METHOD FOR TRANSMITTING TIME SYNCHRONIZATION MESSAGES IN A COMMUNICATION NETWORK, NETWORK COMPONENT, AND COMMUNICATION NETWORK

Abstract

A method for transmitting time synchronization messages in a communication network between a master clock and a slave clock to be synchronized with the time of the master clock. A network component of the communication network receives the time synchronization messages on one port and sends the time synchronization messages on another port. The network component determines a dwell time of a respective time synchronization message between the receipt and the sending with an internal clock and transmits dwell-time information to the slave clock. The slave clock synchronizes to the master clock using the received time synchronization messages and the associated dwell-time information. In order to perform accurate determination of the dwell-time information in a network component with an internal clock having comparatively low accuracy, the network component suspends all other messages within a time period in which the network component expects to receive a time synchronization message.

Claims

1-9. (canceled)

10. A method for transmitting time synchronization messages in a communication network, the method comprising: transmitting time synchronization messages via the communication network between a master clock and a slave clock to be synchronized with a clock time of the master clock; receiving, with a network component of the communication network having at least two ports, the time synchronization messages at one port and dispatching the time synchronization messages via another port; determining by way of an internal clock of the network component, a dwell time of a respective time synchronization message within the network component between receiving and dispatching the time synchronization message and conveying the dwell time information specifying the dwell time to the slave clock; synchronizing the slave clock to the master clock by using the time synchronization messages and the respectively associated dwell time information; and during a time period in which the network component expects to receive a time synchronization message, suspending a dispatch by the network component of all other messages that are not time synchronization messages.

11. The method according to claim 10, which comprises continuing to dispatch the other messages after the time synchronization message expected in the period has been received and dispatched.

12. The method according to claim 10, wherein the suspending step comprises interrupting, with the network component, processing of a message queue in which the other messages are temporarily stored before dispatch.

13. The method according to claim 10, wherein the period in which the reception of a time synchronization message is expected is predetermined by the fact that the time synchronization messages are dispatched at regular intervals by the master clock and/or the slave clock.

14. The method according to claim 10, which comprises: before dispatching a time synchronization message, dispatching from the master clock and/or the slave clock an announcement message which announces a subsequent dispatching of the time synchronization message; and using the announcement message by the network component for determining the period in which to expect a reception of a time synchronization message.

15. The method according to claim 10, wherein the network component enters the dwell time information directly into the associated time synchronization message and dispatches the time synchronization message, modified with the dwell time information, instead of the time synchronization message originally received.

16. The method according to claim 10, wherein the network component enters the dwell time information into a follow-up message and dispatches the follow-up message after the associated time synchronization message.

17. A network component for operation in a communication network for transmitting time synchronization messages between a master clock and a slave clock to be synchronized with the clock time of the master clock, the network component comprising: at least two ports, including a first port configured to receive the time synchronization messages and a second port configured to dispatch the time synchronization messages; the network component being configured to determine, by way of an internal clock, a dwell time of a respective time synchronization message within the network component between receiving and dispatching the time synchronization message and to convey dwell time information specifying the dwell time to the slave clock; and the network component being configured to stop dispatching other messages which are not time synchronization messages within a period in which a reception of a time synchronization message is expected.

18. A communication network for transmitting time synchronization messages between a master clock and a slave clock to be synchronized with a clock time of the master clock, the communication network comprising: a network component with at least two ports, including a port for receiving the time synchronization messages and another port for dispatching the time synchronization messages; said network component being configured to determine, by way of an internal clock, a dwell time of a respective time synchronization message within said network component between receiving and dispatching the time synchronization message and to convey dwell time information specifying the dwell time to the slave clock; the slave clock being configured to perform a synchronization to the master clock by using the respectively received time synchronization messages and the respectively associated dwell time information; and said network component being configured to suspend dispatching other messages that are not time synchronization messages within a period in which a reception of a time synchronization message is expected.

Description

[0038] In the figures:

[0039] FIG. 1 shows a first exemplary embodiment of a communication network comprising a master clock and a number of slave clocks to be synchronized with the master clock;

[0040] FIG. 2 shows a second exemplary embodiment of a communication network comprising a master clock and a number of slave clocks to be synchronized with the master clock; and

[0041] FIG. 3 shows a diagrammatic flow chart for explaining the transmission of time synchronization messages via a network component.

[0042] FIG. 1 shows in a diagrammatic view a communication network 10 to which network-capable devices in the form of a master clock 11 and a number of slave clocks 12a-e are connected. The devices can be, in particular, automation devices of an automation system, e.g. for the automation of an electrical power supply system. This can be, for example, protective devices, measuring devices, phasor measuring devices, power meters, power quality devices, management and control devices, switch controllers etc. of an electrical power automation system. Generally, such automation devices can also be called field devices or intelligent electronic devices (LEDs). However, since the time synchronization functionality is in the foreground at this point, the devices are subsequently called master or slave clocks, respectively, from this point of view. As already mentioned previously, the term master clock also comprises the selected grandmaster clock to which lastly all devices are synchronized in the communication network.

[0043] In addition, the communication network 10 comprises a network component 13 which can be, for example, a switch, a bridge or a router having a number of ports 14.

[0044] The network component 13 represents a transparent clock in the sense of the IEEE 1588-2008 standard.

