NG-RAN Registration Retry via Cell Redirection for Unsupported S-NSSAI
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Solution Overview
Problem
Existing solutions for network slice selection in cellular communication systems fail to ensure successful registration when a requested network slice is not supported by the current cell, leading to unclear redirection and retry processes, especially when release with redirection or handover fails.
Innovation Solution
The proposed method involves a radio access network node detecting unsupported network slices and performing release with redirection or RRC reconfiguration, sending an indication to the user equipment to retry registration in a target cell, and providing a list of network slices that can be accessed in the target cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the network redirects the UE to a new tracking area when the current TA does not support the requested S-NSSAI, then the UE can access supported network slices, but the registration process becomes complex and may fail if redirection or handover fails
Solution Approach 1:
The network performs preliminary actions by determining supported S-NSSAIs per gNB before redirection, and includes this information in the redirection command to the UE. This allows the UE to proactively prepare for registration retry with appropriate S-NSSAI selection, reducing registration failures and simplifying the overall process.
Solution Approach 2:
The network provides feedback to the UE about which S-NSSAIs are supported at the target gNB by including this information in the redirection command. This feedback enables the UE to make informed decisions about which S-NSSAIs to request during registration retry, improving registration success while maintaining a manageable process complexity.
2Measurement precision
If the AMF knows per gNB basis about supported S-NSSAIs per TA, then the network can better determine likelihood of overlap and improve redirection accuracy, but the NSSF only receives supported S-NSSAIs per TA without gNB identification information
Solution Approach 1:
The AMF acts as an intermediary that enriches the S-NSSAI support information by adding gNB identification. The AMF receives basic S-NSSAI per TA information from NSSF, correlates it with gNB-specific support information, and provides the enhanced information to the RAN for accurate redirection decisions.
Solution Approach 2:
The S-NSSAI support information is segmented into two levels: NSSF level (per TA) and AMF level (per gNB within TA). This segmentation allows the NSSF to maintain a simplified view while the AMF provides detailed gNB-specific information needed for precise redirection without overloading the NSSF.
3Reliability
If the UE retries registration in the target cell after redirection, then the UE can access the requested network slices, but the RRC message size increases due to additional indication information
Solution Approach 1:
The S-NSSAI support information is extracted from the core network and placed in the RRC redirection command. This allows the information to be used efficiently for registration retry without requiring large message exchanges between UE and network during the retry process, as the UE already has the necessary information from the initial redirection command.
Data Source
AI summary
Redirection and retry of registration is disclosed herein. In some embodiments, a User Equipment (UE) of a Next Generation Radio Access Network (NG-RAN) is adapted to transmit a Non-Access Stratum (NAS) registration request comprising one or more Single-Network Slice Selection Assistance Information (S-NSSAI), indicated as one or more requested S-NSSAI. The UE is further adapted to receive, in an Access Stratum (AS) protocol, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration request in a target cell. The UE is also adapted to reattempt the NAS registration in the target cell, responsive to receiving the AS-level registration reattempt indication.