SRVCC Signaling Bearer Security Key Mapping
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Solution Overview
Problem
The handover of signaling radio bearers (SRBs) from packet switched (PS) to circuit switched (CS) domains during Single Radio Voice Call Continuity (SRVCC) results in an unsustainable state due to maintaining two different CS keys for the control plane (C-plane) and user plane (U-plane), which is not allowed and represents an error case.
Innovation Solution
The solution involves using the mapped CS keys for protecting SRBs across the handover and employing synchronization of SRB sequence numbers (SNs) through a controlled suspension and reset procedure similar to SRNS relocation, ensuring consistent protection and avoiding complex key handling situations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two different CS keys are maintained for C-plane and U-plane during SRVCC handover, then security protection for both planes is preserved, but the system enters an unsustainable error state
Solution Approach 1:
The patent merges the key handling procedures for C-plane and U-plane by applying the same mapped CS key to both planes during SRVCC handover. This consolidation eliminates the unsustainable state of maintaining two different keys while preserving security protection through the unified key application.
Solution Approach 2:
The patent changes the key parameter state by suspending and resetting SRB sequence numbers during the handover process. This parameter reset ensures that the system transitions from a state with potential key divergence to a consistent state where both C-plane and U-plane use the same mapped CS key.
2Reliability
If SRB sequence numbers are synchronized during handover, then consistent protection is achieved, but additional control procedures are required
Solution Approach 1:
The patent performs preliminary suspension of SRB sequence numbers before the actual key application during SRVCC handover. This preliminary action prepares the system for consistent key protection by ensuring sequence number synchronization is initiated before the handover completes, avoiding later inconsistencies.
Solution Approach 2:
The patent implements a feedback mechanism where the completion of SRVCC handover triggers the suspension and reset of SRB sequence numbers. This feedback loop ensures that sequence number synchronization occurs automatically in response to handover events, maintaining consistent protection without requiring external intervention.
Data Source
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AI summary
The exemplary embodiments of the invention provide at least a method, apparatus, and computer program to detect a single radio voice call continuity activation event indicating a handover of a user equipment between a packet switched domain and a circuit switched domain (4A), consistent with a serving radio network subsystem relocation procedure, suspend control plane signaling radio bearers (4B), reset the suspended signaling radio bearers (4C), and resume the suspended signaling radio bearers in the domain handed over to, where resuming comprises protecting control plane signaling radio bearers of a domain handed over to using a same mapped security key that is used to cipher user plane radio access bearers in the domain handed over to (4D).