2. Technological standard created for control and sensor
networks
Based on the IEEE 802.15.4 standard
Wireless personal area networks(WPANs)
High level communication
Frequency band up to 2.4GHz
3. Data rates of 20 kbps and up to 250 kbps
Support for Low Latency Devices
CSMA-CA Channel Access
Low Power Usage consumption
3 Frequencies bands with 27 channels
Extremely low duty-cycle (<0.1%)
Supports large number of nodes
Very long battery life
5. • Transmitting
• Receiving
• Sleeping
Activation and deactivation
of the radio transceiver
• Estimating received signal powerReceiver Energy
Detection
• Quality of a received signal
• Tune its transceiver in to specific channelLink Quality Indication
• Energy Detection mode
• Carrier Sense mode
• Carrier Sense with Energy Detection mode
Clear Channel Assessment
• Tune its transceiver in to specific channel
Channel Frequency
Selection
12. NETWORK DATA
SERVICE
Generates NPDU
Topology specific
routing
NETWORK
MANAGEMENT
SERVICE
Configuring a new
device
Starting a network
Joining or leaving a
network
Addressing
Neighbor discovery
Route discovery
Reception control
13. • Maintaining tables for binding
• Message forwarding between bound end
devices
• Providing services
APPLICATION
SUPPORT
SUB-LAYER
• Key Value Pair service
• Generic Message serviceTHE APPLICATION
FRAMEWORK
• Manufacturer defined component
• Holds key-value attributesAPPLICATION
OBJECTS
• Role of the device
• Responsible for DiscoveryZIGBEE DEVICE
OBJECT
Defined in 802.15.4 standardThe IEEE 802.15.4 defines the physical (PHY) layer and the Medium Access (MAC) layer. The specification for the PHY defines a low-power spread spectrum radio operating at frequency bands such as 2.4 GHz, 915 MHz and 868MHz. The specification for the MAC layer defines how multiple 802.15.4 radios operating in the same area can share the airwaves. The MAC layer specification also defines different network topologies. The ZigBee specification defines application profiles that allow devices from different manufacturers to communicate with each other.n/w :Handles network address and routing by invoking actions in the MAC layer. Its tasks include startingthe network (coordinator), assigning network addresses, adding and removing network devices,routing messages, applying security, and implementing route discovery.
Activation and deactivation of the radio transceiver. The radio transceiver can operate in three different states: transmitting, receiving, or sleeping. The radio is turned ON or OFF upon request of the MAC sub-layer. Receiver Energy Detection (ED). Estimation of the received signal power within the bandwidth of an IEEE 802.15.4 channel. Typical usage is determination whether the channel is busy or idle in the Clear Channel Assessment (CCA) procedure or by the Channel Selection Algorithm of the Network Layer. Link Quality Indication (LQI). A measurement characterizing the strength/quality of a received signal on a link. Clear Channel Assessment (CCA). This operation is responsible for reporting the medium activity state: busy or idle. CCA can be performed in three different operational modes:Energy Detection mode. If the received energy is higher than a given threshold, referred to as ED threshold, the CCA reports that the medium is busy. Carrier Sense mode. Only if CCA detects a signal with the modulation and the spreading characteristics of IEEE 802.15.4 and which may be higher or lower than the ED threshold, the medium is reported busy. Carrier Sense with Energy Detection mode. A combination of the above mentioned methods. Channel Frequency Selection. IEEE 802.15.4 defines 27 different wireless channels and a network can choose to operate within a given channel set. The task of the PHY layer is to tune its transceiver into a specific channel upon the reception of a request from a higher layer.
BEACON-ENABLED MODEIf the coordinator selects the beacon-enabled mode, it forces the use of a so called super frame structure (see subsection) to manage communication between devices. In this mode beacons are periodically sent by the PAN coordinator to synchronize nodes that are associated with it, and to identify the PAN. A time limit is defined during which frames are exchanged between different nodes in the PAN. Thus a beacon frame delimits the beginning of a super frame. Medium access is basically handled by slotted CSMA/CA (see section 4.2.3). For nodes requiring guaranteed services, the beacon-enabled mode also enables the allocation of some time slots, Guaranteed Time Slots (GTSs), in a super frame.NON BEACON-ENABLED MODEIf the PAN coordinator selects the non beacon-enabled mode, there are no beacons and no super frames. An unslotted CSMA/CA mechanism is used to provide medium access control. According to the CSMA/CA mechanism all messages, except acknowledgement frames and any data frame that immediately follows the acknowledgement of a data request command, must be dispatched.
A super frame has an active portion and an inactive portion. The coordinator interacts with its PAN only during the active portion of the super frame. During the inactive portion the coordinator enters a low power (sleep) mode. The active portion consists of CAP (Contention Access Period) and CFP (Contention Free Period). Any device wishing to communicate during the CAP shall compete with other devices using a slotted CSMA/CA mechanism. On the other hand, the CFP contains GTSs (Guaranteed Time Slots). The GTS always appears at the end of the active super frame starting at a slot boundary immediately following the CAP. The PAN coordinator may allocate up to seven of these GTSs and a GTS can occupy more than one slot period.
