- Email: [email protected]
Analysis of Field Bus Systems for High Speed Trains
Copyright @ IFAC TransportAtion Systems. Tiaojio. PRC. 1994
ANALYSIS OF FIELD BUS SYSTEMS FOR HIGH SPEED TRAINS J. KIEFER and E. SCHNIEDER Technischc UlIivcrsitat Braunschwcig. Institut for Rcgclungs. und Automatisiuungstcclmik. /Angu Kamp 8. D-38106 Braullschweig. Germany. Internet: [email protected] AbstDCL Due to the fact that the use of intelligent systems in high speed railways increases rapidly. the demand for an efficient communication becomes more and more important. Field bus systems serve many of those tasks but both. the development tools for the choice of one field bus protocol and the optimization of its parameters are poor. In the paper the requirements of train communication are specified and a tool is introduced allowing the above mentioned evaluations from the users point of view. As an example the requirements for on-board communication of high speed trains like the ICE is examined using CAN-protocol. Key Words. communication. field bus systems. requirement analysis. train. InterCity Express (lCE). Controller Area Network (CAN)
1. INTRODUCTION
into an efficient engineering of bus systems for control and vital systems.
The use of automation systems in all fields of transportation is increasing rapidly. Cars, trains, ships and planes are equipped with highly sophisticated technical systems for control of drives or engines, localization, automatic driving, communication, passenger comfort and so on. During the last decade, the architecture of those systems changed from stand-alone solutions to open systems implying strong communication links. This led to the requirement of cheap communication channels providing data exchange with a high reliability and which do not depend on the
2. STRUCTURE OF DATA COMMUNICATION
time scale [sI log
venue Im)
essential operation cycle time Is)
rate
application. Considering that cabling and maintenance of directly wired connections is quite expensive, serial bus systems are getting more and more important in this context. Cars and even the first trains have been equipped with on-board field busses.
memory capacity [bit] performance [MFLOPS)
Nowadays, many communication protocols are known, each of them being developed for a special purpose. The increasing number of bus protocols and the increasing complexity of automation systems require a careful study of this field lO gel
11
Operational Layer
ill
Tactical Layer
1::::::::::;'::1
Dispositive Layer
t ·]
Strategical Layer
Fig. 1 Criteria for the hierarchical order of automation systems
965
With this approach, the idea of taking a sen.-ll bus system distributing information to many modules comes quite close.
2.1. Data Communication and Hierarchical Order Most of the automation systems have an hierarchical structure which can be divided into strategical, dispositive, tactical and operational layers. There are quite a few criteria for attaching a special task to one of the hierarchical layers. Some of them can be taken from Fig. 1. Not explaining all of them in detail, it is necessary to stress the difference in communication. It is important that the time scale for which a decision is taken differs considembly. For instance there is some data communication with a large data contents which has to be transmitted rarely (strategical layer). On the
2.2. Essential Requirements of the Process Every user of a communication system regarding the technical part of data transfer, is neither interested in the way the data are transmitted nor in the protocol being used for the coordination of every communication device. Instead of this, the user wants to know how the process is temporally influenced by the data communication and about the way the individual devices have to be coupled
other hand some short telegmms need to be sent isocbronously (operational layer).
mechanically. The last aspect will to be ignored in this paper.
Fig. 2 shows the functional system structure of the mobile unit of a modern train. The several tasks are spread out over the different layers neglecting that some tasks have to be implemented vitally leading to even more modules. It is easy to imagine that the modules are closely linked together exchanging data frequently. The following example states this fact: The drive control receives orders from the movement control and provides itself commands onto drives and brakes. For the internal calculations, information is required from the localization, the dist.:'Ulce measurement unit, the door control, the emergency indicator and from several sensors monitoring drives and brakes.
For the definition of the required time behaviour of the transmission system some criteria are needed describing the process demands, only. It has to be stressed that these criteria must not depend on the transmission protocol at all. Only this condition allows a comparison of data transmission systems using completely different principles. The following criteria are used for the examinations by means of comparison of cbraracteristic values. They are chosen because they are standards in automation and suitably meet the demands of communication in railway systems.
Strategical Layer
Dispositive Layer
Tactical Layer
Operational Layer Fig. 2
Hierarchical layers for the tasks of a high speed train
966
system. This problem will not be dealt with in the further parts of this paper.
