Patent Application
20130195114
The present invention relates to a communication system as well as a method for isochronous transmission of real time-critical data over a real time-controlled Ethernet data network having at least one first communication device with a synchronized timer and is designed to transmit real time-critical data telegrams using a scheduled real time control.
Such a real time-controlled Ethernet data network is defined by the PROFINET IRT Standard, for example.
For some time now, Ethernet-based data networks which enable cycle times of a few milliseconds have been in use as field buses in automation systems. However, there are applications such as control of complex drive systems, which require much shorter communication cycles in the millisecond range, for example. The control of the drive systems is extremely time critical, i.e., they must be triggered at certain times to prevent malfunctions. A communication system that can transmit real time-critical data in short communication cycles is therefore needed.
To be able to use the Ethernet technology in real time-critical systems, the above-mentioned PROFINET IRT Standard has been introduced. The abbreviation IRT here stands for Isochronous Real Time, i.e., a technology which permits a clock-controlled data transmission in real time.
PROFINET IRT systems make it possible to transmit real time-critical and non-real time-critical data in communication cycles of an adjustable chronological length over a switchable Ethernet data network. To do so, each communication cycle is subdivided into a first time domain, in which real time-critical data can be transmitted, and a second time domain, in which non-real time-critical data can be transmitted. To be able to ensure the required time precision in such a system, the points in time of transmitting or relaying the real time-critical data or real time-critical data telegrams are scheduled. The PROFINET IRT Standard provides in this regard that the forwarding, sending and receiving points in time of the real time-critical data telegrams to be transmitted are saved in all participating coupling equipment and consumers, which capable of relaying, sending and/or receiving the real time-critical data telegrams, and namely more advantageously before the start of the data transmission. Coupling equipment and consumers must therefore be capable of forwarding and/or sending PROFINET IRT data telegrams in the millisecond range. To be able to maintain the precision scheduling of times for transmission and forwarding, the coupling equipment and consumers need special hardware components, which are available on the market. In particular each IRT-capable coupling unit and each IRT-capable consumer have their own clocks, which are synchronized with one another using an essentially known standardized method. Such a method is defined by the IEEE 1588 standard, for example. In order not to interfere with or endanger the required time precision within PROFINET IRT systems, non-IRT-capable equipment, for example, standard Ethernet devices must not be used between the IRT-capable coupling equipment and IRT-capable consumers.
The detailed design and functioning of such a real time-controlled Ethernet data network according to the PROFINET IRT Standard are disclosed in EP 1 388 238 B1, for example, and are sufficiently well known by those skilled in the art.
The present invention is now based on the problem providing a communication system and a method for isochronous data transmission with which components that are not capable of a real time-controlled data transmission can transmit real time-critical data over a real time-controlled Ethernet data network without any impairment of the time precision required for the real time-critical data transmission.
A basic idea of the present invention is to link up traditional communication equipment such as computers and the like which are not capable of a real time-controlled data transmission and would nevertheless like to enable real time-critical data transmission via a special bridge device to a real time-controlled Ethernet data network, for example, a PROFINET IRT system. Such communication equipment has only a communication interface, for example, a standard Ethernet interface which is not suitable for transmission of real time-critical data with the time precision required for this purpose. Furthermore, standard Ethernet communication equipment often cannot be expanded through additional cards because no more expansion sites are available due to the deep integration of Ethernet interfaces.
