PDCP Sequence Alignment for Seamless MBS Handover
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Solution Overview
Problem
In current multimedia broadcast multicast services (MBS) in LTE and NR systems, the inconsistency in MBS service transmission progress between different access network devices leads to packet loss and discontinuity when user equipment (UE) moves between these devices.
Innovation Solution
The method ensures consistent PDCP SNs for data packets across different access network devices by determining PDCP SNs based on a shared SN from the core network, using GTP-U SN or QFI SN, and reporting mapping relationships between QoS flows and DRBs to maintain synchronized transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If different access network devices independently transmit MBS service with independent PDCP SN assignment, then each device can operate autonomously, but packet loss occurs during UE handover due to inconsistent transmission progress
Solution Approach 1:
The patent applies equipotentiality by establishing a unified reference point for PDCP SN assignment across multiple access network devices. The core network device serves as this reference point, sequentially assigning the same PDCP SNs to identical data packets sent to different access network devices. This ensures that all devices operate at the same 'potential' level regarding transmission progress, eliminating inconsistencies during handover and preventing packet loss.
2Device complexity
If PDCP SNs are determined independently by different access network devices, then device complexity is reduced, but transmission consistency across devices deteriorates
Solution Approach 1:
The patent introduces an intermediary mechanism where the core network device mediates PDCP SN assignment between multiple access network devices. Instead of devices independently determining PDCP SNs, the core network device acts as an intermediary that sequentially assigns consistent PDCP SNs to the same data packets before distributing them to different access network devices. This intermediary approach maintains transmission consistency while keeping individual device complexity low.
3Adaptability or versatility
If MBS service transmission progress is not synchronized between access network devices, then each device can manage its own resources independently, but packet loss occurs during UE handover
Solution Approach 1:
The patent applies preliminary action by having the core network device pre-assign consistent PDCP SNs to data packets before distributing them to different access network devices. This preliminary assignment ensures that transmission progress is synchronized across devices from the outset, rather than attempting to synchronize during handover. The core network device performs this assignment in advance, allowing access network devices to independently manage resources while maintaining consistent transmission state.
Data Source
AI summary
This application provides example communication methods and apparatuses. In one example method applied to an first access network device, the method comprises receiving a first data packet of a first session from a core network device, where the first data packet comprises a first sequence number (SN). A second data packet is sent to a terminal device, where the second data packet belongs to data of a first data radio bearer (DRB), the second data packet comprises a packet data convergence protocol (PDCP) protocol data unit (PDU), the PDCP PDU is obtained based on the first data packet, and a PDCP SN of the PDCP PDU is determined based on the first SN.