WO2000011905A1

WO2000011905A1 - Error detection in a communication device

Info

Publication number: WO2000011905A1
Application number: PCT/DE1999/002390
Authority: WO
Inventors: Horst Sander; Rudolf Stelzl; Richard Waldhauser
Original assignee: Siemens Aktiengesellschaft
Priority date: 1998-08-17
Filing date: 1999-08-02
Publication date: 2000-03-02
Also published as: EP1106030A1; DE19837245A1; CA2340769A1

Abstract

The invention relates to a method for detecting errors in a communication system, especially an ATM communication system (Asynchronous Transfer Mode). In the absence of communication signals, monitoring signals are applied at the beginning of at least one monitoring line (7, 8) of said communication system and then extracted at the end of said monitoring line (7, 8). According to said invention, the monitoring line (7, 8) is located within a communication device (1) of said communication system. The absence of signals at the end of the monitoring line (7, 8) corresponds to the presence of an error in the communication device (1). In addition, a communication device (1) has a monitoring line (7, 8) at the beginning of which a power supply (2) is provided and at the end of which an extraction unit (3) is provided. Said extraction unit is designed for detecting and extracting monitoring signals applied by the power supply (2). The invention makes it possible to trigger an alarm-indicating signal (AIS) very quickly after detection of an error in the communication device (1).

Description

description

Error detection in a com munication system

The invention relates to a method for detecting errors of a communication system, in particular an ATM (Asynchronous Transfer Mode) communication system that, where at the beginning of at least one Uberwachungsstrecke a Kommunikati ^¬ onsverbindung fed in the absence of communication signals Uberwachungssignale and at the end of Uberwachungs ^¬ distance back from the communication link be coupled out. The invention further relates to a switching ^¬ means for switching communication links of a communication system, in particular a standardized ATM communication system, with a feed unit, m is the communication link in order to feed in a lack of communication signals via an active communication link Uberwachungssignale, and with a Auskopplungsem-, to decouple monitoring signals from an active communication link and to trigger an error message if any signals are missing.

From the recommendation of the International Telecommunications Union, Telecommunication Standardization Sector: "Integrated Services Digital Network (ISDN), Maintenance Prmciples", B-ISDN Operation and Maintenance Prmciples and Functions, 1-610 (11/95), in the following briefly Called ITU-T Recommendation 1.610, an ATM communication system is known in which the communication signals are transmitted in so-called cells. The ATM cells have a cell header which contains information by means of which switching devices at network nodes of the ATM communication system recognize which of the several transmission links starting at the network node are to be used to send the cell. So-called physical and so-called virtual or ATM layers are defined in the ATM communication system. In the physical layers, ATM cells are transmitted along physical equalizing sections transferred _ü with unique zellenunabhangigen start and end points. The virtual layers include each ^¬ weils the physical layers and, moreover, other elements of the ATM communications system. Within the virtu ^¬ economic layers virtual communication links de ^¬ are finiert, said via a virtual Kommunikationsverbin ^¬ dung _ü bert ragenen ATM cells at least once at a Ver ^¬ averaging means are mediated by their cell header information on the correct transmission link.

Endation from ITU-T Recom 1610 it is known permanent virtual connections in reliability ge to the particularly high by the operators requirements ^¬ be assumed to monitor as follows: The operator shall along the permanent virtual connection has a beginning point and an end point of a Monitoring route fixed. At the starting point, which is, for example, at the output interface of a switching device and at the beginning of a physical transmission link, monitoring signals in the form of so-called CC cells (Contmuity Check Cells) are fed into the permanent virtual connection if there is no ATM at the starting point for one second - cell has arrived. If there are still no ATM cells arriving at the starting point of the monitoring link, a CC cell is fed into the permanent virtual connection again every one second. In this way, a cell stream is maintained on the monitoring path even when no ATM cells arrive at the starting point of the monitoring path. If there are no cells at the end point of the monitoring path, this can result in

There is an error m of the permanent virtual connection to be closed. If such an error is detected, the signal forward is fed in as an AlS signal (Alarm Indication Signal) and the permanent virtual connection. Furthermore, the operator is

Alarm message informs about the presence of the error. Such alarm messages are used especially in the calculation connection-dependent fees used to later determine in a post-treatment at what times a permanent virtual connection was not available.

