WO2010133637A2

WO2010133637A2 - Method for transmitting data

Info

Publication number: WO2010133637A2
Application number: PCT/EP2010/056894
Authority: WO
Inventors: Wolfram Kress
Original assignee: Wolfram Kress
Priority date: 2009-05-19
Filing date: 2010-05-19
Publication date: 2010-11-25
Also published as: DE102009021908B4; WO2010133637A3; DE102009021908A1

Abstract

The invention relates to a method for transmitting data over an Ethernet network by means of coupling units, wherein participants, for example automation devices, exchange data. Outbound data telegrams which are not to be exclusively preferred are aborted by the coupling units if in the coupling unit inbound data telegrams which are to be exclusively preferred require the same output port. The coupling units can be switched between two modes. In the interruption mode, inbound data telegrams which are to be exclusively preferred interrupt outbound data telegrams which are not to be exclusively preferred if the inbound data telegrams require the same output port of the coupling unit. In the standard mode, the data telegrams which are not to be exclusively preferred are not interrupted.

Description

Method for transmitting data

The invention relates to a method for transmitting data in an Ethernet by means of coupling units.

A coupling unit may for example be a switch.

DE 10 2006 021 930 describes a method in which automation devices can exchange messages within a guaranteed period of time by means of special switches, referred to below as RT switches (real-time swatches). The time determinism is brought about by means of special RT switches by recognizing these exclusively preferred, ie high-priority automation telegrams, forwarding them in the cut-through method and terminating low-priority Ethernet telegrams which occupy the output port of a switch claimed by the automatic telegram telegram. In order not to disturb the quality of the message exchange in the Ethernet, the aborted Ethernet telegrams in the RT switch are completely buffered until they have been completely transmitted. This method enables a deterministic data exchange in an Ethernet, without having to make special demands on the participants of the network. All participants can be equipped with standard Ethemet interfaces. The deterministic data transport described in DE 10 2006 021 930 is preferred by the Automatic message telegrams (or real-time telegrams) before low-priority message telegram (or non-realtime telegrams).

A disadvantage of this method is that the bandwidth that is available for non-reaitime telegrams or remains, is reduced and under certain circumstances non-real-time telegrams can not be transmitted or only very delayed. Such a situation can arise as follows:

Automation solutions based on Ethernet usually work according to the producer / consumer process. This means that sensors "publish" their data to the Ethernet at fixed times and thus act as producers.The controllers or processing units consume this data to a receiver and in turn publish the result of their processing into the network.Actuators, such as drives, consume them Results and perform appropriate functions.

In the case of PLC control, it can generally be assumed that all processing results are output directly one after the other. As shown in Figure 1, this results in an ideal network load in favor of unscheduled non-realtime telegrams. These are forwarded with high probability as long as the entire network load (real-time telegram runtime plus non-realtime telegram runtime) is below 100%

The situation is different, however, in the case of the data produced by the sensors in the network. Even if the times at which each sensor sends its data into the network were planned equidistantly in time and all sensors start their cycles together at the start time of the automation system, it can not be assumed that a load distribution over a longer period of time, as in FIG shown, can be guaranteed. The real-time telegrams are distributed over the cycle time z over time, which generally corresponds to the cycle time of the process control. The distribution depends on the timers integrated in each sensor. At the start of the automation system, a synchronized time in the system can still be assumed. However, because generally the times of the participants are not re-synchronized, the timers do not run equally well due to differences in hardware and environmental conditions. Thus, in the worst case, a distribution of the real-time telegrams equidistant over the cycle time z, as shown in Fig. 2. Unless the time gaps between the ReaStime telegrams in this bad case! are smaller than the duration of a non-realtime telegram, it is in the previously described method no longer possible to transmit non-realtime telegrams, although the total claimed bandwidth can be well below 100%. This can cause the network to become unavailable for longer non-real-time message rooms,

The object of the invention is to provide a method for transmitting data in an Ethernet, in particular between automation devices, in which a temporal determinism with respect to the transmission time can be achieved, and in which the transmission of non-exclusively preferable data telegrams can be improved.

The object is achieved according to the invention by the features of claim 1.

