EP3022987A1

EP3022987A1 - System of devices

Info

Publication number: EP3022987A1
Application number: EP14735562.2A
Authority: EP
Inventors: Jens NIEMEIER; Peter Schröder
Original assignee: Hanning and Kahl GmbH and Co KG
Current assignee: Hanning and Kahl GmbH and Co KG
Priority date: 2013-07-15
Filing date: 2014-07-03
Publication date: 2016-05-25
Also published as: DE202013103146U1; WO2015007528A1

Abstract

A system, having a control and/or monitoring apparatus (14) as master and devices (10) as slaves for being arranged along emergency routes or traffic routes, wherein, in a net-work chain, a first receiver (20) of a device (10) is connected to a first transmitter (22) of a predecessor through a differential signal line (32), and a second receiver (26) is connected to a second transmitter (28) of a successor through an other differential signal line (34), wherein a data packet, which is received by the first receiver (20) and is ad-dressed to an other device (10), is forwarded to the successor; a data packet, which is received by the first receiver (20) and is addressed to the own device (10), is received; response data are output through the second transmitter (28); and response data from an other device (10), which are received by the second receiver (26), are forwarded through the second transmitter (28) to the predecessor.

Description

SYSTEM OF DEVICES

The invention relates to a system comprising multiple devices for being arranged distributed along emergency routes or traffic routes. In particular, the invention relates to a system of devices in the form of a lighting system, wherein several of the devices are adapted for controlling and/or monitoring at least one lighting unit of the lighting system which is connected to the respective device.

In particular in order to improve the reliability and safety of a lighting system for emergency routes of railroad infrastructures, such as tunnels, it is desirable to monitor the functional capability of individual lighting units.

It is therefore an object of the invention to provide a device of the kind mentioned initially, which allows for a central control and/or monitoring of individual system components in a manner as robust and reliable as possible.

According to the invention, this object is solved by a system of devices according to claim 1.

Thus, data packets stemming from the control and/or monitoring apparatus may be forwarded or relayed from device to device in the first direction of communication in the chain, wherein the first transmitter of the respective device determines the signal level on the differential signal line connected thereto. In the opposite or counter direction, response data of a device may forwarded by the respective devices that are positioned between the device and the control and/or monitoring apparatus in the chain, wherein, again, the second transmitter of the respective device determines the signal level on the differential signal line. However, when a data packet from the master is addressed to the respective device, the device may transmit own response data through the second transmitter. Since the signal levels of the forwarded data are "refreshed" by each device, very high chain lengths and a large number of devices in the chain are made possible. In one embodiment, the connection of two successive devices may be effected by two differential signal lines, each having two conductors, or the connection may be effected by only a single differential signal line having two conductors.

Preferably, the transmitters and receivers comply with the interface standard EIA-485, also known as RS-485. Therein, a differential signal line in the form of a pair of conductors (twisted-pair) transmits an inverted level of a 1-bit data signal on one conductor, and a non-inverted level of the signal on the other conductor. Bits of a data packet or bits of response data are transmitted sequentially.

In a conventional RS-485 bus system, the length of the bus and the number of the devices connectable to the bus are limited to 1,2 km and up to 32 devices, or up to 128 devices using special drivers. In contrast, the structure according to the invention allows a system that extends over several kilometers, and wherein the number of the devices is not limited by a permissible load of a receiver. Moreover, by providing for a digital, differential, serial signal transmission, a high immunity to interference and a simple wiring are achieved at the same time.

Advantageous embodiments and further developments of the invention are indicated in the dependent claims. In the following, preferred embodiments are exemplified with reference to the drawings, of which:

Fig. 1 shows a schematic illustration of a lighting system;

Fig. 2 shows a schematic, simplified diagram of a network having 2-wire connections; Fig. 3 shows a schematic, simplified diagram of a network having 4-wire connections;

Fig. 4 shows a schematic illustration of a network device with galvanic isolation and relay-controlled bypass;

Fig. 5 shows a schematic illustration of a branching of the network;

Fig. 6 shows a schematic illustration for explaining a ring topology of the network; and

Fig. 7 shows a schematic, simplified diagram of a network device for the ring topology according to Fig. 6.

