WO2001043326A1

WO2001043326A1 - Method for switching over between transmission channels, and a transmission module, a back-up module and an alternate circuit

Info

Publication number: WO2001043326A1
Application number: PCT/DE2000/003943
Authority: WO
Inventors: Bernhard Weiler
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-12-07
Filing date: 2000-11-10
Publication date: 2001-06-14
Also published as: AU2501901A; DE19958893A1

Abstract

The invention relates to a method for switching over between transmission channels, preferably for bypassing faults, and to an alternate circuit, a transmission module (8.X.X) and a back-up module (9.1; 9.2). The invention is characterized in that a unidirectional ring main (12.1; 12.2) is produced between the transmission modules (8.1.X; 8.2.X) and the back-up module (9.1; 9.2).

Description

description

Method for switching between transmission channels and transmission module, replacement module and replacement circuit

The invention relates to a method for switching between transmission channels according to the preamble of claim 1 and an equivalent circuit according to the preamble of claim 7, a transmission module according to the preamble of claim 12 and a replacement module according to the preamble of claim 18 for carrying out the method.

Transmission systems with transmission modules and with a multitude of connections for signal transmission are known from telecommunications, which provide an equivalent circuit for each transmission module to increase operational reliability (1: 1 protection). If a transmission module fails, it is separated from the transmission system and an assigned replacement module is switched on in its place. However, this creates an enormous amount of circuitry.

In order to reduce the circuit complexity and thus the costs, the patent specification DE 195 28 742 Cl proposes to provide only a single replacement module for several transmission modules (1: n protection). Since it is very unlikely that several transmission modules will fail at the same time, there is little loss in security compared to 1: 1 protection. The connection between the transmission modules and the replacement module is made bidirectionally. Another 41: 59 protection system is described in DE 41 32 598 AI. However, this system goes beyond the function of a pure equivalent circuit, because it also offers the possibility of checking the equivalent circuit with the help of switchovers. Here, however, the times to come from ^¬ leadership of the review as an interruption of supply to Signalubertra-. Furthermore, a large number of high-bit-rate, bidirectional connections are required to set up this system.

It is therefore an object of the invention to provide a method for switching between transmission channels, a compensation circuit, and a replacement module Ubertragungsmodul ^¬ wrap to the effect to ent, that a significant reduction in benotigten connection technology is achieved for the construction of the equivalent circuit.

The object of the invention is achieved by the features of the respective independent claims.

The inventor has recognized that it is sufficient for an equivalent circuit of a transmission system if the connection between the individual transmission modules and the replacement module is unidirectional and ring-shaped.

Accordingly, the inventor proposes to use the known method for switching between transmission channels, preferably for

Error bridging for a transmission system with a multiplicity of bidirectional connections, in which each bidirectional connection runs through a transmission module on each side of the transmission system and when one of the bidirectional connections is interrupted, the transmission of signals of the failed bidirectional connection is redirected via a replacement module, further develop in such a way that the signals of the failed bidi- directional connection can be redirected via a unidirectional line.

In a further development of the inventive method the Ubertragungsmodule and the replacement module are so angeord ^¬ net that each module is connected uni-directionally with two adjacent modules, wherein a module that restli ^¬ chen modules representing the replacement module, the Ubertragungsmodule. This effectively creates a bidirectional signal transmission between any two modules despite the use of unidirectional connections.

In an inactive equivalent circuit, the replacement module advantageously functions as a transmission module for less important signals (signals of lower priority), the transmission of these less important signals being interrupted when the equivalent circuit is activated. The replacement module then takes over the transmission of the signals of the failed connection. In addition, the replacement module can also be activated, only in the case of rerouting, of signals, and otherwise remains in a stand-by mode.

A preferred further development of the method according to the invention provides that the replacement module monitors the fault-free function of the equivalent circuit both in normal operation and during an active equivalent circuit, preferably by passing a control signal via the ring line to the transmission modules and checking whether such a control signal arrives , Normal operation means that error-free signal transmissions take place on the bidirectional connections of the transmission system. The self-monitoring of the equivalent circuit now ensures that the equivalent circuit functions reliably and without maintenance. The smallest possible amount of data, such as a bit or a byte, can now be routed through the ring as a control signal. The control signal is either "InBand or" OutOfBand *. In "InBand * is the con- troll signal within, for" outofband * outside a Rah ^¬ mens. Such frames are generated in SDH and SONET transmission systems (SDH = Synchronous Digital Hierarchy; SONET = Synchronous Optical Network), which effectively transmit low-rate data streams (user data), such as telephone channels or IP packets (IP = Internet) Protocol). The user data are divided into these frames and provided with additional information that can serve the transmission quality.

