ZigBee Overview Mike Armel The George Washington University V 1.1

Overview Introduction to ZigBee Evolution of technology to ZigBee Comparison to other wireless standards standard and where fits in and how ZigBee fits in Inside standard Traffic and Packet analysis Types of Topologies ZigBee Routing

Introduction – What is ZigBee ZigBee is a working group much the same as the WiFi alliance or the WiMAX forum for the promotion of the standard

Introduction – ZigBee Applications Wireless monitoring, control of lights, security alarms, motion sensors, thermostats, pressure sensors, smoke detectors. A wireless mouse that works for YEARS not weeks without needing new batteries

Introduction - ZigBee Most complex ZigBee node requires only 10% of the code a typical Bluetooth node would require Simplest ZigBee node requires only 2% of the code a typical Bluetooth node would require ZigBee nodes currently come in at ¼ the cost of Bluetooth nodes

Introduction – ZigBee Alliance Focus Defining the network, security and application software layers Providing interoperability and conformance testing specifications Promoting the ZigBee brand globally to build market awareness Managing the evolution of the standards *Membership in the ZigBee alliance is not free entry level will require $3500 for access to the specification

Introduction – First There Was X10

Used the AC power lines as a transmission mechanism Addressing was “house” A through P and “module” codes 1 through 16 Slow speed effective rate of 60bps Not reliable! Ahead of it’s time and offered a coolness factor Clap On Clap Off …

Review of the popular wireless 802 standards a WiMAX WLAN WPAN Frequency 2 – 11GHz 2.4GHz Varies Range31 miles100 Meters 10 Meters Data Rates 70 Mbps Mbps 20k – 55Mbps NodesThousandsDozens Dozens

Review of the popular wireless 802 standards Data Rate (Mbps) Range ZigBee a c WPAN WLAN WMAN WWAN WiFi Bluetooth IEEE WiMax IEEE IEEE Courtesy ZigBee Alliance

Review Alphabet Soup Wireless Personal Area Networks (WPAN) WPANs based on Bluetooth Coexistence of WPAN’s and WLAN’s High data rates 20Mbps+ on WPAN aHigh speed PHY enhancements b High speed MAC enhancements Low data rate, simple multi year battery life Mesh Networking

IEEE /ZigBee Standard Low data rate, simple multi year battery life /ZigBee – “Consortium of many companies working together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard. ”

IEEE /ZigBee Standard IEEE Defines only the PHY (physical layer) and the MAC (media access controller) PHY Layer MAC Layer Network/Security Application Application Framework IEEE Defined ZigBee Alliance User Defined

IEEE Frequency Bands and Data Rate PHY Frequency Band Channel Numbering Chip Rate Mod Bit Rate Symbol Rate Modulation 868 MHz868 – 870 MHz 0300k chip/S BPSK20 kb/s 20 kbaud BPSK 915 MHz902 – 928 MHz k chip/s BPSK40 kb/s 40 kbaud BPSK 2.4 GHz2.4 – GHz M chip/s O- QPSK 250 kb/s 62.5 kbaud 16-ary Orthagonal Spreading ParametersData Parameters

IEEE Channel Division BPSK 868MHz/ 915MHz PHY MHz Channel 0 Channels 1-10 Channels MHz902 MHz 5 MHz 2 MHz QPSK 2.4 GHz PHY Courtesy Anton Kruger – The University of Iowa

Traffic Types Periodic data Application defined rate (e.g. sensors) Intermittent data Application/external stimulus defined rate (e.g. light switch) Repetitive low latency data Allocation of time slots (e.g. mouse)

Packet Structure Packet Fields Preamble (32 bits) - synchronization Start of Packet Delimiter (8 bits) - specifies one of 3 packet types PHY Header (8 bits) - Sync Burst flag, PSDU length PSDU (0 to 127 bytes) - Data Preamble Start of Packet Delimiter PHY Header PHY Service Data Unit (PSDU) 6 Bytes0-127 Bytes

Device Addressing All devices have IEEE addresses Short addresses can be allocated Addressing modes: Network + device identifier (star) Source/destination identifier (peer-peer) Source/destination cluster tree + device identifier (cluster tree)

General Data Packet Structure PRESPDLENPCCRCLink Layer PDUADDRESSING Preamble sequence Start of Packet Delimiter Length for decoding simplicity Flags specify addressing mode Data sequence number CRC-16 DSN Addresses according to specified mode Courtesy Anton Kruger – The University of Iowa

ZigBee Device Classes Full function device (FFD) Available in any topology Capable of becoming a network coordinator Talks to any other device Typically continuously active looking for stimuli Reduced function device (RFD) Limited to only star topologies Cannot become a network coordinator Communicates only to a network coordinator Simple implementation efficient and low power

