Communication device and method for operating a communication system for transmitting time critical data

Abstract

A communication device and method for operating a communication system for transmitting time-critical data, wherein a respective individual time window within predefined time intervals is specified for data flows assigned to selected control applications running on terminals, where time windows each have an individual cycle time that is a multiple of a general cycle time or corresponds to the general cycle time, first and second communication devices each check, for the selected control applications, whether a specified time window is available for data transmission, where information about a beginning of the time window within the predefined time intervals is in each case transmitted to the terminal upon which the respective selected control application is executing in the event of an available time window, and where data flows that are assigned to selected control applications are each transmitted according to the information about the beginning of the individual time window.

Claims

1. A method for operating a communication system for transmitting time-critical data, the method comprising: transmitting selected datagrams from first communication devices at source network nodes to second communication devices at destination network nodes within predefined periodic time intervals; assigning the selected datagrams to data streams and transmitting the assigned selected datagrams via paths which comprise third communication devices at intermediate network nodes; synchronizing the predefined periodic time intervals at all network nodes; specify, by terminals connected to the first communication devices, in each particular case, quality of service parameters for the data streams to reserve resources to be provided by the first and third communication devices and second communication devices; specifying, by terminals connected to the second communication devices, in each particular case, a data stream identifier for a reservation request; assuming, by each communication device along a path for a data stream of the data streams the quality of service parameters as a basis for checking, in each particular case, in an event of a reservation request, whether sufficient resources are available in the respective communication device for data transmission while observing the specified quality of service parameters; ascertaining, by configuration control units of the communication devices along a path, in each particular case, configuration information for a data stream and setting up the respective communication device for resource provision for the data streams in accordance with the ascertained configuration information if sufficient resources exist; specifying an individual time window within the predefined time intervals, in each particular case, for data streams assigned to selected control applications executing on the terminals, the time windows having, in each particular case, an individual cycle duration which is a multiple of a general cycle duration or corresponds to the general cycle duration; checking, by at least one of the first and second communication devices, in each particular case, for the selected control applications whether a specified time window is available for data transmission; transmitting information about a beginning of the time window, in each particular case, within the predefined time intervals to the terminal upon which the respective selected control application executes if a time window is available; and transmitting data streams assigned to selected control applications, in each particular case, in accordance with the information about the beginning of the individual time window.

2. The method as claimed in claim 1, wherein the resources to be provided by the communication devices comprise at least one of (i) usable transfer time windows, (ii) bandwidth, (iii) assured maximum latency, (iv) number of queues, (v) queue cache and (vi) address cache in switches or bridges.

3. The method as claimed in claim 2, wherein the communication devices are connected to one another via a time-sensitive network.

4. The method as claimed in claim 3, wherein the time-sensitive network operates in accordance with at least one of (i) Institute of Electrical and Electronics Engineers (IEEE) standard 802.1Q, (ii) IEEE standard 802.1AB, (iii) IEEE standard 802.1AS, (iv) IEEE standard 802.1BA and (v) IEEE standard 802.1CB.

5. The method as claimed in claim 1, wherein the communication devices are connected to one another via a time-sensitive network.

6. The method as claimed in claim 5, wherein the time-sensitive network operates in accordance with at least one of (i) Institute of Electrical and Electronics Engineers (IEEE) standard 802.1Q, (ii) IEEE standard 802.1AB, (iii) IEEE standard 802.1AS, (iv) IEEE standard 802.1BA and (v) IEEE standard 802.1CB.

7. The method as claimed in claim 5, wherein forwarding of the selected datagrams is controlled via at least one of (i) frame pre-emption, (ii) time-aware shapers, (iii) credit-based shapers, (iv) burst limiting shapers, (v) peristaltic shapers and (vi) priority-based shapers.

8. The method as claimed in claim 7, wherein said frame pre-emption is performed in accordance with Institute of Electrical and Electronics Engineers (IEEE) standard 802.1Qbu, said time-aware shapers is performed in accordance with IEEE standard 802.1Qbv and said credit-based shapers is performed in accordance with IEEE standard 802.1Qav.

9. The method as claimed in claim 1, wherein the data streams are set up, in each particular case, bidirectionally upon reservation requests.

