Simultaneous Connectivity Handover With SN Continuity Transfer
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Solution Overview
Problem
Existing solutions for simultaneous connectivity based handover in LTE and NR mobility enhancement are unclear on how to transfer sequence number (SN) status information from the source network device to the target network device during activation and ensure SN continuity upon release, particularly for RLC acknowledged mode (AM) and RLC unacknowledged mode (UM).
Innovation Solution
A method for data transmission during simultaneous connectivity handover involving SN assignment and HFN management, where the source network device transfers SN and HFN information to the target network device, ensuring continuous SN assignment and reducing reordering latency by using control PDUs and RRC signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If simultaneous connectivity based handover is implemented to reduce data interruption, then data transmission continuity is improved, but sequence number assignment and status information transfer become complex and unclear
Solution Approach 1:
The source network device performs SN assignment and HFN determination in advance during the simultaneous connectivity period, before the handover is complete. This preliminary action ensures that the target network device receives ready-to-use SN status information, eliminating the complexity of real-time SN coordination during handover and ensuring continuous data transmission.
Solution Approach 2:
The source network device acts as an intermediary that collects SN status information from the terminal device and forwards it to the target network device. This intermediary role simplifies the handover process by centralizing the SN management function, avoiding direct complex interactions between the target network device and terminal device during handover.
2Reliability
If SN status information is transferred from source to target network device during handover activation, then SN continuity is ensured, but data transmission latency increases due to information transfer overhead
Solution Approach 1:
The SN status information transfer is merged with the existing handover signaling procedures. The source network device includes SN status information in the handover request message sent to the target network device, combining multiple functions (handover coordination and SN status transfer) into a single signaling exchange, thereby reducing overall handover latency.
Solution Approach 2:
The source network device determines and prepares the SN status information in advance during the simultaneous connectivity period, so that when handover is triggered, the information is already ready for immediate transfer. This eliminates the need for separate SN status queries during handover execution, reducing time loss.
3Productivity
If reordering latency is reduced through optimized SN management, then data transmission efficiency is improved, but packet loss risk increases during the transition period
Solution Approach 1:
The terminal device maintains a buffer to store received packets during the handover transition period. This buffer acts as a cushion that prevents packet loss by holding packets temporarily while SN reordering is performed. The buffer ensures that even if packets arrive out of order or are delayed during handover, they are preserved and delivered in the correct sequence after reordering, thus preventing packet loss while maintaining transmission efficiency.
4Reliability
If control PDUs and RRC signaling are used for SN assignment and HFN management, then data integrity is enhanced, but signaling overhead and processing complexity increase
Solution Approach 1:
Existing control PDU and RRC signaling mechanisms are used for multiple purposes: both for general control messaging and specifically for SN assignment and HFN management during handover. By making these signaling mechanisms multi-functional, the patent avoids creating entirely new complex signaling protocols while still ensuring data integrity through established reliable messaging channels.
Data Source
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AI summary
Embodiments of the present disclosure relate to methods, devices and computer readable media for data transmission during simultaneous connectivity based handover. A method of communication comprises in response to a second connection being established between a second network device and a terminal device having a first connection with a first network device, determining, at the first network device, a first set of SDUs to be transmitted by the second network device to the terminal device; determining first information regarding a SN assigned to each of the first set of SDUs and a HFN associated with the SN; and transmitting the first set of SDUs and the first information to the second network device. The method further comprises receiving, at the second network device, the first set of SDUs and first information; and transmitting the first set of SDUs to the terminal device based on the first information. The method further comprises receiving, at the terminal device, a first set of PDUs corresponding to the first set of SDUs from the second network device; receiving a second set of PDUs corresponding to the second set of SDUs from the first network device; determining the first information; and determining an order of the first and second sets of PDUs based on the first information. Embodiments of the present disclosure can facilitate correct data transmission during a simultaneous connectivity based handover and improve data transmission efficiency.