Except permanent virtual connections are ATM communication nikationssystemen also signaled virtual connections are known which are based on the request of a user of the communi cation ^¬ system. Again at the request of the user or another participant in the connection, the signaled connection is terminated again, for example by hanging up a telephone handset. Bonds for such virtual Ver ^¬ m of ITU-T Recommendation proposed 1610 no ent ^¬ speaking monitoring method as permanent virtual connection. On the one hand, significantly lower requirements are placed on signaled virtual connections with regard to reliability, on the other hand, the effort for setting up monitoring routes is relatively high at the beginning of a signaled virtual connection and is often not adequately related to the connection duration or to the Effort to establish a new connection between the same participants if such a signaled connection should ever be interrupted. If monitoring, as described above for permanent virtual connections, was nevertheless desired for a signaled connection, the subscriber or the operator of the communication system either had to wait to see which physical transmission paths the communication system would choose when establishing the virtual connection, or the options for communicating - restrict the on-system, which can lead to ineffective management in the switching of connections.

It is known to provide switching devices in an ATM communication system, from which communication connections are switched or chains of physical transmission links are set for the respective communication connections. In particular, mediation emπchtungen, which have a central switching computer on ^¬, _j in each case controls a plurality of peripheral modules. However, switching devices are also known in which the control function is performed by the peripheral modules themselves or by a computer external to the switching system.

For example, external physical transmission links are connected to an interface m of an interface module LIC (Lme Interface Card). Of the LIC, incoming ATM cells via a first multiplexer assembly AMX (ATM Multiplexmg Unit), a Koppelfeldbau ^¬ group ASN (ATM Switchmg Network) and a second multiple-xerbaugruppe AMX to an output-side interface to egg ner output side, the second interface module LIC forwarded. The operation of these peripheral modules ^¬ nen hardware failures and software errors Kings occur that break the From ^¬ drove a virtual Kom unikationsverbmdung. Gene ^¬ is rell of the Bellcore specification GR-1248-Core Issue 2, chap. 6.1.2. (September 1995 edition) requires that if an interruption of a virtual connection occurs within 500 ms after detection of the interruption em error signal m, the virtual connection must be fed in. The previously mentioned AIS (alarm indication signal) in the forward direction of the virtual connection and the RDI (Remote Defect Indication) backward direction of the virtual connection are known as error signals.

If one or more peripheral modules of a switching device with a central control computer of the type described above fail, it is known that the presence of the error is first reported to the associated central control computer. The control computer then determines the affected virtual connection or the affected virtual connections and notifies the associated interface modules LIC concerned. The LIC feeds the required signals on the message from the control computer AIS and RDI m the virtual connection em. According to this ^method , the above-mentioned requirement to feed in the error signal (s) within 500 ms after detection of the error could not be met.

Object of the present invention is to provide em method of the type mentioned, which makes it possible to specifically detect errors within a switching means of communi ^¬ cation systems and short a time as possible after discovery of the error em error signal m inject a Kom ^¬ munikationsverbindung. Another object of the invention is to provide a Vermittlungsemrichtung to Vermitt ^¬ development of communication links of a Kommunikationssy ^¬ stems to provide the aforementioned type that allows rapid fault detection and Emspeisung the error signal.

The tasks are solved by a method with the features of claim 1 or by a switching device with the features of claim 9. Further training is the subject of the respective dependent claims.