Delay time tL, ..... The delay time describes the time interval a message
takes
from
the
input
of the
data
transmission system to its output. It is given for
Tbe dependability of the data channel has to be
every single communication cbannel between two
very high for the use on railway vebicles. This is
units a and b. It is evident that this value only
due to the fact that a loss of communication would
depends on the communication system and no
possibly lead to loss of control over the train which
process parameters are included.
might end in wrong side failures. RedunruUlcy of communication channels consideres this problem
Reaction time t R• • : J
and some field bus protocols are even equipped
This value is needed when a system device requires
with a doubled trllDsmission media Nevertheless,
information from one or more other devices. It specifies the time from the request for data of the
redundancy does not mainly effect the temporal behaviour of the protocol and will be neglected in
unit a to the reception of the information I . It bas to
the following discussion.
be mentioned that a lot of other communications lUld calculations may be needed for information 1 3. TEST
lUld therefore, process parameters of the application
FOR
THE
EXAMINATION OF BUS SYSTEMS
like calculation time or process time constants influence this value.
Age of transmitted data
ENVIRONMENT
t A . .....
The age of a message being received by unit b is quite similar to the delay time tl., Q-+b' Tbe difference is the starting point of the time measurement at unit
a: The age is calculated from the generation of the message
instead
of
the
band-over
to
the
communication system. This is important in cases where
the
generation
of a
message
is not
automatically leading to the start of communication. When
message
polling
is
used
by
the
communication system the age should be used in place of delay time.
2.3. Deperuiability of Communication Fig. 3 Test environment for bus examinations
There are two more constraints for the use of field bus systems on a train wbich bave to be taken into
Communication
account:
conveniently by means of generalized, stochastic
systems
can
be
modelled
petri nets. Some of the data is safety critical and therefore, bas to be transmitted vitally. Regarding the ISO/OSI
A petri net based simulator has been designed
reference model for data communication this is a
giving the possibility for a comparison of several
task of the application layer. From another point of
field bus systems. It splits up into several units.
view, the field bus can be seen as a gray channel
Tbey normally run independently and off-line but
for communication and a vital message band ling
there are only minor changes for the realization of
will be implemented within the application itself.
an integrated system. Tbe whole system is shown in
Hence, this does not affect the actual protocol. It
Fig. 3 and will be explained briefly.
and only increases the load of the transmission
967
realistic temporal behaviour and a determined examination of bus system failures and their effect on the data transmission.
isochronous
random with limits exponential binomial / poisson with / without limits
All modules are implemented by means of colored, timed petri nets giving the possibly of simulation and analysis. A visualization unit and analysis unit are integrated, as well.
t illlerspace Fig. 4 Implemented distributions for tbe mode ling of data flows
The simulation environment serves for complex system analysis, as outlined. During simulation mode the actual bus status is monitored. Therefore , it is easily possible to see ~Uly interferences between data messages that can lead to a serious delay, as it appears in arbitrating protocols. In analysis mode monitoring of single data links ~Uld visualization of performance parameters are possible. Some examples are shown ill the next chapter.
First, it is imponant to set up the application proflJe for the process operations. Therefore, a formal definition of each input and output data flow of every module of the train control system has to be deduced with respect to its temporal behaviour. It has to be considered that there are isochronous and stochastical message generation. Fig. 4 shows possible distributions which can be combined. Modelling has to be done for the input data flows but also for those tasks calculating data as a result of an input These are required for the calculation of the reaction time mentioned in Chapter 2.2 and therefore, should be modelled precisely. All application data is well known from the system design process and does not demand any additional examinations at all.
In addition to simulation, petri nets allow a formal analysis. Therefore, it is necessary to set up a timed reachability graph allowing the proof of maximum lransmission times for communication links. This might be required for the proof of safety which is needed for some components within train conlrol systems.
4. COMMUNICATION OF THE ICE-TRAIN
~
l.
_
~trigger
4.1. Communication links of the ICE
I________~gger mode
_...L._"""""....
At this point, the communication for a future lrain
tinterspace
control system like of the german high speed train ICE will be examined. It is not the aim of this example to justify the use of one special field bus protocol but to demonstrate the way a standard protocol can be tested for later usage without any implementation work.
