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Wireless Control That Simply Works
‘Under the Hood‘ of a ZigBee 2006
Network
Ian Marsden
Chairman ZigBee NWG
Director, Software Engineering, Integration Associates
Copyright © 2007 ZigBee
TM
Alliance. All Rights Reserved.
ZigBee is built upon the foundations provided
by the IEEE 802.15.4 standard.
Application Framework
ZPUI
Application
Object 240
Application
Object 1
[On Endpoint 240]
[On Endpoint 1]
[On Endpoint 0]
APSDE-SAP
APSDE-SAP
APSDE-SAP
APSME-SAP
APSSE-SAP
Application Support (APS) Layer
NLDE-SAP
NLME-SAP
NLSE-SAP
Security
Service
Provider
ZigBee Device
Object (ZDO)
Network (NWK) Layer
MCPS-SAP
MLME-SAP
Medium Access Layer (MAC) Layer
PD-SAP
PLME-SAP
Physical (PHY) Layer
ZigBee Stack
TM
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ZigBee Devices Type Model
•
•
Application
Device Type
e.g.
Light
Sensor
e.g.
Lighting
Controller
ZigBee Logical
Device Type
ZigBee
Coordinator
ZigBee
Router
802.15.4
Device Type
FFD –
Full Function Device
...
ZigBee
End
Device
RFD –
Reduced Function
Device
• Distinguishes the type
of device from an
end-user perspective
• Distinguishes the
Logical Device Types
deployed in a specific
ZigBee network
• Distinguishes the type
of ZigBee hardware
platform
ZigBee products are a combination of Application, ZigBee Logical, and ZigBee Physical device types
Profiles may define specific requirements for this combination, but can also leave this up to manufacturers
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802.15.4 Architecture:
■ Defines basic network structure
■ Provides methods for locating networks
■ Provides methods for joining / rejoining networks
■ Defines direct / indirect data transmission
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Architecture:
Network Structure in 802.15.4
802.15.4 FFD
802.15.4 RFD
Network Association
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MLME_SCAN: Locating Networks
■ Active Scan
MLME-SCAN.request
ScanChannels
■ Asks on the requested
ScanDuration
channels for other PANs
■ Returns a list of
PANDescriptors
ScanType = “Active Scan”
MLME-SCAN.confirm
status
ScanType
UnscannedChannels
ResultListSize
EnergyDetectList
PANDescriptorList
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MLME_START: Initiating a Network
■ Starts the requested PAN
MLME-START.request
PANId
LogicalChannel
BeaconOrder
SuperframeOrder
PANCoord
BatteryLifeExtension
Realignment
SecurityEnable
MLME-START.confirm
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status
7
MLME_ASSOCIATE: Joining a Network
■ Associates with the
MLME-ASSOCIATE.request
requested coordinator
LogicalChannel
CoordAddrMode
CoordPANId
CoordAddress
CapabilityInformation
SecurityEnable
MLME-ASSOCIATE.confirm
AssocShortAddress
status
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MLME_SCAN: Rejoining a Network
■ Orphan Scan
MLME-SCAN.request
ScanChannels
■ Asks on the requested
channels for its former
parent
ScanType = “Orphan Scan”
ScanDuration
MLME-SCAN.confirm
status
ScanType
UnscannedChannels
ResultListSize
EnergyDetectList
PANDescriptorList
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Data Transmission:
Direct
■
The receiving device has its receiver on (RxOnIdle)
■
The data packet can be set unsolicited
■
The MAC schedules it for immediate delivery (using CSMA-CA)
In-Direct
■
The receiving device is asleep with its receiver off
■
The data packet has to be requested (Polled)
■
The MAC stores it for later retrieval by the RFD.
