ZigBee networks

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ZigBee Alliance Standards

Introduction

A good reference about ZigBee is Silicon Labs’s 2015 youtube playlist

IEEE 802.15.4

  • designed for low power, low data rate, lot cost network
  • PAN (Personal Area Network)
  • raw bit rate with 2.4GHz DSS PHY = 250 kbps
  • channel access vis CSMA-CA
    • Collision avoidance using CCA, random backoffs
  • link layer ack (MAC ACK) on unicast transmissions
  • frequency
    • 16 channels in 2.4GHz ISM band (2MHz each, numbered from 11 to 26)
    • 10 channels in 915MHz ISM band
    • 1 channel in the European 868MHz band
  • packet size has 128 bytes maximum (including a 16 bit CRC)
  • REF: [Youtube] ZigBee Concepts 2: MAC and PHY Concepts for ZigBee Networks

Node types

PAN ID

  • 16-bit identifier shared by all nodes in PAN
  • used in MAC header filter
  • ZC picks values upon forming network
  • stacks detects conflicts and updates network automatically

Extended PAN ID

  • 64-bit extended PAN ID (EPID) know to all nodes in PAN
    • unique per PAN
  • chosen by ZC at time of network formation
  • only sent over-the-air in response to Active Scan
  • enables recognition of network after PAN ID change
  • might not be totally random

Individual Node Address 

 ---------------------------------------------------
| EUI-64         | Net Addr | Endpoint | Cluster ID |
|----------------|----------|----------|------------|
| 64-bits        | 16-bit   | 8-bit    | 16-bit     |   
 ---------------------------------------------------
  • EUI-64
    • 64-bit unique address (IEEE “MAC Address”)
    • never changes
  • network address
    • 16-bit (“node ID”)
    • assigned to a device when it joins the network
    • may change over time
  • endpoint
    • 8-bit logical address within a device (similar to TCP port)
  • cluster ID
    • 16-bit field used as an application specific message type

Application Profiles

  • similar to a miniature protocol on top of ZigBee stack
  • defines device types with different capabilities (clusters)
    • 16-bit “device ID” enumerates device type withing the profile
  • identified by 16-bit application profile ID
    • assigned by ZigBee Alliance
  • Examples
    • Home Automation (HA)
    • Commercial Building Automation (CBA)
    • Smart Energy (SE)
    • Manufacturer-Specific Profile (MSP)

Clusters

  • each device definition in a profile contains clusters
  • Cluster is a set of message types related to a certain device function
    • enumerated by 16-bit Cluster ID
  • ZigBee Cluster Library (ZCL)
    • defines clusters for use in public profiles
      • same cluster (and ID) can be used in multiple profiles
    • defines “attributes” and “commands” for a given cluster
    • group clusters into “functional domains” (e.g. Lighting, HVAC)
    • uses “client” and “server” model of communication
      • client sends messages to server
      • server maintains attributes
  • REF: [Youtube] ZigBee Concepts 5: Application Profiles, Clusters, and Endpoints

ZigBee Endpoints

  • An endpoint is a service point within a ZigBee node (up to 255 per node)
  • up to 255 endpoints per node
  • endpoints 0, 240 to 255 are reserved for special functions
    • endpoints 1 to 239 = available for user applications
    • endpoint 0 = ZigBee Device Object (ZDO). used for network config / admin
    • endpoint 255 = broadcast endpoint
  • each endpoint implements a single device type from a single application profile
  • different endpoints on a single node may represent devices from different application profiles
  • each endpoint has a descriptor and a cluster list
  • cluster list describes capabilities of device by enumerating supported inbound (client) and outbound (server) clusters
  • Endpoint descriptor contains
    • Application Profile ID
    • Device ID (withing the specific profile)
    • Number of supported inbound and outbound clusters
    • Bitmask indicating version/capabilities
  • REF: [Youtube] ZigBee Concepts 5: Application Profiles, Clusters, and Endpoints

ZigBee Home Automation (ZHA) Profile

  • ZigBee Residential Security (NWK layer encryption - Network Wide Key)
  • clusters used
    • general (basic, on/off, groups, scenes, …)
    • measurement / sensing (light, temp, pressure)
    • lighting (color control)
    • HVAC (thermostat, fans, pumps)
    • closures (shade control)
    • security / safety (alarm, zones, …)
  • device types
    • general
      • range extender
      • on/off switch
      • level control switch
      • mains outlet
      • remote control
    • lighting
      • light
      • switch
      • dimmer
      • occupancy and Light Sensor
    • closures
      • shade control
    • HVAC
      • heater/cooler
      • thermostat
      • temp / pressure / flow sensor
      • pump controller
    • Intruder alarm system (IAS)
      • warning device
      • controller/indicator zone
  • Designed for consumer-grade lighting device, small networks
  • uses similar cluster to ZHA
    • groups
    • scenes
    • lighting control
    • on/off
  • No Coordinator
  • Touch Linking
  • Coexists easily with HA

ZigBee Smart Energy (SE) Profile

  • Interface between AMI (Advanced Metering Infrastructure) and HANs (Home Area Network)
  • Security is a key concern
    • NWK layer encryption among all nodes
    • APS layer encryption among pairs of device
    • trust center facilitates key installation
    • key establishment cluster to negotiate unique key via ECC
  • anonymous messaging for AMI to HAN comms hub (pricing events, etc)
  • fragmentation for larger messages
  • prioritize channels that don’t overlap with WiFi
  • Clusters used
    • Key Establishment
    • Price
    • Demand response / Load Control (DRLC)
    • Simple Metering
    • Message (for updating displays)
    • Tunneling
    • Pre-payment
  • Device Types
    • Metering Device (gas, water, electric, …)
    • In-Home Display (IHD)
    • Programmable Communicating Thermostat (PCT)
    • Load Control Device (e.g. remote disconnect)
    • Smart Appliance
    • Prepayment terminal
    • Range extender