Fig. 1 schematically shows the structure of a system of devices in the form of a lighting system for emergency routes of railroad infrastructures, such as e.g. a tunnel. The system comprises multiple devices 10, each of which control one or more lighting units 12, wherein the devices 10 are connected to a control and monitoring apparatus or device 14 to form a network. In particular, the network comprises a chain, which, in turn, com- prises the apparatus 14 and further members in the form of devices 10.

The lighting units 12 may, for example, be light strips or light bands, which e.g. each comprise multiple light emitting diodes (LEDs) 16. For example, a lighting unit 12 may comprise a flexible light strip having light emitting diodes 16 which are encapsulated in a casing of the light strip. For example, the lighting units 12 are arranged in a row along an emergency route, and serve, in the illuminated state, for marking and illuminating the emergency route.

For example, the power supply and control of the respective lighting units 12 is effected by the respective device 10, which is assigned to the respective unit 12, through outputs

18. The apparatus 14 is adapted for outputting commands in the form of data packets to the devices 10, in particular, commands addressed to individual devices 10, and for receiving the responses that are output by a device. The commands (data packets) are forwarded from one device 10 to the next in the chain of devices 10 in the first direction of communication, as is explained in detail further below.

A response, for example in the form of response data of an addressed device 10, is forwarded in the reverse direction (second direction of communication) in the chain of devices 10, and finally reaches the apparatus 14.

For example, the apparatus 14 is adapted for querying a status signal of the individual devices 10, one after another, at time intervals, and for detecting the status of the respective device 10 based on a received response, and for detecting a failure or malfunction, e.g. a breakdown, of the respective device 10 in the absence of a response.

Furthermore, the apparatus 14 may be adapted for outputting control commands to the devices 10 for controlling the lighting units 12. Fig. 2 shows an embodiment of the network of Fig. 1, in which the connections between successive devices 10 in the chain are each implemented by only a single 2-wire connection according to the RS-485 standard. The apparatus 14 is implemented as a master device or master, and the devices 10 are each implemented as a slave device or slave. The network is configured for half-duplex operation, since a response of a device to a data packet from the apparatus 14 may only be sent back after the data packet has been completely received through the same 2-wire connections.

A first direction of communication, master-slave, is represented by an arrow A, and a second, opposite direction of communication, slave -master, is represented by an arrow B. Each device 10 in the inside of the chain has, with respect to the first direction of communication, on the input side a first differential receiver 20, also denoted as R, and on the output side a first differential sender or transmitter 22, also denoted as Ds, both of which are connected to a local control unit 24 in the form of a microcontroller. The out- put of the first receiver 20 is connected to the control unit 24, so that the control unit 24 is able to receive a signal received by the first receiver 20, in particular a data packet. For example, an enable input of the first receiver 20 is permanently set to enable. A data input ("data input") as well as an enable input ("data enable") of the first transmitter 22 are connected to the control unit 24.

When the control unit 24 receives a data packet through a first receiver 20, it determines, based on an address that is contained in the data packet, whether the data are directed to (or meant for) the own device 10. For example, the device 10 may comprises switches, e.g. one or more code switches, for setting an an address of the device 10. When the control unit 24 determines, based on the address, that the data packet is not directed to the own device 10, it activates the first transmitter 22 through the enable input thereof, and transmits the received data packet through the first transmitter 22 to the successive device 10, also denoted as the successor.

When the control unit 24 determines, based on the address, that the data packet is directed to the own device 10, it evaluates the contained data. For example, as a result of the evaluation, a controlling of the lighting unit 12 that is connected to the device 10 may be effected, and/or the control unit 24 may send a response in the form of response data to the apparatus 14, as will be explained in the following.