If the control signal is now transported with an active equivalent circuit in such a frame of the signal to be switched in the unidirectional line “InBand”, the control signal lies in an unused area of this frame (that is, an unused byte of a so-called “section overhead *) If there is no signal to be switched in the unidirectional ring due to an inactive equivalent circuit, an auxiliary signal is generated which has an equivalent section overhead, the control signal is now transported in this section overhead and the rest Part of the auxiliary signal is filled with any bytes.

If the control signal "OutOfBand '" is transported, the signal to be switched for replacement is not changed in an active equivalent circuit, since the control signal of the unidirectional ring line, encapsulated, is a high-frequency signal is transported. The high-frequency signal contains the signal to be replaced and additionally at least the control signal. If no signal to be switched due to an inactive equivalent circuit is transported in the unidirectional ring line, the area of the signal to be switched for the high-frequency signal is occupied by an equivalent amount of any bits.

According to the invention, the transmission modules recognize the incoming control signal. They confirm the correct receipt and forward the control signal. If the replacement circuit ring functions properly, the control signal sent by the replacement module arrives at the replacement module after it has passed through the ring line, so that the replacement module can recognize the functionality of the replacement circuit ring.

An advantageous embodiment of the invention provides that the transmission modules report when they do not receive a control signal. If there is an error in the equivalent circuit, the reception of the control signal is interrupted. An error that occurs is, for example, an interruption of the unidirectional ring due to a break in a connecting line, such as an optical fiber. Furthermore, errors occur when connections have not been made correctly, a chip has been destroyed or a module is defective, ie there is another HW error in the Rmleitung.

A further embodiment provides that the software localizes the location of the error. If the error occurs, for example, between two transmission modules, all transmission modules following in the flow direction report that no control signal has been received. The software recognizes that the error is located in the first flow direction Ubertragungsmodul m, wel ^¬ ches reports the absence of the control signal.

In a further development of the method according to the invention, the control signal is sent in a timed frame. This control signal is also expected this time frame, and each module continues to report if the control signal is missing in a defined number of frames. An alarm is therefore not triggered when the first control signal is missing, but only after a predetermined number of missing control signals. The limits for triggering an alarm should be selected so that small, short-term transmission errors that are not particularly relevant for the transmission of signals do not lead to false alarms. On the other hand, the maximum number of tolerated missing control signals should be less than or equal to the number of control bytes that are transmitted in the typical time until a complex hardware error is detected in the system.

According to the concept of the invention, the inventor furthermore proposes an equivalent circuit for a transmission system with a multiplicity of bidirectional connections, with each bidirectional connection going through a transmission module on each side of the transmission system, whereby means for detecting an interruption of the bidirectional connections and a replacement line is provided, the transmission of the failed connection to a replacement module being redirected via the replacement line in the event of an interruption in one of the bidirectional connections, so that the replacement line is designed as a unidirectional ring line. In a special embodiment of the equivalent circuit, at least one software is provided which evaluates error messages and controls an equivalent switch, an input switch and an output switch. Interrupts, for example, a connection in the transmission path or is a Übertra ^¬ supply module is defective, the software reacts in all Übertra ^¬ supply modules and controls the switch so that the module having the error is associated with the replacement module. The signals are therefore redirected from the defective transmission module to the replacement module.

In an advantageous embodiment of the equivalent circuit, the switches are designed as ASICs, that is to say digital, application-specific integrated circuits.

To check the readiness for use of the equivalent circuit, a means for outputting a control signal is provided, preferably in the replacement module, the control signal passing through the unidirectional ring line. If the transmitted control signal reaches the replacement module again, the equivalent circuit is functional.

In a further development of the invention, the means for outputting the control signal has a timer. This timer causes the control signal to be sent to the ring line in a timed frame.

To implement the equivalent circuit described above, it is also proposed to use the transmission modules described below.