According to this, a communication system for isochronous data transmission is provided, comprising a real time-controlled Ethernet data network with at least one first communication device having a synchronized timer. The first communication devices are designed to transmit real time-critical data telegrams using a scheduled real time control. It should be pointed out that the first communication device may be designed as a coupling device, as a consumer or as a component having a consumer with an integrated coupling unit. In addition, a communication system comprises at least one bridge device connected to the real time-controlled Ethernet data network. At least one second communication device is connected to the bridge device by means of a non-real time-controlled communication link. Such a communication link may be a standard Ethernet connection. The second communication device has a device for supplying real time-critical data telegrams, each containing a predetermined transmission point in time and a communication interface for transmitting real time-critical data telegrams to the bridge device. The communication interface, for example, a standard Ethernet interface, a USB interface, a WLAN interface, a FireWire interface or a PCI interface—none of these support real time-controlled data transmission. The bridge device in turn has a timer that is synchronized with the timers of the first communication devices, for example, being time synchronized or cycle synchronized. In addition, the bridge device contains another device for analyzing the transmission point in time of a real time-critical data telegram coming from the second communication device and a control device which controls the forwarding of the respective real time-critical data telegram to the at least one first communication device of the Ethernet data network as a function of the transmission point in time analyzed.
It should be pointed out here that an isochronous data transmission is understood to be a transmission of data in communication cycles with a predefined adjustable duration. One advantage of this communication system may be seen in the fact that the second non-real time-controllable communication device can transmit real time-critical data to the real time-controlled Ethernet data network without disturbing the time precision required for the real time-controlled Ethernet data network. It should be emphasized here that the bridge device for relaying the real time-critical data telegrams coming from the first communication device does not require a transmission schedule.
To be able to control the forwarding of incoming real time-critical data telegrams in the bridge device at high data traffic levels, phase information is advantageously also contained in the real time-critical data telegrams supplied by the second communication device. The phase information, also known as the cycle number, denotes a certain communication cycle within the Ethernet data network. The transmission point in time which is also transmitted in such a real time-critical data telegram thus indicates the transmission point in time with respect to the defined communication cycle. In this way, real time-critical data belonging together can be sent in multiple communication cycles. The analysis unit is therefore designed for analyzing the phase information of a received real time-critical data telegram. The control unit of the bridge device controls the forwarding of the respective real time-critical data telegram in the desired communication cycle to the at least one first communication device as a function of the analyzed transmission point in time and the analyzed phase information.
An advantageous embodiment provides that the real time-controlled Ethernet data network forms a PROFINET IRT Ethernet data network. The PROFINET IRT Ethernet data network is also referred to below as an IRT domain.
In this case, the first communication devices are designed according to the PROFINET IRT Standard. In addition, the real time-critical data telegrams supplied by the second communication device have a data structure according to the PROFINET IRT Standard. This ensures that the real time-critical data telegrams supplied by the second communication device can be forwarded unchanged to the Ethernet data network.
This is achieved in particular by the fact that the transmission point in time and/or the phase information is available at a predetermined location in the payload data field of the respective real time-critical data telegram. To do so, the start of the payload data is projected accordingly and the first communication device can easily mask out this information.
To be able to forward the real time-critical data telegrams arriving in the bridge device in a targeted manner, the number of a predetermined output port of the bridge device may be contained in each of the real time-critical data telegrams supplied by the second communication device. This achieves the result that the bridge device can output received real time-critical data telegrams at the selected output ports at the transmission point in time.
To permit a compact design of the communication system, the bridge device may be implemented in a first communication device.
Furthermore, the bridge device may also perform the function of a PROFINET synchronization master or synchronization slave.
The bridge device also has a memory device for temporary storage of real time-critical data telegrams of the second communication device. This ensures that no real time-critical data telegrams to be forwarded are lost in the bridge device when more real time-critical data telegrams are arriving than being sent, for example.
To also enable data transmission from the first communication device to the second communication device, the bridge device is designed for receiving real time-critical data telegrams generated by the first communication device and for forwarding these real time-critical data telegrams to the second communication device. In order for the second communication device to be able to determine the reception time of a real time-critical data telegram in this case, the bridge device is designed to write the reception time in a time critical data telegram coming from the first communication device.
According to this, a method for isochronous transmission of real time-critical data telegrams within a real time-controlled Ethernet data network is made available. The Ethernet data network comprises at least one first communication device that has a synchronized timer and is designed to transmit real time-critical data telegrams using a scheduled real time control.
