DEVICE AND METHOD FOR COMPUTER-AID MONITORING TWO TIMEBASES OF TWO COMMUNICATION DEVICES

Description

[0001] The invention relates to a method for computer-assisted monitoring of a first time base of a first communication device and a second time base of a second communication device. Furthermore, the invention relates to a system comprising a first communication device, having a first time base, a second communication device, having a second time base, and an interface for establishing a communication connection between the first communication device and the second communication device. Finally, the invention relates to a computer program product and a device for providing this computer program product, wherein the computer program product is equipped with program instructions for implementing this method.

[0002] As is known, a time offset may occur between a first time base of a first communication device and a second time base of a second communication device.

[0003] A basic method for synchronizing time bases is known, for example, from the publication "Probabilistic clock synchronization" (Flaviu, Christian, Distributed Computing (1989) 3:146-158). The method described therein will be referred to as the Christian algorithm and can essentially be described by the process steps specified at the beginning in a first process flow, where at each measurement step at a first point in time related to the first time base, a first message is sent from the first communication device to the second communication device, at a second point in time related to the second time base, the first message is received by the second communication device, at a third point in time related to the second time base, a second message is sent from the second communication device to the first communication device, and at a fourth point in time related to the first time base, the second message is received by the first communication device, a time offset interval in which a time offset can lie between the first time base and the second time base is determined from the first point in time, the second point in time, the third point in time and the fourth point in time.

[0004] A method using the Christian algorithm to estimate a time offset between two time bases is described in WO 2019 / 223951 A1. Using the Christian algorithm, several time offset intervals are determined. By extrapolating consecutive time offset intervals, taking into account an assumed drift of the time offset, auxiliary windows for a possible time offset can be created. By intersecting several auxiliary windows, a resulting time offset interval can be determined that exhibits a smaller error compared to the time offset intervals of the previous measurements.

[0005] This is achieved by repeating the procedure several times for an earlier measurement step and a later measurement step in a second run of the procedure. a maximum possible drift in the time between the earlier measurement step and the later measurement step is determined taking into account the lower limit of the time offset interval for the earlier measurement step and the upper limit of the time offset interval for the later measurement step, a minimum possible drift in the time between the earlier measurement step and the later measurement step is determined taking into account the upper limit of the time offset interval for the earlier measurement step and the lower limit of the time offset interval for the later measurement step, an upper limit of a drift interval is calculated taking into account the maximum possible drift and a lower limit of a drift interval is calculated taking into account the minimum possible drift, in which a relative drift describing the temporal change in the time offset can lie,

[0006] The invention is based on the object of specifying a method for computer-assisted monitoring of a first time base of a first communication device and a second time base of a second communication device, with which a time offset between the time bases or a drift of the time offset can be determined as accurately as possible in the shortest possible time in order to monitor the two communication devices using the result. Furthermore, the object of the invention is to specify a computer program product and a device for providing this computer program product, with which the aforementioned method can be carried out.

[0007] This object is achieved according to the invention with the subject matter of the claim (method) specified at the outset in that, in a third sequence of several drift intervals, the lowest upper limit is set as the upper limit of a resulting drift interval for the relative drift and the highest lower limit is set as the lower limit of the resulting drift interval for the relative drift.

[0008] The first process, second process, and third process of the method according to the invention are to be understood as sequences of method steps that are carried out with computer support to achieve the determination results or calculation results described in more detail below. The results of the first process are required in the second process, and the results of the second process are required in the third process. However, this does not mean that the processes have to be carried out one after the other. They can also be carried out in parallel if each process is repeated separately, in which case the results of a previously completed first process are used for the second process currently being carried out, and the results of a previously completed second process are used for the third process currently being carried out.

[0009] The first procedure involves implementing the Christian algorithm described above. After determining the four points in time mentioned above, the time offset interval Δ(n) is determined according to the Christian algorithm. This interval specifies the interval for a possible time offset within which the time offset, i.e., the absolute time difference between the first time base and the second time base based on the measured points in time, can only lie.

[0010] The Christian algorithm proceeds by calculating the time offset Δ(n) from the first time point, the second time point, the third time point, and the fourth time point. A maximum possible error for the time offset e(n) can be calculated from the first time point, the second time point, the third time point, and the fourth time point. Taking the maximum possible error into account, an upper bound and a lower bound for the time offset interval can be calculated (more on this below).

[0011] The first sequence contains at least three measurement steps. This can be justified by the fact that the first sequence must form the basis for carrying out the second sequence. In this sequence, two measurement steps each must be considered several times, namely an earlier measurement step n and a later measurement step n+x. Where n is the number of the measurement step and is a natural number. A later measurement step is a distance x from the earlier measurement step, which is also a natural number. For a neighboring later measurement step, x = 1. If a minimum of three measurement steps are carried out in the first sequence, a maximum of three comparisons can be carried out in the second sequence: namely the comparison of measurement steps 1 and 2, measurement steps 2 and 3, and measurement steps 1 and 3. If n > 3, the possible combinations increase.

