Abstract:
The present invention relates to a digital communication device comprising interconnected modules for processing and/or handling received data signals, wherein said interconnected modules each comprise means for monitoring (monitoring means) said data signal and for generating an output data signal having a predetermined signal status (squelched data signal) if said data signal is erroneous. The invention also relates to a method for processing a data signal within a communication device, preferably a communication device according to the present invention.

Description:
[0001]    The invention is based on a priority application EP 02360343.4 which is hereby incorporated by reference.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to a digital communication device comprising interconnected modules for processing and for handling received data signals. Further, the invention relates to a method for processing and/or handling a data signal within a communication device as mentioned above.  
         BACKGROUND OF THE INVENTION  
         [0003]    Digital communication devices as mentioned above are generally used in modern digital telecommunications systems which have been significantly advanced over recent years, particularly in the rate at which information can be communicated. The extremely high bandwidth now available in digital telecommunications systems have enabled the communication of large volumes of data, for example from computer to computer as well as digital data representative of other media such as video displays. Since a successful transmission of digital data among computers requires high reliability and high quality transmission, digital communication devices, like digital cross-connects, now provide for example performance monitoring by which the error rate of received digital data is monitored by way of cyclic redundancy check (CRC) and other conventional coding techniques. Further, conventional telecommunications systems also generally provide some amount of redundancy so that failure of a telecommunications line or network element does not result in the loss of the communicated message. Conventional telecommunications systems with performance monitoring have implemented certain alarm conditions by which events such as “loss of signal” and error rates exceeding various thresholds are alerted. In response, the system can switch to a redundant line to again enable communication of the digital data in the system.  
           [0004]    Conventional fiber optic terminals have implemented 1:1 redundancy for the fiber optic lines in a system, with some amount of automatic switching. According to this 1:1 redundancy scheme, the overhead portion of the bandwidth is monitored to determine if a loss of signal or alarm indication signal condition is being received. In these redundancy schemes, upon receipt of such an alarm signal the terminal will automatically switch its transmission to the other of the two fiber optic lines, enabling transmission of the data despite the failure of the first fiber optic line.  
           [0005]    Beside these protection techniques for ensuring a failure-free data transmission between digital communication devices within the communications system, there are also protection techniques focussing on the failure-free data transmission within a digital communication device (called “Equipment Protection System EPS”).  
           [0006]    The equipment protection technique is also based on redundant components of the communication device which are fed with a copy of the original data signal received by the communication device. In the event that a component of the communication device fails, the data signal path through the redundant component is selected.  
           [0007]    As already mentioned, the standard method for monitoring and indicating an error is to monitor the content of the received digital data and to indicate errors by writing this information into the digital data.  
           [0008]    However, the increasing bandwidth of modern communications systems require considerable efforts for monitoring the data. Therefore, there is a demand for transparent communication devices. In this context, transparent means that the communication devices shall pass the digital data without analyzing the content of the data.  
           [0009]    Beside this demand for more transparency, there is also a demand for increasing the reliability of communication devices. This is of particular interest in view of cross-connect devices which are physically large systems distributed over several racks. Due to these dimensions, cables are needed to interconnect shelves and racks of the cross-connect device, however, the reliability of cabling is not very good.  
         SUMMARY OF THE INVENTION  
         [0010]    In view of the above, the object of the present invention is to provide a digital communication device and a method for processing a data signal within such a communication device which allows a simple way of signaling detection of signaled effects without the need to terminate high-electrical or optical signals, that is without the need to analyze the content of the signals.  
           [0011]    This object is solved by a digital communication device as mentioned in the outset which is characterized in that that interconnected modules each comprise means for monitoring (monitoring means) said data signal and for generating an output data signal having a predetermined signal status (squelched data signal) if said data signal is erroneous (defect).  
           [0012]    That means in other words that the data signal received by said interconnected module is squelched in the event that the monitoring means detects a signal defect. It is not necessary to analyze the content of the data signal or to encode any signal or alarm status within the data signal, that is within a predetermined section of the data blocks.  
           [0013]    Particularly, for the subsequent modules or communication devices receiving the squelched data signal, it is readily possible to detect a defect and to pass it to the next device or module without any modification of the data signal.  
           [0014]    Hence, the transparency of the data signal flow through the communication device is enhanced. Particularly, the inventive digital communication device allows signaling of defects through several stages or modules within the device transparently.  
           [0015]    In a preferred embodiment, the digital communication device comprises a first I/O module for receiving a data signal and transmitting two copies of said data signal, at least two of said interconnected modules for processing said data signal, wherein a first group of said interconnected modules receiving said first copy of said data signal and a second group of said interconnected modules receiving said second copy of said data signal, and a second I/O module for receiving said copies of the data signal transmitted by said interconnected modules, said second I/O module comprising means for monitoring said received copies of said data signal and transmitting those copy of said data signal which has not said predetermined signal status.  
           [0016]    This means that the digital communication device selects a redundant data signal in the event that the original data signal is detected as squelched.  
           [0017]    This measure has the advantage that a so-called equipment protection is achieved in a simple and cost-effective manner.  
           [0018]    It is preferred that the monitoring means comprises a threshold detector if optical signals have to be detected. If, however, electrical signals have to be detected, said monitoring means comprises a frequency detector. The frequency detector may be implemented as a counter which counts rising or falling edges of the electrical signal. A more complicated but also more precise implementation may be seen in a PLL (phase locked loop) based frequency detector.  
           [0019]    In both cases the monitoring means is able to check whether the data signal is erroneous and defect, respectively. Particularly, the monitoring means checks the frequency of the data signal and determines whether there is a loss of lock.  
           [0020]    The advantage of these measures is that the monitoring means operate transparently without analyzing the content of the data signal.  
