1. ZigBee
and
IEEE

2. Network topologies and communication models AODV Routing
Lecture Overview
Technical overview
Applications / uses
Device Types
Protocols
Network topologies and communication models
AODV Routing
Network Technology Richard Anthony The University of Greenwich

3. The 802 Wireless Space
ZigBee is NOT intended to provide high bandwidth service of WLAN
ZigBee is NOT intended to provide moderate bandwidth wireless link over short range
(as Bluetooth does)
ZigBee IS intended to provide LOW bandwidth, robust connectivity at moderate range.
ZigBee IS ideally suited to sensing and control applications.
Network Technology Richard Anthony The University of Greenwich

4. General characteristics Overall design goals
Low power, low cost, flexible wireless communication technology
Range
10 – 100M low power, up to 1000M high power
Data rates
20 kilobits/second to 250 kilobits/second
Transmission frequency
2.4 GHz in the Industrial, Scientific and Medical (ISM) radio band
Transmission power levels
1mW and mW
Communication structure / Topology
Ad-hoc, dynamic
Network Technology Richard Anthony The University of Greenwich

5. IEEE 802.15.4 defines the Physical layer and MAC layer for ZigBee.
ZigBee extends IEEE
IEEE defines the Physical layer and MAC layer for ZigBee.
This gives a well-defined, standardised wireless link.
ZigBee adds a number of features to facilitate full wireless networks for communities of devices:
Device discovery and neighbour associations
Device roles
Logical grouping (PAN ID)
Routing ….
Addressing
64-bit IEEE address – Unique address – ‘burned in’
16-bit Node-ID – Assigned when a node joins a network
Network Technology Richard Anthony The University of Greenwich

6. – problematic for low-resourced sensor nodes
ZigBee extends IEEE
Various ZigBee modules available, some e.g. ‘EasyBee’ only cover the wireless transmission and require the higher protocol stack to be implemented in software.
– problematic for low-resourced sensor nodes
– potentially useful if only a simple point-point link is needed.
Network Technology Richard Anthony The University of Greenwich

7. Determines if a neighbouring device belongs to the network.
ZigBee Network layer
Performs routing (uses AODV see later)
Determines if a neighbouring device belongs to the network.
Discovers new neighbours (any role, so includes routers).

8. ZigBee Application layer (ZigBee system interface to end users).
Deals with Addressing !
64-bit IEEE address – fixed
16-bit Node ID – dynamically assigned
Devices within a node identified by Endpoint Identifier (1 – 240)
Comprises components added by ZigBee spec (on top of IEEE radio link spec), includes:
ZigBee Device Object (ZDO) responsible for defining role of a device (Coordinator / End device) and for the discovery of new (one-hop) devices and the identification of their offered services.
Application objects (application specific data objects).
Application support sublayer (APS) offers a well-defined interface and control services. Serves as a bridge between the network layer and the other components of the application layer: manages binding tables – maps devices to the services offered by the discovered devices.

9. Application domains targeted by ZigBee:
Application Profiles released
Smart Energy 1.0
Home Automation
Health Care
RF4CE – Remote Control
Telecommunication services
Application Profiles in development
Smart Energy 2.0
Building Automation
Retail Services
Network Technology Richard Anthony The University of Greenwich

10. End Device (E) one or more (FFD or RFD, see below)
Device Types
A ZigZee network comprises several different ‘types’ of device (assigned roles)
Coordinator (C) one
End Device (E) one or more (FFD or RFD, see below)
Router (R) zero or more (FFD, see below)
Classes of devices:
Reduced-Functionality device (RFD)
Full-Functional device (FFD)
FFD nodes can form networks of any type (mesh, star, hybrid).
RFD nodes can only connect to a full function node.
Network Technology Richard Anthony The University of Greenwich

11. Device Types - Coordinator
The Coordinator is the logical equivalent of an access point in a wireless network, in terms of device connectivity, or a master node in Bluetooth,
The role of ‘Coordinator’ is a network-level role (i.e. for establishing the network) and not necessarily an application-level role.
The Coordinator can be the data sink for sensing applications, and can issue commands in remote control applications. However, a node does not have to be the Coordinator to carry out such functions.
Network Technology Richard Anthony The University of Greenwich

12. Device Types – End device
End devices are the nodes deployed within a given application to perform sensing and actuation.
These devices will often be optimised to use low power because will often be placed in low-accessibility positions, or will possibly be attached to mobile objects (consider a trolly in a hospital).
Most sensor applications fall natively into the RFD class, with extended networks making use of both FFDs and network coordinators to form bridges and links required by the network topology.
Network Technology Richard Anthony The University of Greenwich

13. A series of hops through several routers may be required.
Device Types – Router
A Router is a device (class FFD) that will forward messages between end devices and the coordinator.
A series of hops through several routers may be required.
End nodes may be configured to act as routers:
Routers also need to use low amounts of power
Routers may be simple sensor devices with low
processing resources - therefore need a simple and
robust routing strategy:
A modified form of AODV routing is used.
Network Technology Richard Anthony The University of Greenwich

14. Network topologies and communication models Simple topologies
Wireless link to remote data source
Wireless sensing of an environment
A router is positioned to extend range
ZigBee Coordinator
ZigBee Router
ZigBee End Node
ZigBee End Node and Router
Wireless sensing of remote environment
Network Technology Richard Anthony The University of Greenwich

15. Network topologies and communication models Mesh network topologies
Routers facilitate a mesh network
Multi-path connectivity provides robustness but adds complexity and overheads
Generic concept of a mesh connecting the end-devices to the Coordinator
Redundant links provide robustness
Network Technology Richard Anthony The University of Greenwich

