ZigBee

• Introduction

• Architecture

• Node Types

• Network Topologies

• Traffic Modes

• Frame Format

• Applications

• Conclusion

Topics

• The Wireless technologies (WiFi,GSM,and Bluetooth) All have one thing in common :

They send a relatively Large amount of data, at a relatively High data rate.

• Thus , the devices used in these technologies have high bit rates and consume high power .

Introduction

But what if we want to send very small data packets using devices that have low data

rates and consume very low power ?

Well, Here comes the role of ZigBee.

• ZigBee is an established set of specifications

built around the IEEE 802.15.4 wireless protocol

for wireless personal area networking (WPAN) .

• ZigBee is targeted at radio-frequency (RF) applications that require a low data rate ,Small packet transmission , long battery life, and secure networking.

• Specialized in Control and Sensor Networks

What is ZigBee ?

In other words why do we need a standard to use these devices?

Before using ZigBee these low power/low data rate devices were used with no common or shared standard .So , there was no way to form a wireless network between them .

ZigBee made it possible for devices from completely different manufactures to communicate and work together .

Do we really need ZigBee ?

• The name "ZigBee" is derived from the erratic zigging patterns many bees make between flowers when collecting pollen., similar to the way packets would move through a mesh network.

• ZigBee protocol carries all the benefits of the 802.15.4 protocol with added networking functionality ,It was engineered by the ZigBee Alliance, (a group of companies that maintain and publish the ZigBee standard)

The Name ZigBee !

ZigBee Node Types

1. ZigBee Coordinator (ZBC)

• 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

2. ZigBee Router (ZBR)

• full function device FFD

• optional component

• routes between nodes

• extends network coverage

• needs lesser memory than the ZigBee coordinator node

• can operate in all topologies and can act as a coordinator

3. ZigBee End Device (ZBE)

• Reduced function device RFD

• optimized for low power consumption

• cheapest device type

• communicates only with the coordinator

• sensor would be deployed here

• capable of talking in the network; it cannot relay data from

other devices

Using a single PAN coordinator,

each node connects directly to

the central coordinator – all inter-node

communications are passed

through the coordinator.

ZigBee Topologies

In the peer-to-peer topology there

is also a PAN coordinator,

but it differs from the star

topology in that any device can

communicate with any other

device as long as they are in

the range of one another.

The peer-to-peer topology

allows more complex network

formations to be implemented,

such as the mesh topology.

A cluster tree network consists

of a number of star networks

connected whose central

nodes are also in direct

communications with the

single PAN Coordinator.

 

Using a set of routers and

a single PAN coordinator,

the network is formed into an

interconnected mesh of

routers and end nodes

which pass information from

node to node using the most

cost effective path.

Should any individual router

become inaccessible,

alternate routes can be

discovered and used providing

a robust and reliable network topography.

The first FFD that is activated may establish its own network and become a Personal Area Network (PAN) coordinator.

Then both FFD and RFD devices can connect to the

PAN coordinator.

All networks within the radio sphere of influence must have a unique PAN identity.

All nodes in a PAN must talk to the PAN Coordinator.

Network Formation

• 1. Data is periodic. The application dictates the rate, and the sensor activates, checks for data and deactivates. (e.g. sensors)

• 2. Data is intermittent. The application, or other stimulus, determines the rate, as in the case of say smoke detectors. The device needs to connect to the network only when communication is necessitated. This type enables optimum saving on energy. (e.g. light switch)

Data Traffic Types

• ZigBee employs either of two modes, beacon or non-beacon to enable the to-and-fro data traffic.

• Beacon mode is used when the coordinator runs on batteries and thus offers maximum power savings,

• Non-beacon mode finds favor when the coordinator is mains-powered.

Traffic Modes

Traffic Modes

1. Beacon mode:

• beacon send periodically

• Coordinator and end device can

go to sleep between beacons

• Lowest energy consumption

• Precise timing needed

When a coordinator wishes to transfer data to a device in a beacon-enabled network, itindicates in the network beacon that the data message is pending. The device periodicallylistens to the network beacon, and if a message is pending, transmits a MAC commandrequesting this data, using slotted CSMA-CA . The coordinator optionally acknowledgesthe successful transmission of this packet. The pending data frame is then sent usingslotted CSMA-CA. The device acknowledged the successful reception of the data by transmitting an acknowledgement frame. Upon receiving the acknowledgement, themessage is removed from the list of pending messages in the beacon

2. Non-Beacon mode:

• coordinator/routers have to stay awake

(robust power supply needed)

• asymmetric power

When a coordinator wishes to transfer data to a device in a nonbeacon-enabled network,it stores the data for the appropriate device to make contact and request data. A devicemay make contact by transmitting a MAC command requesting the data, using unslotted CSMA-CA, to its coordinator at an application-defined rate. The coordinatoracknowledges this packet. If data are pending, the coordinator transmits the data frame using unslotted CSMA-CA. If data are not pending, the coordinator transmits a data frame with a zero-length payload to indicate that no data were pending.

Why ZigBee?• Standards based• Low cost• Can be used globally• Reliable and• Supports large number of nodes• Easy to deploy• Very long battery life• Secure

Conclusion