U.S. patent number 9,270,481 [Application Number 13/809,195] was granted by the patent office on 2016-02-23 for communication system and method for isochronous data transmission in real time.
This patent grant is currently assigned to Phoenix Contact GmbH & Co. KG. The grantee listed for this patent is Eugen Breit, Gunnar Lessmann, Carsten Pieper, Sebastian Schriegel, Markus Schumacher. Invention is credited to Eugen Breit, Gunnar Lessmann, Carsten Pieper, Sebastian Schriegel, Markus Schumacher.
United States Patent |
9,270,481 |
Lessmann , et al. |
February 23, 2016 |
Communication system and method for isochronous data transmission
in real time
Abstract
A communication system which has a PROFINET IRT system with
first communication devices for isochronous transmission. A special
IRT bridge device is created, so that a traditional standard
Ethernet communication device can also transmit real time-critical
data over the PROFINET IRT system. The bridge device has a timer,
which is synchronized in time with the timers of the first
communication devices. In addition, a device for analysis of the
transmission point in time of a real time-critical data telegram
received by the communication device and a control unit are
provided, such that the control unit controls the forwarding of the
respective real time-critical data telegram to at least one second
communication device as a function of the analyzed transmission
point in time.
Inventors: |
Lessmann; Gunnar (Nieheim,
DE), Pieper; Carsten (Lippetal, DE),
Schriegel; Sebastian (Steinheim, DE), Breit;
Eugen (Blomberg, DE), Schumacher; Markus
(Borchen, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lessmann; Gunnar
Pieper; Carsten
Schriegel; Sebastian
Breit; Eugen
Schumacher; Markus |
Nieheim
Lippetal
Steinheim
Blomberg
Borchen |
N/A
N/A
N/A
N/A
N/A |
DE
DE
DE
DE
DE |
|
|
Assignee: |
Phoenix Contact GmbH & Co.
KG (DE)
|
Family
ID: |
44454681 |
Appl.
No.: |
13/809,195 |
Filed: |
July 7, 2011 |
PCT
Filed: |
July 07, 2011 |
PCT No.: |
PCT/EP2011/003380 |
371(c)(1),(2),(4) Date: |
March 25, 2013 |
PCT
Pub. No.: |
WO2012/007128 |
PCT
Pub. Date: |
January 19, 2012 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20130195114 A1 |
Aug 1, 2013 |
|
Foreign Application Priority Data
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Jul 14, 2010 [DE] |
|
|
10 2010 027 167 |
Nov 25, 2010 [DE] |
|
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10 2010 052 322 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
12/40013 (20130101); H04L 47/564 (20130101); H04L
12/4625 (20130101); H04L 12/4015 (20130101) |
Current International
Class: |
H04L
12/40 (20060101); H04L 12/46 (20060101); H04L
12/875 (20130101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
1572075 |
|
Jan 2005 |
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CN |
|
10228823 |
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Apr 2003 |
|
DE |
|
0243336 |
|
May 2002 |
|
WO |
|
03027784 |
|
Apr 2003 |
|
WO |
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WO03027784 |
|
Apr 2003 |
|
WO |
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03036832 |
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May 2003 |
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WO |
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Other References
Zdenek Hanzalek, et al., "Profinet IO IRT Message Scheduling With
Temporal Constraints", "IEEE Transactions on Industrial
Informatics", Jul. 1, 2010, pp. 369-380, vol. 6, No. 3, Publisher:
IEEE Service Center, New York, NY ISSN: 1551-3203, Published in:
US. cited by applicant .
Sergio Lupia, "International Patent Application No.
PCT/EP2011/003380 International Search Report", Aug. 29, 2011,
Publisher: PCT, Published in: EP. cited by applicant .
Examiner: Qin Xiaofang, "Related Chinese Application No. CN 2011
80034777.4", Dec. 3, 2014, Publisher: SIPO, Published in: CN. cited
by applicant .
Examiner: Sergio Lupia, "Related EP Application No. EP 11 731
265.2", "Examination Report", Jan. 5, 2015, Publisher: EPO,
Published in: EP. cited by applicant .
