KNX (standard)

KNX is an open standard (see EN 50090, ISO/IEC 14543) for commercial and domestic building automation. KNX devices can manage lighting, blinds and shutters, HVAC, security systems, energy management, audio video, white goods, displays, remote control, etc. KNX evolved from three earlier standards; the European Home Systems Protocol (EHS), BatiBUS, and the European Installation Bus (EIB or Instabus). It can use twisted pair (in a tree, line or star topology), powerline, RF, or IP links . On this network, the devices form distributed applications and tight interaction is possible. This is implemented via interworking models with standardised datapoint types and objects, modelling logical device channels. 
KNX standard.
The KNX standard has been built on the OSI-based EIB communication stack extended with the physical layers, configuration modes and application experience of BatiBUS and EHS.
KNX installations can use several physical communication media:
KNX is not based on a specific hardware platform and a network can be controlled by anything from an 8-bit microcontroller to a PC, according to the demands of a particular building. The most common form of installation is over twisted pair medium. 
KNX is an approved standard by the following organisations, (inter alia):
It is administered by the KNX Association cvba, a non-profit organisation governed by Belgian law which was formed in 1999. The KNX Association had 443 registered hardware and software vendor members from 44 nations as at 1 July 2018. It had partnership agreements with over 77,000 installer companies in 163 countries and more than 440 registered training centres. This is a royalty-free open standard and thus access to the KNX specifications is unrestricted.
KNX architecture.
KNX devices are commonly connected by a twisted pair bus and can be modified from a controller. The bus is routed in parallel to the electrical power supply to all devices and systems on the network linking:
Classifying devices as either "sensor" or "actuator" is outdated and simplistic. Many actuators include controller functionality, but also sensor functionality (for instance measuring operating hours, number of switch cycles, current, electrical power consumption, and more).
Application software, together with system topology and commissioning software, is loaded onto the devices via a system interface component. Installed systems can be accessed via LAN, point to point links, or phone networks for central or distributed control of the system via computers, tablets and touch screens, and smartphones.
The key features of the KNX architecture are: 
Applications, interworking and binding.
Central to the KNX architecture concepts are datapoints (inputs, outputs, parameters, and diagnostic data) which represent process and control variables in the system. The standardised containers for these datapoints are group objects and interface object properties. The communication system offers a reduced instruction set to read and write datapoint values. Datapoints have to confirm to standardised datapoint types, themselves grouped into functional blocks. These functional blocks and datapoint types are related to applications fields, but some of them are of general use (such as date and time). Datapoints may be accessed through unicast or multicast mechanisms.
To logically link applications datapoints across the network, KNX has three underlying binding schemes: one for free, one for structured and one for tagged binding:
Common Kernel and Message protocol.
The common kernel sits on top of the physical layers and the medium-specific data link layer and is shared by all the devices on the KNX Network. It is OSI 7-layer model compliant:
Configuration modes.
An installation has to be configured at the network topology level and at individual nodes or devices. The first level is a precondition or “bootstrap” phase, prior to the configuration of the distributed applications, i.e. binding and parameter setting. Configuration may be achieved through a combination of local activity on the devices (such pushing a button), and active network management communication over the bus (peer-to-peer, or more centralized master-slave). 
The KNX configuration mode: 
Some modes require more active management over the bus, whereas some others are mainly oriented towards local configuration. There are three categories of KNX devices:
KNX encompasses tools for project engineering tasks such as linking a series of individual devices into a functioning installation and integrating different media and configuration modes. This is embodied in an "Engineering Tool Software" (ETS) suite.
Devices.
A KNX installation always consists of a set of devices connected to the bus or network. Device models vary according to node roles, capabilities, management features and configuration modes, and are all laid down in the profiles. There are also general-purpose device models, such as for bus coupling units (BCUs) or bus interface modules (BIMs).
Devices may be identified and subsequently accessed throughout the network either by their individual address, or by their unique serial number, depending on the configuration mode. (Unique serial numbers are allocated by the KNX Association Certification Department.) Devices can also disclose both a manufacturer specific reference and functional (manufacturer independent) information when queried. 
Logical topology and individual address space.
A KNX wired network can be formed with tree, line and star topologies, which can be mixed as needed; ring topologies are "not" supported. A tree topology is recommended for a large installation.
KNX can link up to 57,375 devices using 16-bit addresses.
Coupling units allow address filtering which helps to improve performance given the limited bus signal speed. An installation based on KNXnet/IP allows the integration of KNX sub networks via IP as the KNX address structure is similar to an IP address.
Physical transmission media.
TP 1.
The TP1 twisted pair bus (inherited from EIB) provides asynchronous, character oriented data transfer and half-duplex bidirectional differential signaling with a signaling speed of 9600 bit/s. Media access control is via CSMA/CA. Every bus user has equal data transmission rights and data is exchanged directly (peer-to-peer) between bus users. SELV power is distributed via the same pair for low-power devices. A deprecated specification, TP0, running at a slower signalling speed of , has been retained from the BatiBUS standard but KNX products cannot exchange information with BatiBUS devices.
PL 110.
PL 110 power-line transmission is delivered using spread frequency shift keying signalling with asynchronous transmission of data packets and half duplex bi-directional communication. It uses the central frequency 110 kHz ( CENELEC B band) and has a data rate of 1200 bit/s. It also uses CSMA. KNX Powerline is aimed at smart white goods, but the take-up has been low. An alternative variant, PL 132, has a carrier frequency centred on 132.5kHz (CENELEC-C band).
RF.
RF enables communication in the 868.3 MHz band for using frequency shift keying with Manchester data encoding.
IP.
KNXnet/IP has integration solutions for IP-enabled media like Ethernet (IEEE 802.2), Bluetooth, WiFi/Wireless LAN (IEEE 802.11), FireWire (IEEE 1394) etc.
Frame (telegram) overview.
Ignoring any preamble for medium-specific access and collision control, a frame format is generally:
Security.
KNX Telegrams can be signed or encrypted thanks to the extension of the protocol that was developed starting in 2013, KNX Data Secure for securing telegrams on the traditional KNX media TP and RF and KNX IP Secure for securing KNX telegrams tunnelled via IP. KNX Data Secure became an EN standard (EN 50090-3-4) in 2018, KNX IP Secure an ISO standard (ISO 22510) in 2019.
Conformity.
Any product labeled with the KNX trademark must be certified to conform with the standards (and thus interoperable with other devices) by accredited third party test labs. 