Networks), TS 29.594 (Wireline-Wireless Convergence (WWC) for 5G System), TS 31.102 (UICC applications), and TS 43.033 (Security for wireline and wireless convergence) define its format, storage (e.g., on a UICC), and usage in various procedures. Its primary role is to enable the core network to recognize the specific fixed-line access context, which can influence charging, quality of service (QoS), and access control decisions.
Purpose & Motivation
The GCI was introduced to support the convergence of fixed (cable) and mobile networks, a trend that gained significant momentum with 3GPP Release 8 and the EPS architecture. As operators began offering bundled services, there was a need to seamlessly authenticate and provide services to users regardless of whether they were connected via a cellular radio interface or a fixed broadband cable modem. Previous approaches lacked a standardized, globally unique identifier for cable access points that could be reliably used by the mobile core network for security and policy binding. The GCI solves this by providing a common identifier that can be stored on a user's SIM/USIM (as per TS 31.102) and used during authentication when the device connects via the cable network. This enables operators to offer a unified subscriber identity and consistent service experience across access types. Its creation was motivated by the business and technical drive towards Fixed-Mobile Convergence (FMC) and later Wireline-Wireless Convergence (WWC), allowing for streamlined operations, simplified billing, and enhanced security for multi-access scenarios.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (36 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, the Global Cable Identifier (GCI) was newly introduced as a specific type of Subscription Permanent Identifier (SUPI) for the 5G System, taking the form of a Network Access Identifier (NAI). It was defined alongside the Global Line Identifier (GLI) as a non-IMSI SUPI type, where its Home Network Identifier is a domain name string and it uses the null protection scheme for generating a Subscription Concealed Identifier (SUCI). This addition was part of broader work on external identifiers and subscription identifier privacy support for 5G.
- Subscription identifier privacy suppport TS 31.102CR0778
- Correction relating to the introduction of the General Public Subscription Identifier TS 29.594CR0026
- External Identifier on Sh TS 23.003CR0468
- External identifier in 5G TS 23.003CR0498
- Changed length and mapping of 5GS Temporary Identifiers TS 23.003CR0503
- Internal-Group Identifier TS 23.003CR0520
+ 1 more changes
In Release 16, the GCI (Global Cable Identifier) was formally defined as a new type of SUPI, specifically for cable network subscribers, taking the form of a Network Access Identifier (NAI). This release introduced the ability to use a GCI within a SUCI for privacy protection, utilizing the null protection scheme, and defined the corresponding Home Network Identifier for a GCI as a domain name. Additionally, Release 16 specified the NAI format for a SUCI containing a GCI and enabled its use for routing signaling to the correct network functions.
- Support of SUCI for SUPI Type GLI and GCI TS 31.102CR0896
- Correct network identifier for SNPN TS 29.561CR0067
- Network Identifier for SNPN TS 23.003CR0539
- Clarification of possible values for Home Network Public Key Identifier of SUCI TS 23.003CR0549
- Definition of Global Line Identifier TS 23.003CR0550
- Global uniqueness of NID TS 23.003CR0553
+ 5 more changes
In Release 17, the Global Cable Identifier (GCI) was formally defined as a new type of Subscription Permanent Identifier (SUPI), taking the form of a Network Access Identifier (NAI). Key enhancements included the capability for the GCI to be reported to authentication servers, specifically to both RADIUS and Diameter DN 3GPP AAA servers, as part of the network access procedures. Furthermore, the specification clarified that when used in a Subscription Concealed Identifier (SUCI), the GCI must use the null protection scheme.
In Release 18, the Global Cable Identifier (GCI) was formally defined as a new type of Subscription Permanent Identifier (SUPI), taking the form of a Network Access Identifier (NAI). This addition allows cable network subscribers to be uniquely identified within the 5G system, alongside other SUPI types like IMSI and GLI. When used, the GCI's Home Network Identifier is represented as a domain name, and it must use the null protection scheme for SUPI concealment.
- SNPN Identifier based N3IWF FQDN TS 23.003CR0687
- NSI Identifier definition TS 23.003CR0678
- NSAC Service Area Identifier TS 23.003CR0677
- Adding LCS specific identifiers TS 23.003CR0701
- Adding MPQUIC specific identifier TS 23.003CR0702
- Correction of DF Identifier for 5MBSUECONFIG TS 31.102CR0984
+ 1 more changes
In Release 19, the new work on the Global Cable Identifier (GCI) function clarified its role as a specific type of Subscription Permanent Identifier (SUPI) formatted as a Network Access Identifier (NAI). The release explicitly defined the GCI, alongside the Global Line Identifier (GLI), as a SUPI type that uses a domain name for the Home Network Identifier and mandates the use of the null protection scheme. This provided a clearer technical foundation for GCI usage within the 5G system architecture.
- Non-3GPP Device Identifier TS 23.003CR0708
- Definition of AIoT Device Permanent Identifier TS 23.003CR0713
- LCS identifiers TS 23.003CR0715
- Correction of LCS User Plane Binding Identifier Definition and Reference TS 23.003CR0728
- Define LCS-UP Connection Identifier for identifying secured user-plane connections between UE and LMF TS 23.003CR0729
- Correction and Cleanup on Ambient IoT Identifiers TS 23.003CR0738
Explore further
Broader topics and technologies where GCI plays a role.
Defining Specifications
3GPP specifications that define or reference GCI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.003 vj50 | Numbering, addressing and identification in 3GPP | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 29.594 vj20 | 5G Spending Limit Control Service Stage 3 | Rel-19 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TS 43.033 vd00 | Lawful Interception Stage 2 for GSM/GPRS | Rel-13 |