MCPS-DATA.request
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SrcAddrMode,
SrcPANId,
SrcAddr,
DstAddrMode,
DstPANId,
DstAddr,
msduLength,
msdu,
msduHandle,
TxOptions
10
Architecture: NWK layer details
■ ZigBee Device Types
■ Stack Profile, Network Rules
■ Network Management and Addressing
■ Message Routing
■ Route Discovery and Maintenance
■ Security
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Architecture:
Network Structure in ZigBee
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Architecture: Stack Profile
Sets the rules that the network adheres to:
■
nwkMaxDepth = 5
■ nwkMaxChildren = 20
■ nwkMaxRouters = 6
■ nwkSecurityLevel = 5 (ENC-MIC-32)
And many more
■ Minimum Table sizes (Neighbor, Routing)
■ Timeouts (Broadcast)
■ Route Cost Calculation Algorithm
■ Disables features (Multicast, Aggregation routing)
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Architecture: ZigBee Device Types
ZigBee Coordinator (ZC)
■
One and only one required for each ZigBee network.
►
■
First one to the party
Initiates network formation.
►
Selects the time and place (Channel, PANId, Stack Profile)
■
Acts as IEEE 802.15.4 2003 PAN coordinator (FFD).
■ Also performs as router once network is formed.
■ Not necessarily a dedicated device can
perform an application too.
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Architecture: ZigBee Device Types
ZigBee Router (ZR)
■
Optional network component.
■
Discovers and associates with ZC or ZR.
►
Extends the network coverage
■
Acts as IEEE 802.15.4 2003 coordinator (FFD).
■
Manages local address allocation / de-allocation
■
Participates in multi-hop / mesh routing of messages.
■
Looks after its ZED’s when it comes to
broadcasting and routing messages
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Architecture: ZigBee Device Types
ZigBee End Device (ZED)
■
Optional network component.
■
Discovers and associates with ZC or ZR.
■
Acts as IEEE 802.15.4 2003 device (RFD).
■
Can be optimised for very low power operation
■
Relies on its parent to let it sleep
■
Shall not allow association.
■
Shall not participate in routing.
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General Frame Format
Octets:
2
Frame
Control
2
2
Dest
Addr
Srce
Addr
1
1
0/8
0/8
0/1
Variable
Variable
Radius
Sequence
Number
Dest
IEEE
Addr
Srce
IEEE
Addr
Multicast
Control
Srce
Route
Frame
Payload
Routing Fields
NWK
Payload
NWK Header
Bits: 0-1
2-5
6-7
8
9
10
11
12
13-15
Frame type
Protocol
version
Discover
route
MCast
Security
Srce
Route
Dest
IEEE
Addr
Srce
IEEE
Addr
Reserved
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Bits: 0-1
2-4
5-7
Multicast
Mode
Non
Member
Radius
MaxNon
Member
Radius
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Network Initiation: ZC
■ Initiates a ZigBee network
NLME-NETWORKFORMATION.request
■ Performs an Energy Detect
SuperframeOrder
■ Performs an Active Scan
■ Selects an unused PANId
ScanDuration
BeaconOrder
Scan
■ Selects the “nicest” channel
ScanChannels
BatteryLifeExtension
NLME-NETWORKFORMATION.confirm
status
■ Starts a network
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Network
Initiation: ZC
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Network Discovery: ZR & ZED
■ Locates ZigBee Networks
NLME-NETWORKDISCOVERY.request
ScanChannels
NLME-NETWORKDISCOVERY.confirm
NetworkCount
ScanDuration
■ Performs an Active Scan
■ Selects a compatible
network
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NetworkDescriptor
status
20
Network Association:
ZR & ZED
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Network Association: ZR & ZED
NLME-JOIN.request
ExtendedPANId
■ Join a ZigBee Network
JoinAsRouter