In the second direction of communication B, the device comprises, on the input side, a second differential receiver 26, also denoted as R, and, on the output side, a second dif- ferential sender or transmitter 28, also denoted as D_R. In the illustrated 2-wire version of the connections, both the conductors of the second transmitter 28 are connected to the two conductors of the first receiver 20 of the same device 10, and both the conductors on the input side of the second receiver 26 are connected to the two conductors on the output side of the first transmitter 22.

A data input as well as an enable input of the second transmitter 28 are connected to the control unit 24. A data output of the second receiver 26 is also connected to the control unit 24. For example, the second receiver 26 is permanently set to enable through an enable input.

In the case of a response of the control unit 24 to a received data packet, the control unit 24 activates the second transmitter 28 through the enable input thereof, and sends response data through the second transmitter 28 to the predecessor in the chain, also denoted as the preceding device, in the second direction of communication B.

After forwarding a received data packet through the first transmitter 22, the control unit 24 again deactivates or disables the first transmitter 22, so that the 2-wire connection to the successor is cleared and ready for transmitting a response in the second direction of communication B. After sending a response through the second transmitter 28, the control unit 24 again deactivates second transmitter 28, so that the 2-wire connection to the predecessor is cleared and ready for receiving a new data packet in the direction of communication A.

When the device 10 receives a response of an other device 10 through its second receiver 26, the control unit 24 receives the response data through the second receiver 26 and forwards the response data through the second transmitter 28. In this manner, the response is forwarded in the second direction of communication B. After sending the forwarded response, the second transmitter 28 is deactivated, again.

In the described manner, the apparatus 14 may address a command to one of the devices 10 and receive a response of the device, wherein the command and the response are forwarded by each of the devices 10 that are positioned therebetween in the chain. The transmitters 22, 28 and receivers 20, 26 are also termed output driver or, respectively, input drivers. In particular, they are RS-485 drivers. The output voltage of the differential signals is, for example, at least +/- 2 volts, within the limits of the absolute value of the supply voltage of the device 10, while a level difference having an absolute amount of at least 0,2 volts is still recognized as a valid signal.

Fig. 3 shows an embodiment, wherein the connections of the network each comprise two differential data lines, and, for example, are 4-wire connections.

Again, a device 10 comprises, with respect to the first direction of communication A, on the input side, the first receiver 20, which is denoted as Rs here, and, on the output side, the first transmitter 22, again denoted as Ds. The data output of the first receiver 20 is directly connected to the data input of the first transmitter 22. The first receiver 20 and the first transmitter 22 are permanently activated through the enable inputs. Furthermore, the device 10 comprises the control unit 24, which also is connected to the data output of the first receiver 20. The control unit 24 is adapted for receiving a data packet that is received through the first receiver 20, and for determining, based on an address contained in the data packet, whether the data packet is directed to the own device 10. The comparison with an own address of the device 10, and the evaluation and subsequent processing of the addressed data packet, for example, corresponds to the example of Fig. 2 as explained above, wherein differences are indicated in the following explana- tion of the interconnection of the control unit 24 with the second receiver 26 and the second transmitter 28.

With respect to the second direction of communication B, the device 10 comprises, on an input side, the second receiver 26, which is here denoted as R_R, and, on an output side, the second transmitter 28, again denoted as D_R. A data output of the second re- ceiver 26 is directly connected to a data input of the second transmitter 28. The control unit 24 is connected to the enable input of the second receiver 26. Furthermore, the control unit 24 is connected to the data input of the second transmitter 28 through a tri-state output 30. For example, the second transmitter 28 is permanently set to enable through its enable input. The control unit 24 is adapted for exclusively activating the data output of the second receiver 26 or the tri-state output 30, both of which are connected to the data input of the second transmitter 28. In Fig. 3, there are provided respective differential lines of the 4-wire connection dedicated to the first direction of communication A and the second direction of communication B, respectively. The first receiver 20 of a device 10 is connected to the first transmitter 22 of the predecessor in the chain through a first differential line 32. The second transmitter 28 of a device 10 is connected to the second receiver 26 of the predecessor in the chain through a second differential line 34 that runs parallel to the first line 32. Correspondingly, the first transmitter 22 of a device 10 is connected to the first receiver 20 of the successor in the chain through a further first line 32, and the second receiver 26 of a device 10 is connected to the second transmitter 28 of the successor in the chain through a respective further second line 34. Due to separated first lines 32 for the first direction of communication A and second lines 34 for the second direction of communication B, the network is full-duplex capable.