The inventor thus also proposes to use a transmission module for transmitting signals with at least one transmitter / receiver-side input, a transmitter / receiver-side output, a ubertragungsseitigen input, a ubertragungsseitigen output a compensation input and a compensation ^¬ exit to Anbmdung by more Ubertragungsmodule, an input switch and an output switch, which the white ^¬ terzuleitenden signals between inputs and / or switch outputs, so that the replacement input and the replacement output are unidirectional.

The input changeover switch and the output changeover switch are advantageously designed such that the input changeover switch feeds an input signal either from the transmission-side input or from the replacement input to the transmitter / receiver-side output, and the output changeover switch em input signal from the transmitter / receiver-side input either to the transmission-side output or the replacement output.

Furthermore, means for error monitoring can be provided. The error monitoring includes, for example, the monitoring of the transmission link and the monitoring of the functional units of the transmission module. The means for error monitoring can detect an occurring error and cause the signals to be diverted (activation of the equivalent circuit). This means can have software, for example.

In an advantageous embodiment of the transmission module, at least one replacement switch is provided for opening and closing the replacement line. If the replacement switch in the transmission module is closed, on the one hand the control signal for checking the replacement line and on the other em redirected signal for fault bridging by the ring and be sent through the transmission module. If an error occurs in the transmission module itself, the replacement switch is opened. A connection is created to the replacement line, and the signals to be transmitted can now be redirected to the replacement module in connection with the input and output switches.

A further embodiment of the transmission modules provides sensors in the modules which recognize the incoming control signal, confirm correct receipt and forward this control signal to the replacement module.

In another development of the invention, the transmission modules have means for generating a control signal, means for sending this control signal and means for checking a control signal. This makes it possible to check the topology of the equivalent circuit, that is, the order of the modules of the Rmleitung. For example, the Rmgtopologie consists of n modules and a replacement module and a connection of the Rmgleitung from module 1 to 2, 2 to 3, etc., ..., n-1 to n, n to replacement module and replacement module to 1. The topology of Rmleitung can now be checked by generating and forwarding a control signal from module 1. This control signal generated by module 1 is expected only at module 2, but not passed on. After receiving the control signal, another control signal is generated by module 2, forwarded and expected to module 3, but not forwarded from there, and so on. Finally, the control signal is generated and forwarded by the replacement module, expected at module 1 and not forwarded from there. After successful completion of this procedure, the correct topology of the guiding was verified. This can be used, for example, to check whether the order of the modules of the transmission system has been correctly connected.

According to the inventive concept, the inventor also suggests em replacement module with at least one transmission side

To improve input, a transmission-side output, a replacement input and a replacement output for connection to the transmission modules to the effect that the replacement input and the replacement output are unidirectional. In the event of the failure of a transmission module, the replacement module can switch as a redundant component of the system. It forwards the signals instead of the failed transmission module.

In an advantageous further development, at least one transmitter / receiver-side input, at least one transmitter / receiver-side output, one input switch and one output switch can be provided. With this configuration, the replacement module is allowed to take over the tasks of a transmission module by routing signals from a transmitter to a receiver.

In addition, means for generating a control signal, a means for sending the control signal to the transmission modules and a further means for checking the incoming control signal can be provided. If the received control signal is the same one that was sent, the equivalent circuit is electrically functional.

Further features of the invention result from the following description of a preferred exemplary embodiment of a 1: 5 equivalent circuit with reference to the drawings. Show it: Figure 1 idle equivalent circuit according to the invention; FIG. 2 active equivalent circuit according to the invention; FIG. 3 checking the functionality of the equivalent circuit according to the invention;

FIG. 4 checking the functionality of the equivalent circuit according to the invention with a connection error occurring.

1 shows a schematic representation of a stationary 1: 5 equivalent circuit according to the invention. Such He is ^¬ set circuit for example architectures of SDH and SONET transmission system common.

The transmission system consists of a large number of bidirectional connections 14.X. Each of these bidirectional connections 14. X consists of an Hm and a reverse direction, shown schematically with two connecting strands. It goes without saying that these two connecting strands can run in a line, for example in the case of a glass fiber.

On each side of the transmission system, each bidirectional connection 14. X runs through each transmission module 8.1.X or 8.2.X. Furthermore, the equivalent circuit on each side of the transmission system contains an equivalent module 9.1 and 9.2, as well as an equivalent line 12.1 and 12.2, which is designed as a redirectional line. Starting from the replacement module 9.1, the trunk line 12.1 runs through all the transmission modules 8.1.1 to 8.1.5 on one side of the transmission system (on the left in FIG. 1) and mutes the replacement module 9.1 again. On the other hand, starting from the replacement module 9.2, the trunk line 12.2 runs through all transmission modules 8.2.1 to 8.2.5 and also m again the replacement module 9.2.

