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Chapter 2. Related Work/Fundamentals 7

two actuators. Connections are unidirectional, which means that actuators cannot send signals

but just receive them. Due to the missing acknowledgement, sensors do not know, if the actuators

received their signals and if they have switched to the desired state. Examples are Intertechno

(section 2.2.4 on page 14) and HomeEasy (section 2.2.4 on page 12). In the network on the

right hand side of ﬁgure 2.2, all nodes are connected bidirectionally over a bus-system. Package

losses and failures can be registered, allowing more sophisticated and reliable communication.

In contrast to unidirectional networks, bidirectional networks result in higher costs and higher

complexity. Nevertheless, this principle is widely used by wired solutions like KNX (section 2.2.4

on page 9).

The diﬀerent bus systems are not compatible with each other and therefore the diﬀerent automa-

tion systems cannot be easily linked together. However, they can still be connected via special

gateways. Some of these gateways are discussed in section 2.3.1 on page 19. For cost reasons,

home automation is normally restricted to a single bus system. In building automation, cost plays

a secondary role, therefore the most suitable type of bus is selected for each task. Examples of

other bus systems are TCP/IP, KNX, Power-Line Communication, CAN and RS485.

2.2.3. Transmission media

There are many diﬀerent transmission technologies available for transmitting data over a bus

network, but the principles are based on just a few physical eﬀects. By dividing the system

by the transmission medium into separate groups, there are three major representatives: wired,

optical and radio-based systems. Optical systems are mainly used in multimedia, for example in

a TV remote control. They are not common in HA, because a direct line of sight is needed and

they typically have a short range. By contrast, both wireless and wired systems are widely used.

Therefore, there is a brief summary of their pros and cons.

Radio-based systems:

Radio-based systems are widespread and represent the preferred transmission method in HA. The

high and rapidly growing popularity of such systems is primarily due to the following advantages:

High ﬂexibility: Devices are not ﬁxed to their initial deployment and can be relocated. This

allows the user to easily reposition the devices and add further nodes.

Easy to install: No laborious installation, which reduces time and costs. Wireless systems can

be put into operation very quickly.

Beside these advantages, there are several disadvantages:

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RFXCOM RFXtrx433 Especificaciones Pagina 14