First, at least one real time-critical data telegram is supplied to by a second communication device, wherein the real time-critical data telegram contains a predetermined transmission point in time. The real time-critical data telegram is transmitted over a communication interface of the second communication device to a bridge device connected to the Ethernet data network area. The communication interface, which may be a standard Ethernet interface, is not capable of real time-controlled data transmission. The bridge device has a timer, which is synchronized with the timer of the at least one first communication device. The transmission point in time transmitted in the received real time-critical data telegram is then analyzed in the bridge device and monitored with the help of the timer. The received real time-critical data telegram is forwarded by the bridge device to the at least one first communication device as soon as the transmission point in time has been reached.
The received real time-critical data telegram is expediently stored temporarily in the bridge device until the transmission point in time has been reached.
To enable a rapid forwarding of the real time-critical data telegram, the real time-critical data telegram is forwarded already after the analysis of the transmission point in time, namely before being completely received by the bridge device.
To be able to efficiently forward coherent real time-critical data, phase information which defines the communication cycle within the Ethernet data network is also contained in the real time-critical data telegram supplied by the second communication device. The phase information contained in the received real time-critical data telegram is analyzed in the bridge device. The real time-critical data telegram is forwarded by the bridge device to at least one first communication device, namely in the defined communication cycle and at the defined transmission point in time.
To be able to efficiently forward real time-critical data telegrams within the bridge device when there is a high level of traffic, it is advantageous to write the number of an output port of the bridge device in the real time-critical data telegram being supplied. Then the output port number contained in the received real time-critical data telegram is analyzed in the bridge device and next the real time-critical data telegram is forwarded via the selected output port of the bridge device to the corresponding first communication device, namely in the defined communication cycle and at the defined transmission point in time.
In an advantageous embodiment, the real time-controlled Ethernet data network forms a PROFINET IRT domain. In this case, the first communication devices are designed according to the PROFINET IRT Standard. In addition, the real time-critical data telegrams supplied by the first and/or second communication devices have a data structure according to the PROFINET IRT Standard.
To be able to transmit unchanged the real time-critical data telegrams supplied by the second communication device through the Ethernet data network, the transmission point in time and/or the phase information and/or the output port number is/are written at a predetermined location within the payload data field of the real time-critical data telegram.
Since the transmission point in time, the phase information and/or the output port number in the Ethernet data network are no longer needed, this data can be removed from the real time-critical data telegram before the latter is forwarded.
The present invention will now be explained in greater detail below on the basis of an exemplary embodiment in conjunction with the accompanying drawings, in which:
The real time-controlled Ethernet data network 40, which is only diagramed schematically in
To ensure a real time-controlled data transmission within the IRT domain 40, schedules containing the transmission point in time for forwarding the real time-critical data telegrams to be transmitted are stored in the coupling devices 55 and 65 in the present case. The coupling devices 55 and 65 are therefore also referred to as IRT-capable coupling devices. The connecting links which belong to the transmission points in time and by which the real time-critical data telegrams are also forwarded may optionally also be saved. The schedules are advantageously created before the actual data transmission and stored in the coupling devices. Each IRT-capable coupling devices 55 and 65 thus knows when and at which output port a real time-critical data telegram is to be sent or forwarded. To determine the precise transmission point in time, each coupling device 55 and 65 has its own clock 57 and/or 67. These two clocks are synchronized with one another. The data to be transmitted is transmitted in communication cycles with an adjustable duration. Each communication cycle is subdivided into two time domains. The real time-critical data telegrams are transmitted in the first time domain, and the non-real time-critical data telegrams are transmitted in the second time domain. The points in time when real time-critical data telegrams can be transmitted within the first time domain of a communication cycle are also fixedly predetermined. PROFINET IRT systems operate with a time precision in the μs range. Specially designed coupling devices 55 and 65 are needed to achieve this transmission accuracy. Corresponding modules with which the precise scheduling of the real time communication is ensured are already available on the market.