10. The method as claimed in claim 1, wherein a multicast address assigned to the specified data stream identifier is transmitted, in each particular case, to a requesting terminal connected to a destination network node if sufficient resources exist.

11. The method as claimed in claim 10, wherein the reservation requests are handled in accordance with Institute of Electrical and Electronics Engineers (IEEE) standard 802.1Qcc.

12. The method as claimed in claim 11, wherein the terminals connected to source network nodes each include an assigned talker function and wherein the terminals connected to destination network nodes each include an assigned listener function.

13. The method as claimed in claim 10, wherein the terminals connected to source network nodes each include an assigned talker function and wherein the terminals connected to destination network nodes each include an assigned listener function.

14. The method as claimed in claim 1, wherein the paths for the data streams are ascertained via shortest path bridging in accordance with Institute of Electrical and Electronics Engineers (IEEE) standard 802.1aq.

15. The method as claimed in claim 1, wherein at least one of the first and second communication devices, to each of which is connected a terminal on which a selected control application executes, check, in each particular case, whether a specified time window is available for data transmission.

16. A communication device, comprising: a plurality of connections for connection to further communication devices; a coupling element via which the connections are switchably connectable to one another; wherein the communication device is configured to: transmit selected datagrams from first communication devices at source network nodes to second communication devices at destination network nodes within predefined periodic time intervals, the selected datagrams being assigned to data streams and being transmitted via paths that comprise third communication devices at intermediate network nodes, synchronize the predefined time intervals with other network nodes, assume quality of service parameters specified for a data stream as a basis for checking, in an event of a reservation request, whether there are sufficient resources available in the communication device for data transmission while observing the specified quality of service parameters, utilize a configuration control unit to ascertain configuration information and to set itself up for resource provision for the data streams in accordance with the ascertained configuration information, check, in each particular case, for selected control applications whether a specified time window is available for data transmission, wherein an individual time window within the predefined time intervals is specifiable, in each particular case, for data streams assigned to selected control applications running on terminals, the time windows having, in each particular case, an individual cycle duration which is a multiple of a general cycle duration or corresponds to the general cycle duration, transmit, in each particular case, information about a beginning of the time window within the predefined time intervals to the terminal upon which the respective selected control application executes if a time window is available, and transmit, in each particular case, data streams assigned to selected control applications in accordance with the information about the beginning of the individual time window.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is explained in more detail below using an exemplary embodiment with reference to the drawing, in which:

(2) FIG. 1 shows a communication system comprising multiple communication devices for an industrial automation system in accordance with the invention,

(3) FIG. 2 shows a schematic depiction of a distribution of individual time windows for control applications within a general cycle for periodically transmitted data frames; and

(4) FIG. 3 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(5) The communication system for an industrial automation system depicted in FIG. 1 comprises multiple communication devices 101, 102, 103. The communication devices 101, 102, 103 can be bridges, switches or routers, for example, and used for connecting programmable logic controllers 201, input/output units (I/O modules) or operating and observation stations 202 of the industrial automation system. In the present exemplary embodiment, the communication network comprising the communication devices 101-103 is designed as a time-sensitive network, in particular in accordance with IEEE 802.1Q, IEEE 802.1AB, IEEE 802.1AS, IEEE 802.1BA or IEEE 802.1CB.

(6) Programmable logic controllers 201 typically comprise, in each particular case, a communication module, a central unit and at least one input/output unit. Input/output units can fundamentally also be formed as local peripheral modules that are arranged remotely from a programmable logic controller. The communication module connects a programmable logic controller 201, for example, to a switch or router or additionally to a fieldbus. The input/output unit is used for interchanging control and measured variables between the programmable logic controller 201 and a machine or apparatus 300 controlled by the programmable logic controller 201. The central processing unit is provided in particular for ascertaining suitable control variables from captured measured variables. The above components of the programmable logic controller 201 are connected to one another via a backplane bus system in the present exemplary embodiment.

(7) An operating and observation station 202 is used for visually displaying process data or measured and control variables that are processed or captured by programmable logic controllers, input/output units or sensors. In particular, an operating and observation station 202 is used for displaying values of a control loop and for altering control parameters. Operating and observation stations 202 comprise at least a graphical user interface, an input device, a processor unit and a communication module.