Fig. 5 Time defmition in trigger mode
It has to be considered as well
that data
transmission in automation systems can not always be defmed for only one data. Some messages are triggered by other data transmissions. For this purpose, a mode is implemented allowing an external trigger of a data transmission from another message. This mode is useful for the description of tasks calculation new data. Both possibilities for time defmition are shown in Fig. 5.
A brief discussion of the components in the train control system will be given at the beginning. It is not intended to describe all its functions but rather the mechanisms leading to couununication. This will be referred to Fig. 2 without explicitly mentioning it
Further on, the bus system has to be modelled. For our examinations protocols like CAN, MVB, FIP, ... were taken into account The models allow a
968
The movement command being valid for the next block is transmitted from the track via track conductor. The command is interpreted from the on-board equipment using the quantities of motion being provided from a distance measurement unit and data from the automatic train stop system Indusi. These commands are split up into actual orders for brakes and drives wbicb are coordinated by an integrated automatic movement control
Table 1 Data flows of ICE-train
communication
I
lz. ,.;"
I ...
I,
Ibit)
Ims)
Ims)
Ims]
requirements
(AFB).
result
track conductor antenna -+ train control system
100
100
lOoo
train control system -+ track (conductor antenna) -+ AFB -+ display, recorder
50 40 700
100 85 600
1000 1.356 85 0.792 200 1.293
2
na
IO
0.351
100 100
0.543 0.734
1.678
The distance measurement unit is a main computer receiving its data from different measurement components like radar, incremental position resolver, accelerometer and defined position reference points. Further on, data from the locomotive control are used. Tbe quantities of motion are transmitted to the track for use in the train supervision system, as well.
distance measurement unit -? track (conductor antenna) -+ train control system
240 240
100 1000
radar -+ distance measurement unit
40
2
0. 123
All commands are recorded and visualized to the driver.
incremental position resolver -+ distance measurement unit
40
2
0.234
4.2. Definition of the Requirements
accelerometer -+ distance measurement unit
40
2
0.427
distance measurement reference -+ distance measurement unit
48
7000
locomotive control -+ distance measurement unit
20
2
Indusi -+ train control system
In Table I the requirements for the communication are listed. All control flows for parametrization and acknowledge are neglected for purposes of clearness. Furthermore, the average length of a message /, the minimum cycle time tz. ..... , and the message age after the transmission t", are sbown, only.
2
0.315
0.545
I
0 .8
'-~----------------~~J . . .. . .
0.8
4.3. Results with CAN-Protocol
~
For demonstration purposes the CAN-Protocol (Boscb AG, Germany) bas been cbosen. The bus parameters (especially the identifiers) for the above mentioned data flows bave been set for simulation. In addition, the parameters for the transmission rate of the bus cable was set to 1.5 Mbitls and a failure rate (corrupted bits per transmitted bits) of 0.001 was estimated. 18000 telegrams were used for the examination.
Fig. 6 Monitoring of a single data link (train control system to AFB) with CAN-protocol
The results from Table I (t,: transmission time) show that every data channel meets the
969
specifications (I, < lA). This can easily be seen from Fig. 6 where the result for the communication from the train control system to the AFB is shown. The cumulative probability of messages being transmitted is plotted versus transmission time. Due to the fact that there is no time delay from the
6. REFERENCES Ajmone Marsan, M.; Chiola, G.; Fumagalli, A. (1987). An Accurate Performance Model of CSMAlCD Bus LAN. In: Leclure Notes in Computer Science, ( G. Rosenberg, Ed.), Vol.
generation of messages to the band-over to the trrulsmission system in the CAN-protocol, transmission time is equal to the message age after trlmsmission
266. Advances in Petri Nets, pp. 146-161, Springer Verlag; Berlin, Heidelberg, New York. DEUFRAKO-Bus (1992). Auswahlkriterien fUr den
lA.
ARTEMIS-Bus. Bundesbahnzentralrunt Munchen, Munchen, Paris.
Using this mode, it can be validated whether the specifications are met with the current protocol and its parameters. The performance of the system can be judged from the different parameters. Simulating different field bus protocols allows even a comparison of the different performances. The user gets the possibility of choosing the right system without implementing it at all.
