PDU Session Collision Handling in 5G NR Networks

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Solution Overview

Problem

In 5G/NR systems, collisions occur between PDU session establishment and release procedures due to lost messages, leading to undefined behaviors for both user equipment (UE) and network entities when a PDU session release command is not received, causing re-transmissions and repeated attempts to establish or release sessions.

Innovation Solution

The proposed solution involves the UE ignoring a PDU session release command when initiating a new establishment procedure and the network locally releasing the old session upon receiving a new establishment request, ensuring both entities proceed with the new session establishment without waiting for a complete release message.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the network re-transmits PDU session release command messages when timer expires, then the reliability of session release is improved, but collision with UE-initiated establishment procedure occurs causing undefined behavior

Engineering Contradiction:
Improvesession release reliabilityVSAvoidprocedure definition clarity
Core Design Contradiction:
ReliabilityVSEase of operation

Solution Approach 1:

The UE applies preliminary anti-action by ignoring the PDU session release command message upon detecting the collision condition (establishment request sent with same PSI). This pre-emptive ignoring prevents the undefined behavior that would occur if the UE processed both establishment and release simultaneously, while the network's re-transmission mechanism maintains release reliability.

Inventive Principle:
Principle #9Preliminary anti-action

Solution Approach 2:

The network performs preliminary action by starting timer 3592 when sending the release command and preparing to re-transmit the release command when the timer expires without receiving release complete message. This preliminary timing mechanism ensures the release procedure persists despite potential message loss or UE collision conditions.

Inventive Principle:
Principle #10Preliminary action

2Speed

If the UE sends PDU session establishment request messages, then the session establishment speed is improved, but message loss leads to collision with network release procedure

Engineering Contradiction:
Improvesession establishment speedVSAvoidprocedure coordination reliability
Core Design Contradiction:
SpeedVSReliability

Solution Approach 1:

The UE performs preliminary action by sending the PDU session establishment request message immediately when needing to establish a session, without waiting for confirmation that no release command is in transit. This preliminary establishment attempt improves speed, while the collision detection and ignoring mechanism maintains reliability.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The system uses feedback through timer 3592 and the release complete message exchange to detect whether a collision condition exists. When the UE detects it has sent an establishment request with the same PSI used in a pending release, it provides feedback by ignoring the release command, thereby coordinating the procedures despite message loss.

Inventive Principle:
Principle #23Feedback

3Reliability

If the network waits for PDU session release complete message, then the reliability of release confirmation is improved, but procedure completion time increases

Engineering Contradiction:
Improverelease confirmation reliabilityVSAvoidprocedure completion time
Core Design Contradiction:
ReliabilityVSLoss of time

Solution Approach 1:

The network performs preliminary action by starting timer 3592 immediately when sending the release command, rather than waiting indefinitely for the release complete message. This preliminary timing allows the network to re-transmit the release command or proceed with resource release after a predetermined interval, reducing completion time while maintaining reliability through re-transmission.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The network applies skipping by proceeding with resource release or re-transmission after timer expiration without requiring explicit confirmation from the UE. This rushes through the confirmation step when necessary, reducing procedure completion time while maintaining reliability through the timer-based re-transmission mechanism.

Inventive Principle:
Principle #21Skipping (Rushing through)

Data Source

PatentEP3841825B1Handling of collision between PDU session establishment and release procedures
Publication Date: 2023.08.23 MEDIATEK INC

AI summary

A method of handling collision between PDU session establishment and PDU session release procedures is proposed. At UE side, a UE first initiates a PDU session establishment procedure to establish a PDU session having a PDU session ID. If UE receives a PDU session release command message on the same PSI, UE should ignore the PDU session release command message, and proceed with the PDU session establishment procedure. At NW side, a network entity initiates a PDU session release procedure to release a PDU session having a PDU session ID. If the network entity receives a PDU session establishment request message from UE on the same PDU session ID, the network entity should locally release the PDU session and proceed with the PDU session establishment procedure.