(8) First automation devices, which are communication terminals connected to source network nodes and have a talker function, are used to provide information or services for use to second automation devices, which are communication terminals connected to destination network nodes and have a listener function, by way of multicast data streams. An automation device can simultaneously have both a talker function and a listener function, for example, if it firstly provides automation services and secondly uses automation services of other devices.

(9) In the present exemplary embodiment, the programmable logic controller 201 has a talker function, whereas the operating and observation station 202 has a listener function and in particular receives information provided by the programmable logic controller 201. Fundamentally, the operating and observation station 202 could analyze information received from the programmable logic controller 201 and predefine control parameters for the programmable logic controller 201 therefrom. Both the programmable logic controller 201 and the operating and observation station would therefore perform both functions. To simplify illustration, it is assumed below that both devices have only one assigned function in each particular case.

(10) Datagrams 400 selected in the present exemplary embodiment are transmitted as multicast data streams from first communication devices 101 at source network nodes to second communication devices 102 at destination network nodes via third communication devices 103 at intermediate network nodes within predefined periodic time intervals 20 (see also FIG. 2). The predefined time intervals 20 are synchronized at all network nodes, in this case. Forwarding of the selected datagrams can in particular be controlled via frame pre-emption in accordance with IEEE 802.1Qbu, time-aware shapers in accordance with IEEE 802.1Qbv, credit-based shapers in accordance with IEEE 802.1Qav, burst limiting shapers, peristaltic shapers or priority-based shapers.

(11) Terminals connected to the first communication devices 101, for example, the programmable logic controller 201, specify, in each respective case, quality of service parameters for the data streams during a data stream registration in order to reserve resources to be provided by the first, second and third communication devices 101, 102, 103. The resources to be provided by the first second, and third communication devices 101, 102, 103 comprise, for example, usable transfer time windows, bandwidth, assured maximum latency, number of queues, queue cache or address cache in switches or bridges. If data stream registration is successful or specified quality of service demands can fundamentally be met, a data stream identifier is assigned in each respective case. Terminals connected to the second communication devices 102, for example, the operating and observation station 202, specify a respective data stream identifier for a reservation request. In the present exemplary embodiment, the reservation requests are handled in accordance with IEEE 802.1Qcc. Furthermore, data streams are preferably set up, in each particular case, bidirectionally upon reservation requests.

(12) In accordance with a local approach to reserving resources for transmitting data streams, each communication device 101, 102, 103 along a path for a data stream takes the quality of service parameters as a basis for checking, in each particular case, in the event of a reservation request, whether there are sufficient resources available in the respective communication device for data transmission while observing the specified quality of service parameters. A central entity for resource management or path ascertainment is not necessary with the local approach for resource reservation for data streams. The paths for the data streams can be ascertained via shortest path bridging in accordance with IEEE 802.1aq, for example. If there are sufficient resources then a multicast address assigned to the specified data stream identifier is transmitted, in each respective case, to a requesting terminal connected to a destination network node. Moreover, if there are sufficient resources then configuration control units of the communication devices along a path ascertain, in each particular case, configuration information for a data stream and set up the respective communication device for resource provision for the data streams in accordance with the ascertained configuration information.

(13) In accordance with FIG. 2, the periodic time intervals 20 for data streams assigned to selected control applications running on terminals are overlaid, in each particular case, with individual application-specific time windows 411-417 that form a subset of a sequence of time windows 410 available in total and, in the present exemplary embodiment, have a standard duration T. The application-specific time windows 411-417 each have an individual cycle duration that is a multiple of a general cycle duration, which is 1 ms in the present exemplary embodiment. Fundamentally, the respective individual cycle duration can also correspond to the general cycle duration. By way of illustration, FIG. 2 depicts: first application-specific time windows 411 with a cycle duration of 2 ms, second application-specific time windows 412 with a cycle duration of 4 ms, third application-specific time windows 413 with a cycle duration of 8 ms, fourth application-specific time windows 414 with a cycle duration of 16 ms, fifth application-specific time windows 415 with a cycle duration of 32 ms, sixth application-specific time windows 416 with a cycle duration of 64 ms, and seventh application-specific time windows 417 with a cycle duration of 128 ms.