Funke, A. (1992). Machbarkeitsanalyse von Feldbusanwendungen. FOrlschrittberjclue VDI, Reihe 10 Nr. 222. VDI-Verlag, Dusseldorf. Gemmeke, W. (1992). Zugbussysteme. In: ETG Fachberichl 37, (W. Lawrenz, Ed.), Datenubertragung auf Fahrzeugen mittels serieller Bussysteme, pp. 37-58. VDE-Verlag; Berlin, Offenbach. Kiefer, 1. (1992). DatenfluBdiagramm
5. CONCLUSIONS / OUTLOOK
Schienenfabrzeug, Studie. Institut ftiT Regelungs- und Automatisierungstechnik, TU Braunschweig, Braunschweig. Lutz. P. (1992). Fabrzeugbussysteme. In: ETG Fachbericht 37, (W. Lawrenz. Ed.). Datenubertragung auf Fallrzeugen mittels serieller Bussysteme, pp. 26-36. VDE-Verlag; Berlin, Offenbach. Neumann, P. (1990). Kommunikationssysteme in der Automatisierungstechnik. Reihe
The input data which are needed for the application profile are mostly known in the design process. so additional examinations are not necessary. Feasibility of the communication via bus system is provable. Parameters for the bus systems can be adjusted off-line saving a lot of time during implementation of the system.
AUlomalisierungslechnik 242. Verlag Technik.
This approach allows easy comparison of different serial bus systems without implementing them. The effect of a bus communication on the
Berlin. Schielke. A. G., Schnieder, E. (] 993). General hierarchical multilayer structure of a railway operations control system as an example for an abstract theoretical representation of operations control systems. Int. Conf. on Speedup Technologie for Railway and Maglev Vehicles.
process can be judged from the simulation results. The presented methodical approach is not application dependent and can be used in any field of industrial automation.
Yokohama. Schnieder, E. (1993). ProzeBinformatik Automatisierung mit Rechensystemen,
It is planed to modify the system allowing a parameter optimization of the field bus systems, as well. Therefore, a mathematical function is needed rating the results in comparison with the user demands. Further on, this value can be used for
Einfiibrung mit Petrinetzen. 2. Edition. ViewegVerlag, Braunschweig. Seifart, M.; Beikirch, H.; Raucbbaupt. L. (1993). Anforderungen und Leistungen serieller Bussysteme im sensomaben ProzeBbereich. In: iNet'93, KongreB-VortrJge (K. Bender, Ed.), pp. 59-66. Karlsruhe.
objective lmd automatic comparison of different bus systems.
970
ANALYSIS OF FIELD BUS SYSTEMS FOR HIGH SPEED TRAINS J. KIEFER and E. SCHNIEDER Technischc UlIivcrsitat Braunschwcig. Institut for Rcgclungs. und Automatisiuungstcclmik. /Angu Kamp 8. D-38106 Braullschweig. Germany. Internet: [email protected] AbstDCL Due to the fact that the use of intelligent systems in high speed railways increases rapidly. the demand for an efficient communication becomes more and more important. Field bus systems serve many of those tasks but both. the development tools for the choice of one field bus protocol and the optimization of its parameters are poor. In the paper the requirements of train communication are specified and a tool is introduced allowing the above mentioned evaluations from the users point of view. As an example the requirements for on-board communication of high speed trains like the ICE is examined using CAN-protocol. Key Words. communication. field bus systems. requirement analysis. train. InterCity Express (lCE). Controller Area Network (CAN)
1. INTRODUCTION
into an efficient engineering of bus systems for control and vital systems.
The use of automation systems in all fields of transportation is increasing rapidly. Cars, trains, ships and planes are equipped with highly sophisticated technical systems for control of drives or engines, localization, automatic driving, communication, passenger comfort and so on. During the last decade, the architecture of those systems changed from stand-alone solutions to open systems implying strong communication links. This led to the requirement of cheap communication channels providing data exchange with a high reliability and which do not depend on the
2. STRUCTURE OF DATA COMMUNICATION
time scale [sI log
venue Im)
essential operation cycle time Is)
rate
application. Considering that cabling and maintenance of directly wired connections is quite expensive, serial bus systems are getting more and more important in this context. Cars and even the first trains have been equipped with on-board field busses.
memory capacity [bit] performance [MFLOPS)
Nowadays, many communication protocols are known, each of them being developed for a special purpose. The increasing number of bus protocols and the increasing complexity of automation systems require a careful study of this field lO gel
11
Operational Layer
ill
Tactical Layer
1::::::::::;'::1
Dispositive Layer
t ·]
Strategical Layer
Fig. 1 Criteria for the hierarchical order of automation systems
965
With this approach, the idea of taking a sen.-ll bus system distributing information to many modules comes quite close.
