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

ZigBee

Faculty of Computer Science Chair of Computer Networks, Wireless Sensor Networks, Dr. W. Dargie

Dresden, 14.11.2006

Jan Dohl Fabian Diehm Patrick Grosa

TU Dresden, 12.11.06 ZigBee – Short range comunication slide 2 of 56

Structure

Introduction Concepts Architecture Implementation Evaluation Reference


Introduction


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


ZigBee Alliance - Members

and many more....


Concepts


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)



picture taken from [9]



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


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


ZigBee Frequency Bands


ZigBee Protocol Stack

IEEE 802 Model7 Application User Application <<ZigBee6 Presentation5 Session Application Profile Upper Layers4 Transport3 Network Network2 Data Link Data Link Logic Link Control (LLC) <<802.14.5

Media Access Control (MAC)1 Physical Physical Physical

7Layer ISO-OSI-Model

Simplified 5Layer ISO-OSI-Model


Protocol Stack



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)


Architecture


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


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


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


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


Addressing/Binding ZigBee Endpoints



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


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]


Beacon-Mode



Traffic-Modes

1. Non-Beacon mode:

• coordinator/routers

have to stay awake

(robust power supply

needed)

• heterogeneous

network

• asymmetric powerpicture taken from [1]


Topologies

Mesh-Topology



Topologies

Tree-Topology



Implementation


PHY layer

2400MHz Band specs

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

Bitto

Symbol

QPSKMod.

Symbolto

Chip

Binary Data

Medium



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)

Diff.Encoder

BPSKMod.

Bitto

Chip

Binary Data

Medium


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 threshold2.Carrier sense only3.Carrier sense with energy above threshold


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]


MAC layer

Channel access specification

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


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


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


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


MAC layer

How far have we come?

0

1

2

4

3

5

6

7

Problem: How do 6 and 7 talk to coordinator 0?Solution: Routing (NWK Layer)


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


NWK layer

Distributed address assignment - Example

• Cm=2 ; Rm=2 ; Lm=2

Depth in network d Offset Value0 31 12 0

0

1

4

5

6

?2


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


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


NWK layer

Route discovery

RREQRREP

1 2 3

4

2

1

5


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


Application Level



Application Level



Application Layer

Application Support Sub-layer (APS):

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



Application Level



Application Layer

Application Framework:

• Specifies Datatypes• Devices describe themselves by ZigBee descriptor:

– frequency band– power description– application flags– application version– serial number– manufacturer– ...


Application Layer

Supported Data-types

table taken from [1]


Application Level



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



Evaluation


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)


Gadget example

Pantech & Curitel P1 phone

• Only a prototype

• control electrical

appliances

• Check temperature &

humidity

• Sending messages in case

of trespasspicture taken from [9]


References


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

http://www.tutorial-reports.com/wireless/zigbee

http://www.cens.ucla.edu/sensys03/sensys03-callaway.pdf

http://www.i4u.com/article2561.html

http://www.korwin.net/eng/infor/info_zb_01.asp


Thank youfor

your attention!

Documents

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