PDCP Discard Timer Coordination with RLC for Buffer Overflow Prevention
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Solution Overview
Problem
In wireless communications, the PDCP sublayer's buffering of PDCP SDUs leads to challenges in determining discard triggers and avoiding buffer overflow, particularly due to latency exceeding Quality of Service (QoS) profiles, necessitating an improved data discard procedure that coordinates between PDCP and RLC sublayers.
Innovation Solution
The proposed solution involves initiating PDCP SDU discard based on timer expiration, notifications from the RLC sublayer, and PDCP Status Reports, with coordinated timer management between PDCP and RLC entities to optimize data discard operations and prevent buffer overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PDCP sublayer buffers PDCP SDUs for retransmission, then reliability of data delivery is improved, but buffer overflow risk increases and data discard timing becomes complex
Solution Approach 1:
The patent applies preliminary action by starting a discard timer when the PDCP SDU is received from upper layers, before actual transmission occurs. This proactive timing mechanism allows the system to automatically discard stale data that exceeds QoS latency requirements, preventing buffer overflow and simplifying buffer management while maintaining reliability for time-critical data
Solution Approach 2:
The patent implements feedback through coordinated timer management between PDCP and RLC sublayers. The PDCP discard timer works in conjunction with RLC status reports and acknowledgments, where successful delivery feedback can stop the discard timer, preventing unnecessary discards while ensuring timely removal of undelivered data, thus managing buffer complexity without sacrificing reliability
2Productivity
If PDCP SDU discard timer is started upon receiving SDU from upper layers, then data discard timing is simplified and QoS compliance is improved, but risk of premature discard increases
Solution Approach 1:
The discard timer is started preliminarily when the PDCP SDU is received, establishing a maximum waiting time before automatic discard. This ensures QoS compliance by removing stale data that would exceed latency requirements, while the coordinated feedback mechanism with RLC prevents premature discard of valid data
Solution Approach 2:
The system uses feedback from RLC layer status reports and acknowledgments to interact with the discard timer. When successful delivery is confirmed via feedback, the discard timer is stopped, preventing premature discard. This feedback loop maintains reliability while allowing efficient discard of undelivered data that exceeds QoS thresholds
3Quantity of substance
If coordinated timer management between PDCP and RLC is implemented, then buffer overflow is prevented and QoS is improved, but inter-layer coordination complexity increases
Solution Approach 1:
The patent merges timer management functions between PDCP and RLC sublayers into a coordinated system. The PDCP discard timer is synchronized with RLC transmission status and acknowledgment mechanisms, allowing unified buffer occupancy control that prevents overflow while maintaining relatively simple individual layer implementations through standardized interaction protocols
Data Source
AI summary
A method and apparatus for discarding a packet data convergence protocol (PDCP) service data unit (SDU) are disclosed. A PDCP layer sets a timer and discards a PDCP SDU upon expiration of the timer. The timer may be set upon receiving the PDCP SDU from an upper layer or upon submitting the PDCP SDU to a lower layer for transmission. The timer and a radio link control (RLC) discard timer may be coordinated. Alternatively, the PDCP layer may discard the PDCP SDU based on a notification from an RLC layer or based on a PDCP status report.