Presents Seminar on “ ZigBee” By K.Gireesh 63,First floor, 5th Main Road, CIT Nagar, Nandanam, Chennai-35. Tel: 044-65253457 Mobile: 98405 77448 Website: www.vetechnologies.org Email: [email_address]
What is ZIGBEE Emerging standardized protocol for Ultra Low Power Wireless Personal Area Networks (WPANs) ZigBee is an established set of specifications for wireless personal area networking (WPAN) i.e, digital radio connections between computers and related devices. ZigBee is targeted at radio-frequency (RF) applications which require a low data rate, long battery life, and secure networking.
ZigBee Technical Goals
10 kbps to 115 kbps data throughput
10 to 75 m coverage range
Up to 100 collocated networks
Up to 2 years of battery life on standard alkaline
The ZigBee Alliance is an association of companies working together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard.
Zigbee is set of high level communication protocols based upon the specification produced by 802.15.4 - standard for wireless personal area networks (WPANs )
A personal area network ( PAN ) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person
A wireless PAN consists of a dynamic group of less than 255 devices that communicate within a range of about a 33-feet.
IEEE 802 Wireless Space
ZigBee Vs Bluetooth
Bluetooth targets medium data rate continuous duty
– 1 Mbps over the air, ~700 kbps best case data transfer
– File transfer, streaming telecom audio
– Point to multipoint networking
ZigBee targets low data rate, low duty cycle
– 250 kbps over the air, 60-115 kbps typical data transfer
– Long battery life (weeks to months)
– More sophisticated networking
ZigBee Vs Other Wireless Protocols
IEEE 802.15.4 Standard Basics
Channel access is via CSMA with collision avoidance and optional time slotting
Three bands, 27 channels specified
- 2.4 GHz: 16 channels, 250 kbps
- 868.3 MHz : 1 channel, 20 kbps
902-928 MHz: 10 channels, 40 kbps
Message acknowledgment and an optional beacon structure
Works well for selectable latency for controllers, sensors, remote monitoring and portable electronics
Configured for maximum battery life - has the potential to last as long as the shelf life of most batteries
IEEE 802.15.4 Characteristics
Maximum data rates allowed for each of these frequency bands are fixed as 250 kbps @2.4 GHz, 40 kbps @ 915 MHz, and 20 kbps @868 MHz
Channel access using Carrier Sense Multiple Access with Collision Avoidance (CSMA - CA)
Addressing space of up to 64 bit IEEE address devices, 65,535 networks
Architecture These layers facilitate the features that make ZigBee very attractive: low cost, easy implementation, reliable data transfer, short-range operations, very low power consumption and adequate security features
ZigBee Alliance – IEEE- Customer Relations
Physical Layer Functionalities
The IEEE802.15.4 PHY physical layer accommodates high levels of integration by using direct sequence to permit simplicity in the analog circuitry and enable cheaper implementations.
Activation and deactivation of the radio transceiver
Energy detection within the current channel
Link quality indication for received packets
Channel frequency selection
Data transmission and reception
IEEE 802.15.4 Physical Layer Frequency Band
IEEE 802.15.4 PHY/MAC Characteristics
PHY (2.4GHz and 868/915 MHz)
Data rates of 250 kbps (@2.4 GHz), 40 kbps (@ 915
MHz), and 20 kbps (@868 MHz)
Optimized for low duty-cycle applications (<0.1%)
CSMA-CA channel access
Optional guaranteed time slot for applications requiring low latency (Beaconing and GTS not used by ZigBee at this point)
The IEEE 802.15.4 MAC media access control layer permits use of several topologies without introducing complexity and is meant to work with large numbers of devices.
