U.S. patent application number 15/302241 was filed with the patent office on 2019-06-27 for redundant prp transmission system.
The applicant listed for this patent is HIRSCHMANN AUTOMATION AND CONTROL GMBH. Invention is credited to Tobias HEER.
Application Number | 20190199485 15/302241 |
Document ID | / |
Family ID | 53008456 |
Filed Date | 2019-06-27 |
United States Patent
Application |
20190199485 |
Kind Code |
A1 |
HEER; Tobias |
June 27, 2019 |
REDUNDANT PRP TRANSMISSION SYSTEM
Abstract
A method of operating a transmission system (1) having a first
network (2) and at least one second network (3) where data is
exchanged between these at least two networks (2, 3) in that data
of the first network (2) is fed to duplicating means (4), then is
transmitted wirelessly to separating means (5) via at least two
transmission paths (6, 7) by PRP, and is forwarded by the
separating means (5) to the connected second network (3),
characterized in that the data is transmitted via the first
transmission path (6) as data packets and, if a data packet was not
transmitted, this data packet is retransmitted via at least the
second transmission path (7).
Inventors: |
HEER; Tobias;
(Frickenhausen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HIRSCHMANN AUTOMATION AND CONTROL GMBH |
Neckartenzlingen |
|
DE |
|
|
Family ID: |
53008456 |
Appl. No.: |
15/302241 |
Filed: |
April 9, 2015 |
PCT Filed: |
April 9, 2015 |
PCT NO: |
PCT/EP2015/057787 |
371 Date: |
October 22, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 45/28 20130101;
H04L 2001/0096 20130101; H04L 1/22 20130101; H04L 1/08 20130101;
H04L 1/0041 20130101; H04L 1/004 20130101 |
International
Class: |
H04L 1/22 20060101
H04L001/22; H04L 12/703 20060101 H04L012/703; H04L 1/00 20060101
H04L001/00; H04L 1/08 20060101 H04L001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2014 |
DE |
10 2014 206 873.8 |
Claims
1. A method of operating a transmission system having a first
network and at least one second network where data is exchanged
between these at least two networks in that data of the first
network is fed to duplicating means, then transmitted wirelessly to
separating means via at least two transmission paths by PRP, and is
forwarded by the separating means to the connected second network,
the method comprising the steps of: transmitting the data via the
first transmission path as data packets and, if a data packet was
not received, retransmitting the unreceived data packet via at
least the second transmission path.
2. The method according to claim 1, wherein, if a data packet was
is retransmitted, it is retransmitted via the second transmission
path.
3. The method according to claim 1, or 2, wherein the
retransmission of a data packet is carried out more than two
times.
4. The method according to claim 1 further comprising the step of:
suppressing retransmission of a data packet if the transmission of
this data packet is carried out without error.
Description
[0001] The invention relates to a method of operating a
data-transmission system having a first network and at least one
second network where data is exchanged between these at least two
networks in that data of the first network is fed to duplicating
means, then is transmitted wirelessly to separating means via at
least two transmission paths by PRP, and is forwarded by the
separating means to the connected second network, according to the
features of the preamble of claim 1.
[0002] Such known transmission systems are used in safety-critical
applications in process plants, or stationary or mobile work
facilities--for example in work vehicles such as cranes or the
like.
[0003] It is important that data is reliably transmitted from the
first network to the at least one second network. This manner of
safety-critical data transmission is particularly important when
the data is transmitted via a wireless transmission path. To this
end, there has already been an improvement that consists of using
not only one transmission path, but at least two, and preferably
exactly two, transmission paths for this safety application. A
further improvement to this redundant data transmission has been
made by performing the transmission wirelessly--i.e. via radio or
light--by PRP (parallel redundancy protocol) that is a layer-2
redundancy method that is independent of higher layers and, above
all, is suitable for real-time Ethernet mechanisms.
[0004] From the perspective of safety, such a transmission system
already operates satisfactorily, because there is redundancy in the
two transmission paths. For example, if a wireless transmission
path is disturbed or fails, the--at least--second transmission path
can be used to ensure the data transfer from the first to the
second network.
