Wireless Sensor Networks: a Survey on the State of the Art and the 802.15.4 and ZigBee Standards

1. Wireless Sensor Networks: a Survey on the State of the Artand the 802.15.4 and ZigBee Standards Final Presentation 5 August 2008 Omer Alkhnbashi

2. Content • ZigBee and IEEE802.15.4 Overview • IEEE 802.15.4 PHY. • IEEE 802.15.4 MAC. • ZigBee Functional Layers Architecture & Protocol Stack. • Security. • Routing. • Energy Efficiency. • Localization.

3. Introduction • 802.15.4 standard defines the characteristics of the physical and MAC layers for LR WPANs. • ZigBee builds upon the IEEE 802.15.4standard and defines the network layer specifications and provides a framework for application programming in the application layer. Motorola : www.motorola.com/zigbee

4. ZigBee Responsibilities • Designed for wireless controls and sensors • Operates in Personal Area Networks (PAN’s) and device-to-device networks • Connectivity between small packet devices • Control of lights, switches, thermostats, appliances, etc.

5. Why do we need ZigBeetechnology? No standard approach today that addresses the unique needs of most remote monitoring and control applications • Enables the broad-based deployment of reliable wireless networks with low-complexity, low-cost solutions. • Provides the ability to run for years on inexpensive primary batteries for a typical monitoring application. • Capable of inexpensively supporting robust mesh networking technologies.

6. IEEE 802.15.4 PHYOperating Frequency Bands • Direct Sequence Spread Spectrum (DSSS) • Channel switching, link quality estimation, energy detection measurement and clear channel assessment to assist the channel selection ZigBee Alliance Homepage

7. IEEE 802.15.4 PHYPacket Structure • PHY Packet Fields - Preamble (32 bits) – synchronization - Start of Packet Delimiter (8 bits) - specifies one of 3 packet types - PHY Header (8 bits) – PSDU length, Sync Burst flag - PSDU (0 to 127 bytes) – Data field Start of Packet Delimiter PHY Header PHY Service Data Unit (PSDU) Preamble 6 Bytes 0-127 Bytes ZigBee Alliance Homepage

8. IEEE 802.15.4 MACDevice Classes • Full function device (FFD) • Any topology • Network coordinator capable • Talks to any other device • Reduced function device (RFD) • Limited to star topology • Cannot become a network coordinator • Talks only to a network coordinator • Very simple implementation

9. IEEE 802.15.4 MACmodes of operation • Non-beacon mode • 802.15.4 makes use of CSMA-CA (carrier sense multiple access with collision avoidance) • A clear channel assessment (CCA) is carried out before sending on the radio channel. • If the channel is NOT clear, we wait for a random period of time, before trying to retransmit. • Beacon mode • Beacon mode introduces the superframe structure to divide time into different transmission periods (Beacon, CAP, CFP and inactive) • During the CAP (Contention Access Period) communication is carried out like in non-beacon mode. CCA’s are aligned with the transmission/reception of the beacon.

10. IEEE 802.15.4 MACFrame Structure • A beacon frame - used by a coordinator to transmit beacons. • A data frame - used for all transfers of data. • An acknowledgment frame - used for confirming successful frame reception. • A MAC command frame - used for handling all MAC peer entity control transfers.

11. Beacon Beacon Inactive Period CAP GTS Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Active Period IEEE 802.15.4 MACSuper-frame Guarantee Time Slot Contention Access period

12. Inactive Period CAP GTS Beacon Beacon Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Active Period IEEE 802.15.4 MACSuper-frame

13. Inactive Period CAP GTS Beacon Beacon Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Active Period IEEE 802.15.4 MACSuper-frame Data for node B

14. Inactive Period CAP GTS Beacon Beacon Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Active Period IEEE 802.15.4 MACSuper-frame Ack Store message

15. Inactive Period CAP GTS Beacon Beacon Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Active Period IEEE 802.15.4 MACSuper-frame bacon ‘Data pending For B ‘

16. Inactive Period CAP GTS Beacon Beacon Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Active Period IEEE 802.15.4 MACSuper-frame Data request

17. Inactive Period CAP GTS Beacon Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Active Period IEEE 802.15.4 MACSuper-frame Data reply Beacon

18. ZigBee Functional Layers Architecture & Protocol Stack

19. Network Layer Functions • Starting a network –Able to establish a new network. • Joining and Leaving Network –Nodes are able to become members of the network as well as quit being members. • Configuration –Ability of the node to configure its stack to operate in accordance with the network type. • Addressing – The ability of a ZigBee coordinator to assign addresses to devices joining the network. • Synchronization – Ability of a node to synchronize with another node by listening for beacons or polling for data. • Security –Ability to ensure end-to-end integrity of frames. • Routing –Nodes can properly route frames to their destination (AODV, etc.).