In a method for transmitting data in an Ethernet by means of coupling units, eg switches, participants, for example automation devices, exchange data. On the part of the coupling units, exclusively preferable data telegrams (real-time telegrams) are preferably forwarded in the cut-through mode. As a result, a very fast transmission of these data telegrams can be ensured. Excise-preferred data routers are identified as such in their protocol header and are preferably treated against non-exclusively preferable data telegrams. According to the invention, the coupling units can be switched between two modes. In the first mode, an interrupt mode is defined in which expiring, not exclusively preferable, data telegrams are aborted by the copy units if incoming, exclusively preferable data telegrams in the coupling unit require the same output port.

The second mode defines a basic mode in which non-exclusively preferable data telegrams are not interrupted. A time-determinable delay of the exclusively preferable data telegrams occurs through non-exclusively preferable data telegrams which are sent on the claimed output port of the coupling unit. This takes place in that excellently preferable data telegrams on their way through the entire network experience only a pre-definable, limited number of delays due to data telegrams which are not to be preferred. This time-determinable delay occurs only in the basic mode, it being possible to regulate the switching between the basic mode and the interruption mode by various methods described below. In particular, it is possible to determine the point in time at which switching from the basic mode to the interrupt mode in a coupling unit takes place on the basis of various methods. This is preferably done when the coupling units operate by default in the basic mode and are switched only under certain conditions in the interruption mode. Alternatively, it is possible to operate the copy units by default in the interrupt mode, wherein the length of the interrupt mode or the frequency of switching to the basic mode can be made on the basis of various criteria described below. In a first embodiment of the method according to the invention, a delay threshold v is defined which defines how often an exclusively preferable data telegram on its way through all coupling units by a non-exclusively preferable data telegram that is sent on the output port of a coupling unit that exclusively to preferred data telegram claimed may be delayed. Thus, it is possible, for example, to specify by means of the delay threshold value v that a data telegram which is to be preferred exclusively may be delayed a maximum of 3, 2 or 1 times. One or more coupling units are switched from the basic mode to the interrupt mode when an exclusively preferable data telegram in this coupling unit claims an output port, which is occupied by an outgoing, not exclusively preferable data message and the exclusively preferable data telegram by previous coupling units already v times delayed has been. Preferably, switching to the interruption mode takes place only under this condition, whereby in the described embodiment the coupling units are operated by default in the basic mode. Due to the features mentioned, it is possible to transmit exclusively preferable data telegrams in a time-determinable manner, whereby the desired maximum delay of these telegrams can be effected by a suitable choice of the delay threshold value v.

In the first embodiment, it is particularly preferred to enter the number of delays which have hitherto taken place by data telegrams which are not exclusively preferable in preceding coupling units in the header of each data telegram to be preferred. This can preferably be done instead of the quality of service priority bits according to IEEE 802.1 p / Q. These can be set to zero in the header of the exclusively preferred data program. This can be done, for example, when such a data telegram enters an Ethernet, which is spanned by the coupling units according to the invention. Every time, if that _ g ~

may be delayed by a non-exclusively preferable Datenteieegramm, the Quaiity of Service priority bits can be increased by the value of 1. This is done by each coupling unit in which the respective delay takes place. Furthermore, in the case of an incoming data telegram which is to be preferred, each coupling unit checks whether the value of the quality of service priority bits is> than the number of delays that have occurred so far. If this is the case, the respective coupling unit is switched to the interrupt mode when the exclusively preferable data telegram claims the same output port as a non-exclusively preferable data telegram.

In other words, non-exclusively preferable data telegrams exclusively delay preferred data telegrams on their way through the spanned network only with a predetermined, definable frequency or number. Non-exclusively to be preferred Datenenteiegramme are therefore not terminated by the coupling units only when incoming, exclusively preferable data telegrams were delayed as determined by the delay threshold v in the coupling units due to expiring, not exclusively preferable Datenenteiegramme.

The described method does not require fixed cycles in which switching between the two modes.

In an alternative embodiment, two modes are determined within a repeating data transfer cycle. In the interrupt mode, expiring, not preferable, data programs are interrupted as long as incoming, exclusively preferable data telegrams claim the same output port in the coupling unit. In Gruπdmodus, however, the non-exclusively preferable data telegrams are not interrupted. Again, preferably the IMon-Reaitirne telegrams are cached until they have been completely sent by a coupling unit. The interrupt mode is called pass-through mode, while the basic mode is called standard mode. In standard mode, real-time telegrams can not interrupt non-realtime telegrams. This ensures that even non-realtime telegrams can be forwarded. The temporal determinism of the data transport of reaitime telegram menus is still preserved, since it is ensured that a real-time telegram is only delayed once on its way through all coupling units by the standard mode.

