ZigBee

1. Dresden, 14.11.2006 Faculty of Computer Science Chair of Computer Networks, Wireless Sensor Networks, Dr. W. Dargie ZigBee Jan Dohl Fabian Diehm Patrick Grosa

2. ZigBee – Short range comunication Structure Introduction Concepts Architecture Implementation Evaluation Reference

3. ZigBee – Short range comunication Introduction

4. ZigBee – Short range comunication Introduction What is ZigBee? • Specification of protocols for small, low-power radios History May 2003: IEEE 802.15.4 completed December 2004: ZigBee specification ratified June 2005: public availability ZigBee-Alliance Companies developing and promoting the standard 150+ members

5. ZigBee – Short range comunication ZigBee Alliance - Members and many more....

6. ZigBee – Short range comunication Concepts

7. ZigBee – Short range comunication Why do we need another WPAN standard? Decreasing Power consumption ZigBee: 10mA <==> BT: 100mA Production costs In the beginning of 2005 ZigBee: 1.1 $ <==> BT: 3 $ Development costs Codesize ZB/codesize BT = ½ Bit-error-rate (BER)

8. ZigBee – Short range comunication Why do we need another WPAN standard? picture taken from [9]

9. ZigBee – Short range comunication Why do we need another WPAN standard? Increasing Sensitivity ZigBee: -92dbm(0,63pW) <==> BT: -82dbm(6,2pW) flexibility No. of supported nodes ZigBee: 65536 (in a mesh) <==> BT: 7 (in a star) Security ZigBee: AES (128bit) <==> BT: SAFER (64/128bit) Latency requirements ZigBee: optional guaranteed time slot Range ZigBee: up to 75 m in LOS condition <==> BT: 10 m

10. ZigBee – Short range comunication Usage Scenarios Industrial & commercial Consumer electronics Toys & games PC & periphals Personal health care home/building automation • Just everything you can imagine for wireless sensor nodes or in general short range communications

11. ZigBee – Short range comunication ZigBee Frequency Bands

12. ZigBee – Short range comunication ZigBee Protocol Stack

13. ZigBee – Short range comunication Protocol Stack picture taken from [10]

14. ZigBee – Short range comunication ZigBee Profiles Profiles: Definition of ZigBee-Profiles describes a common language for exchanging data defines the offered services device interoperatbility across different manufacturers Standard profiles available from the ZigBee Alliance profiles contain device descriptions unique identifier (licensed by the ZigBee Alliance)

15. ZigBee – Short range comunication Architecture

16. ZigBee – Short range comunication ZigBee Node-Types ZigBee Coordinator (ZBC) (IEEE 802.15.4 FFD) only one in a network initiates network stores information about the network all devices communicate with the ZBC routing functionality bridge to other networks

17. ZigBee – Short range comunication ZigBee Node-Types ZigBee Router (ZBR) (IEEE 802.15.4 FFD) optional component routes between nodes extends network coverage manages local address allocation/de-allocation

18. ZigBee – Short range comunication ZigBee Node-Types ZigBee End Device (ZBE) (IEEE 802.15.4 RFD) optimized for low power consumption cheapest device type communicates only with the coordinator sensor would be deployed here

19. ZigBee – Short range comunication Addressing/Discovering ZigBee Nodes Addressing ZigBee Nodes: optimized unique 64 bit address (IEEE 802.15.4) 16 bit network address (65536 devices) 256 sub addresses for subunits Device Discovery unicast (NWK id known), broadcast (NWK id unknown) ZBC-/ZBR-Response: IEEE address + NWK address + all known network addresses Binding creating logical links between 2 or more end devices

20. ZigBee – Short range comunication Addressing/Binding ZigBee Endpoints picture taken from [11]

21. ZigBee – Short range comunication Traffic-Types 1. Data is periodic application dictates rate 2. Data is intermittent application or stimulus dictates rate (optimun power savings) 3. Data is repetitive (fixed rate a priori) device gets guaranteed time slot

22. ZigBee – Short range comunication Traffic-Modes 1. Beacon mode: beacon send periodically Coordinator and end device can go to sleep Lowest energy consumption Pricise timing needed Beacon period (ms-m) picture taken from [1]

23. ZigBee – Short range comunication Beacon-Mode picture taken from [8]

24. ZigBee – Short range comunication Traffic-Modes 1. Non-Beacon mode: coordinator/routers have to stay awake (robust power supply needed) heterogeneous network asymmetric power picture taken from [1]

25. ZigBee – Short range comunication Topologies Mesh-Topology picture taken from [7]

26. ZigBee – Short range comunication Topologies Tree-Topology picture taken from [7]

27. ZigBee – Short range comunication Implementation

28. ZigBee – Short range comunication PHY layer 2400MHz Band specs 4 Bits per symbol DSSS with 32 Bit chips O-QPSK modulation Sine halfwave impulses Medium Bit to Symbol Symbol to Chip QPSK Mod. Binary Data picture taken from [4]