In this example, the data output of the first receiver 20 is directly connected to the data input of the first transmitter 22, and all data packets that are received through the first receiver 20 are directly forwarded to the successor in the chain by the first transmitter 22. There is only a minimal delay due to the gate times of the transmitters and receivers.

In the case of a data packet that is received by the control unit 24 and is addressed to the own device 10, the control unit 24 is adapted for outputting a response in the form of response data in the second direction of communication B through the tri-state output 30 and the second transmitter 28. If, however, no data packet is received that is addressed to the own device 10, the control unit 24 activates the second receiver 26. Thereby, responses of other devices 10, which are received by the second receiver 26, are directly output through the second transmitter 28, so that the response is forwarded in the second direction of communication B. Again, there is only a slight delay due to the gate times.

In the following, further developments are explained with respect to examples that have 4-wire connections. Fig. 4 schematically shows a simplified diagram of a device 10 of a chain, corresponding to the example of Fig. 3. Here, the network comprises respective galvanic isolators between the receiver 26 and the transmitter 22 of a device 10 and the receiver 20 and the transmitter 28 of a successive device 10 in the respective first and second lines 32, 34 connecting them for transmitting signals. In this example, the galvanic isolators are implemented as photocouplers 36 (optocouplers) which are schematically shown. However, a galvanic or electrical isolation can also be implemented in a different manner, for example using inductive couplers.

Furthermore, the system comprises, for each device 10, a bypass 40 that is controllable by a relay 38. The bypass 40 is adapted for bypassing the respective device 10 in the chain in the currentless or de-energized state of the relay 38. In doing so, the first line 32 that comes from the predecessor is connected to the first line 32 that leads to the successor, wherein the first receiver 20 and the first transmitter 22 are bypassed, wherein the first receiver 20 and, in particular, the first transmitter 22 are separated from the respective connection. In the same manner, the second line 34 that comes from the suc- cessor in the chain is directly connected to the second line 34 that leads to the predecessor, wherein the second receiver 26 and the second transmitter 28 are bypassed, wherein the second receiver 26 and, in particular, the second transmitter 28 are separated from the respective connection.

For example, the relay 38 is controlled by the device 10 to which it is assigned. Thus, in the case of a voltage drop at the device 10, the relay 38 automatically assumes the passive state, in which the device 10 is bypassed. In this manner, the functional capability of the network may be maintained in case of a voltage drop at the device 10 or an other fault. If the device 10, in particular the control unit 24, is adapted for executing a self test or a test of the lighting unit 12 connected thereto, the relay 38 may also be selectively controlled in order to bypass the device 10, for example, in the case of a negative test result. When the device 10 is bypassed, the device 10 will not respond to a status query of the apparatus 14 that is addressed to the device 10. Therefore, the apparatus 14 is able to detect a failure or a breakdown of the device 10.

A bypass 40 having a corresponding structure may also be provided in the version of the network having 2-wire connections according to Fig. 2.

The galvanic isolation between the device 10 and the respective relay 38 may be effected on a side directed to the successor, or an a side directed to the predecessor of the device 10.

Fig. 5 shows an embodiment of a branching of the network, which is exemplarily illustrated in the form of a simplified diagram with respect to a branching into two branches 42 and 44.

At the illustrated branching of a chain, wherein the second branch 44 branches off the chain, a device 10 is connected to two successive devices 46. For example, the respective devices 46 correspond to the devices 10. The respective first transmitter 22 of the device 10 is connected to the first input 20 of the device 46 in the first branch 42, as well as to the first input 20 of the device 46 in the second branch 44. Likewise, the second input 26 of the device 10 is connected to the second transmitter 28 of the device 46 of the first branch 42, as well as to the second transmitter 28 of the device 46 of the second branch 44.

