THE BASICSZwave operates at 908.42 MHz in the US (868.42 MHz in Europe) using a mesh networking topology. A Zwave network can contain up to 232 nodes, although reports exist of trouble with networks containing over 30-40 nodes. Zwave operates using a number of profiles (think of them like languages), but the manufacturer claims they interoperate. Use care when selecting products as some products from certain manufacturers are not compatible with other manufacturers’ products.Zwave utilizes GFSK modulation and Manchester channel encoding.A central, network controller, device is required to setup and manage a Zwave network. Each product in the home must be “included” to the Zwave network before it can be controlled via Zwave (and before it can assist in repeating/hoping within the mesh network).Each Z-Wave network is identified by a Network ID and each device is further identified by a Node ID.The Network ID (aka Home ID) is the common identification of all nodes belonging to one logical Z-Wave network. Network ID has a length of 4 bytes and is assigned to each device by the primary controller when the device is added into the network. Nodes with different Network ID’s cannot communicate with each other.The Node ID is the address of the device / node existing within network. The Node ID has a length of 1 byte.Z-Wave uses a source-routed mesh network topology and has one primary controllers. Secondary controllers can exist, but are optional. Devices can communicate to one another by using intermediate nodes to route around and circumvent household obstacles or radio dead spots that might occur though a message called “healing”. Delays will be observed during the healing process. A message from node A to node C can be successfully delivered even if the two nodes are not within range, providing that a third node B can communicate with nodes A and C. If the preferred route is unavailable, the message originator will attempt other routes until a path is found to the “C” node. Therefore, a Z-Wave network can span much farther than the radio range of a single unit; however, with several of these hops a slight delay may be introduced between the control command and the desired result. In order for Z-Wave units to be able to route unsolicited messages, they cannot be in sleep mode. Therefore, battery-operated devices are not designed as repeater units. A Z-Wave network can consist of up to 232 devices with the option of bridging networks if more devices are required.As a source routed static network, Z-Wave assumes that all devices in the network remain in their original detected position. Mobile devices, such as remote controls, are therefore excluded from routing.Z-wave released later versions with added network discovery mechanisms so that ‘explorer frames’ could be used to heal broken routes caused by devices that have been moved or removed. A Pruning algorithm is used in explorer frame broadcasts and are therefore supposed to reach the target device, even without further topology knowledge by the transmitter. Explorer frames are used as a last option by the sending device when all other routing attempts have failed.
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