2.1. Data Communication and Hierarchical Order Most of the automation systems have an hierarchical structure which can be divided into strategical, dispositive, tactical and operational layers. There are quite a few criteria for attaching a special task to one of the hierarchical layers. Some of them can be taken from Fig. 1. Not explaining all of them in detail, it is necessary to stress the difference in communication. It is important that the time scale for which a decision is taken differs considembly. For instance there is some data communication with a large data contents which has to be transmitted rarely (strategical layer). On the
2.2. Essential Requirements of the Process Every user of a communication system regarding the technical part of data transfer, is neither interested in the way the data are transmitted nor in the protocol being used for the coordination of every communication device. Instead of this, the user wants to know how the process is temporally influenced by the data communication and about the way the individual devices have to be coupled
other hand some short telegmms need to be sent isocbronously (operational layer).
mechanically. The last aspect will to be ignored in this paper.
Fig. 2 shows the functional system structure of the mobile unit of a modern train. The several tasks are spread out over the different layers neglecting that some tasks have to be implemented vitally leading to even more modules. It is easy to imagine that the modules are closely linked together exchanging data frequently. The following example states this fact: The drive control receives orders from the movement control and provides itself commands onto drives and brakes. For the internal calculations, information is required from the localization, the dist.:'Ulce measurement unit, the door control, the emergency indicator and from several sensors monitoring drives and brakes.
For the definition of the required time behaviour of the transmission system some criteria are needed describing the process demands, only. It has to be stressed that these criteria must not depend on the transmission protocol at all. Only this condition allows a comparison of data transmission systems using completely different principles. The following criteria are used for the examinations by means of comparison of cbraracteristic values. They are chosen because they are standards in automation and suitably meet the demands of communication in railway systems.
Strategical Layer
Dispositive Layer
Tactical Layer
Operational Layer Fig. 2
Hierarchical layers for the tasks of a high speed train
966
system. This problem will not be dealt with in the further parts of this paper.
Delay time tL, ..... The delay time describes the time interval a message
takes
from
the
input
of the
data
transmission system to its output. It is given for
Tbe dependability of the data channel has to be
every single communication cbannel between two
very high for the use on railway vebicles. This is
units a and b. It is evident that this value only
due to the fact that a loss of communication would
depends on the communication system and no
possibly lead to loss of control over the train which
process parameters are included.
might end in wrong side failures. RedunruUlcy of communication channels consideres this problem
Reaction time t R• • : J
and some field bus protocols are even equipped
This value is needed when a system device requires
with a doubled trllDsmission media Nevertheless,
information from one or more other devices. It specifies the time from the request for data of the
redundancy does not mainly effect the temporal behaviour of the protocol and will be neglected in
unit a to the reception of the information I . It bas to
the following discussion.
be mentioned that a lot of other communications lUld calculations may be needed for information 1 3. TEST
lUld therefore, process parameters of the application
FOR
THE
EXAMINATION OF BUS SYSTEMS
like calculation time or process time constants influence this value.
Age of transmitted data
ENVIRONMENT
t A . .....
The age of a message being received by unit b is quite similar to the delay time tl., Q-+b' Tbe difference is the starting point of the time measurement at unit
a: The age is calculated from the generation of the message
instead
of
the
band-over
to
the
communication system. This is important in cases where
the
generation
of a
message
is not
automatically leading to the start of communication. When
message
polling
is
used
by
the
communication system the age should be used in place of delay time.
2.3. Deperuiability of Communication Fig. 3 Test environment for bus examinations
There are two more constraints for the use of field bus systems on a train wbich bave to be taken into
Communication
account:
conveniently by means of generalized, stochastic
systems
can
be
modelled
petri nets. Some of the data is safety critical and therefore, bas to be transmitted vitally. Regarding the ISO/OSI
A petri net based simulator has been designed
reference model for data communication this is a
giving the possibility for a comparison of several
task of the application layer. From another point of
field bus systems. It splits up into several units.
view, the field bus can be seen as a gray channel
Tbey normally run independently and off-line but
for communication and a vital message band ling
there are only minor changes for the realization of
will be implemented within the application itself.
an integrated system. Tbe whole system is shown in
Hence, this does not affect the actual protocol. It
Fig. 3 and will be explained briefly.
