SMF PGW-C Network Slice Re-Selection in 4G 5G Interworking
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Solution Overview
Problem
The Mobility Management Entity (MME) lacks sufficient information to select a Session Management Function (SMF)/Packet Data Network Gateway-Control Plane (PGW-C) that supports the correct network slice, leading to potential session creation failures when the selected PGW is not configured to support the subscribed network slice, resulting in poor Key Performance Indicators (KPIs) and repeated request rejections.
Innovation Solution
The SMF/PGW-C redirects or provides information for an alternative SMF/PGW-C that supports the subscribed network slice, using service discovery procedures to ensure the correct network slice is utilized for session management, or includes the Fully Qualified Domain Name (FQDN) in the Create Session Response message to facilitate correct PGW selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the MME selects an SMF/PGW-C using DNS procedures based on APN, then the selection process is simple and fast, but the selected PGW may not support the subscribed network slice, leading to session creation failures
Solution Approach 1:
The patent applies preliminary action by having the SMF/PGW-C check network slice support capability before processing session creation requests. The SMF/PGW-C determines whether it is configured to support the network slice associated with the requested APN/DNN before proceeding with session establishment, preventing failures before they occur. This is implemented through the determination step in clause 5.12.3.3 where the SMF/PGW-C checks its configuration against the subscribed network slice.
Solution Approach 2:
The patent implements feedback through the Create Session Response message that includes the S-NSSAI information element. When the SMF/PGW-C cannot support the requested network slice, it provides feedback to the AMF about the network slice support status. This feedback mechanism allows the AMF to make informed decisions about session establishment and can trigger reselection of alternative SMF/PGW-C instances that do support the required network slice.
2Ease of operation
If the MME uses APN as the key parameter for PGW selection, then the selection process is straightforward, but multiple network slices may support the same APN causing selection ambiguity
Solution Approach 1:
The patent applies segmentation by separating the PGW selection process into two independent stages: first, the MME selects an SMF/PGW-C based on APN using DNS procedures; second, the selected SMF/PGW-C determines network slice support capability. This segmentation allows the selection process to remain simple at the MME level while adding network slice awareness at the SMF/PGW-C level, preventing information loss about network slice requirements.
Solution Approach 2:
The patent introduces the SMF/PGW-C as an intermediary between the MME and the actual session establishment. The SMF/PGW-C receives the APN-based selection from the MME, then mediates by checking network slice support capability and determining whether to proceed with session creation or redirect to another SMF/PGW-C. This intermediary role preserves network slice information that would otherwise be lost in the selection process.
3Reliability
If the SMF/PGW-C redirects to an alternative SMF/PGW-C, then session creation can succeed, but additional signaling and processing time are required
Solution Approach 1:
The patent uses feedback to minimize redirections by having the SMF/PGW-C include S-NSSAI information in the Create Session Response message. This feedback allows the AMF to understand network slice support status and make informed decisions about session establishment, reducing the need for repeated redirections and minimizing overall establishment time.
Solution Approach 2:
The patent applies preliminary action at the SMF/PGW-C level by checking network slice support capability before processing session creation requests. This preliminary determination prevents unsuccessful session creations and reduces the need for repeated redirections, thereby minimizing the time loss associated with multiple selection attempts.
Data Source
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AI summary
Disclosed herein is a method performed by a first network node (e.g., SMF/PGW-C #1) for interworking between a 4G Evolved Packet Network (EPC) and a 5G core (5GC). The method comprises: receiving (3-6), at a first network node, a request to create a session for a UE for a particular APN/DNN; determining (3-9) that the first network node is not configured to support a subscribed network slice of the UE that containsthe particular APN/DNN; identifying (3-11) a second network node (e.g., PGW2 or second SMF/PGW-C) that is configured to support the subscribed network slice of the UE that contains the particular APN/DNN; and transferring (3-12), to the second network node, the request to create a session for the UE for the particular APN/DNN.