Self-healing IP Multimedia Subsystem Core via Secondary S-CSCF
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Solution Overview
Problem
In the IP multimedia subsystem (IMS), when a Serving-Call Session Control Function (S-CSCF) becomes unavailable, it cannot restore user equipment (UE) profile and registration session information, leading to failed SIP messages and incomplete calls, as existing systems lack efficient mechanisms for session re-establishment.
Innovation Solution
Implementing a secondary S-CSCF that can be activated by an Interrogating-Call Session Control Function (I-CSCF) to manage registration, with the restoration data feature disabled, allowing the Home Subscriber Server (HSS) to download profiles from a different S-CSCF and enable re-assignment upon timeout or failure, ensuring seamless session re-establishment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single S-CSCF is used for session control, then the system structure is simple, but the system reliability deteriorates when the S-CSCF becomes unavailable
Solution Approach 1:
The system segments the S-CSCF function into multiple independent instances (first S-CSCF and second S-CSCF), each capable of handling session control independently. This segmentation allows the system to maintain session continuity by switching between instances when one becomes unavailable, resolving the contradiction between simple structure and high reliability.
Solution Approach 2:
The system changes the operational state parameters of the S-CSCF by implementing a standby mechanism where the second S-CSCF remains in a deactivated state with restoration data feature turned off, and can be activated when the first S-CSCF fails. This parameter change enables reliability improvement without permanently increasing system complexity.
2Reliability
If the first S-CSCF maintains restoration data, then session information can be restored, but the HSS cannot allow another S-CSCF to handle session re-establishment
Solution Approach 1:
The HSS acts as an intermediary that manages the restoration data and S-CSCF assignment. When the first S-CSCF becomes unavailable, the HSS can re-assign the session to the second S-CSCF by providing the necessary profile information, enabling both session restoration and S-CSCF re-assignment flexibility simultaneously.
Solution Approach 2:
The second S-CSCF is pre-configured with the restoration data feature turned off, preparing it in advance to receive and handle session restoration requests from the HSS when needed, without requiring complex real-time configuration changes.
3Reliability
If the restoration data feature is enabled, then the S-CSCF can restore sessions, but the device complexity increases
Solution Approach 1:
The restoration data management function is extracted from the S-CSCF and placed in the HSS. The S-CSCF only needs to maintain basic session state, while the HSS handles the complex restoration data storage, management, and retrieval, reducing the complexity burden on the S-CSCF while maintaining session recovery capability.
Data Source
AI summary
A system and method for a resilient and self-recovery IP multimedia subsystem. In response to a subscriber who is registered with a first S-CSCF, a second S-CSCF is established as well and a flag is provided to a database. The database stores data for the session. The second S-CSCF is concurrent and separate from the first S-CSCF. In addition, the restoration data element in the first S-CSCF is deactivated. When the first S-CSCF is timed-out or fail to respond, instead of sending a restoration data, the second S-CSCF activates the flag with the database so that the second S-CSCF may establish with the database to continue with the session for the subscriber. The database identifies the session and restores the session data for the second S-CSCF.