[0005] However, an unacceptable disturbance in data transmission
between the two networks as concerns safety-critical aspects cannot
be ruled out in spite of this redundancy.
[0006] On the one hand, the previously described data transmission
via two, or more than two, transmission paths is advantageous with
respect to the redundancy of data transmission from the perspective
of safety. However, this parallel data transmission via at least
two transmission paths results in higher energy consumption, and
also leads to higher thermal stress on the components of the
transmission system. This leads disadvantageously to reduced
longevity of the power supply, particularly batteries, and can also
reduce the life expectancy of the components of the transmission
system considerably if they are operated under higher temperature
conditions.
[0007] When data is transmitted via transmission paths by radio,
such as WLAN, devices that work according to the 802.11 standard
allow compensation for a higher loss rate on the wireless
transmission path by repeating the transmission of lost packets on
the layer 2 level. It is necessary in this case that the receiver
of the data packets recognizes the reception of a data packet, and
reports this information back to the transmitter of the data
packet. However, this requires the sender of a data packet to know
whether a data packet has successfully arrived at the receiver
after it has been sent via the transmission path. Redundancy
requirements are not taken into account in this type of data
transmission, since only one transmission path is present.
[0008] The problem addressed by the invention is therefore that of
improving a method of operating a transmission system, in terms of
energy consumption, while simultaneously maintaining the redundancy
characteristics for safety-critical issues.
[0009] This problem is addressed by the features of claim 1.
[0010] According to the invention, the data is transmitted as data
packets via the first data path and then, if a data packet was not
transmitted, this data packet is retransmitted via at least the
second transmission path. The advantage of this is that data
packets are transmitted in succession via the first data path, and
each time that a data packet has been successfully transmitted via
the transmission path, this is acknowledged by the receiver
(separating means) and reported back to the transmitter
(duplicating means). For the transmitter, this means that it is no
longer necessary to resend a data packet via the first data path.
Only once a data packet has been sent, but has not arrived at the
receiver for whatever reason (for example because of a faulty
transmission line), this is reported to the transmitter by the
receiver that then transmits this data packet again via at least
the second transmission path--that is, not on the transmission path
on which the first transmission should have taken place. The
receiver can determine for example, after a certain time has
elapsed, that it has not received the data packet sent on the
transmission path, and can then notify the sender that a data
packet has been dropped, so that the same can once again transmit
it via the--at least--second transmission path. If this
retransmission of the data packet via the second transmission path
is confirmed by the receiver, the sender is informed that this
retransmitted data packet has arrived successfully and no
retransmission of this data packet need take place. However, if
there is a retransmission and the receipt of this retransmitted
data packet does not occur, this as well can be reported by the
receiver back to the transmitter, such that it again transmits the
data packet that has already been transmitted unsuccessfully twice,
via the second transmission path. This process can be repeated
until a data packet has been successfully transmitted from the
transmitter to the receiver.
[0011] As a complement thereto, in one implementation of the
invention if a data packet has not been transmitted, this data
packet is retransmitted, not only via the second transmission path,
but via at least two transmission paths, and preferably via exactly
two transmission paths. This manner of transmission of the data
packets is particularly significant, on the one hand, with respect
to redundancy, and on the other hand in terms of energy savings,
because a data packet can in any case be reliably transmitted from
the transmitter to the receiver, yet at the same time the number of
data packets that must be transmitted is reduced. At this point,
reference is made to FIGS. 2 and 3 that illustrate the difference
in the number of data packets transmitted, comparing the prior art
to data transmission according to the invention.
[0012] In one implementation of the invention, the retransmission
of a data packet occurs more than twice. This ensures that a data
packet is transmitted until the data packet transmitted by the
transmitter arrives successfully at the receiver. In terms of
energy conservation, the number of retransmissions can be limited.
This means that, in one implementation of the invention, the
retransmission of a data packet is suppressed if the transmission
of this data packet is carried out without error. As regards energy
consumption, the number of retransmissions of a data packet is
intended to be 2, 3 or 4. Three attempts at transmission of a data
packet is particularly advantageous, as this represents an
advantageous compromise in terms of energy consumption, on the one
hand, and on the other hand reliability and/or redundancy--as well
as the performance of data transmission.