and only increases the load of the transmission
967
realistic temporal behaviour and a determined examination of bus system failures and their effect on the data transmission.
isochronous
random with limits exponential binomial / poisson with / without limits
All modules are implemented by means of colored, timed petri nets giving the possibly of simulation and analysis. A visualization unit and analysis unit are integrated, as well.
t illlerspace Fig. 4 Implemented distributions for tbe mode ling of data flows
The simulation environment serves for complex system analysis, as outlined. During simulation mode the actual bus status is monitored. Therefore , it is easily possible to see ~Uly interferences between data messages that can lead to a serious delay, as it appears in arbitrating protocols. In analysis mode monitoring of single data links ~Uld visualization of performance parameters are possible. Some examples are shown ill the next chapter.
First, it is imponant to set up the application proflJe for the process operations. Therefore, a formal definition of each input and output data flow of every module of the train control system has to be deduced with respect to its temporal behaviour. It has to be considered that there are isochronous and stochastical message generation. Fig. 4 shows possible distributions which can be combined. Modelling has to be done for the input data flows but also for those tasks calculating data as a result of an input These are required for the calculation of the reaction time mentioned in Chapter 2.2 and therefore, should be modelled precisely. All application data is well known from the system design process and does not demand any additional examinations at all.
In addition to simulation, petri nets allow a formal analysis. Therefore, it is necessary to set up a timed reachability graph allowing the proof of maximum lransmission times for communication links. This might be required for the proof of safety which is needed for some components within train conlrol systems.
4. COMMUNICATION OF THE ICE-TRAIN
~
l.
_
~trigger
4.1. Communication links of the ICE
I________~gger mode
_...L._"""""....
At this point, the communication for a future lrain
tinterspace
control system like of the german high speed train ICE will be examined. It is not the aim of this example to justify the use of one special field bus protocol but to demonstrate the way a standard protocol can be tested for later usage without any implementation work.
Fig. 5 Time defmition in trigger mode
It has to be considered as well
that data
transmission in automation systems can not always be defmed for only one data. Some messages are triggered by other data transmissions. For this purpose, a mode is implemented allowing an external trigger of a data transmission from another message. This mode is useful for the description of tasks calculation new data. Both possibilities for time defmition are shown in Fig. 5.
A brief discussion of the components in the train control system will be given at the beginning. It is not intended to describe all its functions but rather the mechanisms leading to couununication. This will be referred to Fig. 2 without explicitly mentioning it
Further on, the bus system has to be modelled. For our examinations protocols like CAN, MVB, FIP, ... were taken into account The models allow a
968
The movement command being valid for the next block is transmitted from the track via track conductor. The command is interpreted from the on-board equipment using the quantities of motion being provided from a distance measurement unit and data from the automatic train stop system Indusi. These commands are split up into actual orders for brakes and drives wbicb are coordinated by an integrated automatic movement control
Table 1 Data flows of ICE-train
communication
I
lz. ,.;"
I ...
I,
Ibit)
Ims)
Ims)
Ims]
requirements
(AFB).
result
track conductor antenna -+ train control system
100
100
lOoo
train control system -+ track (conductor antenna) -+ AFB -+ display, recorder
50 40 700
100 85 600
1000 1.356 85 0.792 200 1.293
2
na
IO
0.351
100 100
0.543 0.734
1.678
The distance measurement unit is a main computer receiving its data from different measurement components like radar, incremental position resolver, accelerometer and defined position reference points. Further on, data from the locomotive control are used. Tbe quantities of motion are transmitted to the track for use in the train supervision system, as well.
distance measurement unit -? track (conductor antenna) -+ train control system
240 240
100 1000
radar -+ distance measurement unit
40
2
0. 123
All commands are recorded and visualized to the driver.
incremental position resolver -+ distance measurement unit
40
2
0.234
4.2. Definition of the Requirements
accelerometer -+ distance measurement unit
40
2
0.427
distance measurement reference -+ distance measurement unit
48
7000
locomotive control -+ distance measurement unit
20
2
Indusi -+ train control system
In Table I the requirements for the communication are listed. All control flows for parametrization and acknowledge are neglected for purposes of clearness. Furthermore, the average length of a message /, the minimum cycle time tz. ..... , and the message age after the transmission t", are sbown, only.
