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Chapter 3. Concept 34

low range and the range of the gateway is limited as well. The use of various gateways enables the

control of larger systems and therefore the database will increase its size which will have a negative

impact on the overall performance - more later on. The low data rate of the IT and HE systems

is also beneﬁcial for the performance of the software. Figure 3.6 shows the various transmission

times. The worst case scenario describes the situation when the minimum required numbers of

packets are received successively from diﬀerent devices. It can occur in a signal superposition of

several diﬀerent messages. However, this can only lead to about 15 actions/s for HE systems,

which is no problem for modern computers.

2 9.8

4 4.9

1 14.8

1.8

204.8

102.4

542

67.4

[actions/s]package count duration [ms]

Figure 3.6.: The diﬀerent transmission times and actions per second. The grey boxes represent

the worst case, when only the minimal numbers of required packages are received suc-

cessively. This can happen when multiple signals from diﬀerent devices superimpose.

IT and HE are both loosely connected systems; a transmitter usually triggers only a few receivers.

This will relieve the database because fewer entries must be changed at once. In addition, receivers

are ﬁrmly bound to their transmitters; they change automatically when a valid message is received.

The software therefore does not need to send their on/oﬀ-commands manually. This will improve

the software performance even further. In summary, the requirements for small systems with

one gateway are very low and there should be no problems with latency, processing time and

bandwidth use. However, the gateway driver allows connecting multiple gateways, consequently,

the controlled network can be much larger and contain many more devices. This may indeed

cause problems for the device manager and visualization nodes, as they have to process all entities,

whereas the gateway driver only handles the devices of one gateway. On this account, the source

code of all nodes was written to be clean and eﬀective and critical processes were optimized.

Chapter 5 on page 65 describes a benchmark, which evaluates the latency in a test environment.

Alongside these basic considerations, IT and HE have other characteristics that may cause prob-

lems. For instance, both systems are unidirectional, which means that devices can either receive or

transmit, but not both. As a consequence, the current state of the system is uncertain, as received

messages cannot be acknowledged and the receiver state cannot be determined subsequently. This

makes IT and HE very unreliable and inappropriate for critical tasks such as HVAC and security

issues. The use of a gateway can counteract this problem, since it can act as range extender by

repeating messages or ensure the state of receivers by periodically resending their last command.

However, this would jam the transmission medium and is not possible for many receivers due the

slow transmission rate. This work only considers the basic connection of HA in IE, therefore this

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