IEEE 802.15.4 MAC Features
Employs 64-bit IEEE & 16-bit short addresses
– Ultimate network size can be 264 nodes (more than probably needed)
– Using local addressing, simple networks of more than 65,000 (216) nodes can be configured, with reduced address overhead
• Three devices specified
– Reduced Function Device (RFD)
– Full Function Device (FFD)
– Network coordinator (FFDC)
• Simple frame structure
• Reliable delivery of data
• Supports association/disassociation
• Supports AES-128 security
• Employs CSMA-CA channel access for better coexistence
• Offers Optional superframe structure with beacons, GTS mechanism
- Standard CSMA-CA communications
Positive acknowledgment for successfully received packets
Optional beacon-enabled network
- Superframe structure
• For dedicated bandwidth and low latency
• Set up by network coordinator to transmit beacons at predetermined intervals
» 15ms to 252sec (15.38ms ∗ 2n where 0 ≤ n ≤ 14)
» 16 equal-width time slots between beacons
» Channel access in each time slot is contention free
Network Pieces : PAN Coordinator PAN Coordinator • “ owns” the network • Starts it • Allows other devices to join it • Provides binding and address-table services • Saves messages until they can be delivered • And more… could also have i/o capability • A “full-function device” – FFD • Mains powered
Network Pieces : Router Routers • Routes messages • Does not own or start network • Scans to find a network to join • Given a block of addresses to assign • A “full-function device” – FFD • Mains powered depending on topology • Could also have i/o capability
Network Pieces : End Devices End Device • Communicates with a single device • Does not own or start network • Scans to find a network to join • Can be an FFD or RFD (reduced function device) • Usually battery powered
IEEE 802.15.4 Device Types
Maintains overall network knowledge; most sophisticated of the three types; most memory and computing power
Full Function Device (FFD)
- Carries full 802.15.4 functionality and all features specified by the standard
- Additional memory, computing power make it ideal for a network router function
- Could also be used in network edge devices where the network touches other networks or devices that are not IEEE 802.15.4 compliant
Reduced Function Device (RFD)
- Carriers limited (as specified by the standard) functionality to control cost and complexity
- General usage will be in network edge devices
ZigBee Device Model
ZigBee Coordinator (ZC)
- One and only one required for each ZigBee network.
- ZigBee Network has unique PAN ID and channel no
- Initiates network formation.
- Acts as 802.15.4 PAN coordinator (FFD).
- May act as router once network is formed.
ZigBee Router (ZR)
- Optional network component.
- May associate with ZC or with previously associated ZR.
- Acts as 802.15.4 coordinator (FFD).
- Participates in multihop routing of messages.
ZigBee End Device (ZED)
- Joins ZC or ZR.
- Optional network component.
- Acts as 802.15.4 End device (RFD).
- Optimized for very low power operation
- Shall not allow association and shall not participate in routing.
ZigBee Network Formation
ZigBee Network Model
ZigBee Mesh Networking
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, whereas the Non-Beacon mode finds favor when the coordinator is mains-powered .
In the beacon mode, a device watches out for the coordinator's beacon that gets transmitted at periodically, locks on and looks for messages addressed to it. If message transmission is complete, the coordinator dictates a schedule for the next beacon so that the device ‘goes to sleep'; in fact, the coordinator itself switches to sleep mode.
For better latency beacon operation is desired. In this mode, devices are assigned one of 16 time slots between beacons. Beacon intervals can be from 15 ms up to 252 seconds .
The non-beacon mode will be included in a system where devices are ‘asleep' nearly always, as in smoke detectors and burglar alarms. The devices wake up and confirm their continued presence in the network at random intervals
Non-beacon operation implies reliance on the CSMA and acknowledgment features for successful communications.
Data Transfer Model Data transferred from device to coordinator • In a beacon-enable network, device finds the beacon to synchronize to the super-frame structure. Then using slotted CSMA/CA to transmit its data. • In a non beacon-enable network, device simply transmits its data using un-slotted CSMA/CA
Data transferred from coordinator to device • In a beacon-enable network, the coordinator indicates in the beacon that “ data is pending .” • Device periodically listens to the beacon and transmits a MAC command request using slotted CSMA/CA if necessary.