Source SGSN Determination via NAS Addressing Information
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Solution Overview
Problem
Current systems face challenges in determining the source SGSN when the SGSN where a UE is located changes, leading to inconsistencies in addressing information and failure to obtain correct SGSN information during handovers, especially in reverse SRVCC handovers and inter-SGSN handovers.
Innovation Solution
A method and apparatus that involve the MSC requesting and obtaining addressing information of the source SGSN through a NAS message from the UE, and sending this information to a target MME or SGSN, ensuring accurate determination of the source SGSN by including NRI, P-TMSI, RAI, RAC, and IP address.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the RNC relies on NRI reported by UE in initial direct transfer message to determine source SGSN, then the source SGSN can be determined in normal RAU process, but the NRI becomes invalid when RNC fails to connect to source SGSN or when inter-RNC/inter-SGSN handover occurs
Solution Approach 1:
The patent applies preliminary action by having the UE proactively report source SGSN addressing information (including NRI, P-TMSI, RAI, RAC, and IP address) to the MSC before the handover is initiated. This early reporting ensures that the MSC has current and accurate source SGSN information regardless of subsequent connection failures or handover events, resolving the reliability issue with NRI validity.
Solution Approach 2:
The patent introduces the MSC as an intermediary that collects, stores, and manages source SGSN addressing information from the UE. Instead of relying directly on NRI reported to RNC (which may become invalid), the MSC acts as a central repository that provides authoritative source SGSN information to the target MME or SGSN, ensuring accurate determination even when direct RNC-SGSN connection fails.
2Stability of the object's composition
If the UE initiates RAU process after inter-RNC handover to ensure RAI consistency, then RAI consistency is maintained, but the uplink direct transfer message does not include NRI so RNC cannot obtain source SGSN information
Solution Approach 1:
The patent makes the source SGSN addressing information report universal by implementing it as a general mechanism that works across multiple scenarios: normal RAU processes, inter-RNC handovers, and inter-SGSN handovers. Instead of relying on NRI-specific messages that may not be present in all message types, the UE reports comprehensive addressing information (NRI, P-TMSI, RAI, RAC, IP address) that can be used universally to identify the source SGSN regardless of the specific handover or RAU scenario.
3Stability of the object's composition
If the RNC notifies RAI change to UE to maintain consistency, then RAI consistency is improved, but UE initiates RAU process and may change SGSN, making original NRI invalid
Solution Approach 1:
The patent applies preliminary action by having the UE report its current source SGSN addressing information to the MSC before any RAI change or handover occurs. This ensures that even if subsequent RAU processes cause SGSN changes, the MSC already has the original source SGSN information needed for the handover preparation, eliminating the need to wait for RAU completion or worry about NRI validity changes.
4Ease of operation
If the system uses RAI FQDN structure for SGSN addressing, then the target MME or SGSN can be connected to source SGSN using RAI and NRI, but the addressing information becomes insufficient when SGSN changes during handover
Solution Approach 1:
The patent creates a composite addressing information structure that combines multiple identifiers (NRI, P-TMSI, RAI, RAC, and IP address) into a comprehensive source SGSN identification package. This composite approach ensures that even if individual components like NRI become invalid due to SGSN changes, the combination of multiple identifiers allows the target MME or SGSN to reliably determine the original source SGSN through alternative matching criteria.
Data Source
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AI summary
Embodiments of the present invention provide a method and an apparatus for determining a source SGSN. The method for determining a source SGSN includes: obtaining addressing information of a source SGSN through a NAS message sent by a UE; and sending the addressing information of the source SGSN to a target MME or a target SGSN, so that the target MME or the target SGSN determines the source SGSN according to the addressing information of the source SGSN. The embodiments of the present invention may ensure that an MSC obtains latest addressing information of a source SGSN of a UE, so that a target MME or a target SGSN obtains prepare bearer information of the UE from a correct source SGSN.