(14) The first and second communication devices 101, 102, check for locally assigned selected control applications, whether a respective specified application-specific time window 411-417 is available for data transmission. If a suitable time window is available, then the beginning thereof is initially ascertained, in each particular case, within the sequence of time windows 410 available in total and information about the beginning of the time window is transmitted to the terminal upon which the respective selected control application runs or executes. This means that data streams assigned to selected control applications are transmitted, in each particular case, in accordance with the information about the beginning of the individual time window. Advantageously, the first and second communication devices 101, 102, to each of which is connected a terminal upon which a selected control application runs or executes, check, in each particular case, whether a specified application-specific time window 411-417 is available for data transmission.

(15) In accordance with FIG. 2, the respective beginning of the application-specific time windows 411-417 is moved, as indicated by arrows, such that a substantially closed sequence of time windows is produced. The aforementioned synchronization of all network nodes to the periodic time intervals 20 with the general cycle duration means that the time windows have identical window positions at all network nodes. The first and second communication devices 101, 102 can therefore ascertain the beginning of the respective application-specific time windows 411-417 independently of other first, second or third communication devices 101-103.

(16) In the present exemplary embodiment, the beginning of the application-specific time windows 411-417 is placed at the following window positions, depending on the cycle duration of said time windows: at window position 1 for first application-specific time windows 411, at window position 2 for second application-specific time windows 412, at window position 4 for third application-specific time windows 413, at window position 8 for fourth application-specific time windows 414, at window position 16 for fifth application-specific time windows 415, at window position 32 for sixth application-specific time windows 416, and at window position 64 for seventh application-specific time windows 417.

(17) In sum, the beginning of application-specific time windows having a longer cycle duration can be moved such that a distributed, more homogeneous network loading is achieved.

(18) FIG. 3 is a flowchart of the method for operating a communication system for transmitting time-critical data. The method comprises transmitting selected datagrams 400 from first communication devices 101 at source network nodes to second communication devices at destination network nodes 102 within predefined periodic time intervals 20, as indicated in step 310.

(19) Next, the selected datagrams are assigned to data streams and the assigned selected datagrams are transmitted via paths which comprise third communication devices 103 at intermediate network nodes, as indicated in step 315.

(20) Next, the predefined periodic time intervals are synchronized at all network nodes, as indicated in step 320.

(21) Next, terminals 201 connected to the first communication devices 101 specify, in each particular case, specify quality of service parameters for the data streams to reserve resources to be provided by the first and third communication devices and second communication devices, as indicated in step 325.

(22) Next, terminals 202 connected to the second communication devices specify, in each particular case, a data stream identifier for a reservation request, as indicated in step 330.

(23) Next, each communication device 101, 10, 103 along a path for a data stream of the data streams assumes the quality of service parameters as a basis for checking, in each particular case, in an event of a reservation request, whether sufficient resources are available in the respective communication device for data transmission while observing the specified quality of service parameters, as indicated in step 340.

(24) Next, configuration control units of the communication devices 101, 102, 103 along a path ascertain, in each particular case, configuration information for a data stream and setting up the respective communication device for resource provision for the data streams in accordance with the ascertained configuration information if sufficient resources exist, as indicated in step 350.

(25) Next, an individual time window 411-417 within the predefined time intervals is specified, in each particular case, for data streams assigned to selected control applications executing on the terminals 201, 202, the time windows having, in each particular case, an individual cycle duration which is a multiple of a general cycle duration or corresponds to the general cycle duration, as indicated in step 355.

(26) Next, either the first and/or second communication devices 101, 102 check, in each particular case, for the selected control applications whether a specified time window is available for data transmission, as indicated in step 360.

(27) Next, information about a beginning of the time window is transmitted, in each particular case, within the predefined time intervals to the terminal 201, 202 upon which the respective selected control application executes if a time window 411-417 is available, as indicated in step 365.

(28) Next, data streams assigned to selected control applications are transmitted, in each particular case, in accordance with the information about the beginning of the individual time window, as indicated in step 370.

(29) Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.