[0012] If the time offset intervals of an earlier measurement step and a later measurement step are known, the resulting time offset interval of both measurements can be used to determine a maximum possible change in the time offset (also called drift) and a minimum possible change in the time offset, taking into account the measurement uncertainty determined by the time offset interval. A maximum possible drift results when the time offset in the earlier measurement step is assumed to be minimal and the time offset in the later measurement step is assumed to be maximum within the respective time offset interval. Therefore, the lower bound of the time offset interval for the earlier measurement step and the upper bound of the time offset interval for the later measurement step are taken into account. Conversely, a minimum possible drift results when the time offset in the earlier measurement step is assumed to be maximum and the time offset in the later measurement step is assumed to be minimal.Therefore, in this case, the upper bound of the time offset interval of the earlier measurement step and the upper bound of the time offset interval of the later measurement step are taken into account.

[0013] Unlike the prior art, however, the drift determined from two measurement steps is not used to determine an auxiliary window by extrapolation. Instead, several, preferably at least three, drift intervals are determined and combined in the manner described above. This allows a resulting drift interval to be determined, which can advantageously be narrowed down much more precisely. Furthermore, measurements (measurement steps) in a comparatively short period of time already enable relatively reliable statements about the existing drift, since errors such as transmission-related delay differences between the first message and the second message are not systematically eliminated as best as possible.This is achieved in particular if, in the second process, each time offset interval determined in the first process is combined with each other time offset interval determined in the first process to determine an associated drift interval.

[0014] Therefore, the method according to the invention can determine a comparatively accurate drift result in a comparatively short period of time. Alternatively, the drift can be used to calculate a comparatively accurate relative time offset between the first time base and the second time base, taking the period into account. This advantageously also enables the operation of safety-relevant communication devices, whose synchronous communication is a prerequisite for the method in question, with COTS (commercial off-the-shelf) components as the time base. An example of an application is communication technology in railway operations, which must meet high safety standards.

[0015] In the third run, according to the invention, the lowest upper bound of the several intervals determined in the second run is set as the upper bound of the resulting drift interval, and the highest lower bound is set as the lower bound of the resulting drift interval for the drift. This is based on the finding, important for the invention, that each of the individual drift intervals was determined with the same certainty regarding the occurrence of errors. However, since the prerequisites of the individual measurements can contain errors of varying magnitudes, which depend on the respective applicable transmission conditions, the unknown errors of varying magnitudes can be limited by taking into account the lowest upper bound and the highest lower bound of the available intervals for the resulting interval.

[0016] The objective of the method can, for example, be to monitor the synchronization of the two time bases. This involves determining a relative time offset between the first time base and the second time base. Monitoring can also be performed by determining the drift. If monitoring reveals that synchronization can no longer be maintained due to an increasing time offset or progressive drift, appropriate countermeasures must be initiated (more on this below). These countermeasures can, for example, consist of an error message or a correction, i.e., reducing the time offset.

[0017] In the context of the invention, "computer-aided" or "computer-implemented" can be understood as an implementation of the method in which at least one computer carries out at least one method step of the method.

[0018] The term "computer" covers all electronic devices with data processing capabilities. Computers can include, for example, personal computers, servers, handheld computers, mobile devices and other communication devices, processors, and other electronic devices for data processing, which can preferably also be connected to a network.

[0019] In the context of the invention, a "processor" can be understood as, for example, a converter, a sensor for generating measurement signals, or an electronic circuit. A processor can be, in particular, a central processing unit (CPU), a microprocessor, a microcontroller, or a digital signal processor, possibly in combination with a memory unit for storing program instructions, etc. A processor can also be understood as a virtualized processor or a soft CPU.

[0020] In the context of the invention, a "storage unit" can be understood as meaning, for example, a computer-readable memory in the form of a random-access memory (RAM) or data storage device (hard disk or data carrier).

[0021] "Interfaces" can be implemented in hardware, for example, via a wired or wireless connection, or in software, for example, as interaction between individual program modules of one or more computer programs.

[0022] "Program modules" are understood to mean individual functional sequences that enable a program sequence of computer-aided process steps according to the invention. These functional sequences can be implemented in a single computer program or in several communicating computer programs. The interfaces implemented in this way can be implemented in software within a single processor or in hardware if multiple processors are used.

[0023] Unless otherwise stated in the following description, the terms "create," "determine," "determine," "calculate," "generate," "configure," "modify," and the like preferably refer to processes that create, modify, or convert data into other data. The data is present, in particular, as physical quantities, for example, as electrical impulses or measured values. The required instructions are summarized as program commands in a computer program as software. Furthermore, the terms "send," "receive," "read," "read out," "transmit," "transfer," and the like refer to the interaction of individual hardware components and / or software components via interfaces.

[0024] According to one embodiment of the invention, it is provided that the time offset in a measuring step n is calculated on the basis of the transmission time of the first message as a time difference between the first time and the second time and the transmission time of the second message as a time difference between the third time and the fourth time.

[0025] In particular, the difference between the two time differences mentioned can be used to assess a potential time offset between the two time bases. The idea behind this is that a time offset leads to a shift in the measured times compared to the actual times. This makes the measured transmission time of one message shorter and the measured transmission time of the other message longer, with the messages being the first message and the second message in the first run of the procedure. In this respect, the time offset has a double effect on the measured transmission times.

