AMF SMF Selection via NAS Identification for PDU Session Continuity
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Solution Overview
Problem
The existing mechanism fails to ensure that the Access and Mobility Management Function entity (AMF) selects the same Session Management Function entity (SMF) for two PDU sessions connected to the same data network in SSC mode 3, leading to potential disruptions in session continuity.
Innovation Solution
The method involves the terminal transmitting a NAS message with both the first identification information of the initial PDU session and the second identification information assigned to the new PDU session, allowing the AMF to select the same SMF for both sessions, ensuring that the new PDU session is established in accordance with the first and second identification information, thereby maintaining session continuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the AMF selects SMF independently for each PDU session, then the selection process is simple and fast, but the same SMF cannot be ensured for multiple PDU sessions to the same data network
Solution Approach 1:
The terminal performs preliminary action by including the first identification information of the initial PDU session in the NAS message before the AMF makes the SMF selection. This allows the AMF to proactively select the same SMF for the new PDU session, ensuring session continuity without requiring complex post-selection coordination mechanisms.
Solution Approach 2:
The first identification information of the initial PDU session acts as an intermediary that carries the SMF selection criterion from the terminal through the AMF to the SMF selection process. This intermediary enables the AMF to identify and select the appropriate SMF without direct terminal-AMF-SMF coordination complexity.
2Productivity
If a new PDU session is established with a new SMF, then the SMF selection is independent and simple, but session continuity cannot be maintained
Solution Approach 1:
The terminal includes the first identification information in the NAS message before SMF selection occurs, enabling the AMF to pre-determine the appropriate SMF. This preliminary action maintains fast session establishment while ensuring the correct SMF is selected for continuity.
Solution Approach 2:
The first identification information serves as feedback from the terminal to the AMF about the existing PDU session context. This feedback enables the AMF to make an informed SMF selection that maintains session continuity while keeping the process efficient.
3Ease of operation
If the AMF uses existing SMF selection mechanisms, then the selection process is straightforward, but it cannot ensure consistent SMF selection for SSC mode 3 PDU sessions
Solution Approach 1:
The terminal performs preliminary action by embedding the first identification information in the NAS message, which guides the AMF's SMF selection. This maintains operational simplicity while achieving consistent SMF selection through the provided identification criterion.
Solution Approach 2:
The first identification information acts as an intermediary that bridges the simple AMF selection process with the requirement for consistent SMF selection. It carries the necessary context without requiring complex selection logic in the AMF.
Data Source
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AI summary
A method and an apparatus for session reestablishment, an Access and Mobility Management Function entity AMF, a Session Management Function entity SMF and a terminal are provided. The method includes: AMF obtaining a Non-Access Stratum NAS message transmitted by a terminal, where the NAS message is to request to establish a new packet data unit PDU session connected to a same data network as an initial PDU session, and the NAS message carries first identification information of the initial PDU session and second identification information of the new PDU session assigned by the terminal; and transmitting a session management request to SMF corresponding to the first identification information. The session management request carries the first identification information and the second identification information, and the session management request is to cause the SMF to establish the new PDU session based on the first identification information and the second identification information. The new PDU session is connected to the SMF selected for the initial PDU session.