On the procedural side, at least one monitoring link is set up within the switching device of the communication system, at the beginning of which monitoring signals are fed in in the absence of communication signals and coupled out again at the end of the monitoring link. Monitoring path is understood to mean a physical or virtual transmission path for the transmission of communication signals. The monitoring link can be part of one or more communication connections. These communication connections can not only be permanent virtual connections, but also signaled subscriber connections, system-internal connections for the transmission of organizational information and / or signaled permanent virtual connections (SPVC) that the operator or user of the communication system sets up in a particularly simple manner and that of the communication system at least partially wise how signaled connections are handled. The Uberwachungsstrecke is not dependent on the type of attached to them ^¬ closed or connectable Kommunikationsverbmdungen. Rather, it is also possible, for example ^¬ onsverbindungen the Vermittlungsemrichtung to their operability at Prue ^¬ fen that Uberwachungsstrecke without connected Kommunikati or operate ^¬ onsverbindungen only for non-activated Kommunikati so that m any case at the beginning of the Uberwachungsstrecke no communication signals eintref- fen . Therefore, at least em

Monitoring signal fed. Meets the monitoring signal at the end of Uberwachungsstrecke em, at least is the Fä ^¬ ability of Uberwachungsstrecke laid to transmit signals.

Communication signals are understood to mean any signals that may arrive at the beginning of the monitoring path. For example, these are user signals that are transmitted by users of the communication system via a Kommunikati ^¬ onsverbindung or mation to Organisationsmfor- that is transferred between remote components of the communication system. An internal monitoring link or a monitoring link located within a switching device of the communication system is understood to mean a monitoring link that can extend to the limits of the switching device or is only connected to interfaces to external transmission links via other partial links of the switching device.

The monitoring method according to the invention allows errors of any type and cause to be determined which lead to the absence of any signals at the end of the monitoring path. The absence of any signals is understood to mean that no signal arrives in its expected form at the end of the monitoring path. This includes the case with em that, for example, only muted signals arrive or signals that are no longer recognizable by type and format are, for example ATM cells with a damaged cell head. Em we ^i¬ teres example, hardware failures that lead to interrup ^¬ the Uberwachungsstrecke chung drove.

In response to the detection of an exchange-internal fault, a fault diagnosis is made, for example, initiated and a re ^¬ dant unit instead of the faulty unit by operating m a localization of a hardware failure. This happens, for example, within a few milliseconds. Software errors can also be the cause of a connection failure.

The monitoring method can also erfmdungsgemaße equal ^¬ time the be carried out from the ITU-T Recommendation 1.610 to known methods. For example, a first Uberwachungsstrecke is set on a permanent virtual connection in previously known manner to a first switching device of the communication system to their ^¬ has caught and ends the lungsemπchtung on a second, from the first intermediary remote switching device. Furthermore, in the example, a second monitoring section according to the invention is set up within the first switching device. Signals of the permanent virtual connection can also be transmitted via the monitoring link according to the invention. The monitoring section according to the invention forms a subsection of the previously known monitoring section. If no communication signal em arrives at the beginning of the known monitoring link via the permanent virtual connection, monitoring signals are transmitted via the known monitoring link. These also pass through the monitoring section according to the invention, so that communication signals are transmitted over them. Only if the permanent virtual communication link fails or is triggered, or after deactivating the known monitoring link, can it happen that no communication signal is transmitted via the monitoring link according to the invention. In this case, the beginning of the monitoring section according to the invention, at least one monitoring signal is fed in.

In contrast to the ITU-T Recommendation 1610 Working signed prior art, m particular it is possible to monitor not only a ^¬ Zige permanent virtual connection by monitoring the Uberwachungsstrecke but at least along the Uberwachungsabschnitts all the Uber ^¬ wachungsstrecke-using communication links to monitor. The interior of the Uberwachungsstrecke as active Uberwachungsstrecke for all running over her communication links preferably automatically, in particular ^¬ sondere for construction of the individual communication links.

In a development is verbmdung for each active communication, which runs on the Uberwachungsstrecke, at the beginning of Uberwachungsstrecke em connection ^¬ specific monitoring signal fed in the absence of any signals of the respective communication link. This enables connection-specific errors to be recognized on the monitoring link, which, for example, do not affect the other communication connections, so that only one communication connection has failed. This can be hardware and / or software errors.

Preferably, in the presence of at least one bidirectional communication link, which is connected to the monitoring path according to the invention, m is in the opposite direction, i.e. Monitoring is also carried out in accordance with the invention between the end point of the monitoring section and the starting point of the monitoring section.