[0013] The presented method can be applied to a transmission system
as shown in FIG. 1.
[0014] FIG. 1 shows a basic arrangement of a transmission system
comprising two networks 2 and 3 that are intended to exchange data.
This data exchange can either be unidirectional from the network 2
to the network 3 (or vice versa), or can be bi-directional between
the two networks 2 and 3.
[0015] The networks 2 and 3 can be simple or complex networks, for
example in a ring or linear topology or the like. However, it can
also be contemplated that such a network 2 or 3 comprises only a
single element, such as a sensor, an actuator, a controller or the
like.
[0016] To transmit the data of the network 2, for example to the
network 3, duplicator 4 is provided. This duplicator 4 divides the
supplied data stream into two data substreams. Then, the two data
substreams are merged after their receipt by a separator 5, and the
received data streams are forwarded to the network after merging.
The transmission of data between the duplicator and the separator 5
occurs wirelessly, by PRP, via two identical or different
transmission paths 6, 7. It can also be contemplated that one
transmission path 6 is a radio transmission path, and the second
transmission path 7 is an optical data transmission path. If both
transmission paths 6, 7 are radio transmission paths, for example,
the data--and more specifically, the data packets--can be
transmitted via these two radio transmission paths, for example on
the same frequency or different frequencies, and with otherwise
identical or differing transmission parameters. Identical
transmission paths a 6, 7 are preferable in terms of their
structure, although different transmission paths 6, 7 (for example
optical/radio, or different transmission parameters) are preferable
in terms of increasing redundancy.
[0017] After the data has been relayed by the first network 2 to
the duplicator 4 (where PRP is used, also termed the redundancy
box), it functions such that each data packet is transmitted
several times over the same transmission path 6, 7 and/or an error
correction value is assigned to each data packet. Subsequently, in
a corresponding manner, the data packets are transmitted via the
transmission paths 6, 7, and are accordingly evaluated by the
separator 5 (where PRP is used, also termed the redundancy box),
optionally processed, and relayed as data packets to the second
network 3.
[0018] The above description of FIG. 1 relates to a unidirectional
data transmission from the first network 2 to the additional, in
particular the second, network 3. For this purpose, the duplicator
4 are designed to divide the data stream, and the separator 5 to
merge the received data stream.
[0019] If data transmission from the network 3 to the network 2 is
desired, further a duplicator 4 and/or separator 5 can be included
in the transmission path between the network 3 and the network 2,
such that there is a doubled structure. Alternatively, the means 4,
5 can also be designed to double not only the relayed data stream,
but also to separate the data streams relayed via the transmission
paths 6, 7, which also applies to the separator 5.
[0020] FIG. 2 shows the manner in which data packets are
transmitted by devices that work via WLAN--that is, according to
the 802.11 standard. These devices that use the 802.11 standard,
are suitable for and designed to retransmit data packets on the
second layer to compensate for loss of data packets.
[0021] The manner of the retransmission of lost data packets with
respect to the second layer is shown in FIG. 2. The figure shows
that, if a data packet was not transmitted, this data packet is
retransmitted via the at least two transmission paths (the upper
and lower transmission paths in FIG. 2).