[0026] For example, it can be provided that the time offset Δ( n ) at a measuring step n is calculated according to the formula: Δ n = T 2 n − T 1 n − T 4 n − T 3 n / 2

[0027] Dividing the result by two (in the denominator) takes into account the fact that, as already mentioned, the time offset has a double effect on the measured transmission times. However, dividing the result by two is not necessary if this is taken into account later in the procedure (more on this below).

[0028] According to one embodiment of the invention, it is provided that a maximum possible error for the time offset in a measuring step n is calculated taking into account a message runtime measured in the first communication device as a time difference between the first time and the fourth time and a reaction time measured in the second communication device as a time difference between the second time and the third time.

[0029] The measured message delay is not the actual message delay. This can be explained by the fact that the measurement is subject to measurement errors. The most significant measurement error is that the time difference between the first and fourth times does not take into account the reaction time in the second communication device from receiving the first message to sending the second message.

[0030] The latter measurement error, however, is easily identifiable. It consists of the measured response time, which can be calculated as the time difference between the second and third times. Therefore, the measured message runtime is reduced by the measured response time. Therefore, subtracting the measured response time from the measured message runtime will provide a better approximation of the actual message runtime.

[0031] At the same time, the result provides a measure of the maximum possible error, considering that signal propagation times can fluctuate due to irregularities in the transmission path. These fluctuations are large compared to the measurement accuracy in determining the respective points in time to be measured. Therefore, a measurement error due to fluctuations in the transmission, which are determined by taking into account the response time of the second communication device, can be estimated with sufficient accuracy.

[0032] For example, it can be provided that the maximum possible error e(n) of the respective measurement step n is calculated according to the formula: e n = T 4 n − T 1 n − T 3 n − T 2 n / 2

[0033] The time difference between the fourth time and the first time indicates the measured signal propagation time. The response time of the second communication device, determined by the time difference between the third time and the second time, can be subtracted from this. Since two transmissions are involved, the result (denominator) can be divided by two to determine the maximum possible error per transmission.

[0034] Alternatively, dividing by two can be omitted if this is taken into account in the subsequent calculation procedure. The maximum possible error can thus also be calculated using the denominator mentioned above alone.

[0035] In other words, it can be determined that the actual time offset δ(n) of a measurement step n lies reliably in the following interval. Δ u n = Δ n − e n ≤ δ n ≤ Δ n + e n = Δ o n where Δu(n) the lower bound of the time offset interval of the measurement step, Δ O(n ) is the upper bound of the time offset interval of the measurement step.

[0036] Inserting formulas (1) and (2) into formula (3), we obtain the upper bound and the lower bound of the time offset interval for the actual time offset δ(n): Δ u n = T 3 n − T 4 n ≤ δ n ≤ T 2 n − T 1 n = Δ o n

[0037] According to one embodiment of the invention, the lower limit of the time offset interval Δu(n) of the measuring step n is calculated according to the formula: Δ u n = T 3 n − T 4 n and the upper bound of the time offset interval Δ o(n) of the measuring step (n) is calculated according to the formula: Δ o n = T 2 n − T 1 n .

[0038] As explained above, these formulas, which are parts of formula (4), use both the measurements for the time offset Δ( n ) as well as the estimation of the error e ( n ) taken into account.

[0039] According to one embodiment of the invention, it is provided that a time difference between the earlier measuring step and the later measuring step n+x is calculated, wherein the measured first times or the measured second times or the measured third times or the measured fourth times of the earlier measuring step and the later measuring step are taken into account to determine the time difference.

[0040] The time difference indicates the period of time between the earlier measurement step and the later measurement step. This time difference is required to determine the drift based on the determined time offsets, since drift is defined as the temporal change in the time offset. It is advantageous to use points in time that are already available when determining the measurement results of the measurement steps. Comparable points in time are used in each case, for example, the fourth point in time of the earlier measurement step and the fourth point in time of the later measurement step (the same applies to the first, second, and third points in time). Insert

[0041] According to one embodiment of the invention, it is provided that the upper limit Ω O (n, n+x) of the drift interval is calculated using the formula: Ω o n , n + x = Δ o n + x − Δ u n / T 4 n + x − T 4 n and the lower bound Ω u (n, n+x)of the drift interval is calculated using the formula: Ω u n , n + x = Δ u n + x − Δ o n / T 4 n + x − T 4 n where n the previous measurement step, n+1 the later measurement step, Δu(n) the lower bound of the time offset interval of the previous measurement step, Δ u (n+x) the lower bound of the time offset interval of the later measurement step, Δo(n) the upper bound of the time offset interval of the previous measurement step, Δ O (n+x) the upper limit of the time offset interval of the later measurement step, T4(n) the fourth time point of the previous measurement step, T4(n+x) the fourth time point of the later measurement step is.

[0042] The expression (T4(n+x)-T4(n))There is a time difference between the earlier measuring step (n) and the later measuring step (n+x), whereby the measured first times, the measured second times or the measured third times of the earlier measuring step and the later measuring step can alternatively be used to determine the time difference, as already described above.

