AP Multi-Link Roaming Context Transfer for 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 leads to issues like data loss or duplication due to the lack of coordination of context information such as sequence numbers, buffer state, and media access control protocol data unit delivery progress, compromising network performance.

Innovation Solution

Implement mechanisms for coordinating sequence number (SN) state, buffer occupancy, and media access control protocol data unit delivery status between serving and target access point multi-link devices during roaming, including options for SN coordination, data flushing, and buffer state reporting to ensure uninterrupted uplink and downlink data transfers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If context information coordination mechanisms are implemented between serving and target AP MLDs, then data loss and duplication are reduced, but device complexity increases

Engineering Contradiction:

Improvedata transfer reliabilityVSAvoidroaming coordination complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The serving AP MLD acts as an intermediary by transferring context information (sequence numbers, buffer states, delivery progress) to the target AP MLD during roaming. This mediator approach ensures the target AP MLD can continue data transmission without duplication or loss, resolving the reliability-complexity contradiction by establishing a controlled information transfer protocol between APs.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The context information transfer occurs before the actual roaming completion, allowing the target AP MLD to be pre-configured with necessary state information. This preliminary action ensures that when roaming occurs, data transmission can continue seamlessly without requiring complex real-time coordination during the transition.

Inventive Principle:

Principle #10Preliminary action

2Duration of action of stationary object

If context information is transferred during roaming, then seamless data transfer is maintained, but loss of time occurs during context coordination

Engineering Contradiction:

Improvedata session continuityVSAvoidcontext transfer time

Core Design Contradiction:

Duration of action of stationary objectVSLoss of time

Solution Approach 1:

Context information transfer is initiated during the roaming preparation phase before the actual handover occurs. The serving AP MLD transfers sequence numbers, buffer states, and delivery progress to the target AP MLD in advance, minimizing the time impact during actual roaming while maintaining data session continuity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The context transfer mechanism enables the data transmission function to continue uninterrupted during roaming. By maintaining sequence number continuity and buffer state information, the system ensures that useful action (data transfer) persists throughout the roaming process without significant time loss.

Inventive Principle:

Principle #20Continuity of useful action

3Reliability

If sequence number coordination is implemented, then data duplication is reduced, but device complexity increases

Engineering Contradiction:

Improvedata integrityVSAvoidsequence number management complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The serving AP MLD transfers sequence number state information to the target AP MLD, acting as an intermediary that ensures sequence number continuity. This approach reduces data duplication by maintaining proper sequence tracking without requiring complex peer-to-peer sequence coordination between multiple entities.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The target AP MLD receives a copy of the relevant sequence number state information from the serving AP MLD. This copying mechanism allows the target AP to continue sequence number management independently while maintaining consistency with the original data stream, reducing complexity compared to distributed sequence coordination.

Inventive Principle:

Principle #26Copying

Data Source

PatentUS20260075403A1Uplink and downlink data and context handling for roaming

Publication Date: 2026.03.12 CISCO TECHNOLOGY INC

AI summary

The present disclosure provides techniques for seamless roaming with uplink/downlink context transfer. A first AP MLD of a SMD establishes an association between the SMD and a non-AP MLD, receives UL MPDUs from the non-AP MLD, each UL data MPDU having a corresponding SN, transmits content of the UL data MPDUs received from the non-AP MLD to a distribution system, maintains UL context information of the association, receives a roaming request from the non-AP MLD, transfers UL context information to the second AP MLD, the UL context information comprising a SN of the last UL data MPDU received from, and acknowledged to, the non-AP MLD and forwarded to the distribution system, and transmits a roaming response to the non-AP MLD, the roaming response comprising an indication of the SN of the last UL data MPDU received from, and acknowledged to, the non-AP MLD and forwarded to the distribution system.