IP Caching for Fast Layer 3 Handoff in Mobile Access Points

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Solution Overview

Problem

Current 802.11 wireless networks do not provide mechanisms for informing devices connected to a mobile access point about subnet changes, leading to delays in layer 3 handoff when a vehicle moves from one subnet to another, particularly due to lengthy DHCP exchanges and detection of IP subnet changes.

Innovation Solution

Implementing IP caching and Mobility Domain Information Elements (MDIE) to store and reuse IP addressing information, allowing for fast layer 3 handoff by skipping lengthy DHCP exchanges when roaming back to previously visited subnets, and using subnet change notifications to inform attached devices of subnet changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional DHCP exchange is used for IP address acquisition during subnet transition, then topologically correct IP addresses are obtained, but layer 3 handoff delays are significantly increased

Engineering Contradiction:

ImproveIP address correctnessVSAvoidhandoff delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary actions by caching IP addressing information (IP addresses, subnet masks, default gateways, DNS servers) in the mobile access point before handoff occurs. When roaming back to a previously visited subnet, this cached information is reused immediately, eliminating the need for lengthy DHCP exchanges and reducing handoff delays while maintaining IP address correctness

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent creates copies of IP addressing information from the original DHCP lease and stores them in a cache within the mobile access point. These cached copies are then used during subsequent handoffs to the same subnet, replacing the need for real-time DHCP communication and significantly reducing handoff time while preserving the validity of IP configuration data

Inventive Principle:

Principle #26Copying

2Measurement precision

If subnet change detection mechanisms are implemented, then IP subnet changes are detected, but devices connected to MAP are not informed about subnet changes

Engineering Contradiction:

Improvesubnet change detectionVSAvoidsubnet change notification

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The system implements a feedback mechanism where the mobile access point detects subnet changes by comparing the Mobility Domain Identifier in received beacons against cached values, and then actively notifies all attached devices of the subnet change through wireless notifications. This ensures that both the MAP and connected devices are synchronized about subnet transitions, enabling them to update their IP configurations appropriately

Inventive Principle:

Principle #23Feedback

3Loss of time

If IP caching is implemented for fast handoff, then handoff delays are reduced, but additional memory and caching mechanisms are required

Engineering Contradiction:

Improvehandoff delayVSAvoidcaching mechanism

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The mobile access point leverages its existing multi-functional capabilities by using its processor and memory resources, which already serve routing and network management functions, to also perform IP address caching. This approach reuses existing hardware resources for the caching function, minimizing additional device complexity while enabling fast handoff through IP address reuse

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS8134969B2IP layer-handoff using mobility domains and IP caching

Publication Date: 2012.03.13 MOTOROLA SOLUTIONS INC

AI summary

The disclosure relates to fast roaming techniques which can reduce L3 handoff delay when a mobile access point and/or a mobile host roams back to a previously visited subnet. These fast roaming techniques can allow the mobile access point and/or the mobile host to skip a lengthy DHCP exchange when loading an IP address thereby reducing L3 handoff delays.