■ Selects the highest
RejoinNetwork = 0
ScanChannels
acceptable router
ScanDuration
■ Associates with the
PowerSource
chosen router
RxOnWhenIdle
■ Allocated an address on
the network
NLME-JOIN.indication
ShortAddress
ExtendedAddress
■ Inform the NHL
CapabilityInformation
SecureJoin
NLME-JOIN.confirm
ShortAddress
PANId
HaveNetworkKey
Status
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Network Association:
ZR & ZED
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Commencing Router Function:
ZR
■ Commence Router Function
NLME-STARTROUTER.request
■ Once authenticated on the
children
SuperframeOrder
BateryLifeExtension
network
■ Prepares addresses for its
BeaconOrder
NLME-STARTROUTER.confirm
Status
■ Starts up the router function
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Addressing:
Tree-structured Address Assignment
■ CSkip based address assignment
■ Address determined from tree location
0x7FFF
Address 0x0
0xFFFF
Depth 0
Depth 1
nwkMaxDepth
Depth 2
Depth 3
nwkMaxChildren
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Sending Data
■ Used by the NHL for
NLDE-DATA.request
DstAddrMode
DstAddr
sending broadcasts and
unicasts
NsduLength
Nsdu
■ DstAddr defines the target
NsduHandle
device
Radius
NonmemberRadius
■ Radius limits the number
DiscoverRoute
of hops for the message to
traverse, if appropriate
■ DiscoverRoute can inhibit
discovery
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SecurityEnable
NLDE-DATA.confirm
NsduHandle
Status
26
Receiving Data
■ Created on reception of
data for the local device
NLDE-DATA.indication
DsrAddrMode
DstAddr
SrcAddr
■ SrcAddr is the originator of
the message
NsduLength
Nsdu
LinkQuality
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Tree Routing:
■ The address tells you where the destination is
■ Simple equation gives ‘route up’ or ‘route down’
■ If LocalAddr < DestAddr < LocalAddr + CSkip(d-1) Route Down
■ Else Route Up
0x7FFF
Address 0x0
0xFFFF
Depth 0
Depth 1
Depth 2
Depth 3
CSkip d= 1
Obviously not necessarily the most efficient route
CSkip d= 2
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Neighbour Routing:
■ A ZC or ZR maintains a table of devices in its neighbourhood
■ If the target device is physically in range it can send the
message directly.
0x7FFF
Address 0x0
0xFFFF
Depth 0
Depth 1
Depth 2
Depth 3
Devices Neighbourhood
But what happens if the destination is not in the local neighbourhood?
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Mesh Routing:
■ ZC or ZR maintains a routing table of next hop addresses
■ If the target device has a routing table entry then the message
can be sent using this route.
0x7FFF
Address 0x0
0xFFFF
Depth 0
Depth 1
Depth 2
Depth 3
That’s great, but where do the routing table entries come from?
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Routing: Route Discovery
■ A device wishing to discover a route issues a route request
command frame which is broadcast throughout the network.
■ When the intended destination receives the route request
command frame it responds with a route reply command
frame.
■ Potential routes are evaluated with respect to a routing cost
metric.
■ Best route is added to the routing tables of all devices on the
route
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Message Routing:
The Basic Algorithm
1.
See if the destination is in the Neighbour Table
2.
Check for a Routing Table entry
3.
Finally resort to Tree Routing
NB. ZRs store messages for sleeping ZED’s
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Broadcast:
The Basic Algorithm
■ Transmit broadcast message
■ Rebroadcast by local ZRs if it is new.
■ Time & radius limited.
