Speaker: Li-Wen Chen
Date: 2010-11-30
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FAULT-TOLERANCE MECHANISMS FOR ZIGBEE WIRELESS SENSOR NETWORKS
Skender Ben Attia, André Cunha, Anis Koubâa, M ário Alves
OPEN-ZB, 2007
OUTLINE
Introduction ZigBee
Device types and network topologiesCluster-Tree Network ModelThe Orphaned Device Realignment
Fault-Tolerance MechanismsThe Parent Adoption Indicator (PAI)Reactive Re-association MechanismProactive Re-association Mechanism
Conclusion Reference 2
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)
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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
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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
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
THE ORPHANED DEVICE REALIGNMENT (CONT.)
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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 device
s
orphan device
THE ORPHANED DEVICE REALIGNMENT (CONT.)
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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 device
s
orphan device
start a new association to the network
complete the channel scan without finding its
parent
no coordinator realignment
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
REACTIVE RE-ASSOCIATION MECHANISM
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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
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PROACTIVE RE-ASSOCIATION MECHANISM
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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
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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
networks14
REFERENCE
Fault-Tolerance Mechanisms for Zigbee Wireless Sensor Networks
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