AP Multi-Link Roaming Window Control for MPDU Reordering Limits
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Solution Overview
Problem
In multi-AP wireless local area networks (WLANs), the uncoordinated advancement of transmission windows during roaming leads to premature discarding of older data packets, causing significant data loss and reduced reliability, which contradicts the goals of ultra-high reliability (UHR) systems.
Innovation Solution
A method and apparatus for coordinating sequence number (SN) limitation between access point multi-link devices (AP MLDs) to prevent premature advancement of transmission windows, ensuring that downlink transmissions from one AP MLD do not exceed the reordering buffer window of the non-AP MLD, thereby avoiding data loss and improving communication reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If parallel downlink transmissions are performed from both current AP MLD and target AP MLD during roaming, then transmission speed is improved, but data loss increases due to premature window advancement
Solution Approach 1:
The current AP MLD performs preliminary action by transmitting sequence number limitation information to the target AP MLD before the non-AP MLD completes roaming. This preliminary coordination prevents the target AP MLD from transmitting packets that would cause premature window advancement, thereby avoiding data loss while maintaining parallel transmission capability
Solution Approach 2:
The system implements feedback mechanism where the current AP MLD provides sequence number limitation information to the target AP MLD based on the non-AP MLD's reordering buffer window state. This feedback loop ensures coordinated window management across both AP MLDs, preventing packets from being discarded due to uncoordinated window advancement
2Productivity
If reordering buffer window advances dynamically as MPDUs are received, then reception efficiency is improved, but older MPDUs are discarded when SNs fall outside valid range
Solution Approach 1:
The current AP MLD applies preliminary anti-action by proactively limiting the sequence numbers transmitted by the target AP MLD to a maximum value that ensures packets remain within the non-AP MLD's reordering buffer window. This preventive measure stops older MPDUs from being discarded before it happens, maintaining reception efficiency while preserving data integrity
3Device complexity
If BA window and reordering buffer window are synchronized, then transmission coordination is simplified, but uncoordinated advancement causes data loss during roaming
Solution Approach 1:
The system segments the window management function by introducing sequence number limitation information as a separate control mechanism from the standard BA window synchronization. This segmentation allows independent control of the target AP MLD's transmission window based on the non-AP MLD's reordering buffer state, preventing uncoordinated advancement while maintaining simplicity
Data Source
AI summary
A method and apparatus for coordinating downlink transmission during a wireless roaming process are disclosed. A first access point multi-link device (AP MLD) performs frame exchanges with a non-AP MLD. During a roaming process where the non-AP MLD transitions to a second AP MLD, the first AP MLD transmits first information indicative of sequence number (SN) limitation to the second AP MLD. In response, the second AP MLD controls its downlink transmission based on the first information. The control is performed to ensure that MAC Protocol Data Units (MPDUs) transmitted from the second AP MLD to the non-AP MLD are within a reordering buffer window of the non-AP MLD, thereby preventing data loss and increasing communication reliability.