An ffd is capable of performing all duties described in IEEE standard and can accept any role in the network.anrfd has limited capabilities.foreg. An ffd can communicate with any otherdevice in a network,but an rfd can talk only with an ffd device.rfd devices are intended for very simple aplications such as turning on or off a switch.the processing power and memory size of rfd devices are normally less than those of ffd devicesDevice roles: in an ieee 802.15.4 n/w,anffd device can take three different roles:coordinator,pan coordinator and device.A coordinator is an ffd device that is capable of relaying messages.if the coordinator is also the principal controller of a personal area network(pan)it is called a pan coordinator.if a device is not acting as a coordinator,it is simply called a device.The zigbee standards uses slightly different terminology.azigbee coordinator is an ieee 802.15.4 pan coordinator……A zigbee end device has the least memory size and fewest processing capabilitiesandfeatures.an end device is least expensive device in the n/wThere are three different types of ZigBee devices:ZigBee coordinator (ZC): The most capable device, the coordinator forms the root of the network tree and might bridge to other networks. There is exactly one ZigBee coordinator in each network since it is the device that started the network originally. It is able to store information about the network, including acting as the Trust Centre & repository for security keys.ZigBee Router (ZR): As well as running an application function, a router can act as an intermediate router, passing on data from other devices.ZigBee End Device (ZED): Contains just enough functionality to talk to the parent node (either the coordinator or a router); it cannot relay data from other devices. This relationship allows the node to be asleep a significant amount of the time thereby giving long battery life. A ZED requires the least amount of memory, and therefore can be less expensive to manufacture than a ZR or ZC.
Star: n/w is simple in setup and deploymentData forwarding is possible only by coordinator(two hops only)Coverage area is limited by one hop transmission rangePeer to peer: data frames can be delivered via several intermediate nodeLarge spatial areas can be covered by a single n/wComplex packet routing algorithm are required
In beacon-enabled networks, the special network nodes called ZigBee Routers transmit periodic beacons to confirm their presence to other network nodes. Nodes may sleep between beacons, thus lowering their duty cycle and extending their battery life.In non-beacon-enabled networks, an unslotted CSMA/CA channel access mechanism is used. In this type of network, ZigBee Routers typically have their receivers continuously active, requiring a more robust power supply.Because ZigBee can activate (go from sleep to active mode) in 15 msec or less, the latency can be very low and devices can be very responsive — particularly compared to Bluetooth wake-up delays, which are typically around three seconds. Because ZigBees can sleep most of the time, average power consumption can be very low, resulting in long battery life.
In this mode, the network coordinator will periodically "wake-up" and send out a beacon to the devices within its network. This beacon subsequently wakes up each device, who must determine if it has any message to receive. If not, the device returns to sleep, as will the network coordinator, once its job is complete. Non-beacon mode, on the other hand, is less coordinated, as any device can communicate with the coordinator at will. However, this operation can cause different devices within the network to interfere with one another, and the coordinator must always be awake to listen for signals, thus requiring more power.In any case, ZigBee obtains its overall low power consumption because the majority of network devices are able to remain inactive over long periods of time.
The NLDE enables an application to transport APDUs (Application Protocol Data Units) between two or more devices in the same network. Two services are provided by the NLDE:Generation of NPDU (Network Level Protocol Data Unit). This means generation of a NPDU from an APDU.Topology specific routing. The ability to transmit a NPDU to an appropriate device in the network. This device is either the final destination in the communication chain or the next step towards the final destination. NETWORK MANAGEMENT SERVICEThe NLME allows an application to interact with the ZigBee stack by providing the following services:Configuring a new device. The ability to sufficiently configure the required stack operation. Configuring options are beginning operation as a ZigBee coordinator or joining an existing network. Starting a network. Ability to establish a new network. Joining or leaving a network. The ability to join or leave a network and also the ability for a ZigBee coordinator or ZigBee router to request a device to leave the network. Addressing. ZigBee coordinators are able to assign addresses to devices joining the network. Neighbor discovery. Information pertaining to the one-hop neighbors of a device can be discovered, recorded and reported. Route discovery. The ability to discover and record paths through the network whereby messages can be routed efficiently. Reception control. A device is able to control when the receiver is activated and for how long. This enables the MAC sub-layer synchronization or direct reception.
APPLICATION SUPPORT SUB-LAYERThe three key responsibilities of the APS are: maintaining tables for binding (the ability to match two devices together based on their services and their needs), message forwarding between bound end devices, and providing services for discovery and binding of end devices.APPLICATION FRAMEWORK The application framework provides two data services: KVP (Key Value Pair) service and MSG (Generic Message) service. KVP service is used for getting/setting of attributes within the application objects using tagged data structures in compressed XML. MSG service is for developer defined data structures. Application objects are hosted in the application framework. The data service for the application objects is provided through the APSDE-SAP. The control management of these objects is provided through the ZDO public interfaces. The data service includes request, confirm, response, and indication primitives. APPLICATION OBJECTSAn application object can be described as a manufacturer defined component of the top portion of the application layer that actually implements the application. Upon one ZigBee stack (node) there can be 240 distinct application objects. The application objects holds key-value attributes formatted in XML. These can be requested or changed through the application framework. ZIGBEE DEVICE OBJECTThe ZDO is responsible for defining the role of the device within the network (e.g. ZigBee coordinator or end-device), initiating and/or responding to binding requests and establishing a secure relationship between network devices. Another responsibility of the ZDO is discovery. Discovery means the ability to determine which other devices are operating in the PAN in which the device is associated.
The route discovery in a ZigBee network is similar to the AODV routing protocol Links with lower cost will be chosen into the routing path. The cost of a link is defined based on the packet delivery probability on that linkRoute discovery procedure The source broadcasts a route request packet Intermediate nodes will rebroadcast route request if They have routing discovery table capacitiesThe cost is lowerOtherwise, nodes will relay the request along the treeThe destination will choose the routing path with the lowest cost and then send a route reply