In the two leading devices 46 of the respective branches 42 and 44, the control unit 24 are respectively adapted for determining, based on an address contained in a data packet that is received through the first receiver 20, whether the data packet is directed to a successive device 10 in the own branch of the branching. The control unit 24 of the respective device 46 is further adapted to deactivate the second transmitter 28 through its enable input, whein the control unit 24 detects, based on an the address contained in a last data packet previously received in the first direction A of communication, that the address does not belong to an address space of the successive devices 10 of the own branch 42 or, respectively, 44. For this purpose, the enable input of the second transmitter 28 is connected to the control unit 24, insofar differing from Fig. 3. In this manner, it may be ensured that for forwarding the response, which is to be forwarded in the second direction B of communication to the device 10 preceding the devices 46, only one of the second transmitters 28 of the devices 46 is active on the second connection 34 to the predecessor thereof.

In order to coordinate the enabling of the second transmitters 28 of the devices 46, or, respectively, the output of responses onto the branching connection, there may also be applied bus protocols like in a conventional RS-485 bus topology.

In case of a network having a 2-wire connection according to Fig. 2, the second transmitters 28 of the devices 46 are controlled in a corresponding manner.

Optionally, the control unit 24 of the respective device 46 may be adapted for forwarding through the first transmitter 22 a data packet, which is received through the first receiver 20, only if it is detected, based on an address contained in the data packet, that the data packet is directed to a successive device in the own branch 42 or, respectively, 44. For this purpose, for example, the first input 20 and the first transmitter 22 may be connected to the control unit 24 as in the example of Fig. 2.

Due to the branching, the devices and lighting units 12 may also be distributedly ar- ranged along branching routes. Because of the spatial proximity of the devices 46, at which the branching takes place, the resulting cable lengths of the branching first and second lines 32, 34 are noncritical and do not limit the overall length of the branches. Fig. 6 shows a simplified diagram of a network, wherein, different from the example of Fig. 3, the control and monitoring apparatus 14 is connected to two chains of devices 50, which are connected at the chain end to form a closed ring. The devices 50 correspond to the above devices 10, wherein differences are explained in the following with reference to Fig. 6 and Fig. 7.

The respective last device 50 of a respective chain is schematically shown in the simplified diagram. The other devices 50 are symbolically shown by their three-digit address. Preferably, the devices 50 have identical structures and, for example, comprise a switch or an other coding device, by which the device 50 may be defined as being the last device of a chain. The respective last device 50 is adapted for deactivating its first transmitter 22 on the output side, with respect to the first direction of communication A, in a normal operation mode.

At the end of a first chain 52, the first transmitter 22 of the device 50 is connected to the second receiver 26 of the device 50 of the second chain 54, and, in a corresponding manner, at the end of the second chain 54, the first transmitter 22 of the device 50 is connected to the second receiver 26 of the device 50 of the first chain 52. Due to the deactivation of the first transmitter 22 of the devices 50, however, no forwarding takes place in the respective first direction of communication A of the first chain 52 or the second chain 54 beyond the end of the respective chain. The first and second chains 52, 54 behave like independent chains, which, for example, may each correspond to the example of Fig. 3. However, the control and monitoring apparatus 14 is a part of both chains.

The apparatus 14 is adapted for selecting, based on an address of a data packet that is to be addressed to a device, the chain 52, 54 that has an address space, to which the desired address belongs. However, the structure of the devices 50 and the further devices of the chains 52, 54 differs from the example of the devices 10 of Fig. 3, as will be explained in the following with reference to Fig. 7. Fig. 7 schematically shows the structure of a device 50 in the chains 52, 54 of the example of Fig. 6.

The device 50 is designed symmetrically for the first and second directions A, B of communication. The data output and the enable input of the first input 20 and of the second input 26 are, respectively, connected to the control unit 24. The first transmitter 22 and the second transmitter 28 are each connected to a respective tri-state output 30 of the control unit 24. For example, in a device 50 in the inside of the chain, the enable inputs of the first and second transmitters 22, 28 are permanently set to enable, as illustrated. As already mentioned, however, different from that, in the respective last devices 50 of the chains, the enable input of the first transmitter 22 is connected to the control unit 24, and the first transmitter 22 is deactivated in a normal operation mode.