20. Application Support Layer Functions • Zigbee Device Object (ZDO) maintains what the device is capable of doing and makes binding requests based on these capabilities. • Discovery –Ability to determine which other devices are operating in the operating space of this device. • Binding – Ability to match two or more devices together based on their services and their needs and allow them to communicate. ZigBee Alliance Homepage

21. Routing

22. Routing Ad hoc On Demand Distance Vector (AODV) Used for mesh topologies Cluster-Tree Algorithm Form clusters of nodes that make a tree ZigBee Coordinator ZigBee Router ZigBee End Device Heile, B. Wireless Sensor and Control Networks, 2006

23. RoutingTreebased Routing • Routing only along parent-child links. • Routers maintain their address and the address info associated with their children and parent. • Given an address assignment in treebased network, router can determine if the destination belongs to a tree rooted at one of its router children or is one of its enddevice children • If destination belongs to one of its children, it routes the packet to appropriate child. • If destination does not belong to one of its children, it routes the packet to its parent

24. Packet to router Packet addressed to this nod ? Yes Pass to higher layer No Packet addressed to one of end-device children ? Yes Route to child directly No Is there a routing table entry for the destination ? Yes Route to next hop No Are there resources to start a route discovery ? Yes Initiate route discovery No Route along tree Routing • Simplified execution flow of the routing algorithm • A device is said to have routing table capacity if: • It is a ZigBee coordinator or ZigBee router. • It maintains a routing table. • It has a free routing table entry or it already has a routing table entry corresponding to the destination

25. RREQ message RDT entry exist for this RREQ Yes No Create RDT entry and record fwd path cost Does RREQ report a better fwd path cost? Yes Update RDT entry Better fwd path cost RREQ for local node One of end-device Children? Yes No Drop RREQ Send RREP No Create RT entry (Discovery_Underway ) and rebroadcast REEQ RoutingRouter Discovery(1) • Route Request message processing • RREQ when node S wants to send packet to node D. - Setup forward router (to D).

26. Are RDT and RT entries available ? RREP message Drop REEP Is local node REEP destination ? Does RREP report a better residual path cost? Does RREP report a better residual path cost? Is RT entry status Active ? Drop REEP Update RDT entry residual path cost and RT entry next hop Set RT entry status to Active Update RDT entry residual path cost and RT entry next hop Forward RREP RoutingRouter Discovery(2) No • Route Reply message processing • RREP from node D to node S Yes No Yes Yes No No No Yes Yes

27. Ad hoc On Demand Distance Vector (AODV) D • The Ad hoc On-Demand Distance Vector protocol is both an on-demand and a table-driven protocol. • AODV supports multicasting and unicasting within a uniform framework. • Each route has a lifetime after which the route expires if it is not used. • A route is maintained only when it is used and hence old and expired routes are never used. S H. Karl, A. Willig Protocols and Architectures for Wireless Sensor Networks, 2005

28. Cluster-Tree Algorithm • Protocol of logical link and network layers. • Forms single/multi cluster tree networks. • Forms self-organizing network with redundancy and self-repair capabilities. • Nodes select cluster heads and form clusters in a self-organized manner. • Self-developed clusters then connect to each other through a designated Device (DD). H. Karl, A. Willig Protocols and Architectures for Wireless Sensor Networks, 2005

29. Security

30. WSN’s SecurityRequirements for WSN Security Data Confidentiality - omission of data leaks to neighboring networks. Relies on centralized infrastructure. Data Authentication - verification of sender/receiver. Data Integrity - non altered transmission of data. Data Freshness - ensuring data is recent while allowing for delay estimation. .