[0022] In this case, it is assumed that the first data packet "1"
was sent via the upper transmission path, but has been lost. For
this reason, it is marked with an X. This causes the transmitter to
retransmit this data packet "1" via the upper transmission path. At
the same time, it is also retransmitted via the further
transmission path (lower transmission path). Since the upper packet
data "1" arrives first at the receiver that is not shown, the data
packet "1" on the lower transmission path can be rejected by the
receiver. The data packet "2" is transmitted on the upper
transmission path and arrives successfully at the receiver. This is
reported back by the receiver to the transmitter, and a repeated
transmission of the data packet "2" on the upper transmission route
can be suppressed. However, since a certain time is needed until
the data packet "2" arrives at the receiver and this receipt is
acknowledged by the same, the transmitter has already had the
occasion to transmit the data packet "2" on the lower path. Since
it has successfully arrived in the meantime via the upper
transmission path, the retransmitted data packet "2" was able to be
rejected on the lower transmission route. After data packet "2", a
data packet "3," was transmitted on the upper transmission path,
and was lost. It was then retransmitted on the upper transmission
path. As it was lost again (that is, no successful data
transmission occurred for a total of three times), the transmission
of the data packet "3" on the lower transmission path was
initiated. It then successfully reached the receiver, and this was
acknowledged by the receiver such that a retransmission of the data
packet "3" was suppressed. After that, the data packet "4" was
transmitted on the upper transmission path. Since a certain amount
of time was needed in this case as well before it was received by
the receiver and the successful reception was acknowledged, it was
retransmitted via the lower transmission path again. This
retransmission can, however, be discarded.
[0023] This above-described manner in which the data is transmitted
can be repeated for each subsequent data packet, according to
whether a data packet has been successfully transmitted or not.
[0024] Because a certain amount of time is always required to
transmit a data packet sent by the transmitter via the transmission
path to the receiver, and a certain amount of time is also required
by the receiver to report the successful reception back to the
sender, it can also be contemplated that a data packet is first
transmitted via the second transmission path. This is the case in
the example according to FIG. 2, with data packet "5". Because in
this case the data packet "5" transmitted first has been lost, it
is retransmitted on this transmission path. Alternatively, it can
be contemplated that it is resent on the upper transmission path
after the first delivery on the lower transmission path. In the
case shown in FIG. 2, the data packet "5" resent on the lower
transmission path arrives successfully at the receiver, such that
retransmission does not occur. Also, for another data packet "6",
that was sent on the upper transmission path, that initially
transmitted data packet "6" is lost, such that the same procedure
is carried out as has been described above for the packet data "1".
Due to the different possibilities shown in FIG. 2, data packets
that are lost on one and/or other transmission paths can be
successfully transmitted between the transmitter and the receiver
(that is, the duplicator 4 and the separator 5 according to FIG.
1).
[0025] From the perspective of reducing energy consumption, the
type of data transmission according to FIG. 3 is of particular
interest and particularly advantageous.
[0026] In this method, the data is once again initially transmitted
as data packets via the first (upper) data path. Since the first
data packet "1" was not successful by the transmitter and receiver,
this data packet is again transmitted via at least the second
(lower) transmission path, but optionally also via the upper
transmission path. If the receiver recognizes that the data packet
"1" was successfully transmitted either via the upper transmission
path or, preferably, via the lower transmission path, this is
reported back to the transmitter. The same sends a further data
packet "2" on the upper transmission path. This data packet "2" is
successfully transmitted, such that the transmission of the next
data packet "3" can then be initiated. Because this data packet "2"
is lost on the first transmission path, it can be retransmitted on
the upper transmission path and/or the lower transmission paths
thereof. In the example according to FIG. 3, the data packet "3" is
lost on the upper transmission path, but is retransmitted
successfully one the lower transmission path. Once this has been
determined by the receiver and reported back to the transmitter, it
allows the transmission of the next data packet "4". This is
successfully transmitted via the first data path, such that a
retransmission can be suppressed, on whichever of the transmission
paths. The same applies for the following data packet "5". The same
procedure is used for the following data packet "6" as that
illustrated and described in FIG. 3 with respect to the data packet
"1".
[0027] As can be seen by examining FIG. 3, the number of
transmitted data packets, in particular on the lower transmission
path, is significantly reduced such that a significantly reduced
energy consumption and a lowering of the operating temperature is
achieved as a result. At the same time, however, it can also be
seen that all data packets "1" to "6" were reliably transmitted
from the transmitter (the first network 2) to the receiver (the
second network 3). This approach therefore achieves a reduction in
energy consumption, reduction in the operating temperature, and a
redundant data transmission, in a particularly advantageous manner
as concerns safety-critical aspects.
TABLE-US-00001 List of reference numbers 1 transmission system 2
first network 3 second network 4 duplicating means 5 separating
means 6 first transmission path 7 second transmission pat
* * * * *