In a preferred embodiment of the method according to the invention, the internal monitoring signals are indicated on a first line interface between a signal upstream direction before the switching device. ordered or arrangable external route of a communication line and the switching device, fed. As an alternative or in addition, the internal monitoring signals are decoupled at a second line interface, between the switching device and a signal ^running direction behind the switching device, of an external link of a communication line which can be arranged or arranged. The switching device can thus be monitored up to its outer limit or its outer limits hm. In a variant of the Uberwachungssignale at a different peripheral module, for example, be a group Koppelfeldbau ^¬ fed and / or extracted. Especially before ^¬ is Trains t a configuration gene in at all vermittlungs ^¬ internal connection portions of Kommunikationsverbmdun- that terminate at the line interface to external connecting portions and / or start, and the signals transmitted, in each case at least one connection internal Uberwachungsstrecke is operated. In this way, it is possible to monitor internal sections of the switch from all active communication connections. It is therefore not necessary for the operator or user of the communication system to explicitly request or set up the monitoring routes when a connection is established. The respective monitoring link is preferably set up automatically by the communication system.

It is known to carry out time interval measurements in order to determine connection-dependent fees. In a further development of the method according to the invention, if there are no signals at the end of the internal monitoring path, such a time interval measurement is stopped. An associated payer is preferably provided directly on or on a peripheral module of the switching device, which is arranged at the end of the monitoring path. A post-treatment in the calculation of fees to subsequently determine downtimes can thus be omitted. In a preferred embodiment em Uberwachungs ^¬ is fed signal is ignal arrived when m a period of predetermined length at the beginning of Uberwachungsstrecke no Kommumkations- _S. In particular, the Emspeisung a monitoring signal is repeated in each case, is tion signal arrived when m a further period of predetermined length no communica ^¬. This ensures that the specified length of communication signal or monitoring signal is given to the monitoring path at the latest when a time period has elapsed. Accordingly, an error within the Vermitt ^¬ averaging means is closed for the presence, if no communication signal m of a period of time prior ^¬ given length or Uberwachungs- signal has arrived at the end of Uberwachungsstrecke. The predefined length for error detection is either set to a significantly greater value than the predefined length for feeding in monitoring signals at the beginning of the monitoring path, or it is set to about the same value, but with a mostly negligible reaction and execution time for feeding in of monitoring signals at the beginning of the monitoring path must be taken into account.

On the device side, a switching device of a

Communication system, in particular an ATM communication system, proposed, which is characterized in that the feed unit and the decoupling unit are arranged on an internal monitoring link of a common communication link, the feed unit being at the beginning and the decoupling unit at the end of the monitoring link. The decoupling unit is designed in such a way that it detects and decouples monitoring signals fed in by the feed unit. From the above description of the method according to the invention and its further developments, device devices features are for erfmdungsgemaße Vermittlungseinrich ^¬ tung or its developments erfmdungswesentlich.

In particular, in a development of the mediation is emrichtung feeding unit at a first line ^¬ interface arranged first in the e external Verbin ^¬-making portion of a communication link to the m Si ^¬ gnallaufπchtung subsequent switch-internal Uberwa ^¬ monitoring circuit is connected, and / or is the Auskopp- lungsemheit angeord on a second line interface ^¬ net, is connected to the switch-internal Uberwachungsstrecke m to a direction of signal propagation subsequent second external connecting portion of a communication link Toggle closable.

The invention will now be described with reference to exemplary embodiments. It is, however, not limited to this Ausfuhrungsbei ^¬ games. In the description of the exemplary embodiments, reference is made to the attached drawing. The only figure in the drawing, which is designated by FIG. 1, shows:

a monitoring link within a switching facility, which is connected to external sections of a signaled subscriber connection.

