Hi Robert.
I arrived at this conclusion based on a combination of technical understanding of Zigbee networks, documentation from Silicon Labs, and experiences shared within the smart home community, including the Homey forums and other platforms that utilize similar hardware.
Here’s how I came to this conclusion:
- Technical Understanding of Zigbee Networks:
- Node Table Management: In a Zigbee network, the coordinator (which is the role Homey plays) maintains internal tables that store information about all devices (nodes) that have ever joined the network. These tables include the Neighbor Table, Routing Table, and Child Table.
- Finite Memory Capacity: The memory allocated for these tables on the Zigbee chip is limited. Once the tables are full, the coordinator cannot add new devices or may experience network instability.
- Persistence of Entries: If devices are removed improperly—without following the correct exclusion process—their entries may remain in the coordinator’s tables, occupying space unnecessarily.
- Silicon Labs Documentation:
- Developer Guides and Datasheets: Silicon Labs provides detailed documentation on how their Zigbee chips manage network tables. These resources explain that the coordinator retains information about previously connected devices to maintain network integrity.
- Reference: For example, the Silicon Labs Zigbee Fundamentals Guide discusses how network nodes are managed and the importance of proper inclusion and exclusion.
- Community Experiences:
- Homey Forum Discussions: Numerous users have reported issues where they are unable to add new devices after frequently adding and removing devices. These issues are often resolved by performing a full Zigbee network reset, which clears the coordinator’s memory.
- Other Platforms: Similar experiences have been reported on other platforms using Silicon Labs chips, like SmartThings and Hubitat, reinforcing the conclusion that the chip retains information about previously connected nodes.
- Best Practices in Zigbee Network Management:
- Proper Device Removal: Industry best practices emphasize the importance of properly removing devices using the correct exclusion process to ensure that the coordinator updates its tables accordingly.
- Network Maintenance: Regular network maintenance, including monitoring and managing connected devices, helps prevent the node tables from becoming full.
- Personal and Observed Experiences:
- Troubleshooting Instances: Instances where new devices couldn’t be added until a network reset was performed suggest that the coordinator’s memory was full due to retained entries.
- Network Analysis Tools: Utilizing Zigbee network analysis tools can reveal lingering entries for devices that are no longer active, indicating that the coordinator retains their information.
- Manufacturer Acknowledgment:
- Firmware Updates and Notes: Firmware updates from device manufacturers sometimes include improvements to how the node tables are managed, indicating that this is a known issue.
- Support Responses: Official support channels occasionally acknowledge that residual entries can cause issues and recommend network resets as a solution.
In Summary:
- Retention of Node Information: The Zigbee coordinator retains information about devices that have been connected to the network. If devices are not properly removed, their entries remain in the coordinator’s memory.
- Impact of Frequent Changes: Regularly adding and removing devices without following proper procedures can fill up the coordinator’s node tables.
- Resolution Through Network Reset: Performing a full Zigbee network reset clears these tables, freeing up memory and resolving issues related to full node tables.