[0043] The above-mentioned calculation formulas advantageously provide an algorithm with which the intervals from an earlier measurement step and a later measurement step can be calculated in a computer-assisted manner while adhering to short arithmetic symbols.

[0044] According to one embodiment of the invention, it is provided that a resulting drift value Qr is determined as the mean value of the upper bound of the resulting drift interval and the lower bound of the resulting drift interval.

[0045] The determination of the resulting value in this way is based on the consideration that setting the drift value as the mean value in the resulting interval ensures that any error associated with the determination can be no more than half the interval width. This minimizes the risk of a larger error in the resulting drift value.

[0046] According to one embodiment of the invention, it is provided that a critical drift value Ωc is determined and a check is carried out to determine whether the critical drift value is in the resulting drift interval and / or whether the resulting drift value Ωr exceeds the critical drift value.

[0047] By defining a critical drift value, a decision can be made as to how long an application that depends on communication via the two communication devices can operate safely. In particular, synchronization of the units executing the application may be necessary for the safe operation of the application, enabling process steps of the application to be synchronized with data exchange via the first communication device and the second communication device. A threat to smooth synchronization over a minimum required period may be jeopardized if the critical drift value is reached or exceeded, allowing further measures to be derived (e.g., a correction of the time bases to reduce the time offset).

[0048] According to one embodiment of the invention, it is provided that a time interval is defined for the second sequence in which all previous measurement steps and later measurement steps to be considered must lie.

[0049] An evaluation can be performed after each time interval by executing the third process. When determining the length of the time interval, it can be considered that the following conditions must be met for the second process to be executed.

[0050] The time interval must be long enough to allow the required number of measurement steps to be performed. Furthermore, it must be considered that the time interval must be long enough to allow any drift in the time offset to be detected by measurement.

[0051] On the other hand, it should be considered that changes in external conditions, especially temperature, can cause an increase or decrease in the drift, but these changes should not be taken into account when assessing the drift. Temperature fluctuations create a reversible increase or decrease in the time offset, so to speak, and therefore, within a permissible range, no need or should be reacted to. If the time interval is not too large and the drift interval is not too small, then the actual drift will always be within the drift interval, despite fluctuations.

[0052] On the other hand, a drift due to a temperature change cannot be distinguished from a drift due to the accuracy of the first time base and the second time base from a measurement perspective. Therefore, the time interval should be short enough so that a temperature change has only a minimal impact on the determination of the time offset performed in the measurement steps within the time interval, relative to the expected accuracy of the first time base and the second time base.

[0053] For example, it can realistically be assumed that the resulting interval determined by measurement has an interval size (span) of 20 ppm. Furthermore, it is realistic that a possible time offset is shifted by one ppm per Kelvin temperature change. This value applies to typical COTS oscillators (i.e., commercial-off-the-shelf components) with the operating principle of an oscillating crystal. If an environment is now assumed in which a maximum temperature change of 1 K / min is possible, a drift of the time offset within a measurement time interval of 1 minute is a factor of 20 smaller than the span of the resulting interval. As a result, there is a high probability that the actual drift lies within the resulting drift interval.It is therefore advantageous to set the length of the time interval of the second sequence to a maximum of 1 minute, preferably a maximum of 30 seconds, and even more preferably a maximum of 10 seconds.

[0054] According to one embodiment of the invention, it is provided that the time base of one communication device is defined as a reference by the first communication device and the second communication device and the time base of the other communication device is modified taking into account the resulting drift.

[0055] If the time base of one communication device is set as a reference, a measure can be taken to reduce the time offset of the other communication device if necessary. This ensures that the first time base and the second time base are permanently synchronized within the permissible deviations, thereby advantageously ensuring synchronized communication between the first communication device and the second communication device.

[0056] To align the first and second time bases, the following well-known measures can be taken. The time base not used as a reference can be slowed down or accelerated as needed to reduce any time offset from the time base used as a reference. Another option is to make a step-by-step correction to the time measurement.

[0057] The method can also be used to keep more than two time bases synchronized. One of the time bases to be synchronized is used as the reference time base, and the method according to the invention, in particular the aforementioned modification step, is performed with each of the other time bases.

[0058] The above-mentioned object is alternatively also achieved according to the invention with the subject matter of the claim (plant) specified at the outset in that the plant is designed to carry out a method for computer-aided monitoring according to one of the aforementioned claims.

[0059] A system within the meaning of the invention is understood to be a technical system in which data exchange is required between different communication devices of the system. This is particularly the case if the system comprises multiple computers that must be operated in such a way that synchronized data exchange via the first communication device and the second communication device is required.

[0060] According to one embodiment of the invention, the interface for establishing the communication connection is provided by a cloud.

[0061] In this case, the system can consist of individual technical components, whose communication connection is provided as a service, for example, by a cloud provider. When communicating via a cloud, transmission times can fluctuate, so the method according to the invention can be used particularly advantageously to mitigate the effects of these fluctuations as best as possible by forming the resulting drift interval.

[0062] The term "cloud" refers to an environment for cloud computing. This refers to an IT infrastructure made available via network interfaces such as the internet. It typically includes storage space, computing power, or software as a service, without requiring these services to be installed on the local computer using the cloud. The services offered within the framework of cloud computing encompass the entire spectrum of information technology and include, among other things, infrastructure, platforms, and software.