For static equivalent circuit, that is, if there is no fault in the transmission system occurs, is a transfer of Sig ^¬ tional over the bidirectional connections 14.x of the respective modules 8.1.x and 8.2.x instead, so for example between the Ubertragungsmodul 8.1.1 and the Ubertragungsmodul

8.2.1 via the bidirectional connection 14.1. The signal transmission from the transmission module is for clarification

8.1.2 to the transmission module 8.2.2 highlighted in bold on the connection 14.2. So there is 8.1.2 em transmitter and 8.2.2 em receiver.

The replacement modules 9.1 and 9.2 also transmit signals via a bidirectional connection 14.6. However, these signals have lower priority than the signals forwarded by the transmission modules 8.X.X.

Furthermore, each replacement module 9.1 and 9.2 has the option of using a control signal generator 15 to generate a control signal 10 which can be routed to the equivalent circuit ring and is used to check the functionality of the equivalent circuit set. This possibility is described in more detail in FIGS. 3 and 4.

Each transmission module 8.XX has an input changeover switch 5, an output changeover switch 11 and a replacement switch 13, which can be actuated when an equivalent circuit is activated. In the idle state shown here, the input changeover switches 5 are set in such a way that signals are passed from the transmission-side input 3 to the transmitter / receiver-side output 2. At the same time, the output switches 11 m an operative position to direct the receiver-side signals to be transmitted from the transmitter / input 1 to the ubertra ^¬ supply-side output. 4 In closed replacement ^¬ switches 13, the ring lines 12.X that all over- tragungs odules 8.1.x and on each side of the closed 8.2.x Ubertra ^¬ supply system through.

The Figure 2 shows the Figure 1 illustrated em dormant 1: 5- equivalent circuit m an activated mode with an interruption m of the bidirectional connection of 14.2 Ubertra ^¬ supply system.

Both at the sender and at the recipient of the message or signal, the message or signal is redirected.

When the bidirectional connection 14.2 is interrupted, shown as a dashed line, the signals to be transmitted are redirected via the spare lines 12. X. Here, the switches, namely the substitute switch 13, the input changeover switch 5 and the output changeover switch 11, of the transmission modules 8.2.1 and 8.2.2 affected by the interruption of the connection, change their operating position. By opening the replacement switches 13, the unidirectional ring connections are now converted into bidirectional connections between the transmission modules 8.2.1 and 8.2.2 concerned and the respective replacement modules 9.1 and 9.2, respectively. Furthermore, the output changeover switches 11 of the modules 8.2.1 and 8.2.2 change their position and cause em input signal to be transmitted to be routed from the transmitter / receiver-side input 1 to the replacement output 7. The input changeover switches 5 also switch over and now route an incoming signal from the replacement input 6 to the transmitter / receiver-side output 2. In the replacement of modules 9.1 and 9.2, the transfer is interrupted by signals having lower priority and then who the input switch 5 and the output changeover switch 11 converted as in the affected transmission modules 8.1.2 and 8.2.2 ^¬.

The path of the redirected signals by the equivalent circuit is shown in bold by a Stπchpunktlmie: The Sig nal ^¬ is diverted from the Ubertragungsmodul 8.1.2 via the output switch 11 to the Rmgleitung 12.1. It runs through the Ubertragungsmodul ^¬ 8.1.1 and reaches the input 6 of the replacement spare module 9.1. The signal is fed with the aid of the input switch 5 to the transmission-side output 4 of the replacement module 9.1 and passed via the bidirectional connection 14.6 to the receiver-side replacement module 9.2. Here, the signal from the transmission-side input 3 is fed via the output changeover switch 11 to the replacement output 7 and passed to the unidirectional ring line 12.2. The signal passes through the transmission module 8.2.1 and is fed via the input switch 5 of the module 8.2.2 to its transmitter / receiver output 2 and to the receiver of the signal.