In the normal operation mode, the device 50 works as explained above with reference to Fig. 3. The first receiver 20 is activated, and the tri-state output 30, which is connected to the first transmitter 22, is deactivated. The apparatus 14 is adapted for detecting a break or interruption of a respective chain, based on the absence of responses to status queries in the chain 52 or, respectively, 54.

For example, in Fig. 6, the first chain 52 contains devices having the addresses 000 to 010, and the second chain 54 contains devices having the addresses 011 to 020. As an example, it shall be assumed that a connection is interrupted (i.e. broken) between the devices 014 and 015 in the second chain 54, for example, due to an accident in which the respective connection is damaged. Then, the apparatus 14 detects that, in the second chain 54, only the devices with the addresses 011 to 014 are accessible. In this case, the apparatus sends a command to the last device 50 in the other chain, here the first chain 52, to switch to a forwarding mode. At this comand, the control unit 24 of the last de- vice 50 switches to a forwarding mode, in which mode the first transmitter 22 is activated. In the forwarding mode, the last device 50 of the first chain 52 forwards data packets, which are obtained through the first receiver 20, through the first transmitter 22 to the last device 50 of the second chain 54. The last device 50 of the first chain 52 forwards any responses, which are received through the second receiver 26, in the usual way through the second transmitter 28 in the second direction of communication B in the first chain 52. Those devices 50 of the second chain 54, which are positioned, in the first direction of communication A, behind the interruption or break of the connection, i.e. the devices with the addresses 015 to 020, determine that they are not reached or accessed anymore by the apparatus 14 in the second chain 54, based on the absence of regular status queries from the apparatus 14. The control unit 24 of the devices 50 is adapted for switching to an operation mode with reversed directions of communication, in such a case. In doing so, the last device 50 of the second chain 54 activates the first transmitter 22 in a suitable manner, which now takes over the role of the second transmitter 28.

In the operation mode with reversed direction of communication, the functions of the first and second receivers 20, 26 are interchanged, and the functions of the first and second transmitters 22, 28 are interchanged. Therefore, the devices with the addresses 015 to 020 are accessible by the apparatus 14 through the first chain 52, extending the first chain 52, and, correspondingly, the responses are forwarded in the opposite direction. Thus, in the case of a interruption or break of the network, those parts of the respective chain 54 which are positioned behind the interruption in the original first communication direction A, may be linked or connected through the other chain 52.

Claims

1. A system comprising multiple devices (10) for being arranged distributed along emergency routes or traffic routes, wherein the system comprises a control and/or monitoring apparatus (14), wherein the devices (10) are connected to the control and/or monitoring apparatus (14) through a wired network for digital data transmission, wherein the control and/or monitoring apparatus (14) is designed as a master, and the devices (10) are designed as slaves, wherein the network comprises a chain of devices (10), of which each two successive devices (10) are connected through at least one differential signal line (32; 34),

wherein a respective device (10), which, in a first communication direction (A) originating from the control and/or monitoring apparatus (14), is arranged between a respective predecessor (10) and a respective successor (10) in the chain, comprises a first receiver (20), a first transmitter (22), a second receiver (26), a second transmitter (28) and a local control unit (24),

wherein the first receiver (20) is connected to the first transmitter (22) of the predecessor through a differential signal line (32),

wherein the second receiver (26) is connected to the second transmitter (28) of the successor through an other differential signal line (34), and

wherein the first transmitter (22) is connected to the control unit (24) and/or the first receiver (20) for forwarding a data packet from the control and/or monitoring apparatus (14), which is received by the first receiver (20) and is addressed to an other device (10), to the first receiver (20) of the successor,

wherein the control unit (24) is connected to the first receiver (20) for receiving a data packet from the control and/or monitoring apparatus (14), which is received by the first receiver (20) and is addressed to the own device (10),

wherein the control unit (24) is connected to the second transmitter (28) for out- putting response data, which are generated by the control unit (24), through the second transmitter (28) to the control and/or monitoring apparatus (14), and wherein the control unit (24) is adapted for controlling the second transmitter (28) and/or the second receiver (26) such that response data from an other device (10), which are received by the second receiver (26), are forwarded through the second transmitter (28) to the predecessor.