Examiner: Sergio Lupia, "Co-Pending EP Patent Application No. EP 11
731 265.2", "EP Office Action", Jan. 5, 2015, Publisher: EPO,
Published in: EP. cited by applicant.
|
Primary Examiner: Vu; Huy D
Assistant Examiner: Shao; Hong
Attorney, Agent or Firm: Kaplan Breyer Schwarz &
Ottesen, LLP
Claims
What is claimed is:
1. A communication system for isochronous data transmission,
comprising: a real time-controlled Ethernet data network having at
least one first communication device, which has a synchronized
timer and is designed to transmit real time-critical data telegrams
using a scheduled real time control; at least one bridge device;
and at least one second communication device that is connected to
the bridge device and has a device for supplying real time-critical
data telegrams, each of which contains a predetermined transmission
time, and that has a communication interface by means of which the
real time-critical data telegrams are transmitted to the bridge
device, wherein the transmission time is a time at which the bridge
device has to forward a data telegram to the first communication
device after previously having received the data telegram from the
second communication device, and the communication interface does
not support any real time-controlled data transmission, and wherein
the bridge device comprises: (i) a timer, which is synchronized
with the timer of the first communication device, (ii) a device for
analyzing the transmission time of a real time-critical data
telegram sent by the second communication device, and (iii) a
control device, which controls the forwarding of the real
time-critical data telegram to the at least one first communication
device of the Ethernet data network as a function of the
transmission time included in the real time-critical data telegram,
so that the bridge device does not require a transmission schedule
for forwarding the real time-critical data telegrams.
2. The communication system according to claim 1, wherein the real
time-critical data telegrams supplied by the second communication
device each contain phase information, which defines the
communication cycle within the real time-controlled Ethernet data
network; and wherein the analysis device is designed for analyzing
the phase information of a real time-critical data telegram
received by the second communication device and the control unit
controls the forwarding of the respective real time-critical data
telegram in the desired communication cycle to the at least one
first communication device of the Ethernet data network as a
function of the analyzed transmission time and the analyzed phase
information.
3. The communication system according to claim 1, wherein the real
time-controlled Ethernet data network forms a PROFINET IRT-based
Ethernet data network; wherein the at least one first communication
device is designed according to the PROFINET IRT Standard; and
wherein the real time-critical data telegrams supplied by the
second communication device have a data structure according to
PROFINET IRT Standard.
4. The communication system according to claim 3, wherein the
transmission time and/or the phase information appear(s) in a
predetermined location in the payload data field of a respective
real time-critical data telegram.
5. The communication system according to claim 1, wherein the
number of a predetermined output port of the bridge device is
contained in the real time-critical data telegrams supplied by the
second communication device.
6. The communication system according to claim 1, wherein the
bridge device is implemented in a first communication device.
7. The communication system according to claim 1, wherein the
bridge device performs the function of a PROFINET synchronization
master or a synchronization slave.
8. The communication system according to claim 1, wherein the
bridge device has a memory device for temporary storage of real
time-critical data telegrams received from the second communication
device.
9. The communication system according to claim 1, wherein the
bridge device is designed for reception of real time-critical
telegrams, which are generated by the first communication device,
and for forwarding these real time-critical data telegrams to the
second communication device.
10. The communication system according to claim 9, wherein the
bridge device is designed to write the respective reception time
into the time-critical data telegrams arriving from the first
communication device.
11. The communication system according to claim 1, wherein the
communication interface is a standard Ethernet interface, a USB
interface, a WLAN interface, a FireWire interface or a PCI
interface.
12. A method of isochronous transmission of real time-critical data
telegrams within a real time-controlled Ethernet data network,
which contains at least one first communication device having a
synchronized timer, the first communication device being designed
to transmit real time-critical data telegrams using a scheduled
real time control, the method comprising: supplying by a second
communication device of at least one real time-critical data
telegram in which a predetermined transmission time is included,
the transmission time indicating a time at which a bridge device
has to forward the data telegram to the first communication device
after previously having received the data telegram from the second
communication device; sending the real time-critical data telegram
over a communication interface of the second communication device
to the bridge device, which is connected to the real
time-controlled Ethernet data network and has a timer that is
synchronized with the timers of the first communication devices,
wherein the communication interface does not support a real
time-controlled data transmission; analyzing in the bridge device
the transmission time that is transmitted in the received real
time-critical data telegram; monitoring the transmission time with
the help of the timer; and forwarding the received real
time-critical data telegram from the bridge device to the at least
one first communication device of the Ethernet data network at the
transmission time included in the real time-critical data telegram,
so that the bridge device does not require a transmission schedule
for forwarding the real time-critical data telegrams.
13. The method according to claim 12, wherein the received real
time-critical data telegram is stored temporarily in the bridge
device until the transmission time is reached.
14. The method according to claim 12, wherein the real
time-critical data telegram is forwarded already after analysis of
the transmission time and before it has been received completely in
the bridge device.
