How to Troubleshoot Apps for the Modern Connected Worker
Zigbee1
1. Faculty of Computer Science Chair of Computer Networks, Wireless Sensor Networks, Dr. W. Dargie
ZigBee
Jan Dohl Fabian Diehm Patrick Grosa
Dresden, 14.11.2006
2. Structure
Introduction
Concepts
Architecture
Implementation
Evaluation
Reference
TU Dresden, ZigBee – Short range slide 2 of 56
4. 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
TU Dresden, ZigBee – Short range slide 4 of 56
5. ZigBee Alliance - Members
and many more....
TU Dresden, ZigBee – Short range slide 5 of 56
7. 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)
TU Dresden, ZigBee – Short range slide 7 of 56
8. Why do we need another WPAN standard?
picture taken from [9]
TU Dresden, ZigBee – Short range slide 8 of 56
9. 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
TU Dresden, ZigBee – Short range slide 9 of 56
10. 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
TU Dresden, ZigBee – Short range slide 10 of 56
12. ZigBee Protocol Stack
7Layer Simplified 5Layer
ISO-OSI-Model ISO-OSI-Model IEEE 802 Model
7 Application User Application < ZigBee
<
6 Presentation
5 Session Application Profile Upper Layers
4 Transport
3 Network Network
2 Data Link Data Link Logic Link Control (LLC) < 802.14.5
<
Media Access Control (MAC)
1 Physical Physical Physical
TU Dresden, ZigBee – Short range slide 12 of 56
13. Protocol Stack
picture taken from [10]
TU Dresden, ZigBee – Short range slide 13 of 56
14. 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)
TU Dresden, ZigBee – Short range slide 14 of 56
16. 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
TU Dresden, ZigBee – Short range slide 16 of 56
17. 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
TU Dresden, ZigBee – Short range slide 17 of 56
18. 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
TU Dresden, ZigBee – Short range slide 18 of 56
19. 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
TU Dresden, ZigBee – Short range slide 19 of 56
21. 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
TU Dresden, ZigBee – Short range slide 21 of 56
22. Traffic-Modes
1. Beacon mode:
• beacon send
periodically
• Coordinator and end
device can go to sleep
• Lowest energy
consumption
• Pricise timing needed
picture taken from [1]
• Beacon period (ms-m)
TU Dresden, ZigBee – Short range slide 22 of 56
23. Beacon-Mode
picture taken from [8]
TU Dresden, ZigBee – Short range slide 23 of 56
24. Traffic-Modes
1. Non-Beacon mode:
• coordinator/routers
have to stay awake
(robust power supply
needed)
• heterogeneous
network
picture taken from [1]
• asymmetric power
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25. Topologies
Mesh-Topology
picture taken from [7]
TU Dresden, ZigBee – Short range slide 25 of 56
26. Topologies
Tree-Topology
picture taken from [7]
TU Dresden, ZigBee – Short range slide 26 of 56
28. PHY layer
2400MHz Band specs
• 4 Bits per symbol
• DSSS with 32 Bit chips
• O-QPSK modulation
• Sine halfwave impulses Medium
Binary Data Bit Symbol
QPSK
to to
Mod.
Symbol Chip
picture taken from [4]
TU Dresden, ZigBee – Short range slide 28 of 56
29. 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
Binary Data Bit
Diff. BPSK
to
Encoder Mod.