16. Network topologies and communication models
Application-specific topologies
Densely sensed area # 1
Densely sensed area # 2
Sparsely sensed area
An example where environmental sensing is non-uniform.
The application could be, for example, security systems at an airport
Network Technology Richard Anthony The University of Greenwich

17. Network topologies and communication models
Topology / connectivity formation
Each node maintains Neighbour, Routing and Binding Tables
Coordinator is responsible for initialising, maintaining and controlling the network.
An End device is said to ‘belong’ to a parent node
A parent node can be the coordinator or a router.
The End device polls to find a Parent node.
The parent node ‘discovers’ the end device by receiving these polls.
The parent node adds the end device to a Table
Network Technology Richard Anthony The University of Greenwich

18. ZigBee hardware - Modules
‘EasyBee’ provides the wireless hardware and minimal ZigBee support
(need to implement the protocol stack in software)
Antenna is a track on the PCB
‘ProBee’ module supports almost entire ZigBee Pro spec.
Various antenna options
Antenna screws onto here
Network Technology Richard Anthony The University of Greenwich

19. ZigBee hardware – Evaluation Board and Modules (1)
ProBee module on ZigBee evaluation board – with ‘chip’ antenna
Network Technology Richard Anthony The University of Greenwich

20. ZigBee hardware – Evaluation Board and Modules (2)
ProBee module on ZigBee evaluation board – with Dipole antenna.
Network Technology Richard Anthony The University of Greenwich

21. Very small physical module, no RF amplifier is needed
Transmission Power
The standard ZigBee transmission power is approximately 1mW. This power level can be driven directly from the ZigBee chips.
Advantages include:
Very small physical module, no RF amplifier is needed
No external antenna is needed, can be on-chip / on circuit board
Very low power usage when transmitting.
Usable range of about 10m to 100m depending on the environment,
antenna, and frequency band.
An amplifier can be added, boosting power to approximately 100mW.
This power level gives:
Far greater range.
Better SNR and performance in terms of dealing with obstacles.
Shortens battery life or requires replenishable power source.
Network Technology Richard Anthony The University of Greenwich

22. Transmission Power – Range illustration
Image from
Network Technology Richard Anthony The University of Greenwich

23. Application-specific transmission power settings
Example – Livestock monitoring on a farm
Enclosure area # 2
Enclosure area # 1
Enclosure area # 3
Key
Low power (1mW) link used by small collar mounted devices with small battery
100mW link between fixed devices with (large battery, solar or mains power)
Network Technology Richard Anthony The University of Greenwich

24. Protocols – Multiplexing and Separation and coding Channel
There are 16 ZigBee channels in the 2.4 GHz band.
Each channel requires 5 MHz of signal bandwidth (separation). The 2.4 GHz band Each channel can transmit up to 250 kbit/s.
(actual data throughput < max specified bit rate due to packet overhead and processing delays).
Coding
The radios use direct-sequence spread spectrum coding (DSSS)
Offset quadrature phase-shift keying (OQPSK) is used in the 2.4 GHz band (enables transmission of four bits per symbol).
Grouping
A ‘PAN ID’ enables logical grouping / separation of nodes.
- A 16-bit value which is used to uniquely define a PAN. 
- Devices identify which networks to join based on their PAN ID.
Network Technology Richard Anthony The University of Greenwich

25. Protocols (Transmission options)
Each transmission can be sent secured or unsecured
Acknowledged: originator data is confirmed by recipient
Unacknowledged: no confirmation
Unicast: send to a specific recipient
Broadcast: send to all recipients
Multichannel: Originator attempts Tx using frequency re-acquisition mechanism
Single channel: Originator attempts Tx on the expected channel
Network Technology Richard Anthony The University of Greenwich

26. Protocols (discovery)
Device discovery
Find other ZigBee devices that can be paired to.
Can be attempted repeatedly
- for fixed duration, or
- until sufficient number of responses received
Service discovery
Information is exchanged between a pair of devices:
Device capabilities: target / controller
mains / battery power
Vendor information
Application information (user-defined description of the device’s
functionality – e.g. Entrance foyer camera control)
Requested Device type (type of device requested through discovery,
e.g. a camera control console might search for PZT cameras)
Network Technology Richard Anthony The University of Greenwich

27. Routing – Ad hoc On-Demand Distance Vector (AODV)
Used in ZigBee’s network layer.
Achieves robust routing in highly dynamic networks (designed for wireless sensor networks (WSN) and mobile ad hoc networks (MANETs).
Reactive - establishes a route to a destination on demand. (Internet routing protocols are proactive; establishment of routing paths is a separate activity to the transmission of packets over those paths. Paths set up in advance of being needed; paths re-established automatically if topology changes.)
Establishes a mesh network through the use of broadcast communication.
A node broadcasts a route request to all of its neighbours.
The neighbours forward broadcast the request to their neighbours, etc. until the destination is reached (this staged broadcast technique is termed ‘flooding’).
Destination receives multiple copies and determines the shortest path taken.
The route reply is unicast following the lowest cost path back to the source.
The source then updates its routing table for the destination address with the next hop in the path and the path cost (number of hops).
Network Technology Richard Anthony The University of Greenwich

28. Routing – AODV in Operation1 2 3a 3b 4
End Device has data to send to sink, passes message to its parent node.
Router broadcasts route request to its neighbours.
Neighbouring routers forward broadcast the route request (flood, steps 3a and 3b nearly simultaneous).
(Assuming that ‘3a’ message arrives first at the Coordinator) The route reply is sent back – using the route.
+Ve points: adaptive, robust
-Ve points: latency, overheads
Network Technology Richard Anthony The University of Greenwich