15. The method according to claim 12, wherein the real
time-critical data telegram supplied contains phase information,
which defines the communication cycle within the Ethernet data
network; wherein the phase information contained in the received
real time-critical data telegram is analyzed; and wherein the real
time-critical data telegram is forwarded from the bridge device to
the at least one first communication device of the Ethernet data
network in the defined communication cycle and at the defined
transmission time.
16. The method according to claim 12, wherein the number of an
output port of the bridge device is contained in the real
time-critical data telegram supplied; wherein the output port
number contained in the received real time-critical data telegram
is analyzed in the bridge device; and wherein the real
time-critical data telegram is forwarded via the selected output
port of the bridge device to the at least one first communication
device of the Ethernet data network in the defined communication
cycle and at the defined transmission time.
17. The method according to claim 12, wherein the real
time-controlled Ethernet data network forms a PROFINET IRT-based
Ethernet data network; wherein the at least one first communication
device is designed according to the PROFINET IRT Standard; and
wherein the real time-critical data telegrams supplied by the
second communication device have a data structure according to the
PROFINET IRT Standard.
18. The method according to claim 17, wherein the transmission time
and/or the phase information and/or the output port number is/are
written in a predetermined location within the payload data field
of the real time-critical data telegram.
19. The method according to claim 12, wherein the transmission
time, the phase information and/or the output port number are
removed from the real time-critical data telegram before forwarding
of same.
Description
FIELD OF THE INVENTION
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.
BACKGROUND OF THE INVENTION
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.
SUMMARY OF THE INVENTION
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.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 shows an exemplary communication system, in which the
invention is implemented,
FIG. 2 shows a detailed block diagram of the IRT bridge shown in
FIG. 1,
FIG. 3 shows the data structure of a PROFINET IRT data
telegram,
FIG. 4 shows a modified data structure of the data telegram
illustrated in FIG. 3 in which the transmission point in time and
phase information are written into the payload data field, and
FIG. 5 time charts to illustrate the functioning of the IRT
bridge.
DETAILED DESCRIPTION
FIG. 1 shows an example of a communication system 5, which can be
used to control complex industrial drive systems in an automation
environment. For control of such drive systems, it must be possible
to transmit real time-critical data in very short cycle times, for
example, in the .mu.s range. To this end, a real time-capable data
transmission system on an Ethernet basis was developed under the
name PROFINET IRT, which was mentioned with its essential features
in the introduction to the description. Such a PROFINET IRT system
is preferably a component of the communication system 5. This
system is labeled with reference numeral 40 in FIG. 1. This area of
the communication system 5 is referred to below as an IRT domain or
a real time-controlled Ethernet data network 40. The data network
40 may be a switched Ethernet data network. Those skilled in the
art will be familiar enough with the design and functioning of a
PROFINET IRT system, so that a detailed description is not
necessary at this point. Such a PROFINET IRT system is disclosed in
EP 1 388 238 B1 in particular.
The real time-controlled Ethernet data network 40, which is only
diagramed schematically in FIG. 1, is indicated by three Ethernet
connections 70, 75 and 77, to which are connected, for example, two
IRT-capable, i.e., real time-controllable communication devices 50
and 60. Each of these IRT-capable communication devices 50, 60
comprises a consumer 52 or 62, respectively, and has an essentially
known coupling device 55 or 65, respectively. The consumers 52 and
62 may be essentially known IRT IO devices (slaves) such as
actuators, sensors, drive systems and the like, IRT IO controllers
(masters), computers and the like. It should be pointed out that
consumers and coupling devices may also be separate communication
devices.
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 .mu.s 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 FIG. 1, it is now possible
for even devices that do not have IRT-capable equipment but instead
only have a communication interface which does not support real
time-controlled data transmission to supply real time-critical data
telegrams that can be transmitted over the IRT domain 40. Such a
communication interface in the present example is a standard
Ethernet interface. This does not interfere with the real
time-critical data communication guaranteed by the PROFINET IRT
system.
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.
FIG. 1 shows a non-IRT-capable communication device, for example, a
traditional standard Ethernet computer 10. The computer 10 contains
only one standard Ethernet interface 12 by means of which it is
connected to the IRT bridge device 30 via an Ethernet cable of a
standard Ethernet data network 20. It should be pointed out that
multiple standard Ethernet devices can be connected to the IRT
bridge device 30 or to another IRT bridge device via the standard
Ethernet data network 20. The term "standard Ethernet data network"
expresses the fact that real time-critical data cannot be
transmitted with a high time precision over such a data network. It
should be pointed out that in the present case the standard
Ethernet data network and the standard Ethernet computer are used
only as examples of devices that do not have any IRT
capability.