1 schematically shows peripheral modules of a switching device 1 on a network node of an ATM (Asynchronous Transfer Mode) communication system. A multiplicity of transmission links for transmitting communication signals to and from the switching device 1 can be connected to the switching device 1 on the input and output sides. For the sake of clarity, only the external transmission link 9 on the input side and the external transmission link 10 on the output side are shown, each of which is a partial route of an active signaled subscriber connection smα. The emgangsseitige external transmission path 9 terminates at an interface module LIC (Lme Interface Card) 2 in the switching device 1. From there, the active signaled ^¬ catalyzed Teilnehmerverbmdung two redundant intermediary lungsmterne Ubertragungsebenen 7, 8 to a second

Interface module LIC continued at which the output-side external transmission link 10 begins.

The first Ubertragungsebene 7 and the second 8 Ubertragungsebene have apart from its start and end points of the first LIC 2 or on the second LIC 3 no common link, are transmitted over the communication signals between them the signaled Teilnehmerverbmdung ^¬ could th. The The first transmission level 7 and the second transmission level 8 each have peripheral assemblies of the switching device 1 which are connected to one another in the signal routing direction. Viewed from the first LIC 2, the redundant copy of a communication signal to be transmitted that is fed to the first 7 or second 8 transmission level first reaches the first multiplexer module AMX (ATM multiplexing unit) 4. From there, the communication signals are sent to a switching matrix module ASN (ATM Switchmg Network) 6 forwarded and coupled to an output connection of the ASN 6 to a second multiplexer module AMX 5. The redundant copies of the communication signal are merged again by the second AMX 5 by being passed to the common second LIC 3.

The above description applies to the error-free or undisturbed operating state of the monitoring link between the first LIC 2 and the second LIC 3. In operation, however, it can happen that one or both transmission levels 7, 8 fail. If only one of the transmission levels 7, 8 fails, the transmission link between the first LIC 2 and the second LIC 3 is still fully functional, because it is sufficient if one copy of the two redundant communication channels on signals arrives at the second LIC 3. Furthermore, the first LIC 2 and the second LIC 3 themselves may be disturbed. Un ^¬ ter circumstances, this leads to the fact that only em copy or no copy of a given communications signal to be transmitted to the Ubertragungsebenen 7. 8 Moreover, it is mög ^¬ Lich that em another component of the switching device 1, for example em unillustrated central Vermitt ^¬ development computer is faulty, so that the transmission of Kom ^¬ munikationssignalen disturbed over transmission link between the ER most LIC 2 and the second LIC 3 is. In particular, the transmission of connection data from the central switching computer to one of the LIC 2, 3 can be disturbed. In ^general , software errors and hardware errors are the cause of the interference in the transmission link.

For monitoring the transmission path between the first LIC 2 and the second LIC 3, the first LIC 2 is an A ^¬ supply unit on to with a lack of communication signals via the output-side external transmission link could 9 arrive at the first LIC 2, Uberwachungssignale to send to the second LIC 3. If there are communication signals of a length of preferably 500 ms from the external transmission link 9 on the output side, the first LIC 2 feeds an ATM cell m the communication link em, which is associated with the ATM cell type OAM (Operation, Administration, Maintenance). Specifically, it is an ICC cell (mternal Contmuity Check-Cell), the cell head of which is given a special identifier. If there are communication signals or ATM cells from the external transmission link 9 on the output side for a further 500 ms, the first LIC 2 repeats the transmission of an IC cell. As with other communication cells arriving from the external transmission link 9 on the output side, two copies of the ICC cell are made, one of which is transferred to the transmission level 7 and one to the second transmission level 8. The second LIC 3 has a Auskopplungsemheit that the _l knows CC-cell on the basis of special identifiers in the cell header it ^¬ and from the communication link from the Uber ^¬ wachungsstrecke between the first LIC 2 and the second LIC 3 couples out. In a variant of the exemplary embodiment, the second LIC 3 either has two outcoupling units, one of which is assigned to the first transmission level 7 and the second transmission level 8, or it has an outcoupling unit that recognizes which of the transmission levels 7, 8 is an incoming one Communication cell arrives at the second LIC 3. In particular, letz ^¬ teres be possible by the fact that the Gesen of the LIC 2 ^¬ Deten redundant copies of communication cells with un ^¬ terschiedlichen identifiers are provided in the cell header. Preferably, however, the only decoupling unit or the two decoupling units of the second LIC 3 recognize the transmission level 7, 8 on the basis of the path via which the respective ATM cell arrives at the second LIC 2. Different cell header IDs are then superfluous. In the variants of the exemplary embodiments, it is possible to determine transmission errors in only one of the two redundant transmission levels 7, 8 and, for example, to trigger a correction of errors if the transmission of communication signals of the signaled subscriber association by the other transmission level 7, 8 functions without errors.

