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-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)

3

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

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.)

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 device

s

orphan device

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 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

10

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

PROACTIVE RE-ASSOCIATION MECHANISM

12

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

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

15