[0063] According to one embodiment of the invention, the system is a railway system.

[0064] As already mentioned, railway systems such as signal boxes benefit particularly from the application of the method according to the invention, since reliable synchronization of communicating components of the railway system must be ensured.

[0065] The system enables the advantages already explained in connection with the process described in more detail above to be achieved. The statements regarding the process according to the invention also apply accordingly to the system according to the invention.

[0066] Furthermore, a computer program product with program instructions for carrying out the said method according to the invention and / or its embodiments is claimed, wherein the method according to the invention and / or its embodiments can be carried out by means of the computer program product.

[0067] Furthermore, a provision device for storing and / or providing the computer program product is claimed. The provision device is, for example, a storage unit that stores and / or provides the computer program product. Alternatively and / or additionally, the provision device is, for example, a network service, a computer system, a server system, in particular a distributed, for example, cloud-based computer system and / or virtual computer system, which stores and / or provides the computer program product, preferably in the form of a data stream.

[0068] The provision takes place in the form of a program data block as a file, in particular as a download file, or as a data stream, in particular as a download data stream, of the computer program product. However, this provision can also take place, for example, as a partial download consisting of multiple parts. Such a computer program product is, for example, read into a system using the provision device, so that the method according to the invention is executed on a computer.

[0069] Further details of the invention are described below with reference to the drawings. Identical or corresponding elements of the drawings are provided with the same reference numerals and are explained several times only to the extent that differences arise between the individual figures.

[0070] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual, independently considered features of the invention, which also further develop the invention independently of one another and are thus also to be considered as components of the invention, either individually or in a combination other than that shown. Furthermore, the described components can also be combined with the features of the invention described above. They show:

[0071] Figure 1 an embodiment of the system according to the invention with its functional relationships schematically, Figure 2 an embodiment of a computer infrastructure of the communication devices in the system according to Figure 1with one computer each as a block diagram of functional units, whereby program modules are processed, each of which can run in one or more processors and whereby the interfaces can be implemented accordingly in software or hardware, Figure 3 an embodiment of the method according to the invention as a flow chart, wherein the individual method steps can be implemented individually or in groups by program modules and wherein the functional units and interfaces according to Figure 2 are indicated by way of example, Figure 4 schematically the implementation of the Christian algorithm with two time bases shifted by a time offset δ in the first run, Figure 5 and 6 the determination of time offset intervals in a representation of the time offset Δ over time t in the second sequence, whereby upper bounds (in Figure 5 ) and lower bounds ( Figure 6 ) for drift intervals, Figure 7 the determination of a resulting drift interval from individual drift intervals in a representation of the drift Ω over respective pairs of measurements n, n+x in a third process.

[0072] Figure 1 schematically shows a system in a railway environment in which an embodiment of the method according to the invention can be implemented. It shows a track GL into which a trackside device SE is installed. This device provides a second communication device K2, which is connected to a cloud CLD via a second interface S2. Another component is provided by a signal box SW. This has a first communication device K1, which is also connected to the cloud CLD via a first interface S1.

[0073] The first communication device K1 and the second communication device K2 can thus communicate with each other via the CLD cloud using the first interface S1 and the second interface S2. Direct communication between the first communication device K1 and the second communication device K2 can also be ensured via a wired or wireless interface (not shown). The railway components that communicate with each other can also be ensured by railway components other than those shown in the interlocking SW and the trackside device SE.

[0074] The SW signal box and the SE trackside equipment with their functional components are Figure 2shown schematically as a block diagram. The interlocking system SW has a first computer CP1, which is connected to a first memory device SE1 via a third interface S3. Furthermore, a first time base ZB1 is provided, which is connected to the computer CP1 via a fourth interface S4 and to the first communication device K1 via a fifth interface S5. Results of an application running on the interlocking system, which are calculated by the first computer CP1, can also be transmitted to the first communication device K1 via a sixth interface S6.

[0075] The first communication device K1 is used for communication with the second communication device K2 in the trackside device SE. This is Figure 1The second communication device K2 is connected to a second time base ZB2 via a seventh interface S7. Synchronized communication between the first communication device K1 and the second communication device K2 is ensured via the first time base ZB1 and the second time base ZB2.

[0076] Otherwise, the hardware infrastructure of the trackside device SE is structured analogously to that of the signal box SW, at least on the Figure 2 This means that the second time base ZB2 is connected via an eighth interface S8 to a second computer CP2, which in turn is connected to the second communication device K2 via a ninth interface S9. The second computer CP2 also has a connection to a second memory device SE2 via a tenth interface S10.

[0077] Based on Figure 3The method according to the invention can be reproduced in a flow chart. After the method is started, a run variable n=1 is set, since the first measurement step n is being performed. n thus represents the measurement step and is therefore 1 during the first run.

