Deferred Contention for Constrained Reliable Multicast in DAG Networks
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Solution Overview
Problem
Conventional multicast deployments in low-power and lossy networks result in unnecessary transmissions and delays, particularly during large-scale firmware upgrades in smart utility systems, due to duplicate multicasting and interference with new data packet transmissions.
Innovation Solution
The implementation of a constrained reliable multicast method using a directed acyclic graph (DAG) with deferred contention, where network devices defer transmission and set longer contention intervals based on distance from the root, allowing parent devices to unicast requests for missing data packets before child devices, minimizing unnecessary transmissions and optimizing data packet dissemination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If network devices use conventional multicast deployments to propagate data messages, then data dissemination can occur independently of routing topology, but unnecessary duplicate transmissions and delays occur due to multiple devices multicasting control messages
Solution Approach 1:
The patent applies preliminary action by having parent devices transmit control messages requesting missing data packets before child devices do. This is achieved through a deferred transmission timer mechanism where parent devices (closer to root) have shorter timers and thus transmit earlier, preventing child devices from sending duplicate requests and eliminating unnecessary transmissions while maintaining efficient data dissemination
Solution Approach 2:
The patent segments the network into hierarchical levels based on distance from the root device, with each device assigned a transmission priority based on its level. This segmentation into parent/child relationships and distance-based tiers allows the system to organize control message transmissions in a structured manner, preventing conflicts and reducing redundant transmissions across the network
2Reliability
If network devices transmit control messages simultaneously to request missing data packets, then all devices can identify and request absent packets, but transmission conflicts and interference with new data packets occur
Solution Approach 1:
The patent ensures reliable missing packet recovery by having parent devices perform the action of requesting retransmission before child devices do. The deferred transmission timer mechanism guarantees that parent devices (which are closer to the root and more likely to have received packets) attempt to request retransmission first, reducing transmission conflicts while maintaining reliable packet recovery
Solution Approach 2:
The patent changes the transmission timing parameter based on device distance from the root. Each device is assigned a deferred transmission timer value proportional to its distance from the root, creating a time-based separation of transmissions. This parameter change transforms simultaneous transmissions into staggered transmissions, eliminating interference while ensuring all devices can request missing packets
3Speed
If child devices transmit control messages before parent devices, then child devices can quickly request missing packets, but duplicate transmissions occur when parent devices also request the same packets
Solution Approach 1:
The patent reverses the conventional approach by having parent devices perform preliminary transmission of control messages before child devices. The deferred transmission timer is inversely proportional to distance from root, meaning parent devices (closer to root) have shorter timers and transmit first. This preliminary action by parents prevents children from sending duplicate requests, maintaining speed while eliminating redundancy
Solution Approach 2:
The patent inverts the conventional transmission order where child devices would normally transmit before parent devices. Instead, it implements an inverted hierarchy where parent devices transmit control messages first based on their closer proximity to the root, and child devices defer their transmissions. This inversion eliminates duplicate transmissions while maintaining efficient packet recovery
Data Source
AI summary
A network device receives a data packet sourced from a root of a tree-based topology and including a data structure identifying transmitted data packets transmitted by the root; in response to determining one or more absent transmitted data packets based on the data structure, the network device starts a deferred transmission timer requiring the network device to wait a first half of a selected minimum contention interval before attempting transmission to a parent at a randomized position within a second half of the selected minimum contention interval, the selected minimum contention interval based on the distance to the root and at least twice that of the parent; the network device selectively transmits a control message to the parent to request the absent transmitted data packets only if, upon reaching the corresponding randomized position of the deferred transmission timer, the network device has not received the absent transmitted data packets.