In an operating variant of the switching device 1 shown in FIG. 1, one of the transmission levels 7, 8 serves as a redundant reserve transmission level in the event of a malfunction. If, for example, the transmission level 7 is active, signals are transmitted via this transmission level. Analogous to the above description, the transmission level 7 is part of the monitoring path. If there are no signals due to a failure or error in the transmission level 7 at the end of the monitoring path, the system switches to the redundant transmission level 8 and operation can continue, usually without a noticeable interruption. The Transmission level 8 becomes part of the monitoring path, so that the monitoring function is also retained.

In the exemplary embodiment described first, the two copies of a communication signal that are transmitted via the different transmission levels 7, 8 are not distinguished. With this configuration, the following errors are detected as ^¬ example:

- hardware errors m the first LIC 2 and / or the second LIC 3, wherein for example the entire LIC 2, 3 ausgefal ^¬ len or only belonging to the monitored or the monitored communication links interfaces have failed.

Software errors of a ren the LIC 2, 3 or both LIC 2, 3, the fuh for interrupting the communication links ^¬ that use the link for the transmission Uberwachungsstrecke as part of its communication signals. Hardware double errors of redundant peripheral modules, both modules 4, 5, 6 of the transmission levels 7, 8, which correspond to one another with regard to their interconnection and function, being faulty or faulty. Hardware cross failures of one peripheral module each of the first transmission level 7 and the second transmission level 8, the faulty modules 4, 5, 6 not being the mutually redundant modules 4, 5, 6. For example, a cross failure of the first AMX 4 of the first transmission level 7 and the second AMX of the second transmission level 8 or a cross failure of the ASM of the first transmission level 7 and the second AMX 5 of the second transmission level 8 can be determined.

In general, any errors that lead to an interruption or failure of the signal transmission over both redundant transmission levels 7, 8 can be determined with this configuration. Preferably 3, the second LIC to a TM-Emheit (Traffic Measurement Emheit), which is used to measure the connection ^¬ duration of one or more leading through the second LIC 3 communication links. When establishing a connection, the TM-ER- Emheit a start pulse stop, so that a entspre ^¬ sponding connection time measurement begins and a entspre ^¬ sponding connection start time is recorded. If it comes to the absence of any communication signals from the communica ^¬ tion connection or take more than 500 ms em long at the LIC 3 no ATM cells are associated with the communication link, the TM-unit obtained by the Auskopplungsemheit or of a further intermediate unit second LIC 3 a stop pulse so that the time measurement is ended or the current time is recorded as the connection end time. Both types, connection time sen to mes ^¬ are meant by the term Zeitmtervallmessung.

If, after a failure of the transmission link between the first LIC 2 and the second LIC 3, the second LIC 3 again receives an ATM cell which is assigned to the signaled subscriber association to be monitored, the sending of AIS, for example, which started after the error was ascertained (Alarm Indication Signal) cells forward direction of the subscriber connection is stopped and in the case of the connection duration measurement an impulse is given to resume the time interval measurement.

In particular in the case of peripheral modules which are able to independently maintain a communication link, the monitoring within the exchange according to the invention preferably serves to determine only errors of the peripheral modules along the monitoring path and their connection to one another. When locating faults, this offers advantages in terms of quick fault detection and correction. In the case of bidirectional connections, a monitoring link is preferably set up and operated in the switching device 1 shown in FIG. 1 both from the LIC 2 to the LIC 3 and also in the opposite direction from the LIC 3 to the LIC 2. Both LIC 2, 3 are therefore both em- speisungs- and Auskopplungsemheit for Uberwachungs ^¬ signals.