EP 1 388 238 B1 also discloses that consumers having only a standard Ethernet interface may be connected to an Ethernet connection of the IRT domain 40. These consumers generate only non-real time-critical data that is transmitted exclusively in the second time domain of a communication cycle without interference in the real time communication.
As already explained above, special IRT-capable hardware is required in the communication devices 50 and 60 to be able to transmit real time-critical data. Because of the deep integration of standard Ethernet interfaces, numerous communication devices, for example, PC architectures, no longer have any free expansion slots, so they cannot be used for a real time-critical data transmission within the IRT domain.
With the communication system 5 shown in
This achieves the result that standard Ethernet devices may be connected to the IRT domain 40 via an IRT bridge device 30. The IRT bridge device 30 may also be referred to as a modified Ethernet switch.
The computer 10 is designed to generate PROFINET IRT-compatible data telegrams, which can be transmitted over the IRT domain 40.
It is now necessary to ensure that the real time-critical data telegrams coming from computer 10 can be transmitted by the IRT bridge device 30 without any interference in the schedules applicable in the IRT domain 40. This is achieved by designing the computer 10 and the IRT bridge device 30 accordingly.
The computer 10 has software, which enables it to write the desired transmission point in time SZ and optionally a phase information P in the payload data field of a PROFINET IRT data telegram to be transmitted, which has the data structure shown in
The basic design of the IRT bridge device 30 is shown in
In addition, the IRT bridge device 30 has a memory 32, in which the data telegrams coming from the computer 10, which may be real time-critical and non-real time-critical data telegrams, are stored temporarily. In addition, a timer 34, which is synchronized in time with the timers 57 and 67 of the coupling devices 55 and 65, is also provided. Methods of synchronizing the timers in a PROFINET IRT system are sufficiently well known and therefore need not be described further here. It is important only that these timers are synchronized with a high precision, i.e., in the μs range, for example, to enable a chronologically precise control of drive systems. In addition, the IRT bridge device 30 may have a switching device 35, which can send real time-critical data telegrams that are to be forwarded to a certain output port of the IRT bridge device 30 as a function of the output port number contained in the payload data field. In the present example, the IRT bridge device 30 has three output ports 36, 37 and 38. Control and monitoring of the IRT bridge device 30 and its components may be executed by a programmable control unit, for example, a microprocessor 33. Furthermore, a cycle counter 39 may also be provided in the IRT bridge device 30 and can be synchronized with a cycle counter of the IRT domain 40, known as a CycleCounter.
The functioning of the communication system 5 and in particular the functioning of the IRT bridge device 30 are explained in greater detail below.
It should first be assumed that the computer 10 would like to transmit multiple real time-critical PROFINET IRT data telegrams and non-real time-critical data telegrams over the standard Ethernet interface 12. These data telegrams are transmitted, for example, over the standard Ethernet data network 20 to the IRT bridge device 30 in communication cycles according to the non-real time-capable PROFINET IRT Standard. As shown in the time chart on the left in
The output port number which indicates over which of the three output ports 36, 37 and 38 the respective real time-critical data telegram is to be transmitted may optionally be contained in the payload data field of the six real time-critical data telegrams to be transmitted. In the present example, it is assumed that the payload data fields do not contain any output port number. For this application case, the IRT bridge device 30 may be adjusted so that all real time-critical data telegrams are sent over the output port 36 to the IRT domain 40.
The analysis unit 31 can recognize the real time-critical data telegrams of the computer 10 on the basis of the “Ethernet-type PROFINET” and “FID” fields. When the analysis device 31 ascertains that the first real time-critical data telegram of the computer 10 has arrived, it reads the transmission point in time t1 and the phase information P1 out of the predetermined location in the payload data field. Similarly, the analysis unit 31 analyzes the five additional real time-critical data telegrams of the computer 10. Some or all of the data telegrams of the computer 10 may be stored in the memory 32 of the IRT bridge device 30. In addition, the information that has been analyzed and an identification of the respective real time-critical data telegrams can be saved in a lookup table in the IRT bridge device 30. The microprocessor 33 monitors the timer 34, the cycle counter 39 and optionally the lookup table.
