Page 100 - 360.revista de Alta Velocidad - Nº 5

Meyer zu Hörste, Michael. Asbach, Lennart. Hardi, Hungar. Lemmer, Karsten.

variables and parameters are filled with values, though some remain to be set dynamically
during execution of the sequence. So the test sequences could be understood as operational
test trips. The relation from the SRS up to the test sequence is shown in Fig. 2.
Finally the fundamental structure of the test sequence should be clarified. Each test sequence
simulates a test trip by stimulating the on-board equipment via the black-box-interfaces. In
addition, the SRS-conformant reactions of the on-board equipment are defined in each test
sequence. The reactions and the stimulating events are bound to the interface where they
should be observed and evaluated or raised. Essentially the test sequences consist of the stimuli
and the expected reactions of the on-board equipment. In the test sequence one stimulus or
reaction is represented by a test step. Fig. 3 shows the structure of a test sequence.
The 775 test sequences contain up to several hundred test steps and their execution in realtime
in the labs need up to several hours. A time rafting testing is not possible due to the fact
that the real time behaviour of the ETCS component is tested. As mentioned above the test
sequences are implemented in the reference labs. Some of the test sequences have been
executed successfully, but the stated problems of duration and unstable inputs on the user
interface by the human being show that automation is needed. As soon as an input is missed or
incorrect the complete test sequence must be repeated.

Figure 3: Symbolic structure of a test sequence for conformity testing

The tests defined by this method are documented in the ETCS subset 076. These are used to
proof the conformity of the constituent European Vital Computer (EVC) which is the core of the
on-board unit.

3.2 Operational Test Sequences

The conformity test sequences which have been discussed in the previous section fulfil the
purpose to show that an application is realising the specification sufficiently complete. They do
not claim to be operationally reasonable. Thus, a railway undertaking tendering ERTMS/ETCS
systems need to check whether these fulfil their operational requirements. These tests are a
separate set of test sequences at the moment. They need to be defined by a similar methodical
approach as shown above, but they have need to fulfil more requirements: The test sequences
must represent the most typical or important scenarios of the operation of the railway. They
need to show the fulfilment of the European requirements as well as the national add-ons.
The approach is to use the same test cases for the operational test sequences as well. Some
specific test steps and test cases are added to represent operational aspects which are not

98 360.revista de alta velocidad