The computer 10 is designed to generate PROFINET IRT-compatible
data telegrams, which can be transmitted over the IRT domain 40.
FIG. 3 shows an example of a data structure of a PROFINET IRT data
telegram. The IRT-capable communication devices 50 and 60 can
transmit such data telegrams. The PROFINET IRT data telegram shown
here contains a header, which has the destination address DA and
the source address SA, for example. Instead of the destination
address DA, an MCFF address which supports the MultiCast Fast
Forwarding Technology of the PROFINET IRT system, which is known
per se, may also be used. The "VLAN" and "PRIO2" data fields serve
to control non-real time-critical data telegrams. The coupling
devices 55 and 65 and also the IRT bridge device 30 can recognize
PROFINET IRT data telegrams on the basis of the data fields
"Ethernet-type PROFINET" and "FID." In addition, the PROFINET IRT
data telegram shown here contains a payload data field, a padding
field and a checksum field FCS. The padding field is necessary so
that the data telegram is no less than 64 bits even if the payload
data length is smaller. Ethernet compatibility can therefore be
guaranteed. As already mentioned, the coupling devices 55 and 65
have schedules which stipulate precisely when a PROFINET IRT data
telegram is to be sent. No such schedule is provided in the IRT
bridge device 30.
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 FIG. 4. The
phase information P corresponds to the number of a communication
cycle within the IRT domain 40. In addition, the computer 10 can
also write the number of an output port of the IRT bridge device 30
in the payload data field. The phase information P, the
transmission point in time SZ and the output port number stand at a
predetermined location within the payload data field, so that the
IRT bridge device 30 can read this information out of the payload
data field of a received data telegram.
The basic design of the IRT bridge device 30 is shown in FIG. 2.
The IRT bridge device 30 has an analysis unit 31, which can analyze
the transmission point in time, the output port number and the
phase information contained in the payload data field of a received
PROFINET IRT data telegram. It should be emphasized here that the
transmission point in time, the phase information and the output
port number are all information for the IRT bridge device for time
control of real time-critical data telegrams of the computer
10.
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 .mu.s 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 FIG. 5, the computer 10 sends six real time-critical
modified PROFINET IRT data telegrams, for example, over its
standard Ethernet interface 12, the data structure of which is
shown in FIG. 4 as an example, and sends three non-real
time-critical data telegrams in a communication cycle to the IRT
bridge device 30. To do so, the computer 10 writes at least the
desired transmission point in time in the payload data field of
each real time-critical data telegram. In the present example, the
computer 10 writes the phase information P1 and the transmission
point in time t1 into the payload data field of the first real
time-critical data telegram. This information goes to the IRT
bridge device 30 of the communication cycle and the transmission
point in time within this communication cycle when the real
time-critical data frame must be transmitted. Similarly, the
computer 10 writes the phase information P1 and a different point
in time t2 in the payload data field of the second real
time-critical data telegram to be transmitted. The computer 10
writes the phase information P1 and the transmission point in time
t3 in the payload data field of the third real time-critical data
telegram to be transmitted while the payload data field of the
fourth real time-critical data telegram to be transmitted contains
the phase information P1 and the transmission point in time t4. In
other words, the first four real time-critical data telegrams
should be forwarded at four different times within the first
communication cycle from the IRT bridge device 30 to the IRT domain
40. The payload data field of the fifth real time-critical data
telegram to be transmitted contains the phase information P2 and
the transmission point in time t1. The phase information P2
indicates that this real time-critical data telegram must be
transmitted in the second communication cycle of the IRT domain 40.
Finally, the payload data field of the sixth data telegram to be
transmitted contains the phase information P2 and the transmission
point in time t2. These six real time-critical data telegrams to be
transmitted may all have the data structure of a modified PROFINET
IRT data telegram as shown in FIG. 4.
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 FIG. 5, the first time domain of a
communication cycle of the IRT domain 40 comprises four
transmission points in time T1, T2, T3 and T4, which are fixedly
defined.
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 FIG. 5.
The IRT bridge device 30 recognizes the non-real time-critical data
telegrams of the computer 10 on the basis of the data in the "VLAN"
and "PRIO" fields of a PROFINET IRT data telegram. The PROFINET
rules for transmission of non-real time-critical data telegrams,
which are essentially known, are taken into account here by the IRT
bridge device 30.
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 FIG. 5.
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 FIG. 3. Depending on the implementation, the bridge device
30 can write the respective reception time into the received real
time-critical data telegrams before forwarding the data telegram to
the computer 10.
* * * * *