29. ZigBee – Short range comunication PHY layer 868/915 MHz Band specs 1 Bit per symbol Differential encoding DSSS with 15 Bit Chips BPSK modulation RC impulses (roll-off = 1) Medium Diff. Encoder Bit to Chip BPSK Mod. Binary Data

30. ZigBee – Short range comunication PHY layer General specs and services Error Vector Magnitude (EVM) < 35% -3dBm minimum transmit power (500µW) Receiver Energy Detection (ED) Link Quality Indication (LQI) Use ED & LQI to reduce TX-power Clear Channel Assessment (CCA) with 3 modes Energy above threshold Carrier sense only Carrier sense with energy above threshold

31. ZigBee – Short range comunication PHY layer PHY Protocol Data Unit (PPDU) frame structure Frame to be sent via radio Preamble for chip and symbol synchronization Contains either data or data acknowlegement Packet size 8-127 Octets Contains MAC Protocol Data Unit (MPDU) table taken from [1]

32. ZigBee – Short range comunication MAC layer Channel access specification Beacon/Nonbeacon Define Superframe structure Slotted/unslotted CSMA-CA

33. ZigBee – Short range comunication MAC layer Managing PANs Channel scanning (ED, active, passive, orphan) PAN ID conflict detection and resolution Starting a PAN Sending beacons Device discovery Device association/disassociation Synchronization (beacon/nonbeacon) Orphaned device realignment

34. ZigBee – Short range comunication MAC layer Transfer handling Transaction based (indirect transmission) Beacon indication Polling Transmission, Reception, Rejection, Retransmission Acknowleded Not acknowledged GTS management Allocation/deallocation Usage Reallocation Promiscous mode

35. ZigBee – Short range comunication MAC layer Frame security Provided security features Access control Data encryption Frame integrity Sequential freshness Avaiable security modes Unsecured mode ACL mode Secured mode Avaiable security suites AES-CTR AES-CCM AES-CBC-MAC

36. ZigBee – Short range comunication MAC layer How far have we come? 4 1 6 0 5 2 7 3 Problem: How do 6 and 7 talk to coordinator 0? Solution: Routing (NWK Layer)

37. ZigBee – Short range comunication NWK layer Distributed address assignment Tree structure or self managed by higher layer 16Bit network space divided among child routers Child routers divide there space again for their children Depends on: Maximum child count per parent Maximum child-routers per parent Maximum network depth

38. ZigBee – Short range comunication NWK layer Distributed address assignment - Example Cm=2 ; Rm=2 ; Lm=2 1 0 ? 2 4 6 5

39. ZigBee – Short range comunication NWK layer Routing cost Metric to compare „goodness“ of routes Base: Link cost between 2 neighbors Path cost = sum of link costs along the path Link cost determination: Link quality indication from PHY Statistical measures

40. ZigBee – Short range comunication NWK layer Route discovery Find or update route between specific source and destination Started if no active route present in routing table Broadcast routing request (RREQ) packets Generates routing table entries for hops to source Endpoint router responds with Routing response (RREP) packet Routes generated for hops to destination Routing table entry generated in source device

41. ZigBee – Short range comunication NWK layer Route discovery RREQ RREP 2 1 3 5 2 1 4

42. ZigBee – Short range comunication NWK layer Routing Check if routing table entry exists Initiate route discovery if possible Hierarchical routing as fallback Route maintenance • Track failed deliveries to neighbors • Initiate route repair when threshold reached • Careful with network load! • In case of total connectivity loss: • Orphaning procedure • Re-association with network

43. ZigBee – Short range comunication Application Level picture taken from [11]

44. ZigBee – Short range comunication Application Level picture taken from [11]

45. ZigBee – Short range comunication Application Layer Application Support Sub-layer (APS): interface to NWK-layer (offers general set of functions) Data transmission, binding and security management picture taken from [1]

46. ZigBee – Short range comunication Application Level picture taken from [11]

47. ZigBee – Short range comunication Application Layer Application Framework: Specifies Datatypes Devices describe themselves by ZigBee descriptor: frequency band power description application flags application version serial number manufacturer ...

48. ZigBee – Short range comunication Application Layer Supported Data-types table taken from [1]

49. ZigBee – Short range comunication Application Level picture taken from [11]

50. ZigBee – Short range comunication Application Layer ZigBee defined Objects (ZDO): provides common function for applications Initializes APS, NWK-Layer and Security Service Specification offers services like device-/service-descovery, binding and security management assembles information about the network for ZBC/ZBR -> e.g. binding table picture taken from [1]