Transceiver Characteristics Transmit Power Capable of at least 1 mW Power reductions capability required if > 16 dBm (reduce to < 4dBm in a single step) Receiver Sensitivity -85 dBm (1 % Packet Error Rate) RSSI measurements Packet Strength indication Clear channel assessment Dynamic channel selection

ZigBee Products

Basic Network Characteristics Theoretical 65,536 network (client) nodes Optimized for timing-critical applications –Network join time: 30 ms (typical) –Sleeping slave changing to active: 15 ms (typical) –Active slave channel access time: 15 ms (typical) Network coordinator Full Function node Reduced Function node Communications flow Virtual links Courtesy the ZigBee Alliance

Topology Models Star Networks (Personal Area Network) Home automation PC Peripherals Personal Health Care Peer-to-Peer (ad hoc, self organizing & healing) Industrial control and monitoring Wireless Sensor Networks Intelligent Agriculture

Topology Models PAN coordinator Full Function Device Reduced Function Device Star Mesh Courtesy the ZigBee Alliance

Cluster Tree Networks Cluster tree networks enable a peer-peer network to be formed with a minimum of routing overhead. Courtesy IEEE

Cluster Tree Networks Employ multi-hop routing Can be very large: 255 clusters of 254 nodes each = 64,770 nodes May span physically large areas Suitable for latency-tolerant applications

ZigBee Device Types ZigBee Coordinator (ZC) Most capable device and Initiates network formation One and only one required for each ZB network. Acts as 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 coordinator (FFD). Acts as an intermediary in multihop routing of messages. ZigBee End Device (ZED) Contains just enough functionality to talk to its coordinator Optional network component. Shall not allow association. Shall not participate in routing hence cannot relay messages

Network Structure Courtesy ZigBee Alliance

Network Structure Courtesy ZigBee Alliance

Network Structure Courtesy ZigBee Alliance

Tree Structures Address Assignment Courtesy ZigBee Alliance

NHLE-Based Addressing nwkNextAddress – The next network address that will be assigned to a device requesting association. nwkAvailableAddresses – A count of the addresses left to assign. Decremented by 1 each time an address is assigned. nwkAddressIncrement – The amount by which nwkNextAddress is incremented each time an address is assigned.

ZigBee Routing Uses AODV (Ad-hoc On-Demand Distance Vector) Capable of both uni/multi-cast routing Reactive protocol, establishes route to destination on demand not proactively like IP routing on the usage of a particular paths Network is silent until a connection is needed When a link fails, a routing error is passed back to a transmitting node, and the process repeats.

ZigBee Routing – Frame Format Courtesy ZigBee Alliance

Tree Routing If the following expression is true then a destination device, D, is a descendent of router A: and the address of the next hop is: if the device is a router or (trivially) D if the device is an end device. Otherwise the destination is not a descendant and the message should be routed through A’s parent. Courtesy ZigBee Alliance

Table Routing Table routing, in the case where a routing table entry for the destination exists, simply consists of extracting the next-hop address from that entry and routing the message through (or to) that address. Courtesy ZigBee Alliance

A device wishing to discover (or repair) 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 at least one route reply command frame. Potential routes are evaluated with respect to a routing cost metric at both source and destination. Route Discovery

Route Request Command Frame Only 1 command option - RouteRepair Courtesy ZigBee Alliance

Route Reply Command Frame Only 1 command option - RouteRepair Courtesy ZigBee Alliance

Route Discovery Table Route discovery table fields Courtesy ZigBee Alliance

Routing Cost For a link l, the cost to send a message across that link is: where p1 is the estimated probability of delivery. The pathcost for a multihop route is just the sum of the link costs along the path. This is the metric used to evaluate routes during route discovery and maintenance. Courtesy ZigBee Alliance

The Route Error Command Frame Courtesy ZigBee Alliance

Routing Options Tree routing may be disallowed (nwkUseTreeRouting). Link cost reported during route discovery may be constant or based on likelihood of reception. Links may be assumed to be symmetrical or not (nwkSymLink).

Future of ZigBee ZigBee has the potential to unify methods of data communication for sensors, actuators, appliances, and asset-tracking devices. Zigbee offers a means to build a reliable but affordable network backbone that takes advantage of battery- operated devices with a low data rate and a low duty cycle. Home automation is likely the biggest market for ZigBee- enabled devices. This follows from the number of remote controlled devices (or devices that may be connected wirelessly) in the average household.

References ZigBee Alliance: Network Layer Technical Overview: How It all Works Mikhail Galeev: Home Networking With ZigBee Callaway Et. Al, “Home Networking With IEEE Bob Heile: Zigbee Alliance Tutorial William C. Craig: ZigBee: Wireless Control That Simply Works Anton Kruge, University of Iowa: Introduction to Wireless Sensor Networks