What is KNX?

This page on KNX technology basics covers KNX RF PHY layer features,frame structure and addressing scheme.KNX home automation concept is used in IoT(Internet of Things).

Alliance of more than 300 companies from 34 countries have agreed on uniform telegram traffic between sensors and actuators in a bus system. From this, the EIB(European Installation Bus) has been developed.

KNX standard is the successor to EHS, BatiBus and EIB. Communication between KNX devices is done using group addresses. It is used in home and residential market. There are various versions of the KNX as mentioned below based on medium over which it is used.
• KNX IP-KNX bus communicaton via Internet Protocol
• KNX RF-KNX bus communication via radio frequency (RF)
• KNX TP-KNX bus communication via 2-wire link (twisted pair)
• KNX over powerline
• KNX over infrared
• KNX over Ethernet

KNX Standards

• International Standard: ISO/IEC 14543-3
• European Standard: CEN ELEC EN50090
• Chinese Standard: GB/T 20965
• US Standard: ANSI/ASHRAE 135

KNX Addressing Scheme

KNX system consists of sensors and actuators. Retransmitter device is used for bigger installations. Both bidirectional and unidirectional implementations are possible in KNX system. The system provides two types of addressing schemes which are used for communication.

• Group Addressing: This type is used for multicast and broadcast transmissions. Used addresses are stored in <<Address Table>>
• Individual Addressing: This type is used for point to point communication. It has 16 bit device address. Here also addresses are stored in <<Address Table>>

In powerline, 48 bit domain address is added to each message.

KNX Features as per KNX RF Physical Layer(PHY)

Following table-1 mentions features of KNX RF physical layer.

Specification KNX support
RF frequency band/Center frequency 868 to 868.6MHz, Fc=868.3MHz
Modulation FSK
RF Bandwidth 300KHz
Bit Coding Manchester
Bit rate/Chip rate 16.384 Kbps/32.768 KChips/Sec
Preamble/sync sequence used and it is 30chips in size/chip sequence '011010010110'
Postamble used and it is 2 to 8 chips in size
Protection CRC error detecction is used.
Data link layer As per specification IEC 870-5-1/2 FT3
Retransmitters Upto 3
Typical Air Time Per Frame About 16ms

Table-1: KNX RF Physical Layer features

KNX frame structure

KNX RF Frame Structure
Fig-1: KNX frame structure

Figure mentions KNX frame structure as per IEC870-5-2(FT3). As mentioned it consists of preamble at the start and postamble at the end. Each block of data is appended with CRC for error detection. Both preamble and postamble is used for synchronization purpose. Block1 = { Length(1byte), C-field(1byte), ESC(1byte), Ctrl(1byte),SN(6bytes)}
Length specifies total no. of user bytes counting from C-field
C-field fixed value of 44h
ESC -Escape code to separate KNX from metering
Ctrl-uni or bidirectional sender signal strength battery state
SN-Serial number or domain address of the sender

Block2= {KNX-Ctrl(1byte), Standard KNX frame(variable),Data(Variable)}
KNX-Ctrl-Standard or Extended

KNX Protocol Stack

KNX protocol stack

The KNX protocol stack consists of physical layer, datalink layer, routing or network layer, transport layer and application layer.
Refer KNX Protocol Stack➤➤.

KNX home automation basics

KNX Home Automation with zigbee
Fig-2: KNX home automation

KNX is widely used in building and home automation to create smart homes and smart city. It has numerous applications for energy efficient networks in schools, houses, buildings and more. Siemens and Schneider Electric are working on many such projects based on KNX technology.

KNX is a mature protocol for wired media and is recognised internationally. To take advantages of wired as well as wireless medium, KNX is used in conjunction with other wireless technologies(zigbee,z-wave etc.) for home automation. Figure depicts one such network using KNX-Zigbee Gateway. This gateway device does protocol conversion from KNX to Zigbee and vice versa. Wired devices of the home is taken care by KNX protocols and wireless devices is taken care by the Zigbee protocols.

IoT Wireless Technologies

WLAN    ➤THREAD    ➤EnOcean    ➤LoRa    ➤SIGFOX    ➤WHDI    ➤Zigbee   ➤6LoWPAN   ➤Zigbee RF4CE   ➤Z-Wave   ➤NFC   ➤RFID   ➤Lonworks   ➤CEBus   ➤UPB  

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