31. WSN’s SecurityApproaches to Security • Key management and Trust setup • Single network-wide key. • Using pairwise-shared key. • Hybrid-wide key approach. • Trusted server approach. • Asymmetric cryptography. • Random key pre-distribution scheme. • Cryptographic mechanisms • Secure network encryption protocol (SNEP).

32. ZigBee Security ZigBee is touted as “highly secure” Relies on centralized infrastructure Coordinator acts as trust center Types of keys: Master key Installed out-of-band Network key Shared by all devices No protection against “insider” attacks Link key Derived from master key

33. ZigBee Security Trust Center Can be the coordinator or a dedicated device on the network Trust during Join Authenticate join requests Network Updates and distributes network key End-to-End Configuration Assists link key setup ZigBee Alliance, ZigBee Security Specification Overview, 2005

34. Energy Efficiency

35. Energy Efficiency • Connected Dominating Set (CDS) Approaches • MAC Layer Approaches • Slot-based Protocols. • S-MAC and T-MAC. • B-MAC. • Cross Layer Approaches • Network Support. • Tree-based Stream Scheduling. • Flexible Stream Scheduling. • Topology Control • A Model for Topology Control • A Taxonomy of Topology Control Approaches

36. Localization

37. Localization • What is Localization in WSN ? • Ability to determine the locations of sensors. • Utilize some help from localization services like GPS. • Importance of Localization • Identifying the location of an event or a sensor of interest. • Helping in routing and coverage optimization. • Some Localization Challenges • Accuracy VS Complexity/Cost • Availability and Feasibility of accurate location systems. (e.g. GPS is not available indoor).

38. LocalizationRange-Based Methods • Sensors calculate absolute point-to-point distance estimates (range) to anchors or angle estimates by utilizing one of the following: • Time of Arrival (TOA). • Time Difference of Arrival (TDOA) • Angle of Arrival (AOA) • Received Signal Strength Indicator (RSSI) • Utilize some help from localization services like GPS. • Complex and depends on medium conditions and time synchronization • High computational power or requirements in sensors. • Too expensive for a large-scale WSN TOA (GPS) AOA Wireless Sensor Network, An information Processing Approach by F. Zhoa & L. Guibas

39. LocalizationRange-Based Methods • Sensors never tries to estimate the absolute point to-point distance between anchors and the sensors. • Advantages • Cheap sensor hardware. • Low computational power • Disadvantages • Less accuracy than Region-Based methods Wireless Sensor Network, An information Processing Approach by F.Zhoa & L.Guibas

40. ZigBee vs. Bluetooth ZigBee Smaller packets over large network. Data rate 250 Kbps @2.4 GHz. Allows up to 254 nodes. Home automation, toys, remote controls, etc. Bluetooth • Larger packets over Smaller network. • Data rate 1Mbps @2.4 GHz. • Allows up to 7 nodes. • Screen graphics, pictures, hands-free audio, Mobile phones, headsets, PDAs, etc. ZigBee Alliance Homepage

41. BUILDING AUTOMATION CONSUMER ELECTRONICS security HVAC AMR lighting control accesscontrol TV VCR DVD/CD remote ZigBee Wireless Control that Simply Works security HVAC lighting control access control lawn & garden irrigation patient monitoring fitness monitoring PERSONAL HEALTH CARE RESIDENTIAL/ LIGHT COMMERCIAL CONTROL What Does ZigBee Do? • Designed for wireless controls and sensors • Operates in Personal Area Networks (PAN’s) and device-to-device networks • Connectivity between small packet devices • Control of lights, switches, thermostats, appliances, etc. ZigBee Alliance Homepage

42. References • Paolo Baronti, Prashant Pillai, Vince Chook, Stefano Chessa, Alberto Gotta, Y.Fun Hu, “Wireless Sensor Networks: a Survey on the State of the Art and the 802.15.4 and ZigBee Standards”, Computer Communication, Volume 30 , Issue 7, pages 16551695,2007. • ZigBee Alliance home page: • http://www.zigbee.org/en/index.asp • IEEE 802.15.4 task group • http://www.ieee802.org/15/pub/TG4.html • Wireless Sensor Network, An information Processing Approach by F. Zhoa & L.Guibas. • H. Karl, A. Willig Protocols and Architecture for Wireless Sensor Networks,2005. • Heile, B Wireless Sensor and Control Networks, 2006

43. Questions Thank you !!