Chip
TU Dresden, ZigBee – Short range slide 29 of 56
30. 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
1. Energy above threshold
2. Carrier sense only
3. Carrier sense with energy above threshold
TU Dresden, ZigBee – Short range slide 30 of 56
31. 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]
TU Dresden, ZigBee – Short range slide 31 of 56
32. MAC layer
Channel access specification
• Beacon/Nonbeacon
• Define Superframe structure
• Slotted/unslotted CSMA-CA
TU Dresden, ZigBee – Short range slide 32 of 56
33. 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
TU Dresden, ZigBee – Short range slide 33 of 56
34. 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
TU Dresden, ZigBee – Short range slide 34 of 56
35. 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
TU Dresden, ZigBee – Short range slide 35 of 56
36. 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)
TU Dresden, ZigBee – Short range slide 36 of 56
37. 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
TU Dresden, ZigBee – Short range slide 37 of 56
38. NWK layer
Distributed address assignment - Example
• Cm=2 ; Rm=2 ; Lm=2
Depth in network d Offset Value
0 3
1 1
2 0
1
2
? 0
6 4
5
TU Dresden, ZigBee – Short range slide 38 of 56
39. 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
TU Dresden, ZigBee – Short range slide 39 of 56
40. 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
TU Dresden, ZigBee – Short range slide 40 of 56
42. 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
TU Dresden, ZigBee – Short range slide 42 of 56
43. Application Level
picture taken from [11]
TU Dresden, ZigBee – Short range slide 43 of 56
44. Application Level
picture taken from [11]
TU Dresden, ZigBee – Short range slide 44 of 56
45. 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]
TU Dresden, ZigBee – Short range slide 45 of 56
46. Application Level
picture taken from [11]
TU Dresden, ZigBee – Short range slide 46 of 56
47. Application Layer
Application Framework:
• Specifies Datatypes
• Devices describe themselves by ZigBee descriptor:
– frequency band
– power description
– application flags
– application version
– serial number
– manufacturer
– ...
TU Dresden, ZigBee – Short range slide 47 of 56
49. Application Level
picture taken from [11]
TU Dresden, ZigBee – Short range slide 49 of 56
50. 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]
TU Dresden, ZigBee – Short range slide 50 of 56
52. Pros and Cons
Pros Cons
• good extension of • Not many end devices
existing standards available yet
• supported by many • Single point of failure
companies (centralized architecture)
• low power consumption
• low cost
• easy implemented
(Designer concentrates
on end application)
• flexible network
structure
TU Dresden, ZigBee – Short range slide 52 of 56
53. Gadget example
Pantech & Curitel P1 phone
• Only a prototype
• control electrical
appliances
• Check temperature &
humidity
• Sending messages in case
of trespass picture taken from [9]
TU Dresden, ZigBee – Short range slide 53 of 56
55. References
[1] ZigBee Specifications v1.0
[2] “Designing with 802.15.4 and ZigBee”, Presentation Slides, available on ZigBee.org
[3] “ZigBee Tutorial”, http://www.tutorial-reports.com/wireless/zigbee
[4] IEEE 802.15.4 Specification
[5] “Network Layer Overview”, Presentation Slides, Ian Marsden, Embedded Systems Show,
Birmingham, October 12th, 2006, 064513r00ZB_MG_Network_Layer_Overview.pdf, available
on ZigBee.org
[6] “Designing a ZigBee Network”, Presentation Slides, David Egan, Ember Corporation, ESS
2006, Birmingham, 064516r00ZG_MG_Network_Design.pdf, available on ZigBee.org
[7] “ZigBee Architecture Overview”, Presentation Slides, Oslo, Norway June 2005,
ZigBee_Architecture_and_Specifications_Overview.pdf, available on ZigBee.org
[8] “Low Power Consumption Features of the IEEE 802.15.4/ZigBee LR-WPAN Standard”,
http://www.cens.ucla.edu/sensys03/sensys03-callaway.pdf
[9] “ZigBee Home Automation Mobile from Pantech”, http://www.i4u.com/article2561.html
[10] “Basic Lecture - ZigBee” http://www.korwin.net/eng/infor/info_zb_01.asp
[11] “Introduction to the ZigBee Application Framework”, Presentation Slides, ZigBee Open
House, San Jose, June 15th, 2006, 053340r06ZB_AFG-Overview-ZigBee-Open-House.pdf,
available on ZigBee.org
TU Dresden, ZigBee – Short range slide 55 of 56
56. Thank you
for
your attention!
TU Dresden, ZigBee – Short range slide 56 of 56