During the operation of the equivalent circuit, the transmission modules 8.1.1 and 8.2.1, which are not affected by the connection failure, route the signal to be rerouted with the aid of their spare inputs 6, spare switches 13 and spare outputs 7 via the spare line 12.1; 12.2 further. Simultaneously they also transmit the regular signals over the bidirectional connections 14.1. The other transmission modules 8.1.3 to 8.1.5 and 8.2.3 to 8.2.5 also transmit signals via the respective intact bidirectional connections 14.3 to 14.5. Finds a signal transmission from the Ubertragungsmodul 8.2.2 to 8.1.2 Ubertragungsmodul, so m 2 from right to left, instead, the signals he diverted via ^¬ fmdungsgemaße equivalent circuit here. Here, the signal on the Rmgleitung 12.2 is al- lerdmgs tragungsmodule on the Uber ^¬ 8.2.3 to 8.2.5 the replacement module 9.2, and passed from there via the connection 14.6 to the replacement module 9.1. The signal is then fed via the line 12.1 and the transmission modules 8.1.5 to 8.1.3 to the module 8.1.2 affected by the connection failure.

FIG. 3 shows the checking of the functionality of the 1: 5 equivalent circuit according to the invention on one side of the transmission system. In this case, the replacement module 9.1 passes the control signal 10 generated with the control signal generator 15, which is shown symbolized as a bold dot, via the replacement line 12.1 to the transmission modules 8.1.1 to 8.1.5. The control signal 10 is preferably sent to the transmission modules 8.1.1 to 8.1.5 via the replacement line 12.1 in a time-determined frame. Each of the transmission modules δ.l.n recognizes the control signal 10, confirms correct receipt and forwards it to the next transmission module 8.1.n-l. In the case of a functional 1: 5 equivalent circuit, the last transmission module 8.1.1 in the direction of flow forwards the control signal 10 back to the equivalent module 9.1.

Simultaneously, signals can be transmitted from a transmitter to a receiver during the entire duration of the check. The functionality of the equivalent circuit can be checked both when the equivalent circuit is active and when it is at rest. So there is one Self-check no failure of the transmission times of signals or data.

FIG. 4 shows the checking of the functionality of the 1: 5 equivalent circuit according to the invention on one side of the transmission system when a connection error occurs. Here, the replacement line 12.1 is interrupted between the transmission module 8.1.3 and the transmission module 8.1.2.

The control signal 10 transmitted by the replacement module 9.1 is received by the transmission modules 8.1.3 to 8.1.5, the correct reception is confirmed and forwarded. However, due to the interruption of the replacement line 12.1 between the modules 8.1.3 and 8.1.2, the control signal 10 is no longer received in the transmission modules 8.1.2 and 8.1.1 and in the replacement module 9.1. The affected transmission modules 8.1.2 and 8.1.1 report that the control signal 10 is missing. A software then localizes the error by assuming that the location of the error is either between the last module with correct reception of the control signal (module 8.1.3) and the first module in the flow direction that reports the error (module 8.1. 2), or is in the first module that reports the error (module 8.1.2).

In order to increase the reliability of self-monitoring, the control signal can be transmitted 10 m in a time frame and can also be expected in a time frame. It can also be specified here that an alarm is only issued when several control signals 10 are missing. As a result, small, short-term transmission errors that can lead to false alarms are not taken into account in the event of an alarm: It goes without saying that the features of the invention mentioned above can be used not only in the respectively specified combination, but also in other combinations or on their own, without leaving the scope of the invention.

The invention is not limited to electrical systems but can also be used in optical networks (optical WDM technology).

Overall, a method for switching between transmission channels, an equivalent circuit, a transmission module and an equivalent module is developed by the invention that a significant reduction in the connection technology required to set up the equivalent circuit was achieved. In addition, the invention provides a self-check of the equivalent circuit without interrupting the signal transmission.

Claims

claims

1. Method for switching between transmission channels, preferably for error bridging for a transmission system with a multiplicity of bidirectional connections (14.X), each bidirectional connection (14.X) on each side of the transmission system each having a transmission module (8.1.X; 8.2.X) and if one of the bidirectional connections (14.X) is interrupted, the transmission of signals of the failed bidirectional connection (14.X) is redirected via the replacement module (9.1; 9.2), characterized in that the signals the failed bidirectional connection (14.X) is diverted via a unidirectional trunk line (12.1; 12.2).

2. The method according to the preceding claim 1, characterized in that in an inactive spare circuit, the spare module (9.1; 9.2) acts as a transmission module for less important signals, the transmission of these signals being interrupted when the spare circuit is activated.

