123380 (2025)

Restoration relies on specific signaling flows and data synchronization methods:

: Handling failures of application servers that provide specific services (e.g., VoLTE, messaging). 3. Key Technical Mechanisms 123380

: During initial registration, the S-CSCF backs up critical data—such as the list of SIP proxies, contact information, and authentication schemes—to the HSS. Restoration relies on specific signaling flows and data

The specification has evolved through multiple "Releases" to keep pace with mobile technology: 123380

: Procedures for when a Serving-Call Session Control Function (S-CSCF) fails or loses registration data. It defines how the Home Subscriber Server (HSS) and other nodes collaborate to re-register users or restore sessions.

The specification covers several critical failure and recovery scenarios across the IMS domain: