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WSN Protocols

WSN Protocols. Marco Benocci, Piero Zappi {marco.benocci, piero.zappi}@unibo.it DEIS Università di Bologna. Outiline. Ambient Intelligence Wireless Sensor Networks overview Motivations Application Design objectives WSN Protocols OSI layers Security Examples Bluetooth ZigBee

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WSN Protocols

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  1. WSN Protocols Marco Benocci, Piero Zappi {marco.benocci, piero.zappi}@unibo.it DEIS Università di Bologna

  2. Outiline • Ambient Intelligence • Wireless Sensor Networks overview • Motivations • Application • Design objectives • WSN Protocols • OSI layers • Security • Examples • Bluetooth • ZigBee • 6LowPAN

  3. Amb. Int. Context-aware computing Ambient intelligence (AmI): Sensor augmented environment able to sense and react with people moving and performing activities within. 3 building blocks: • Ubiquitous computing: distributed data gathering and computation • Ubiquitous communication: nodes communicates and exchange their data • Natural interfaces: Human-Smart Environment interaction through natural means without dedicated devices (voice, gestures etc.)

  4. AmI enabling technologies: WSN The smart environment must understand what is going on Wireless Sensor Networks are the sense of the smart environment • Flexible • The environment may change • Nodes may fall • The information required may grown • Efficient • Real time • Reliable • Deeply integrated with the environment (unobtrusiveness) • Cheap • Easy to deploy • Minimum or no mainenance

  5. Wireless Sensor Networks • Complex systems made up of a large number of sensor nodes • Sensing • Computing • Communication • Power (batteries, scavengers) WSN protocols OS & algorithms Data analysis Communication unit (ZigBee, Bluetooth 6lowpan, WiFi) Processing unit (MCU, DSP, FPGA) Sensor unit (MEMS, temperature light, audio, video,…) Power Supply

  6. Applications (1) • Security application • Surveillance • Object tracking • Military application • Vehicles and soldiers tracking • Anti intrusive systems • Environmental application • Precision agriculture • Biological environment monitoring

  7. Application (2) • Biomedical application • Patient monitoring • Biofeedback • Domotic • Home automation • Smart space • Commercial application • Shipping monitoring • Museum • Thief prevention

  8. Design Objectives (1) • Reduce wireless communication • Reduce idle listening • Alternative sources of power Low power • Require low memory • Require low computational power • Self organize network • Self healing Low cost

  9. Design Objectives (2) Latency • Guarantee delays • Redundancy • Adaptivity • Fault tolerant algorithm Reliability Security • Message encryption • Privacy

  10. Protocol layers WSN protocols define lower levels • Physical • Data Link (MAC) • Network User specific User application, usually, are built over Network layer Protocols specific

  11. Physical layer Provides mechanical, electrical, functional, and procedural characteristics to establish, maintain, and release physical connections (e.g. data circuits) between data link entities • Communication bands and number of channels • Spreading and Modulation • Data Rate Cost – Power consumption – Reactiveness

  12. Physical layer • Communication bands and number of channels • Spreading and Modulation • Data Rate • 20, 40, 250 kbps • 1, 3 Mbps • 54 Mbps

  13. Data link layer (MAC) OSI Network Layer 3 Data link layer: • Mapping network packets • radio frames • Transmission and reception of frames over the air • Error control • Security Data Link Layer 2 MAC Protocol Physical Layer 1

  14. A A B B C C D Data link layer (MAC) (2) Control access to the shared medium • Avoid interference and mitigate effects of collisions Hidden terminal problem Exposed terminal problem

  15. Energy efficient MAC • idle listening (to handle potentially incoming messages) • collisions (wasted resources at sender and receivers) • overhearing (communication between neighbors) • protocoloverhead (headers and signaling) • traffic fluctuations (overprovisioning and/or collapse) • scalability/mobility (additional provisions)

  16. Protocols MAC layer Contention based protocols …listen before send Objective: Multiple Access with Collision Avoidance (MA-CA) Node sense the medium for special packets or energy in order to understand when there are no communication. Carrier Sense Multiple Access (CSMA) • How long device sense the channel? • How long device remain in idle listening State?

  17. A B C DATA DATA Hidden terminal problem A and B are out of range cs Time cs Carrier sense at sender may not prevent collision at receiver

  18. A B C DATA Blocked RTS CTS ACK Hidden terminal problem Multiple Access Collision Avoidance(MACA): • Request To Send • Clear To Send • DATA • Acknowledge cs Time

  19. A B C D cs DATA Blocked RTS RTS CTS ACK Exposed terminal problem cs Time Parallel CSMA transfers are synchronized by CSMA/CA Collision avoidance can be too restrictive!

  20. Protocols MAC layer Schedule based protocols Communication is scheduled in advance • No contention • No overhearing Time-Division Multiple Access • Time is divided into slotted frames • Access point broadcasts schedule • Coordination between cells required • Need of global clock Hard with WSN constraints

  21. Frame n Frame n+1 Frame n+2 Tx Protocols MAC layer • Dedicated slot for transmission (no contention) • Eventually low power period when no transmission is expected • Synchronization hard if number of nodes explodes

  22. Network layer Provides functional and procedural means to exchange network service data units between two transport entities over a network connection. It provides transport entities with independence from routing and switching consideration • Organization of the network • network formation • Joining/leaving the network • Routing of packets through the network • Shortest path • Energy efficient • Tracing of the status of the links • Routing tables • On demand path (e.g. AODV)

  23. Network – Structure Not always predictable but can follow logical structure Mesh Cluster tree Clustering: • Balance load among nodes • Cluster Head must compute more data • energy efficency • Adapt to network changes • Reduce data transfer

  24. Network – Routing Hard, due to node failure and mobility Balance between low duty cycle and frequent path updates Routing algorithm can be classified in three group • Connect dominating • Try to find the shorter path to the destination • Energy dominant • Life of network can be longer if energy consumption is balanced among nodes • Biological model • Ants communication paradigm

  25. Protocols – Security (1) Security Concerns: • Integrity - Ensure that information is accurate, complete, and has not been altered in any way. • Availability - Ensure that a system can accurately perform it’s intended purpose and is accessible to those who are authorized to use it. • Confidentiality - Ensure that information is only disclosed to those who are authorized to see it.

  26. Protocols – Security (2) Possible threats: • Passive threats • Eavesdrop • Active threats • Bogus Routing (against routing information exchanged between nodes) • Selective forwarding (stop messages propagation) • Sink hole (attract messages from neighbor) • Sybil attack (forge multiple identities) • Wormhole (send wrong information about distance in order to force different routing path) • HELLO floods (send packet with higher energy, attract communication) • Acknowledge Spoofing (send fake ack messages to encourage communication)

  27. Protocols – Security (3) Traditional security techniques cannot be applied due to system constraints • Power • Bandwidth • Computation Secure protocols uses: • Encription • Data authentication • Data freshness

  28. IEEE 802 LAN/MAN CONSTRAINTS Coverage area QoS Energy efficienty Lifetime Costs IEEE 802.3 - Ethernet IEEE 802.5 - Token Ring IEEE 802.11 -Wi-Fi IEEE 802.15 - Wireless personal area network IEEE 802.16 - WiMAX - Broadband wireless access

  29. IEEE 802 Performance PowerConsumption Range VS Data rate Mobility VS Data Rate

  30. WPAN – 802.15 802.15.1 MAC and physical layers - based on Bluetooth v1.1. 802.15.2 Coexistence of Wireless Personal Area Networks (802.15) and Wireless Local Area Networks (802.11) Quantify the mutual interference of a WLAN and a WPAN 802.15.3 High Rate WPAN. New standard for high-rate (20Mbit/s or greater) WPANs. Besides: low power, low cost solutions, portable, multimedia applications.  802.15.4 Low Rate WPAN. From multi-month to multi-year battery life, very low complexity. 802.15.5 Mesh Networking. Mechanisms in the PHY and MAC layers of WPANs to enable mesh networking.

  31. ZigBee Wireless Control that Simply Works IEEE 802.15.4 – ZigBee Motivation: define a complete open global standard for reliable, cost-effective, low-power, wirelessly networked products addressing monitoring and control Applications: • Building automation • Consumer electronics • Personal health care • Industrial control • Commercial control

  32. IEEE 802.15.4 – ZigBee • Physical layer • Media Access Control layers • Network layer • Security • Standard interface to the application (APS, ZDO, AF)

  33. IEEE 802.15.4 – ZigBee Physical layer (1) Communication over 26 channel in 3 ISM band • 868 MHz Europe • 915 MHz U.S.A. • 2.4 GHz Worldwide

  34. IEEE 802.15.4 – ZigBee Physical layer (2) Direct Sequence Spread Spectrum modulation (DSSS) • B-PSK: 20kb/s (868MHz), 40kb/s(915MHz) • Q-PSK: 250 kb/s (2.4GHz) DSSS modulation work on a single channel • quicker discovery/association • easyer synchronization • coexistence of multiple Zigbee networks

  35. IEEE 802.15.4 – ZigBee MAC layer (1) Defines two device type • Full Function Device (FFD) • higher cost (35kB FLASH and 200Byte RAM, 8bit CPU) • higher power (typically main powered) • full function • can join another FFD and accept association • Reduced Function Device (RFD) • low cost (22kB FLASH and 200Byte RAM, 8bit CPU) • low power consumption (typically battery powered) • no routing • join a FFD

  36. IEEE 802.15.4 – ZigBee MAC layer (2) Two Roles • Coordinator • Start the network • Associated device • join the network • accept association (if FFD) Three topologies: • Star • Mesh • Cluster Tree

  37. C.A.P. C.F.P. Superframe Beacon GTS IEEE 802.15.4 – ZigBee MAC layer (3) Hybrid contention and scheduled based MAC inactive Low power state Security is available • Encryption: Advanced Encryption Standard (AES) 128bit • ACL, Access Control List

  38. IEEE 802.15.4 – ZigBee Network layer (1) Three device types • Zigbee Coordinator (ZC) • as the MAC Coordinator • starts the network • not a dedicated device • Zigbee Router (ZR) • as MAC FFD Associated device • route packet • manage ZED associated with it • Zigbee End Device (ZED) • as MAC RFD associated device • no routing nor association • low power

  39. IEEE 802.15.4 – ZigBee Network layer (2) Network architecture defined by 4 parameters • Max depth • Max child node • Max router • Security level

  40. IEEE 802.15.4 – ZigBee Network layer (3) Addressing follow a tree structure Routing tables keep trace of spatially close nodes

  41. IEEE 802.15.4 – ZigBee Upper layer (1) • APS sublayer • provide interface to network layer • handle data transmission • handle binding • Application Framework (AF) • the environment where application object are hosted • up to 240 application on a single device (EndPoints, EP) • standard descriptors to define each application • EP 255 to broadcast, EP 0 to ZDO • Zigbee Device Object (ZDO) • provide functionality to interface Application Object and APS • Initialize APS, NWK and security • manage the network (discovery, binding, ecc.)

  42. clusters IEEE 802.15.4 – ZigBee Upper layer (2) Application are modeled by means of Clusters and EndPoints • On a single device up to 240 EP • Different EP communicate through clusters • Cluster are unique set of messages • 2 devices • 2 EP on device 1 • 4 EP on device 2 • 2 clusters

  43. IEEE 802.15.4 – ZigBee Upper layer (3) Service Discovery is the process whereby a services available on endpoints are discovered by external devices • Uses descriptor to find which EP match device needs • matching input/output clusters • matching power capabilities • matching profile • Uses unicast and broadcast messages • Each device can start a service discovery

  44. IEEE 802.15.4 – ZigBee Upper layer (4) Binding is the creation of logical link between Applications

  45. IEEE 802.15.4 – ZigBee Upper layer (5) ZDO manage the role of the device within the network • Network association and/or formation • Access to network API to create/join a network • Discovery managment • application may use ZDO API to start a discovery process • Binding managment • construct and manage binding tables • Security managment • enable/disable secure communication

  46. IEEE 802.15.4 – ZigBee Upper layer (6) Profiles are an agreement on messages, message formats and processing action that enable applications residing on separate devices to create a distribuited application • They are the key to unify solutions • defines a common language • defines action taken on recipt of messages • allow conformance test • They are developed by ZigBee vendors Examples: • Home control • Lighting control

  47. IEEE 802.15.4 – ZigBee Security (1) • 128 bit Link key • shared among two device • used for unicast communication • 128 bit Network key • shared among all device in the network • used for broadcast communication • Master key • used in high level security application Includes method for: • Key estabilishment • Trust center • Key transport • Frame protection • authentication and encryption • freshness • message integrity • Device managment

  48. IEEE 802.15.4 – ZigBee Security (2) Trust center • Device trusted by all other devices in the network • Distribute link and network keys Play three roles • Trust manager • handle master key • Network manager • handle network key • Configuration manager • handle link key

  49. IEEE 802.15.4 – ZigBee • ZigBee protocol specification has been ratified in december 2004 (pubilc since 2nd half 2005 ) • Actual version (1.0) has been updated to version 1.1 • public from first trimester 2007 • use of new IEEE 802.15.4 – 2006 • group devices • easy maintenance (information stored on neighbourn) • target broadcast (e.g. only to awake/sleep device) • Over the air setup Further information and specification can be found at: ZigBee Alliance home page: www.zigbee.org IEEE 802.15 TG 4 home page: www.ieee802.org/15/pub/TG4.html

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