Appendix C - wireless network mesh overview - Johnson Controls - LIT-12013765 - Wireless field bus - SEC - UCB

Smart Equipment Control Wireless Installation Guide

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The WRG1830/ZFR183x Pro Series wireless network is based on a global open networking standard that defines a low-cost, low-power, two-way wireless communication system. Its development reference comes from the ZigBee® Alliance, an organization of manufacturers devoted to providing a cost-effective wireless networking technology for use in commercial and residential applications. The primary advantages that this ZigBee Alliance technology brings to the marketplace include the following:

  • High reliability and security
  • Low power with multi-year battery life
  • Low complexity at an economic cost

Communications technology

The ZFR Pro Series wireless network is a Personal Area Network (PAN) based on the Institute of Electrical and Electronic Engineers (IEEE) 802.15.4 standard for low power, low duty-cycle wireless transmitting systems. Devices on the network use Direct Sequence Spread Spectrum (DSSS) wireless technology and operate on the 2.4 GHz Industrial, Science, and Medical (ISM) band.

Devices on the ZFR183x Pro Series wireless network are different from Bluetooth devices and wireless Universal System Bus (USB) devices in that they form a mesh network between nodes. Mesh networks are a type of daisy chaining from one device to another. This technique expands the typically short range of an individual node into a much larger, widespread network consisting of multiple nodes.

The Media Access Control (MAC) layer uses a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism. This layer transmits beacon requests, synchronizations, and message retries. The physical layer of the ZFR Pro Series wireless network uses the 2.4 GHz radio band.

Figure 1. Mesh network

Network device types

The ZigBee Alliance specification defines three kinds of devices that are part of the mesh network: a coordinator, one or more routers, and one or more end devices.

Parent and child devices

In the ZFR Pro Series wireless network, a parent is a device that assigns unique network addresses to other child nodes as they join the network. Any coordinator or router can be a parent to other routers and end devices, but the coordinator is always a parent device.

Self-healing, multi-hop network

The ZFR Pro Series wireless network is further characterized as a self-healing, multi-hop network. If a wireless communication path experiences interference or drops out, the network automatically reroutes the message through an alternate path to form a new wireless communication path. Each message is received, then retransmitted as it hops along from node to node until it reaches its final destination. Within ZFR Pro Series wireless network, a single message is allowed to hop 30 times between the source and destination node.

End devices, parent, and target routers

An end device communicates through its parent router. This parent may also be the target of the data.

ZFR183x Pro System mesh network technology implementation

The ZFR183x Pro Series Wireless Field Bus system implements mesh technology as follows:

  • The WRG1830 and connected ZFR1831 Router is the Wireless coordinator, which does not accept end devices as child nodes. The Wireless Coordinator is a parent to ZFR1831 Pro Routers.
  • The ZFR1831 Pro Router is the router. The ZFR1831 Pro Router can serve as a child to a Wireless Coordinator or other ZFR Pro Routers, and a parent to other ZFR Pro Routers and WRZ Sensors.
  • The WRZ Series Sensors are the end devices. The WRZ Sensors are battery-operated devices that serve as children to ZFR Pro Routers but are never also children of the Wireless Coordinator.

Physical layer channels

The WRG1830/ZFR1283x Pro Series System is based on an Institute of Electrical and Electronic Engineers (IEEE) 802.15.4 ZigBee network definition.

This network has 16 channels available for use (Channels 11 through 26). In North America, the ZFR Pro Series System uses channels 11 through 25. By default, the ZFR1831 mesh network coordinator is configured for use in North America, and uses channels 15, 20, and 25.

These channels were selected for the ZFR Pro Series System because they do not overlap with channels used on an IEEE 802.11 Wi-Fi network unless 802.11 A or N is used.