5

2. The system according to claim 1, wherein each two successive devices (10) of the chain are connected through a single differential signal line, in particular in the form of a 2-wire connection,

wherein the differential output of the second transmitter (28) and the differential input of the first receiver (20) of a device (10) are jointly connected to a differential signal line, and

wherein the differential output of the first transmitter (22) and the differential input of the second receiver (26) of the device (10) are jointly connected to an other differential signal line.

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3. The system according to claim 1, wherein each two successive devices (10) of the chain are connected through two differential signal lines (32; 34), in particular in the form of a 4-wire connection,

wherein the differential input of the first receiver (20) of a device (10) is con-0 nected through a first differential line (32) to the differential output of the first transmitter (22) of a predecessor (10), and

wherein the differential output of the second transmitter (28) of the device (10) is connected through a second differential line (34) to the differential input of the second receiver (26) of the predecessor (10).

R

4. The system according to any one of the preceding claims, wherein a respective device (10) that is connected to a predecessor and a successor in the chain comprises a bypass (40) that is controlled by at least one relay (38), which bypass is adapted for bridging the device (10) in the chain in the de-energized state of the at least one relay (38).

5. The system according to claim 4, wherein the at least one relay (38) is adapted to 5 be controlled by the control unit (24) of the respective device (10).

6. The system according to any one of the preceding claims, wherein the network comprises, in the chain, a branching to a first branch (42) and at least one further branch (44) between a device (10) and its successor (46), wherein the first branch (42) includes the successor (46), and wherein the at least one further branch (44) comprises a further chain of devices (10; 46),

wherein the device (10) is connected to the said successor (46) in the first branch (42) and to a respective further successor (46) in the at least one further branch (44), and wherein the second transmitter (28) of the respective successor (46) is adapted to5 be deactivated by the control unit (24) of the respective successor (46).

7. The system according to claim 6, wherein the control unit (24) of the respective successor (46) is adapted for:

detecting, based on an address included in the data packet, whether the address0 belongs to an address space of the own branch (42; 44); and

forwarding a data packet from the control and/or monitoring apparatus (14), which is received by the first receiver (20), to the first receiver (20) of the next successor in the own branch (42; 44) only if the address belongs to an address space of the own branch (42; 44).

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8. The system according to any one of the preceding claims, wherein the control and/or monitoring apparatus (14) is connected to two chains (52; 54) of the devices (50), wherein each of the chains (52; 54) comprises a respective last device (50), wherein the first transmitter (22) of the last device (50) of a respective chain (52; 54) is connected to the second receiver (26) of the last device (50) of the respective other chain (54; 52),

wherein the devices (50) are adapted for detecting, based on an absence of data packets from the apparatus (14), that their chain (52; 54) is interrupted, and are adapted for switching, in the case of a detected interruption, to an operation mode having reversed directions of communication directions, in which mode the functions of the first and second transmitters (22; 28) are interchanged, and the functions of the first and second receivers (20; 26) are interchanged, and

wherein the respective last device (50) is adapted for activating a forwarding operation mode at a corresponding command of the apparatus (14), in which mode the respective last device (50) forwards data packets, which are received from the predecessor (50) in the respective chain (52; 54) through the first input (20), through the first transmitter (22) of the last device (50) to the second receiver (26) of the last device (50) of the other chain (54; 52).

9. A system according to any one of the preceding claims, in the form of a lighting system, wherein several of the devices (10) are adapted for controlling and/or monitoring at least one lighting unit (12) of the lighting system which is connected to the re- spective device ( 10).

10. The system according to claim 9, wherein several of the devices (10) are adapted for controlling at least one lighting unit (12) of the lighting system which is connected to the respective device (10).