Preferably, in the subsequent coupling unit aborted data telegrams are detected as incomplete and destroyed.

The exclusively preferable data telegrams can be forwarded by the coupling units independently of the method of prioritized data transport according to IEEE 802.1 p / Q with the highest priority, for example, according to the strict priority queuing strategy.

It is preferred that the coupling units are synchronized with one another and the switching between the two modes takes place simultaneously in the coupling units and in particular at predetermined time intervals,

The length of the basic mode is preferably selected such that a maximum length of non-exclusively preferable data telegrams within the basic mode can be forwarded from one coupling unit to the next. For example, the length of the interrupt mode can be 850 μs and the length of the basic mode 150 μs in a Fast Ethernet system.

Particularly preferably, a coupling unit in the network can send a synchronization command for switching between the interrupt and the basic mode. This synchronization command can be used by all Coupling units are treated as exclusively preferable data telegram. Furthermore, this Synchronisϊerungsbefehl can be output at equal intervals.

It is particularly preferred that the synchronization command is only output to a changeover to the basic mode by a coupling unit if non-exclusively preferable data telegrams have been interrupted n times within a communication cycle in this coupling unit. This means that a threshold is set for a maximum number of interrupts of non-exclusive data telegrams. As soon as this threshold value is exceeded, the respective coupling unit outputs a synchronization command for switching to the basic mode. For example, this can be done after 3, 5 or 7 interruptions. Optionally, only the affected coupling unit or several or all Kopepeleϊnheiten be switched.

The temporal synchronization of the coupling units can be done for example by means of the method described in IEEE 1588. In the above assumed times of 850 μs for the pass-through mode and 150 μs for the standard mode results in a cycle time z of one ms, which corresponds to a very fast PLC control cycle.

The synchronization command for switching to the basic mode can be output via Muiticast or broadcast. This synchronization command can also be provided with an identifier which enforces the preferred message traffic in pass-through mode. Preferably, a switching of the Koppeieinheit that has sent the synchronization command or more or ailer coupling units in the basic mode, if within a waiting time m no further synchronization command of another coupling unit is received. After switching to the second time interval others can Coupling units only after a waiting time w send a re-Synchrontsierungsbefehi for switching to the basic mode.

The proposed Umschaitlösungen ensure that a real-time Teiegramm on its route through the network at most once by the time y, namely the length of the standard mode, can be delayed. The time of the deterministic data transport of real-time telegrams thus increases by a maximum of time y per cycle time z. For example, a message transport time of max. 1 ms can be guaranteed for z = l ms and y = 0.15 ms for a pass-through tent for RT telegrams in pass-through mode of x = 0.85 ms. This applies on the condition that all real-time telegrams can be sent cyclically within the configured pass-through time. This requirement can be met, since the message traffic of automation telegrams can be assumed to be cyclically constant and it is thus known which times are to be assumed for the value x.

In the following, preferred embodiments of the invention will be explained with reference to FIG.

Show it:

Fig. 1, the distribution of real-time and non-real-time telegrams to

Beginning of an automation process,

FIG. 2 shows the distribution of real-time and non-real-time telegrams during an automation process, and FIG

Fig. 3 shows the division of the cycle time z into a first and a second

Time interval. As can be seen from FIG. 3, in the worst case it may happen that real-time part programs are distributed uniformly over the cycle time z. In this case, the time intervals between the reaitime telegrams can have a length that is shorter than the transmission time of a non-realtime telegram. In this case, a non-realtm telegram could not be forwarded even though the total claimed bandwidth is below 100%. In the second embodiment of the invention, non-realtime telegrams are interrupted in the first time interval, which corresponds to the interrupt mode, ie during the pass-through mode x, by incoming real-time telegrams which claim the same output port in a coupling unit. During the second time interval, namely the standard mode (basic mode), on the other hand, there is no interruption of real-time telegrams.

