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Network setup, topology and routing
BACpress: Z-Wave network uses a source-routed mesh network architecture. Mesh networks are also known as wireless ad hoc networks. In such networks, devices use the wireless channel to send control messages which are then relayed by neighboring devices in a wave-like fashion. The source device wanting to transmit is therefore known as the initiator. Hence, the name source-initiated mesh ad hoc routing. There were several source-initiated mesh routing protocols proposed in the period early 1990s. The earlier ones were Ad hoc On-Demand Distance Vector Routing (AODV) and Dynamic Source Routing (DSR).
Devices can communicate to one another by using intermediate nodes to actively route around and circumvent household obstacles or radio dead spots that might occur in the multipath environment of a house .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.
How to add or remove a device to the Z-Wave network
The simplest network is a single controllable device and a primary controller. Additional devices can be added at any time, as can secondary controllers, including traditional hand-held controllers, key-fob controllers, wall-switch controllers and PC applications designed for management and control of a Z-Wave network. A Z-Wave network can consist of up to 232 devices, with the option of bridging networks if more devices are required.
A device must be “included” to the Z-Wave network before it can be controlled via Z-Wave. This process (also known as “pairing” and “adding”) is usually achieved by pressing a sequence of buttons on the controller and on the device being added to the network. This sequence only needs to be performed once, after which the device is always recognized by the controller.
Devices can be removed from the Z-Wave network by a similar process. The controller learns the signal strength between the devices during the inclusion process, thus the architecture expects the devices to be in their intended final location before they are added to the system. Typically, the controller has a small internal battery backup, allowing it to be unplugged temporarily and taken to the location of a new device for pairing. The controller is then returned to its normal location and reconnected.
Network ID In Z-Wave
Each Z-Wave network is identified by a Network ID, and each device is further identified by a Node ID. The Network ID (also called Home ID) is the common identification of all nodes belonging to one logical Z-Wave network. The Network ID has a length of 4 bytes (32 bits) and is assigned to each device, by the primary controller, when the device is “included” into the Network. Nodes with different Network IDs cannot communicate with each other. The Node ID is the address of a single node in the network. The Node ID has a length of 1 byte (8 bits) and must be unique in its network.
The Z-Wave chip is optimized for battery-powered devices, and most of the time remains in a power saving mode to consume less energy, waking up only to perform its function. With Z-Wave mesh networks, each device in the house bounces wireless signals around the house, which results in low power consumption, allowing devices work for years without needing to replace batteries. 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. Mobile devices, such as remote controls, are also excluded since Z-Wave assumes that all repeater capable devices in the network remain in their original detected position.
Security
Z-Wave is based on a proprietary design, supported by Sigma Designs as its primary chip vendor, but the Z-Wave business unit was acquired by Silicon Labs in 2018. In 2014, Mitsumi became a licensed second source for Z-Wave 500 series chips. Although there have been a number of academic and practical security researches on home automation systems based on Zigbee and X10 protocols, research is still in its infancy to analyze the Z-Wave protocol stack layers, requiring the design of a radio packet capture device and related software to intercept Z-Wave communications.
An early vulnerability was uncovered in AES-encrypted Z-Wave door locks that could be remotely exploited to unlock doors without the knowledge of the encryption keys, and due to the changed keys, subsequent network messages, as in “door is open”, would be ignored by the established controller of the network. The vulnerability was not due to a flaw in the Z-Wave protocol specification but was an implementation error by the door-lock manufacturer.(Read more:The British company claims to have a smart lock hack)
On November 17, 2016, the Z-Wave Alliance announced stronger security standards for devices receiving Z-Wave Certification as of April 2, 2017. Known as Security 2 (or S2), it provides advanced security for smart home devices, gateways and hubs. It shores up encryption standards for transmissions between nodes, and mandates new pairing procedures for each device, with unique PIN or QR codes on each device. The new layer of authentication is intended to prevent hackers from taking control of unsecured or poorly-secured devices. According to the Z-Wave Alliance, the new security standard is the most advanced security available on the market for smart home devices and controllers, gateways and hubs.
Hardware
The chip for Z-Wave nodes is the ZW0500, built around an Intel MCS-51 microcontroller with an internal system clock of 32 MHz. The RF part of the chip contains an GisFSK transceiver for a software selectable frequency. With a power supply of 2.2-3.6 volts, it consumes 23mA in transmit mode. Its features include AES-128 encryption, a 100kbps wireless channel, concurrent listening on multiple channels, and USB VCP support.
Comparison to other protocols
For smart-home wireless networking, there are numerous technologies competing to become the standard of choice. Wi-Ficonsumes a lot of power, and Bluetooth is limited in signal range and number of devices.
Other network standards competing with Z-Wave include Wi-Fi HaLow, Bluetooth 5, Insteon, Thread and ZigBee.
Z-Wave has a long open-air operating range at 90 meter (outdoor) and 24+ meter (indoor). Insteon has a large number of maximum devices capability at 17.7 million (to ZigBee’s 65,000 and Z-Wave’s 232).
Thread has a fast data transmission rate at 250 kbps. Z-Wave has better interoperability than ZigBee, but ZigBee has a faster data transmission rate.
Thread operates on the busy Wi-Fi standard frequency of 2.4 GHz, while Z-Wave operates at 908 MHz in the US, which has reduced noise and a greater coverage area.
ZigBee operates on both 915 MHz and 2.4 GHz frequencies. All three are mesh networks. The Z-Wave MAC/PHY is globally standardized by the International Telecommunications Union as ITU 9959 radio, and the Z-Wave Interoperability, Security (S2), Middleware and Z-Wave over IP specifications were all released into the public domain in 2016, making Z-Wave highly accessible to Internet of Things developers.
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