[0078] Depending on the requirements of the ongoing procedure, further procedural steps can then be selected, whereby Figure 3It is not shown in more detail how these requirements are determined. Therefore, the three possible method steps are simply shown in parallel. After that, a sending step SND K1-K2 can be carried out, in which a message is sent from the first communication device K1 to the second communication device K2. Alternatively, a sending step SND K2-K1 can be carried out if a message is to be sent from the second communication device K2 to the first communication device K1. Which direction is required for sending depends on the processes running in the corresponding applications. The sending of messages that have to do with the processing of applications is primarily carried out in relation to the third alternative, which is described below.

[0079] Thereafter, in order to ensure a first sequence AL1 of the method according to the invention, a transmission step SND K1-K2 is first carried out in order to send a message from the first communication device K1 to the second communication device K2. The second communication device K2 reacts by sending a message back from the second communication device K2 to the first communication device K1 in a transmission step SND K2-K1. As will be explained in more detail below, these two transmission steps can be used to calculate a time offset interval COW for the two transmission steps in a calculation step CLC COW, within which a possible actual time offset Δ(n) can lie. Subsequently, in a step n=n+1, the control variable n is incremented by 1.

[0080] Regardless of which of the three alternatives was executed, a subsequent query step t>ZI checks whether the elapsed time t is still less than a defined time interval ZI (which is set to one minute, for example) and has not yet been reached. If this is the case, one of the three alternative procedures mentioned above is repeated. However, if the time interval ZI has elapsed, the first procedure AL1 is completed, with the alternative procedure for determining a time offset interval COW having been executed at least three times.

[0081] After the first AL1 run is completed, the next query step (STP) asks whether the entire application execution process should be stopped. If this is the case, the process ends with STOP. If this is not the case, the run variable is reset to 1 in a step n=1, so that the first AL1 run can begin again.

[0082] As soon as a first sequence AL1 has been completed, a second sequence AL2 can be started. In this second sequence AL2, a past, earlier measurement step n and a later measurement step n+1 are selected in a setting step ST. By comparing the time offset intervals COW (more on this below), an upper bound for a maximum possible drift can be calculated in a calculation step CLC Ωo and a lower bound for a minimum possible drift can be calculated in a calculation step CLC Ωu. Taking these two bounds into account, a drift interval CDW can be calculated in a calculation step CLC CDW, which is important for the further considerations in the third sequence AL3 (more on this below).

[0083] A query step NXT CMB queries whether another combination of measurement steps should be examined. In this case, a different earlier measurement step n and / or a different distance x between the earlier measurement step n and the later measurement step n+x is specified in a change step CNG n,x. The procedure, as explained above, for determining another drift interval CDW can be repeated.

[0084] If no further combinations CMB of measurement steps n, n+x are to be examined, the third sequence AL3 can begin. This consists of a comparison step CMP CDW, in which the available drift intervals CDW determined in the second sequence AL2 are compared with one another. According to the invention, the smallest determined upper bound of the drift interval Ωo and the largest determined lower bound Ωu of the determined drift intervals CDW from the second sequence AL2 are selected, whereby these can belong to different drift intervals CDW. In a subsequent setting step ST RCDW, a resulting drift interval RCDW is determined from these two determined bounds, i.e. the determined upper bound of the drift Ωo and the determined lower bound Ωu, in which measurement errors occurring in the measurement steps n are minimized with regard to the available data.Optionally, a resulting drift value Ωr can be calculated from the resulting drift window RCDW in a calculation step CLC Ωr, in which the resulting drift value Ωr is calculated, for example, as the mean value of the upper bound of the drift Ωo and the lower bound of the drift Ωu (relative to the resulting drift window RCDW).

[0085] The determined resulting drift interval RCDW or the determined resulting drift value Ωr can serve different purposes in the further process flow, of which Figure 3Alternatively, two are shown. For example, an output step OT WS can be performed to output a warning signal WS as soon as the determined resulting drift value Ωr exceeds a critical drift value Ωc that was previously specified. The warning signal can, for example, be output or processed automatically, for example, to stop a running process of user programs for the (railway-specific) application running on the computers CP before synchronization of the first communication device K1 with the second communication device K2 is no longer possible.

[0086] Alternatively, it is possible to correct one of the two time bases ZB in a CRC ZB correction step, i.e., to resynchronize the first time base ZB1 and the second time base ZB2. One time base can be used as a reference, and the other time base can be adjusted to the reference time base (step by step or by accelerating or decelerating the time base to be corrected).

[0087] In Figure 4It is schematically shown how a first time T1, a second time T2, a third time T3, and a fourth time T4 are measured for the Christian algorithm. The times T1 ... T4 are each shown on a first time axis t1 for the first time base ZB1 and a second time axis t2 for the second time base ZB2. This makes it clear that the mentioned times are determined using different time bases, between which a real time offset δ, which is plotted between the first time axis t1 and the second time axis t2, can exist. However, this is not known and is estimated using the Christian algorithm, taking into account the four mentioned times, in the manner already described.