The first embodiment of the method according to the invention can be realized, for example, as follows: If an exclusively preferable data telegram (a real-time telegram) enters the first switching unit, namely the first switch of the network, it is recognized and the quality of service priority bits according to IEEE 802.1 p / Q is set to zero (000) in the V-Lan tag. All switches in the network are given an example that real-time telegrams may only be delayed three times on their way through the network. As long as this value (011), which can be checked by each switch, is not reached, the switch does not abort the non-realtime telegrams. D, h. A real-time telegram may have to wait in a switch until a non-realtime telegram has been completely sent on the corresponding output port. In this case, the value (numerator) of the quaiity of service priority bits is incremented by 1 (001). If the specified value (here three times = 011) is reached, the real-time telegram is transported on the network without adverse delays. This means that all non-realtime telegrams sent on a claimed output port in a coupling unit are aborted. In this example, the reait telegram would be worst case _ 1 i _

delayed three times by non-realtime telegrams with a maximum length of 1,500 bytes. This corresponds to a delay time of approximately three times 125 μs = 375 μs in the case of a 100 Mbit Fast Ethernet. This time must be added to the pure cycle time of the reaitime telegrams (as described in DE 10 2006 021 930). The deterministic message transport of exclusively preferred data telegrams is thus retained.

Since the prioritization in the V ~ Lan tag of most automation telegrams, which are treated as exclusively preferable data telegrams, is known, the last switch to be passed can reassign the original priority value to the leaving real-time telegram.

Alternatively, further methods for the above-described marking are conceivable. For example, Such labeling can be done in the V-Lan field (12 bit). Alternatively, the real-time frame can be extended by the first switch, whereby the tag is removed from the last switch to be traversed in the network.

In the method just described, there is the possibility that a first exclusively preferable data telegram, which has already been delayed v times, by another exclusively preferable data telegram, which has been delayed, for example, not or less, and even to a non-exclusively preferable data telegram waiting, being handicapped. This situation would lead to a destruction of determinism. If, for example, the quality of service priority bits are evaluated, in the case described, the first data telegram to be exclusively preferred has the higher priority. Since the second exclusively preferable data telegram is in the queue, the switch prefers the first telegram and this can cancel the non-exclusively preferable data telegram. This means that in this case the first exclusively preferable data telegram is the second exclusive to overtake preferred data telegram in the queue and then cancel the non-exclusively preferable data telegram.

The methods described in the present application can be combined as desired.

Claims

claims

1, Method for transmitting data in an Ethernet using

Coupling units, in soft subscriber exchange data,

wherein exclusively preferable data sources are identified as such in their protocol header and are treated preferentially over non-exclusively preferable data telegrams,

wherein the coupling units are switchable between two modes,

wherein, in an interrupt mode, expiring, not exclusively preferable data telegrams are aborted by the Koppeieinheiten when incoming, exclusively preferable data telegrams in the coupling unit claim the same output port, and

data telegrams which are not exclusively preferable in a basic mode, so that a time-determinable delay of the exclusively preferable data telegrams occurs due to non-exclusively preferable data telegrams which are sent on the claimed output port of the coupling unit,

characterized in that a delay threshold value v is defined which defines how often an exclusively preferable data telegram on its way through all Koppeieinheiten by a non-exclusively preferable data telegram that is sent on the output port of a coupling unit, which claims the exclusively preferable data telegram , may be delayed and one or more coupling units are switched from the Gruπdmodus in the interruption mode, when an exclusively preferable data telegram in this coupling unit a Ausgaπgsport claimed, which is occupied by an expiring, not exclusively preferable data telegram and the exclusive preferred data telegram was already delayed by previous Koppeieinheiten v,

wherein the number of delays hitherto carried out by not exclusively preferable data telegrams in previous coupling units in the header of each exclusively preferable data telegram is entered.

2. The method of claim l _f characterized in that the Quality of Service priority bits according to IEEE 802.1 p / Q in the header of exclusive preferable data telegram are set to zero and each time when the exclusive preferable data telegram by a not exclusive to-preferred data telegram is delayed to the value of 1, each coupling unit checks in an incoming, exclusively preferred data telegram, whether the value of the Quality of Service priority bits> v and, if so, switches to the interrupt mode, if the exclusive preferred data telegram claims the same output port as a non-exclusively preferable data telegram.

3. The method according to any one of claims 1 to 2, characterized in that not exclusively preferable data telegrams are stored as long as in the coupling units until they have been completely forwarded.

4. The method according to any one of claims 1 to 3, characterized in that in the subsequent coupling unit aborted data telegrams are detected as incomplete and destroyed.

5. The method according to any one of claims 1 to 4, characterized in that the exclusively preferable data telegrams regardless of the method of prioritized data transport to IEEE 802.1 p / Q with highest priority, in particular according to Strä-Priority Queuing- strategy by the KoppeSeinheiten continued become,

6, Method according to one of claims 1 to 5, characterized in that exclusively preferable data telegrams are forwarded by the coupling units in the cut-through method.