1. Speaker: Li-Wen Chen Date: 2010-11-30 1 FAULT-TOLERANCE MECHANISMS FOR ZIGBEE WIRELESS SENSOR NETWORKS Skender Ben Attia, André Cunha, Anis Koubâa, M ário Alves OPEN-ZBOPEN-ZB, 2007

2. OUTLINE Introduction ZigBee Device types and network topologies Cluster-Tree Network Model The Orphaned Device Realignment Fault-Tolerance Mechanisms The Parent Adoption Indicator (PAI) Reactive Re-association Mechanism Proactive Re-association Mechanism Conclusion Reference 2

3. INTRODUCTION The IEEE 802.15.4/Zigbee protocol stack is lacking efficient fault-tolerance. Two fault-tolerance mechanisms for IEEE 802.15.4/ZigBee cluster-tree networks reactive approaches proactive approaches use a quality indicator - Parent Adoption Indicator (PAI) 3

4. DEVICE TYPES AND NETWORK TOPOLOGIES ZigBee Coordinator (ZC) one for each PAN, initiates and configures the network formation ZigBee Router (ZR) associated with the ZC or with a previously associated ZR that participates in multi-hop message routing ZigBee End Device (ZED) a simple device that has sensing capabilities and does not allow other devices to associate with it and does not participate in routing 4

5. CLUSTER-TREE NETWORK MODEL ZR: cluster-head allowing the association of other ZRs and ZEDs in a parent-child relationship. There can be multiple clusters in a network. Direct communication between two children in the same cluster is not possible. 5

6. THE ORPHANED DEVICE REALIGNMENT A native fault-tolerance mechanism which IEEE 802.15.4/Zigbee supports. Occurs when there are repeated communication failures the device loses synchronization with its parent The orphan realignment procedure relies on orphan notification frame broadcast by the orphan device including its extended address coordinator realignment frame sent in response by the parent containing the information about the device and about the network. 6

7. THE ORPHANED DEVICE REALIGNMENT (CONT.) 7 search in its neighbour table verify if the command was sent by one of its child devices orphan notification coordinator realignment stop the channel scan procedure update its PAN information scan all available (or pre- defined) radio channels parent devices orphan device

8. THE ORPHANED DEVICE REALIGNMENT (CONT.) 8 search in its neighbour table verify if the command was sent by one of its child devices orphan notification perform a channel scan searching for a suitable parent synchronization with the new parent scan all available (or pre- defined) radio channels parent devices orphan device start a new association to the network complete the channel scan without finding its parent no coordinator realignment

9. THE PARENT ADOPTION INDICATOR (PAI) LQI: Link Quality Indicator Dp: the depth of the candidate parent in the tree Tl: traffic load Ei: energy indicator The most suitable parent will have the highest PAI value. 9

10. REACTIVE RE-ASSOCIATION MECHANISM 10

11. REACTIVE RE-ASSOCIATION MECHANISM (CONT.) If the parent fails, the child device does not need to perform a second channel scan to find a new suitable parent.  reduce the inaccessibility times and allow a quicker re-association The usage of a PAI encompasses several important metrics for measuring the quality of candidate parent.  more efficient than LQI 11

12. PROACTIVE RE-ASSOCIATION MECHANISM 12

13. PROACTIVE RE-ASSOCIATION MECHANISM (CONT.) improves energy balancing leads to an establishment of connections that offer the best transmission conditions between all the nodes of the network 13

14. CONCLUSION reactive mechanism The device only needs to perform one scan procedure to realign itself with its parent or to associate to a new parent. proactive mechanism Avoiding the device re-association procedures by planning in advance its re-association to a more reliable parent. Enable a faster re-association of the orphaned devices to the network.  reducing or even eliminating inaccessibility times  improving reliability in ZigBee cluster-tree networks 14

15. REFERENCE Fault-Tolerance Mechanisms for Zigbee Wireless Sensor Networks 15