0 ratings0% found this document useful (0 votes) 333 views17 pagesIntroduction To KNX
Intro notes for KNX development
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2 Introduction to KNX/EIB
2.1 Purpose of KNX/EIB
A Building Automation System (BAS) [02] is a network of (programmable) devices that control
the environmental condition of a building like lighting and shading, heating, ventilation and air
conditioning (HVAC). It aims at improving control, monitoring and administration of technical
building subsystems to gain cost efficiency and building control and to improve comfort for the
‘occupants. Management and configuration of an integrated BAS becomes easier and allows
reduction of management tools.
Security critical subsystems like access control and security alarm systems have been
implemented as stand-alone systems. This is due to the fact that they depend on the underlying
control systems to be reliable and robust to avoid malicious manipulation of devices and traffic
However, today the demand for a tighter integration of the traditional BAS and security control
systems exists.
‘The EIB (European Installation Bus) [04] is a fieldbus designed to enhance electrical
installations in homes and buildings by separating the transmission of control information from
traditional electrical wiring. Its main applications are solutions in lighting, window blinds
control and HVAC systems. EIB is based on an open specification, maintained until recently by
the EIBA (EIB Association, {05]). The newly emerged KNX standard [06] is a combination of
EIB, Batibus and EHS (European Home System), combining their best aspects. EIBA, EHS
Association and Batibus Club International formed the Konnex Association, accordingly.
KNX/EIB installations are hierarchically structured, end devices are topologically arranged in
lines and areas. Lines are interconnected with each other by line couplers (LC). Up to 15 lines
can be combined to an area, backbone couplers (BC) can combine up to another 15 areas. A
maximum of 256 devices can be addressed in a line. Thus, a completely extended KNX/EIB
system can accommodate up to 57600 devices.
Page 10 KNX/EIB Simulation 2 Introduetion to KNX/EIB
Figure 2.1: KNX/EIB network with different areas and backbone line
Logically, KNX/EIB is a peer-to-peer system. Devices communicate with each other without the
presence of a dedicated master. In general, two types of communication can be distinguished:
‘management communication using unicast and broadcast and process data communication
ing
multicast communication,
2.2. Introduction to the KNX/EIB Protocol
2.2.1 KNX/EIB and the OSI reference model
‘The Open Systems Interconnection (OSI) model splits the complex tasks of data communication
into 7 defined sub-areas, referred to as layers [07]. Each layer interacts with the layer above and
below. A layer, the service provider, provides a service to the layer immediately above, the
service user. The interface between both layers defines how the service user can access the
service of the service provider, specifies the parameters and the result to be expected. A
protocol defines a set of rules and conventions that is being used by layers of the same level,
allowing communication between devices.
Page I KNX/EIB Simulation 2 Introduetion to KNX/EIB
‘Communication between layer N and layer (N-1) via its services or its interfaces respectively
‘ocours via a Service Data Unit (SDU). Communication between two peer layers is done via a
Protocol Data Unit (PDU) which consists of the user data, the Interface Control Information
(ICI) and the layer specific Protocol Control Information (PCD.
Examining the KNX protocol, not all layers of the OSI protocol are necessary. Only 5 out of 7
layers are being used by the KNX standard, These are:
© Physical Layer
© Data Link Layer
© Network Layer
© Transport Layer
© Application Layer
OSI Model KNX/EIB
7 Application Layer 7. Application Layer
6. Presentation Layer 6
5 Session Layer 5 -
4 Transport Layer 4 Transport Layer
3) Network Layer 3) Network Layer
2 Pala Vink Vaya 2) Mala Vink Vayer
1, Physical Layer 1. Physical Layer
Figure 2.2: KNXJEIB layers ++ OSI layers
Focusing on the communication of peer layers, there are 4 different service primitives: request
(req), indication (ind), confirmation (con) and response (res). Services need not always to make
use of each of the service primitives and can be classified as follows:
Locally confirmed services comprise of a request, an indication and a confirmation. The local
service user calls the layer N service provider. A request and the corresponding PDU is being
‘generated and passed on to the layer (N-1) until itis given over to the physical medium. On the
receiver side, the peer layer N is activated with an indication, the enclosed PDU is decoded and
the data passed to the layer above
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