■ ZRs store messages for sleeping ZED’s
■ ZRs issue broadcasts on behalf of sleeping ZEDs
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NLME-PERMIT-JOINING
■ Enable or Disable devices
joining
NLME-PERMIT-JOINING.request
PermitDuration
NLME-PERMIT-JOINING.confirm
Status
■ Opens up a ZC or ZR for a
possibly limited duration to
new devices associating
■ Sets or clears the
AssociationPermit status
■ PermitDuration in seconds
0 = Disable, 0xFF = Infinite
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Network Orphaning: ZR & ZED
NLME-JOIN.request
ExtendedPANId
■ Rejoin a previous Parent
JoinAsRouter
■ Performs an 802.15.4
RejoinNetwork = 1
ScanChannels
Orphan Scan
ScanDuration
■ Previous parent will
PowerSource
respond
RxOnWhenIdle
NLME-JOIN.indication
ShortAddress
ExtendedAddress
CapabilityInformation
SecureJoin
NLME-JOIN.confirm
ShortAddress
PANId
HaveNetworkKey
Status
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Network Orphaning: ZR & ZED
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Network Rejoining: ZR & ZED
NLME-JOIN.request
■ Rejoin a network (New
ExtendedPANId
JoinAsRouter
Parent)
RejoinNetwork = 2
ScanChannels
■ Performs an Active scan to
ScanDuration
find out who is out there
PowerSource
■ Selects new parent with
RxOnWhenIdle
capacity
NLME-JOIN.indication
ShortAddress
ExtendedAddress
CapabilityInformation
SecureJoin
NLME-JOIN.confirm
ShortAddress
PANId
HaveNetworkKey
Status
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Network Rejoining: ZR & ZED
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NLME-DIRECT-JOIN
■ Pre-join a device to a ZR
NLME-DIRECT-JOIN.request
CapabilityInformation
or ZC
■ Enables the device to join
later through orphaning
DeviceAddress
NLME-DIRECT-JOIN.confirm
DeviceAddress
Status
■ The CapabilityInformation
is as the device would
provide
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NLME-LEAVE
■ Controls the removal of
NLME-LEAVE.request
RemoveChildren
devices from a network
■ Allows a device to leave itself
(DeviceAddress = NULL)
DeviceAddress
Rejoin
NLME-LEAVE.confirm
DeviceAddress
Status
■ Allows a device to request a
child to leave
NLME-LEAVE.indication
DeviceAddress
Rejoin
■ RemoveChildren defines if the
children below the leaving
device should also leave
■ Rejoin defines if the leave is a
transient effect and the device
should attempt to rejoin
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NLME-SYNC
■ Controls the receiving of data
NLME-SYNC.request
Track
NLME-SYNC.confirm
Status
on a ZED
■ Requests a ZED to issue an
MLME-POLL.request to its
parent
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NLME-SYNC.indication
41
NLME-RESET
■ Returns the stack to a known
NLME-RESET.request
state
■ In turn calls a MLME-
NLME-RESET.confirm
Status
RESET.request
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NLME-GET & NLME-SET
■ Requests the value of
configuration parameters from
within the NIB
NLME-GET.request
NIBAttribute
NLME-GET.confirm
Status
NIBAttribute
■ Updates the value of
NIBAttributeLength
configuration parameters
within the NIB
NIBAttributeValue
NLME-SET.request
NIBAttribute
NIBAttributeLength
NIBAttributeValue
NLME-SET.confirm
Status
NIBAttribute
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NLME-ROUTE-ERROR
■ Informs the NHL of some
break down in
communications
NLME-ROUTEERROR.indication
ShortAddr
Status
■ Used if Route Discovery fails
■ Used if Tree links break
■ Used if a packet cannot be
delivered
■ Etc.
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Security: NWK Layer
■ The Stack Profile defines the security level in use.
■ Uses Network Key unless Link Key has been applied.
■ Tool box offers both authentication and encryption
facilities.
■ Auxiliary Header and
Message Integrity Code add
overhead to the packet.
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nibSecurityLevel
Security Suite
0
NONE
1
MIC-32
2
MIC-64
3
MIC-128
4
ENC
5
ENC-MIC-32
6
ENC-MIC-64
7
ENC-MIN-128
46
To summarise the ZigBee network layer:
■ Has 3 device types; ZC, ZR and ZED.
■ Performs network discovery and formation
■ Performs address allocation
■ Performs message routing
■ Configured by the stack profile
■ Provides network wide security
■ Allows low power devices to maximize
their battery life
ZigBee turns 802.15.4 into a low power multi-hop mesh network.
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Contact Details:
Ian Marsden
Integration UK Ltd
Director, Software Engineering
mailto:[email protected]
DDI: +44 (0) 1737 227721
Cell: +44 (0) 7920 105537
Tel: +44 (0) 1737 227722
Fax: +44 (0) 1737 227744
16 - 18 West Street, Reigate, Surrey, RH2 9BS, United Kingdom
http://www.integration.com
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