2
0.315
0.545
I
0 .8
'-~----------------~~J . . .. . .
0.8
4.3. Results with CAN-Protocol
~
For demonstration purposes the CAN-Protocol (Boscb AG, Germany) bas been cbosen. The bus parameters (especially the identifiers) for the above mentioned data flows bave been set for simulation. In addition, the parameters for the transmission rate of the bus cable was set to 1.5 Mbitls and a failure rate (corrupted bits per transmitted bits) of 0.001 was estimated. 18000 telegrams were used for the examination.
Fig. 6 Monitoring of a single data link (train control system to AFB) with CAN-protocol
The results from Table I (t,: transmission time) show that every data channel meets the
969
specifications (I, < lA). This can easily be seen from Fig. 6 where the result for the communication from the train control system to the AFB is shown. The cumulative probability of messages being transmitted is plotted versus transmission time. Due to the fact that there is no time delay from the
6. REFERENCES Ajmone Marsan, M.; Chiola, G.; Fumagalli, A. (1987). An Accurate Performance Model of CSMAlCD Bus LAN. In: Leclure Notes in Computer Science, ( G. Rosenberg, Ed.), Vol.
generation of messages to the band-over to the trrulsmission system in the CAN-protocol, transmission time is equal to the message age after trlmsmission
266. Advances in Petri Nets, pp. 146-161, Springer Verlag; Berlin, Heidelberg, New York. DEUFRAKO-Bus (1992). Auswahlkriterien fUr den
lA.
ARTEMIS-Bus. Bundesbahnzentralrunt Munchen, Munchen, Paris.
Using this mode, it can be validated whether the specifications are met with the current protocol and its parameters. The performance of the system can be judged from the different parameters. Simulating different field bus protocols allows even a comparison of the different performances. The user gets the possibility of choosing the right system without implementing it at all.
Funke, A. (1992). Machbarkeitsanalyse von Feldbusanwendungen. FOrlschrittberjclue VDI, Reihe 10 Nr. 222. VDI-Verlag, Dusseldorf. Gemmeke, W. (1992). Zugbussysteme. In: ETG Fachberichl 37, (W. Lawrenz, Ed.), Datenubertragung auf Fahrzeugen mittels serieller Bussysteme, pp. 37-58. VDE-Verlag; Berlin, Offenbach. Kiefer, 1. (1992). DatenfluBdiagramm
5. CONCLUSIONS / OUTLOOK
Schienenfabrzeug, Studie. Institut ftiT Regelungs- und Automatisierungstechnik, TU Braunschweig, Braunschweig. Lutz. P. (1992). Fabrzeugbussysteme. In: ETG Fachbericht 37, (W. Lawrenz. Ed.). Datenubertragung auf Fallrzeugen mittels serieller Bussysteme, pp. 26-36. VDE-Verlag; Berlin, Offenbach. Neumann, P. (1990). Kommunikationssysteme in der Automatisierungstechnik. Reihe
The input data which are needed for the application profile are mostly known in the design process. so additional examinations are not necessary. Feasibility of the communication via bus system is provable. Parameters for the bus systems can be adjusted off-line saving a lot of time during implementation of the system.
AUlomalisierungslechnik 242. Verlag Technik.
This approach allows easy comparison of different serial bus systems without implementing them. The effect of a bus communication on the
Berlin. Schielke. A. G., Schnieder, E. (] 993). General hierarchical multilayer structure of a railway operations control system as an example for an abstract theoretical representation of operations control systems. Int. Conf. on Speedup Technologie for Railway and Maglev Vehicles.
process can be judged from the simulation results. The presented methodical approach is not application dependent and can be used in any field of industrial automation.
Yokohama. Schnieder, E. (1993). ProzeBinformatik Automatisierung mit Rechensystemen,
It is planed to modify the system allowing a parameter optimization of the field bus systems, as well. Therefore, a mathematical function is needed rating the results in comparison with the user demands. Further on, this value can be used for
Einfiibrung mit Petrinetzen. 2. Edition. ViewegVerlag, Braunschweig. Seifart, M.; Beikirch, H.; Raucbbaupt. L. (1993). Anforderungen und Leistungen serieller Bussysteme im sensomaben ProzeBbereich. In: iNet'93, KongreB-VortrJge (K. Bender, Ed.), pp. 59-66. Karlsruhe.
objective lmd automatic comparison of different bus systems.
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