User Plane Function Bicasting for Seamless RAN Handover
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Solution Overview
Problem
In ultra-reliable and low-latency communications scenarios, existing methods for reducing downlink data packet latency during radio access network device handovers cause packet loss due to the discontinuation of data forwarding from the source to the target RAN device.
Innovation Solution
Implementing a method where the user plane function network element bicasts downlink packets to both the source and target RAN devices, carrying information to indicate the handover and synchronize PDCP sequence numbers, ensuring seamless data transmission and avoiding packet loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UPF network element bicasts downlink packets to both S-RAN and T-RAN devices, then data transmission continuity is improved, but network device complexity increases
Solution Approach 1:
The UPF network element establishes a forwarding path to the T-RAN device in advance before handover occurs. This preliminary action ensures that when handover happens, the T-RAN device already has the downlink data packets ready to send, maintaining transmission continuity without requiring complex real-time coordination during handover execution.
Solution Approach 2:
The patent segments the data forwarding process into distinct phases: before handover (S-RAN receives and forwards packets), during handover (UPF bicasts to both S-RAN and T-RAN), and after handover (T-RAN takes over forwarding). This segmentation allows each network element to have simplified, phase-specific responsibilities rather than complex continuous coordination.
2Speed
If the S-RAN device triggers air interface handover immediately, then handover speed is improved, but packet loss occurs due to discontinuation of data forwarding
Solution Approach 1:
The UPF network element pre-establishes the forwarding path to T-RAN and sends downlink data packets to T-RAN before the air interface handover is triggered. This ensures that when S-RAN immediately triggers handover for speed, T-RAN already has the data packets ready to forward to the UE, preventing packet loss while maintaining fast handover.
Solution Approach 2:
The UPF network element acts as an intermediary that decouples the handover triggering action from the data forwarding action. S-RAN can trigger handover independently for speed, while UPF independently manages data packet distribution to both S-RAN and T-RAN, ensuring no packet loss occurs during the transition.
3Loss of time
If downlink packets are sent before PDCP SN synchronization is established, then transmission latency is reduced, but PDCP SN desynchronization occurs between S-RAN and T-RAN
Solution Approach 1:
The S-RAN device monitors the PDCP sequence numbers of downlink packets it receives from UPF and provides feedback information to T-RAN device. This feedback mechanism ensures that T-RAN can synchronize its PDCP SN with S-RAN, allowing both devices to send packets with proper sequence number alignment, reducing latency while preventing desynchronization.
Solution Approach 2:
The S-RAN device acts as an intermediary that bridges the PDCP SN synchronization between UPF and T-RAN. By monitoring and communicating PDCP SN information from S-RAN to T-RAN, it ensures both network elements maintain synchronized sequence numbers, enabling low-latency transmission without desynchronization errors.
Data Source
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AI summary
This application provides a communication method and a communications apparatus. According to the communication method and the communications apparatus, in a process in which an access network device serving a terminal is handed over from a source access network device to a target access network device, a user plane function network element may transmit first information to the source access network device. The first information is used to indicate that the user plane function network element bicasts downlink packets to the source access network device and the target access network device, so that after determining that a data packet received before the first information is sent to the terminal, the source access network device triggers an air interface handover, to avoid a packet loss in a handover process, or so that the source access network device synchronizes a PDCP SN of the source access network device with a PDCP SN of the target access network device.