Description
Application Level Subscriber Identity (ALSI) is a critical identifier within 3GPP systems that operates at the application layer, distinct from network-level identifiers like IMSI or MSISDN. Unlike network identifiers that are tied to SIM cards or network subscriptions, ALSI provides a service-specific identity that can be used across multiple applications and services. This separation allows application providers to maintain their own identity management systems while still being able to correlate users with their network identities when necessary for authentication or billing purposes.
The architecture supporting ALSI involves coordination between the application layer and the underlying network infrastructure. When a user accesses a service, the application server can request authentication using ALSI through standardized interfaces with the core network. The network then maps the ALSI to the corresponding network-level identifier (such as IMSI) to verify the user's subscription status and permissions. This mapping is typically managed through authentication servers and identity management systems that maintain the relationships between application-level and network-level identities.
ALSI works through a multi-layered identity management approach where the application layer maintains its own identity database that references network identities without exposing sensitive network-level information to application providers. When a user authenticates to an application, the ALSI is presented to the application server, which then communicates with network authentication functions to validate the identity. This validation can include checking subscription status, service permissions, and other attributes associated with the user's network subscription.
Key components in the ALSI ecosystem include the application servers that issue and manage ALSIs, the authentication servers that validate these identities against network records, and the identity mapping databases that maintain the relationships between application-level and network-level identifiers. These components work together through standardized interfaces defined in 3GPP specifications to ensure interoperability between different vendors' implementations.
In the network architecture, ALSI plays a crucial role in enabling value-added services by providing a persistent identity that applications can use to track user sessions, preferences, and service usage across multiple access methods. This allows service providers to offer personalized experiences while maintaining security through network-level authentication when required. The separation of application identity from network identity also enhances privacy by limiting the exposure of network identifiers to application providers.
Purpose & Motivation
ALSI was created to address the growing need for application-layer identity management in mobile networks as value-added services became more prevalent. Before ALSI, application providers either had to create their own identity systems (leading to multiple logins and poor user experience) or rely on network-level identifiers like MSISDN (which exposed sensitive network information to application layers). This created security vulnerabilities and limited the flexibility of service offerings.
The primary motivation for developing ALSI was to enable service providers to offer personalized, seamless experiences across multiple applications while maintaining proper security boundaries between network and application layers. By providing a dedicated application-level identifier, 3GPP systems could support richer service ecosystems where applications could maintain persistent user identities without needing direct access to network authentication mechanisms. This separation also facilitated regulatory compliance by limiting the exposure of personally identifiable information at the network level.
Historically, the introduction of ALSI in Release 4 coincided with the expansion of mobile data services and the emergence of sophisticated application platforms. Previous approaches either forced application providers to build complete identity management systems (increasing complexity and cost) or required them to use network identifiers that were not designed for application-layer use. ALSI solved these problems by providing a standardized way to bridge application and network identity domains while maintaining appropriate security controls and privacy protections.
Key Features
- Application-layer identity separate from network identifiers
- Mapping capability to network-level identities for authentication
- Support for persistent user identity across application sessions
- Standardized interfaces for identity validation
- Privacy protection through limited exposure of network identifiers
- Interoperability between different application and network vendors
Evolution Across Releases
Initial introduction of ALSI with basic application-level identity capabilities. Defined the fundamental architecture for separating application identities from network identifiers, established basic mapping mechanisms between ALSI and IMSI/MSISDN, and specified initial interfaces for application servers to validate ALSIs through network authentication functions.
Defining Specifications
| Specification | Title |
|---|---|
| TS 21.905 | 3GPP TS 21.905 |