[0088] The result of several such estimates n = 1 ... 3 is in Figure 5 where the distance between the individual measurements n is Figure 5on a time axis t (x-axis). The calculated time offset Δ is shown on the y-axis. The measurements n = 1 ... 3 all lie within a specified time interval ZI. The time offset intervals COW1 ... COW3 belonging to the individual measurements n are all calculated according to Figure 4 calculated according to the Christian algorithm. These are intervals within which the actual time offset Δ must lie. These each have, for example, a lower bound Δu(1) and an upper bound Δo(1) for the first measurement (n = 1). In addition, a mean value Δ(1) can be determined, which, however, is not important for the further calculation presented here. This also applies analogously to the second time offset window COW2 and the third time offset window COW3. Further time offset windows COW4 ... can be determined within the time interval ZI (not shown).

[0089] Because the individual time offset intervals COW1 ... COW3 reliably contain the actual time offset Δ within their range, an upper bound Ωo(n, n+x) can be determined, knowing the time intervals of the individual measurements n and considering a pair of measurements, where n represents an earlier measurement and n+x a later measurement with the distance x from the measurement n. Shown in Figure 5For example, the determination of the upper bound Ωo(1, 2) for n = 1 and x = 1 is possible, whereby it becomes clear that the drift when considering the two corresponding time offset intervals COW1, COW2 can be at most so large that it can develop from the lower bound Δu(1) of the first time offset interval COW1 to the upper bound Δo(2) of the second time offset interval COW2. In other words, the gradient of a straight line Δo(1, 2) through the two points mentioned, knowing the time interval between measurements 1 and 2, is precisely the maximum possible drift when considering these two time offset windows. Figure 5 It can be seen that this procedure can also be carried out for n = 1 and x = 2 as well as n = 2 and x = 1. The time intervals between the individual measurements n can be determined, for example, by calculating the difference between the respective times t4 (cf. Figure 1 ) can be determined.

[0090] In Figure 6It is shown how lower bounds Δu(n, n+x) for the drift can be calculated in an analogous manner. In Figure 6 are the same time offset intervals COW1, COW2 and COW 3 as in Figure 5 The determination of the lower bounds for the drift Ωu will be explained using the first time offset interval COW1 and the second time offset interval COW2. Unlike Figure 5 To determine the lower bound Ωu(1, 2), the upper bound Δo(1) of the first time offset interval COW1 and the lower bound Δu(2) of the second time offset interval COW2 are used. Again, connecting these two points results in a straight line Ωu(1, 2). In this case, the lower bound Ωu(1, 3) and the lower bound Ωu(2, 3) can be calculated analogously.

[0091] In Figure 7It is shown that drift intervals CDW were determined for each of the combinations of measurements considered: for measurements 1 and 2, the drift interval CDW(1, 2), for measurements 1 and 3, the drift interval CDW(1, 3), and for measurements 2 and 3, the drift interval CDW(2, 3). These each represent the interval within which a true drift ω reliably lies. It should be noted that the actual drift ω is still unknown.

[0092] However, the presence of several drift intervals CDW allows the resulting drift interval RCDW to be further limited. For this purpose, the smallest upper bound Ωo of the drift intervals CDW (in Figure 7 Ωo(1, 3)) and the largest lower bound Ωu of the drift intervals (in Figure 7Ωu(2, 3)) are defined as the upper bound Ωo and the lower bound Ωu of the resulting drift interval RCDW. One could also say that the resulting drift interval RCDW is the intersection of the evaluated individual drift intervals CDW. This limits this interval and, for example, a resulting drift Ωr can be calculated by calculating the average of the upper bound Ωo and the lower bound Ωu of the resulting drift interval RCDW. This calculation is based on a statistical evaluation and can, as in Figure 7 shown, deviate from the actual drift ω.

[0093] In Figure 7 It is also shown that a critical value Ωc can be defined for the drift in order to be able to assess whether this is acceptable for reliable process control, for example when calculating applications by utility programs. List of reference symbols

[0094] GLTrack SWInterlocking SELineside device CLDCloud ZITime interval ZB1, ZB2Time base SE1, SE2Storage device CP1, CP2Computer S1 ... S10Interface K1, K2Communication device ZB1, ZB2Time base T1 ... T4Time point N1, N2Message nMeasuring steps xDistance between measuring steps tTime ΔTime offset COWTime offset interval ΔoUpper bound of the time offset interval ΔuLower bound of the time offset interval Δactual time offset ΩDrift CDWDrift interval RCDWResulting drift interval ΩoUpper bound of the drift interval ΩuLower bound of the drift interval ΩrResulting value ΩcCritical value ωActual drift AL1 ... AL3Sequence SNDSend step CLCCalculation step STPNquery step End of procedure STDetermination step CMPComparison step CNGChange step OTOutput step CRC ZBCorrection step for time base NXT CMBQuery step for further combinations