As already mentioned, the invention is not restricted to the exemplary embodiments described so far. In this way, there can also be no redundant modules in the switching device. For example, then aS cells are in ^¬ For all signals remain at the end of Uberwachungsstrecke so ^¬ continued fed. A further hardware configuration has a bus structure to which the individual peripheral modules of the switching device are connected. In this case, when a signal arrives, the respective module checks whether the signal, in particular the ATM cell, is intended for it. Here, too, at least one monitoring link is set up and operated between two modules within the switching device in order to monitor at least one communication link.

By monitoring an internal monitoring link, failures or errors of the switching device can be determined reliably and quickly, and an error signal, for example an AlS cell, can be sent practically without delay. In addition, it is possible to precisely determine the duration of the connection without an otherwise customary aftertreatment.

Claims

claims

1. A method for detecting errors of a Kommunikati ^¬ onssystems, in particular an ATM (Asynchronous Transfer Mode) communication system that, where at the beginning of at least fed a Uberwachungsstrecke (7, 8) of the communication system in egg ^¬ nem absence of communication signals Uberwachungssignale and at the end of Uberwachungsstrecke be coupled (7, 8) again, characterized in that the Uberwachungsstrecke (7, 8) is within a switching device (1) of the communication system and that in a lack of any signals at the end of Uberwa ^¬ monitoring section (7, 8) for the presence an error is closed within the switching device (1).

2. The method according to claim 1, characterized in that the internal monitoring signals at a first line interface (2), between an m signal upstream of the switching device (1) arranged or arranged external route (9) of a communication line and the switching device ( 1), can be fed.

3. The method according to claim 1 or 2, characterized in that the internal monitoring signals at a second line interface (3), between the switching device (1) and a m signal direction behind the switching device (1) arranged or arranged external route (10) a communication line.

4. The method according to claim 3, characterized in that in the absence of any signals at the end of vermitt ^¬ lung internal monitoring section (7, 8) has a Zeitmtervall- measurement for determining verbmdungsdauerabhangigen Gebuh ^¬ ren is stopped.

5. The method according to any one of claims 1 to 4, characterized in that a monitoring signal is fed when m a period of a predetermined length at the beginning of the monitoring section (7, 8) no communication signal has arrived.

6. The method according to claim 5, characterized in that in each case the feeding of a monitoring signal is repeated when no communication signal has arrived in a further period of the predetermined length.

7. The method according to any one of Anspr che 1 to 6, characterized in that on all switching-internal connection sections of communication connections that start and / or end at line interfaces to external connection sections (9, 10) and transmit the signals, in each case at least one internal monitoring path ( 7, 8) is operated.

8. The method according to any one of claims 1 to 7, characterized in that the monitoring path is part of a signaled communication link and / or part of a signaled permanent communication link.

9. Switching device (1) for switching communication connections of a communication system, in particular an ATM communication system, with - an infeed unit (2), in order to avoid communication signals via an active communication bmdung monitoring signals to feed the communication link, and a decoupling unit (3) to decouple monitoring signals from an active communication link and to trigger an error message if any signals are absent, characterized in that the feed unit (2) and the decoupling unit (3) are connected to an internal monitoring link (7, 8) of a common communication link, said feeding unit (2) at the end of Uberwachungsstrecke gen at the beginning and the Auskopp ^¬ lungsemheit (3) (7, 8) lie ^¬, and that the Auskopplungsemheit (3) is designed such to recognize and decouple monitoring signals fed in by the feed unit (2).

10. Switching device according to claim 9, characterized in that the feed unit (2) is arranged on a first line interface, on the em first external connection section (9) to the signal direction subsequent switching internal monitoring path (7, 8) can be connected.

11. Switching device according to claim 9 or 10, characterized in that the decoupling unit (3) is arranged on a second line interface, at which the internal monitoring path (7, 8) can be connected to a second external connection section (10) following the signal direction .