It should be pointed out here once again that the communication cycles of the IRT domain 40 each have a first range in which real time-critical data telegrams are transmitted and a second range in which non-time-critical data telegrams are transmitted. As shown by the time chart on the right in
As soon as the microprocessor 33 has recognized that the transmission point in time t1 contained in the first real time-critical data telegram corresponds to the current time of the timer 34, and the phase information P1 corresponds to the current value of the cycle counter 39, then the first real time-critical data telegram is sent via the switch 35 to the output port 36 and from there is forwarded to the IRT domain 40 at time t1 in the first communication cycle. Depending on the destination address DA, the data telegram is transmitted to the consumer 62, for example. Similarly, the microprocessor 33 ensures that the second real time-critical data telegram is forwarded to the IRT domain 40 at the transmission point in time t2 of the first communication cycle, the third real time-critical data telegram is forwarded at the transmission point in time t3 of the first communication cycle and the fourth real time-critical data telegram is transmitted at the transmission point in time t4 of the first communication cycle. Next the three non-real time-critical data telegrams of the computer 10 may be forwarded to the IRT domain 40 in the second time domain of the first communication cycle, as shown in
In response to the results of the analysis device 31, which may be stored in the lookup table mentioned above, the microprocessor 33 knows that the fifth and sixth real time-critical data telegrams must be forwarded in the second communication cycle.
The microprocessor 33 still monitors the timer 34 and the cycle counter 39. As soon as the microprocessor 33 has recognized that the transmission point in time t1 contained in the fifth real time-critical data telegram corresponds to the current time of the timer 34, and that the phase information P2 corresponds to the current value of the cycle counter 39, the fifth real time-critical data telegram is read out of the memory 32 and sent via the switch 35 to the output port 36 and from there is forwarded to the IRT domain 40 at time t1 in the second communication cycle. Depending on the destination address DA, the data telegram is transmitted to the consumer 52, for example. Similarly, the microprocessor 33 ensures that the sixth real time-critical data telegram is forwarded to the IRT domain 40 at the transmission point in time t2 of the second communication cycle, as illustrated in
It should be pointed out here that the real time-critical data telegrams can already be forwarded by the IRT bridge device 30 as soon as the analysis device 31 has analyzed the phase information P and the transmission point in time SZ without the respective data telegram having been completely received or already stored completely in the memory 32.
In addition, it is possible that the IRT bridge device 30 can forward unchanged the real time-critical data telegrams coming from the computer 10 to the IRT domain, depending on the implementation. Alternatively, it is conceivable that the IRT bridge 30 can remove the transmission point in time SZ and optionally the phase information P as well as the output number from the payload data field before forwarding a received real time-critical data telegram because this information is then no longer needed in the IRT domain 40.
Moreover, the IRT bridge device 30 may also be arranged inside the communication device 50 or 60, for example. It is also conceivable for the IRT bridge device to also be able to perform the function of a PROFINET synchronization master, which has long been known.
In addition, it should be pointed out that the coupling devices 55 and 65 know the exact position of the payload data within a PROFINET IRT data telegram and are thus capable of masking out the phase information and the transmission point in time within a payload data field. This permits transparent forwarding of the real time-critical data telegrams supplied by the computer 10 within the IRT domain without having to make any changes in the existing hardware.
Finally, it should be pointed out that the IRT-capable communication devices can transmit real time-critical data telegrams to the bridge device 30 according to the data structure shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 027 167.5 | Jul 2010 | DE | national |
| 10 2010 052 322.4 | Nov 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/003380 | 7/7/2011 | WO | 00 | 3/25/2013 |