3. The method according to any one of the preceding claims 1 to 2, characterized in that both in

During normal operation and during an active equivalent circuit, the equivalent module (9.1; 9.2) monitors the fault-free function of the equivalent circuit, preferably by sending a control signal (10) to the transmission modules (8.1.X; 8.2.X) via a ring line (12.1; 12.2) and / or checks whether such a control signal (10) arrives.

4. The method according to the preceding claim 3, characterized in that the transmission modules (8.X.X) recognize the incoming control signal (10), confirm correct receipt and forward the control signal (10).

5. The method according to any one of the preceding claims 3 to 4, characterized in that the transmission modules (8.X.X) report when they do not receive a control signal (10).

6. The method according to any one of the preceding claims 3 to 5, characterized in that the control signal (10) is sent in a timed frame, this control signal (10) is expected and reported in the timeframe when the control signal (10) in a defined Number of frames is missing.

7. equivalent circuit for a transmission system with a plurality of bidirectional connections (14. X), wherein each bidirectional connection (14.X) on each side of the transmission system runs through a transmission module (8.1.X; 8.2.X), whereby a means for Detection of an interruption of the connections (14.X) and a replacement line (12.1; 12.2) is provided, with the transmission of the failed bidirectional connection via the replacement line (12.1; 12.2) when one of the bidirectional connections (14.X) is interrupted (14.X) is redirected to a replacement module (9.1; 9.2), characterized in that the replacement line (12.1; 12.2) is designed as a unidirectional ring line.

8. equivalent circuit according to the preceding claim 7, characterized in that at least one ^{software is} provided, which evaluates error messages and controls an equivalent switch (13), an input switch (5) and an output switch (11).

9. equivalent circuit according to one of the preceding claims 7 to 8, characterized in that em with ^¬ tel (15) for outputting a control signal (10) which passes through the unidirectional ring line (12.1; 12.2), preferably in the replacement module (9.1; 9.2) vorgese¬

10. equivalent circuit according to the preceding claim 9, characterized in that the means (15) for

Output of the control signal (10) has a timer.

11. Equivalent circuit according to one of the preceding claims 7 to 10, characterized in that the transmission modules (8.X.X) have the features of one of claims 12 to 17.

12. Transmission module for the transmission of signals with at least one transmitter / receiver-side input (1), one transmitter / receiver-side output (2), one transmission-side input (3), one transmission-side output (4), one replacement input ( 6) and a replacement output (7) for connection to further transmission modules (8.XX), an input switch (5) and an output switch (11), which switch the signals to be passed on between inputs and / or outputs, characterized in that the Replacement- are forming the input (6) and spare output (7) umdirektional ^¬ out.

13. Ubertragungsmodul according to the preceding claim 12, characterized in that the Eingangsumschal ^¬ ter (5) and the output switches are taltet (11) such ausges ^¬ that the input switch (5) either em input signal from the input ubertragungsseitigen

(3) or the replacement input (6) feeds the transmitter / receiver side output (2), and the output switch (11) em input signal from the transmitter / receiver side input (1) either the transmission side output (4) or the replacement output (7 ) feeds.

14. Transmission module according to one of the preceding claims 12 to 13, characterized in that em means for error monitoring is provided.

15. Transmission module according to one of the preceding claims 12 to 14, characterized in that em replacement switch (13) is provided for opening and closing the replacement line (12.1; 12.21.

16. Transmission module according to one of the preceding claims 12 to 15, characterized in that sensors are provided which recognize the incoming control signal (10), confirm correct receipt and forward this control signal (10) to the replacement module (9.1; 9.2).

17. Transmission module according to one of the preceding claims 12 to 16, characterized in that em means for generating a control signal (10), em means for sending the control signal (10) and em means for checking a control signal (10) is provided.

18. Replacement module with at least one transmission-side input (3), one transmission-side output (4), a replacement input (6) and a replacement output C ⁷ ) for connection to the transmission modules (8.XX), characterized in that the replacement input (6) and the replacement output (7) are unidirectional.

19. Replacement module according to the preceding claim 18, characterized in that at least em transmitter / receiver side input (1), at least em transmitter / e receiver side output (2), e input switch (5) and em output switch (11) are provided.

20. Replacement module according to one of the preceding claims 18 to 19, characterized in that the em means for generating a control signal (10), em means for sending the control signal (10) to the transmission modules (8.XX) and em further means for checking of the incoming control signal (10) are provided.