Claims

1. Method for computer-assisted monitoring of a first time basis (ZB1) of a first communications facility and a second time basis (ZB2) of a second communications facility, wherein, in a first sequence, at least three measuring steps (n) are carried out, wherein in each measuring step respectively, • at a first instant (T1), which is based on the first time basis (ZB1), a first message (N1) is sent from the first communications facility (K1) to the second communications facility (K2), • at a second instant (T2), which is based on the second time basis (ZB2), the first message (N1) is received by the second communications facility (K2), • at a third instant (T3), which is based on the second time basis (ZB2), a second message (N2) is sent from the second communications facility (K2) to the first communications facility (K1), and • at a fourth instant (T4), which is based on the first time basis (ZB1), the second message (N2) is received by the first communications facility (K1), • a time delay interval (COW), in which a time delay can lie between the first time basis and the second time basis, is determined from the first instant, the second instant, the third instant and the fourth instant, wherein in a second sequence, for an earlier measuring step (n) and a later measuring step (n+x) • a maximum possible drift in the time between the earlier measuring step and the later measuring step is ascertained multiple times by taking into account the lower limit (Δu(n)) of the time delay interval for the earlier measuring step and the upper limit (Δo(n+1)) of the time delay interval for the later measuring step, • a minimum possible drift in the time between the earlier measuring step and the later measuring step is ascertained multiple times by taking into account the upper limit (Δo(n)) of the time delay interval for the earlier measuring step and the lower limit (Δu(n+x)) of the time delay interval for the later measuring step, • an upper limit (Qo(n, n+x)) is calculated multiple times by taking into account the maximum possible drift and a lower limit (Qu(n, n+x)) of a drift interval (CDW), in which a relative drift (ω) describing the change over time in the time delay can lie, is calculated multiple times by taking into account the minimum possible drift, characterised in that in a third sequence, of a plurality of drift intervals (CDW), • the lowest upper limit is set as the upper limit of a resulting drift interval (RCDW) for the relative drift and • the highest lower limit is set as the lower limit of the resulting drift interval (RCDW) for the relative drift.

2. Method according to claim 1 characterised in that the time delay is calculated during a measuring step (n) on the basis of • the sending time of the first message (N1) as the time difference between the first instant (T1) and the second instant (T2) and • the sending time of the second message (N2) as the time difference between the third instant (T3) and the fourth instant (T4).

3. Method according to one of the preceding claims, characterised in that a maximum possible error for the time delay (Δ) is calculated during a measuring step (n) by taking into account • a message runtime measured in the first communications facility (K1) as the time difference between the first instant (T1) and the fourth instant (T4) and • a reaction time measured in the second communications facility (K2) as the time difference between the second instant (T2) and the third instant (T3).

4. Method according to one of the preceding claims, characterised in that the lower limit of the time delay interval Δu(n) of the measuring step (n) is calculated according to the formula: Δ u n = T 3 n − T 4 n the upper limit of the time delay interval Δo(n) of the measuring step (n) is calculated according to the formula: Δ o n = T 2 n − T 1 n .

5. Method according to one of the preceding claims, characterised in that a time difference between the earlier measuring step (n) and the later measuring step (n+x) is calculated, wherein for ascertaining the time difference, the measured first instants (T1) or the measured second instants (T2) or the measured third instants (T3) or the measured fourth instants (t4) of the earlier measuring step and of the later measuring step are taken into account.

6. Method according to claim 5, characterised in that the upper limit Ωo(n, n+x) of the drift interval is calculated according to the formula: Ω o n , n + x = Δ o n + x − Δ u n / T 4 n + x − T 4 n and the lower limit Ωu(n, n+x) of the drift interval is calculated according to the formula: Ω u n , n + x = Δ u n + x − Δ o n / T 4 n + x − T 4 n wherein n is the earlier measuring step, n+1 is the later measuring step, Δu(n) is the lower limit of the time delay interval of the earlier measuring step, Δu(n+x) is the lower limit of the time delay interval of the later measuring step, Δo(n) is the upper limit of the time delay interval of the earlier measuring step, Δo(n+x) is the upper limit of the time delay interval of the later measuring step, T4(n) is the fourth instant of the earlier measuring step, T4(n+x) is the fourth instant of the later measuring step.

7. Method according to one of the preceding claims, characterised in that a resulting drift value (Qr) is determined as the mean of the upper limit (Ωo) of the resulting drift interval (RCDW) and the lower limit (Ωu) of the resulting drift interval (RCDW).

8. Method according to one of the preceding claims, characterised in that a critical drift value (Qc) is defined and it is checked whether the critical drift value lies in the resulting drift interval (RCDW) and / or the resulting drift value (Ωr) overshoots the critical drift value.

9. Method according to one of the preceding claims, characterised in that for the second sequence, a time interval is defined in which all earlier measuring steps (n) and later measuring steps (n+x) to be considered have to lie.

10. Method according to claim 9, characterised in that the time basis of the one communications facility is defined as the reference by the first communications facility (K1) and the second communications facility (K2) and the time basis of the other communications facility is modified by taking into account the resulting drift (Qr).

11. System with a first communications facility (K1), having a first time basis (ZB1), with a second communications facility (K2), having a second time basis (ZB2) and with an interface (S1, S2) for establishing a communications link between the first communications facility and the second communications facility, characterised in that the system is configured to carry out a method for computer-assisted monitoring according to one of the preceding claims.

12. System according to claim 11, characterised in that the interface for establishing the communications link is provided by a Cloud (CLD).

13. System according to claim 11 or 12, characterised in that the system is a rail system.

14. Computer program product with program commands for carrying out the method according to one of claims 1 - 10.

15. Provisioning apparatus for the computer program product according to the immediately preceding claim, wherein the provisioning apparatus stores and / or provides the computer program product.