Roaming Context Transfer for WLAN Sequence Continuity
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Solution Overview
Problem
In wireless local area networks supporting multi-link operation, seamless roaming between access point multi-link devices within the same seamless mobility domain can result in data loss or duplication due to issues with sequence number coordination, buffer state, and media access control protocol data unit delivery, compromising network performance.
Innovation Solution
Implement signaling and context transfer mechanisms for both uplink and downlink directions, including sequence number coordination, data flushing, and buffer state reporting between serving and target access point devices to maintain continuous data transfer between.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If seamless roaming is implemented between access point multi-link devices, then data transfer continuity is improved, but data loss or duplication occurs due to sequence number coordination issues
Solution Approach 1:
The patent applies preliminary action by transferring the buffer state and sequence number context from the source AP MLD to the target AP MLD before the roaming transition is complete. This pre-synchronization of context information ensures that the target AP is ready to continue data transfer without loss or duplication when the client device completes roaming.
Solution Approach 2:
The patent implements feedback mechanisms where the source AP MLD receives buffer state information from the target AP MLD, and the target AP MLD receives sequence number context from the source. This bidirectional feedback ensures proper coordination and synchronization of data transfer state across the roaming transition.
2Reliability
If context information is coordinated between serving and target AP MLDs, then data transfer reliability is improved, but signaling overhead and processing complexity increase
Solution Approach 1:
The patent segments the context transfer process into distinct components: buffer state information transfer for downlink data units, and sequence number context transfer for uplink data units. This segmentation allows each aspect of context coordination to be handled independently through specific signaling mechanisms, reducing overall complexity.
Solution Approach 2:
The patent uses the distribution system as an intermediary to facilitate context transfer between AP MLDs. The distribution system carries the buffer state and sequence number information between source and target APs, simplifying the direct coordination requirements and reducing signaling complexity at the AP interfaces.
3Manufacturing precision
If buffer state and sequence number coordination is implemented, then data delivery accuracy is improved, but network overhead increases
Solution Approach 1:
The patent extracts only the essential context information needed for seamless roaming—specifically the buffer state for downlink and sequence numbers for uplink—separating these critical elements from other MAC layer parameters. This extraction approach minimizes the amount of data that needs to be transferred and coordinated, reducing network overhead while maintaining data delivery accuracy.
Data Source
AI summary
The present disclosure provides techniques for seamless roaming with uplink/downlink context transfer. A serving AP transmits a sequence of downlink data units for a TID to a client device, the sequence of downlink data units having sequence numbers falling within a transmit window for the TID. The serving AP receives, from the client device, a roaming request identifying a target AP. In response, the serving AP sends a roaming context message to the target AP, comprising at least one of a SSN of the transmit window corresponding to the TID, or a NSN for the TID, where the NSN is a first sequence number to be assigned for downlink data units of the TID transmitted by the target AP to the client device.