ZigBee

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

• Dresden, 14.11.2006

2
Structure

• Introduction
• Concepts
• Architecture
• Implementation
• Evaluation
• Reference

3
Introduction
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

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ZigBee Alliance - Members
and many more....
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Concepts
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Why do we need another WPAN standard?

• Decreasing
• Power consumption
• ZigBee 10mA ltgt BT 100mA
• Production costs
• In the beginning of 2005
• ZigBee 1.1 ltgt BT 3
• Development costs
• Codesize ZB/codesize BT ½
• Bit-error-rate (BER)

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Why do we need another WPAN standard?
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Why do we need another WPAN standard?

• Increasing
• Sensitivity
• ZigBee -92dbm(0,63pW) ltgt BT -82dbm(6,2pW)
• flexibility
• No. of supported nodes
• ZigBee 65536 (in a mesh) ltgt BT 7 (in a
  star)
• Security
• ZigBee AES (128bit) ltgt BT SAFER (64/128bit)
• Latency requirements
• ZigBee optional guaranteed time slot
• Range
• ZigBee up to 75 m in LOS condition ltgt BT 10 m

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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

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ZigBee Frequency Bands
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ZigBee Protocol Stack
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Protocol Stack
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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)

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Architecture
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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

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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

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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

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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

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Addressing/Binding ZigBee Endpoints
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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

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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)

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Beacon-Mode
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Traffic-Modes

• 1. Non-Beacon mode
• coordinator/routers have to stay awake
  (robust power supply needed)
• heterogeneous network
• asymmetric power

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Topologies

• Mesh-Topology

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Topologies

• Tree-Topology

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Implementation
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PHY layer

• 2400MHz Band specs
• 4 Bits per symbol
• DSSS with 32 Bit chips
• O-QPSK modulation
• Sine halfwave impulses

Medium
Bit to Symbol
QPSK Mod.
Symbol to Chip
Binary Data
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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
BPSK Mod.
Bit to Chip
Binary Data
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PHY layer

• General specs and services
• Error Vector Magnitude (EVM) lt 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

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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)

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MAC layer

• Channel access specification
• Beacon/Nonbeacon
• Define Superframe structure
• Slotted/unslotted CSMA-CA

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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

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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

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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

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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)
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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

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NWK layer

• Distributed address assignment - Example
• Cm2 Rm2 Lm2

1
0
?
2
4
6
5
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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

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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

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NWK layer

• Route discovery

RREQ
RREP
2
1
3
5
2
1
4
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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

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Application Level
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Application Level
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Application Layer

• Application Support Sub-layer (APS)
• interface to NWK-layer (offers general set of
  functions)
• Data transmission, binding and security management

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Application Level
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Application Layer

• Application Framework
• Specifies Datatypes
• Devices describe themselves by ZigBee descriptor
• frequency band
• power description
• application flags
• application version
• serial number
• manufacturer
• ...

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Application Layer

• Supported Data-types

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Application Level
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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 -gt e.g. binding table

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Evaluation
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Pros and Cons

• Pros
• good extension of existing standards
• supported by many companies
• low power consumption
• low cost
• easy implemented (Designer concentrates on end
  application)
• flexible network structure

• Cons
• Not many end devices available yet
• Single point of failure (centralized architecture)

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Gadget example

• Pantech Curitel P1 phone
• Only a prototype
• control electrical appliances
• Check temperature humidity
• Sending messages in case of trespass

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References
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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_O
verview.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_Overv
iew.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/sensy
s03/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
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Thank you for your attention!