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Evaluating Mobility Support in ZigBee Networks

This paper investigates the current performance of ZigBee networks, particularly their support for device mobility. As ZigBee aims to enhance wireless connectivity for simple appliances, understanding its routing protocols is vital for various applications. Through simulations, we reveal the challenges ZigBee faces in handling mobility, particularly with mobile end devices and routers. Our findings indicate increased packet loss rates under mobility scenarios, especially as mobile nodes travel at higher speeds. We conclude that improvements are necessary to enhance the efficacy of ZigBee in mobile environments.

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Evaluating Mobility Support in ZigBee Networks

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  1. Evaluating Mobility Support in ZigBee Networks Tony Sun1, Nia-Chiang Liang1, Ling-Jyh Chen2, Ping-Chieh Chen1, and Mario Gerla1 1University of California at Los Angeles 2Academia Sinica

  2. Motivation • Simple appliances and numerous traditional wired services can now be efficiently connected wirelessly. • The ZigBee standard is the latest attempt to realize the wireless network vision. • Understanding the performance of ZigBee networks becomes important in determining the applicability of many applications.

  3. Our Contribution • Dissecting ZigBee routing and its current support for device mobility. • Running a rich set of preliminary simulations, illustrating the inefficacy of current standard in handling mobility.

  4. Background - ZigBee • Based on the Low Power, Low Rate IEEE 802.15.4 Standard • ZigBee is the network and application specification developed by the ZigBee alliance. • Back by 150+ member companies and numerous adopters • Released June 2005

  5. ZigBee Coordinator ZigBee Router ZigBee End Device Background- ZigBee • Three device types • Coordinator: FFD • Routers: FFD • End devices: RFD or FFD • End devices with limited functionality to control cost • Can only communicate to parent router • Rely on their parent router for routing functionality • ZigBee node has two addresses • 16-bit network address • 64-bit MAC address

  6. Mobility support in ZigBee mesh topology • Mobile end device: • When an end device moves out of the range of his parent router, • if this end device is receiver • the source nodes will receive a route error message and trigger Device Discovery primitive in the application layer. • if this end device is sender • transmission will be temporally disrupted for the duration it takes for the mobile to find a new parent router to associate itself with. • Mobile router: • Whenever an existing route failed, • whether an router is sender or receiver • Built-in route recovery mechanism (via router discovery and route error) • ZigBee routers are robust to effects from most mobility cased.

  7. Mobility support in ZigBee Tree topology • Every other device is a descendant of the ZigBee coordinator and no device is the descendant of any ZigBee end device. • Each node can check the destination address against its own to determine where the destination is. • When a node change its parent router due to mobility, a new network address will be automatically assigned to preserve the tree addressing structure. • Simple mobility of a router can cause cascading address changes across entire tree branches.

  8. Mobility support in ZigBee Tree topology • Mobile end device: • Route discovery and Device Discovery • Device Discovery mechanism would only work under very limited mobility scenario. • When there are persistent or multiple occurrences of mobility, the longer routes and slower throughput of tree routing tends to hinder the responsiveness of the recovery scheme. • Mobile router: • A cascading network address change to all of its descendant nodes on impacted branches. • Creating varying levels of inconsistency to the tree addressing scheme, thereby reducing the routing protocol’s ability to function properly.

  9. Evaluation • The NS-2 simulator with Samsung’s IEEE 802.15.4 extension • Network component: 36 nodes(70% routers and 30% end devices) • Testing parameters: • Varying percentage of mobile nodes • Mobile node with varying speed • Performance metrics • Packet delivery ratio • The average over the number of flows in the network • Relative routing overhead • A Normalized value of the total overhead of the network with respect to the traffic in the network

  10. Scenarios

  11. Varying percentage of mobile nodes

  12. Varying percentage of mobile nodes

  13. Varying percentage of mobile nodes

  14. Varying percentage of mobile nodes

  15. Scenarios with mobile nodes of varying speed • 20% nodes are selected randomly to be mobile nodes. • the speed of mobile node are constant. (1m/s to 5m/s in 1m/s increments)

  16. Mobile nodes of varying speed

  17. Mobile nodes of varying speed

  18. Mobile nodes of varying speed

  19. Mobile nodes of varying speed

  20. Conclusion • We discussed ZigBee routing and its support for device mobility • We analyzed the adequacy of current provision in dealing with different mobility cases. • The packet loss rate increases under the multiple instances of mobility and when mobile nodes travel at higher speed. • We found that the end devices suffer more packet loss than router under mobile scenarios.

  21. Thank You!

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