[0045] Deviating from the simplified representation according to FIG. 1, the communication network can also comprise a number of series-connected network components which represent such transparent clocks.

[0046] In the communication network 10, messages are exchanged which can contain, for example, measurement values, control commands, status messages, recorded measurement value sequences or software updates. Summarized, such messages are called other messages. In order to also perform a synchronization of the slave clocks 12a-e with regard to the master clock 11, time synchronization messages are additionally also exchanged in the communication network 10. This will be described more accurately later.

[0047] In FIG. 2, a further exemplary embodiment of a communication network 20 is shown, the communication network 20 having an annular topology in comparison with the communication network 10 of FIG. 1. FIG. 2 shows in a diagrammatic view a communication network 20 to which network-capable devices in the form of a master clock 21 and a number of slave clocks 22a-e are connected.

[0048] The master clock 21 and the slave clocks 22a-e comprise integrated network components 23 which can be, for example, integrated 3-port switches. The network components 23 also represent transparent clocks in the sense of the IEEE 1588-2008 standard since, for example, the synchronization of the slave clock 22b with the master clock 21 takes place via the network component 23 of the slave clock 22a as transparent clock.

[0049] In the communication network 20, time synchronization messages are exchanged for synchronization of the slave clocks 22a-e with regard to the master clock 21.

[0050] In addition, other messages are also exchanged.

[0051] In the text which follows, a method for time synchronization by means of time synchronization messages which are transmitted in the communication network 10 will be described by way of example by means of FIGS. 1 and 3.

[0052] The method described in the text which follows can be correspondingly transferred also to the communication network 20 or to other communication networks in which time synchronization is performed. For this purpose, a flow chart is additionally specified in FIG. 3 in which the transmission of a time synchronization message is entered along time rays. In this context, time ray 31 represents the events at the master clock 11, time ray 32 represents the events at a slave clock 12a-e (for the subsequent statements, slave clock 12a will be selected as example for the sake of simplicity) and time rays 33a and 33b represent the events at a first and a second port of the network component 13.

[0053] At a time t=t.sub.1, the master clock 11 sends a time synchronization message sync as broadcast message to the slave clocks 12a-e, among these also to the slave clock 12a. The dispatch time t.sub.1 is added to the time synchronization message sync as information. Alternatively to the direct attachment of the dispatch time, the latter could also be transmitted by means of a subsequent follow-up messageindicated by a dashed arrow 34a.

[0054] The time synchronization message sync is received at the first port of the network component 13 at time t=t.sub.1, processed internally and dispatched at the second port of the network component 13 in the direction of the slave clock 12a at time t=t.sub.1. The network component 13 then acquires the dwell time t.sub.1t.sub.1 and enters it directly into the forwarded time synchronization message sync as dwell time information. Alternatively, the dwell time informationas indicated by a dashed arrow 34b in

[0055] FIG. 3could also be entered by the network component 13 in a follow-up message and dispatched in the direction of the slave clock 12a.

[0056] The slave clock 12a receives the time synchronization message sync (and any follow-up messages 34a, 34b), acquires the receive time t=t.sub.2 and thus has the information about times t.sub.1 and t.sub.2 and about the dwell time information t.sub.1t.sub.1. In the case of a known offset OS and correctly synchronized clocks, the relation

t.sub.2(OS+(t.sub.1t.sub.1))=t.sub.1

[0057] must be fulfilled. Otherwise, the slave clock must be correspondingly corrected for time synchronization. The offset OS can be determined once or regularly according to the method explained further above.

[0058] To be able to determine the dwell time information within the network component 13, the network component has an internal clock which measures the receive time and the dispatch time of the time synchronization messages. In this context, the dwell time must be determined as accurately as possible since it is included directly in the time synchronization of the slave clocks. In particular, in a communication network with a number of series-connected network components (for example an annular communication network as specified in FIG. 2), inaccuracies namely become added together in the determination of the dwell time and thus falsify the result of the time synchronization.

[0059] So that, in order to reduce the inaccuracy in the determination of the dwell time, it is not necessary to access especially accurate and thus expensive internal clocks for the network components, the dwell time itself is influenced in such a manner that it is as short as possible. For this purpose, it is provided that the network component 13 stops the dispatch of other messages within a period at which it expects the reception of a time synchronization message from the master clock. In this way, the main cause of a long dwell time, namely the blocking of the dispatch of a time synchronization message by another message currently still to be dispatched, can be eliminated. For example, the network component interrupts the processing of a queue with other messages to be dispatched temporarily during the period in question so that the time synchronization message, when it arrives, can be forwarded directly, i.e. without having to wait for the dispatch of another message. This reduces the dwell time of the time synchronization message to an absolute minimum, as a result of which only little inaccuracies occur in the determination of the dwell time which is already short per se, even when utilizing an internal clock having comparatively little accuracy.

[0060] After conclusion of the dispatching of the time synchronization message, it is possible to continue the dispatching of the other messages directly.

[0061] The period in question, at which the reception of a time synchronization message is expected, can be derived, for example, from the time of reception of the respective last time synchronization messages in the case of a regular dispatch of the time synchronization messages by the master clock and/or the slave clocks. Alternatively, the master clock or the slave clocks, respectively, can also dispatch announcement messages which announce a speedy transmission of the next time synchronization message in each case.