S-CSCF Registration Context Restoration After Inactivity
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Solution Overview
Problem
In the context of a Serving Call Session Control Function (S-CSCF) within an IP Multimedia Subsystem (IMS), there is a challenge in restoring registration context after a period of failure or inactivity, where the S-CSCF loses registration data and cannot determine if a user equipment's registration has expired, leading to potential call failures due to loss of synchronization with the Home Subscriber Server (HSS).
Innovation Solution
The solution involves receiving a request for communication from a second user equipment after a period of inactivity, retrieving an expiry value for the first user equipment's registration from the Home Subscriber Server, and determining if the registration has expired by comparing the current time with the expiry value. If expired, a server assignment request is sent to the HSS, and a default service is provided, such as forwarding communication to a voice mail service or redirecting to a circuit-switched domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the S-CSCF loses registration data after a period of inactivity, then the device can resume operation after failure, but the registration status cannot be determined leading to call failures
Solution Approach 1:
The S-CSCF performs preliminary actions by retrieving expiry values from the HSS and comparing them with current time immediately upon restoration, before processing any call requests. This ensures registration status is determined proactively rather than reactively when call failures occur.
Solution Approach 2:
The system establishes a feedback mechanism where the S-CSCF continuously monitors registration expiry status by comparing current time with stored expiry values, and automatically triggers re-registration or default service provisioning when expiry is detected, ensuring continuous operational reliability.
2Reliability
If the S-CSCF continuously monitors registration status, then call failures are prevented, but system complexity and processing overhead increase
Solution Approach 1:
The S-CSCF performs self-service by autonomously determining its own registration status through time comparison with expiry values stored in its database, without requiring external verification or complex monitoring infrastructure. This simplifies the system while maintaining reliability.
3Loss of information
If the S-CSCF requests expiry information from HSS after restoration, then registration status is restored, but communication overhead and latency increase
Solution Approach 1:
The S-CSCF retrieves expiry information from the HSS as a preliminary action immediately upon restoration, before any call processing occurs. This minimizes the time penalty by performing the information retrieval once during restoration rather than repeatedly during operation.
Data Source
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AI summary
An apparatus (308) comprising means for: receiving, from a second user equipment (312), a request for communication with a first user equipment (302), after a period of time during which the apparatus was not operating;receiving information from a home subscriber server (310) comprising an expiry value for registration of the first user equipment with the apparatus; and determining that the registration has expired.