           [0021]    In a further preferred embodiment, the communication device is a cross-connect device, wherein said interconnected modules are switching matrix components. It is further preferred that said first I/O module comprises means for monitoring said received data signal and for generating an output data signal having a predetermined signal status (squelched data signal) if said received data signal is erroneous.  
           [0022]    This measure allows to build up a network protection switching, for example SNCP, in addition to the afore-mentioned equipment protection. This may be achieved by providing the monitoring means also in the first I/O module (input module), which transmits a squelched data signal in the event of detecting a signal defect. This squelched data signal will then be replaced with the redundant data signal in the second I/O module of the device.  
           [0023]    In a preferred embodiment, said first I/O module receives a copy of the data signal via a protection line and comprises means for monitoring said received data signal supplied via a working line and for transmitting said copy of said data signal if said received data signal is erroneous.  
           [0024]    This measure has the advantage that the equipment protection of the communication device may be linked with the network protection of a communications system.  
           [0025]    The object of the present invention is also solved by a method for processing a data signal within a communication device, said communication device receiving an input data signal and transmitting an output signal, the method comprising the steps of receiving said input data signal, checking the data signal whether it is erroneous, if the data signal is erroneous, generating a data signal with a predetermined signal status, and transmitting said data signal as said output data signal.  
           [0026]    In a preferred embodiment, the step of checking said data signal comprises the step of checking its frequency. If the data signal is an optical signal instead of an electrical signal, the step of checking said data signal comprises the step of checking the signal level and comparing it with a threshold value. More preferably, said output data signal is checked whether it has said predetermined signal status, and if so, a copy of said input data signal is transmitted as said output data signal.  
           [0027]    The afore-mentioned measures result in the same advantages as pointed out in connection with the communication device. Therefore, it is refrained from repeating these facts.  
           [0028]    Further features and advantages can be taken from the following description and the enclosed drawings.  
           [0029]    It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the scope of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0030]    An embodiment of the invention is shown in the drawings and will be explained in more detail in the description below with reference to same. In the drawings:  
         [0031]    [0031]FIG. 1 is a schematic block diagram of a communication device for illustrating the present invention;  
         [0032]    [0032]FIG. 2 is a schematic block diagram of a portion of an optical cross-connect;  
         [0033]    [0033]FIG. 3 is a schematic block diagram of two communication devices being part of a network; and  
         [0034]    [0034]FIG. 4 are some examples of protection schemes. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    In FIG. 1, a communication device is schematically shown as a block diagram for illustrative purposes only. The communication device is indicated with reference numeral  10 . The communication device  10  may for example be provided as an optical cross-connect  12 . Generally, optical cross-connects are used to obtain a flexible connection in between different parts of a WDM (wavelength division multiplexing) optical network. Typically, an optical cross-connect  12  has 8 to 128 input ports and the same amount of output ports. By a remote command a signal into one of the input ports can be switched in order to exit at anyone of the output ports that is or can be made available. The optical cross-connect can be“all-optical”, i.e. the signal through a cross-connect is carried by light (photons all the way). The optical cross-connect can also be opto-electrical, i.e. the light signal entering the cross-connect is converted to electrical signals by an opto/electrical converter at the entrance. The electric signal is then switched in an electrical switch core and converted to light again by an electrical/opto converter at the exit side of the cross-connect.  
         [0036]    The communication device  10  shown in FIG. 1 comprises two switch matrices  14 ,  16  which are mutually redundant and hence are designed identically. Both switch matrices  14 ,  16  are connected with an input module  18  which supplies identical data signals to both matrices via lines  21  and  22 .  
         [0037]    The output sides of both matrices  14 ,  16  are connected with an output module  24  which is adapted to select one of the data signals output by the matrices  14 ,  16 .  
         [0038]    It is to be noted that for clarity reasons, the single transmission lines shown in FIG. 1 each represent a plurality of lines connecting the respective modules of the communication device  10 . For example, transmission line  21  represents a plurality of separate transmission lines. Nevertheless it is also possible that the shown transmission lines  21  are formed as single lines transporting for example multiplexed signals.  
         [0039]    The diagram in FIG. 1 also indicates that the matrices  14 ,  16  comprise a number of components  26 ,  27  for processing or handling data signals.  
         [0040]    Since the operation of a cross-connect  12  is generally known in the art, it is refrained from giving a detailed description herein. It is for example referred to respective material describing a cross-connect which is manufactured and sold by the applicant under the name 1674 Lambda Gate R2.  
         [0041]    In addition to the structure of a communication device  10 , preferably a cross-connect  12 , as described above, the communication device  10  is provided with means for detection and signaling of defects of the data signal passing through the device  10 . The detection and signaling means comprises a frequency detector in case that electrical signals be detected and comprises a threshold detector in case that optical signals be detected.  
         [0042]    In the first case, the frequency detector checks whether the frequency of the data signal is correct. If not, the data signal has lost its relation to a general clock signal (loss of lock). In this case, a squelch circuit provided in the detection and signaling means squelches the data signal detected as defect and transmits this squelched signal to the next component of the communication device  10 . In the context of the present application, a squelched signal is a signal having a defined signal status. For example, such a squelched signal may have a level of  0  Volt in case of electrical signals.  
         [0043]    It is to be noted that a squelched signal represents a signal incorporating the information that any failure has occurred. It is further to be noted that this signaling of a signal defect is carried out without any analyzing or manipulating of bits or bytes of the data signal. Hence, this kind of detection and signaling is completely transparent. Moreover, the generated squelched signal may be received and transmitted by any other component of the communication device without amendment or modification.  
         [0044]    Generally, the components  26  and  27  of the matrices  14 ,  16  are provided with such detection and signaling means so that any failure occurring along the transmission path of the data signal from the input module  18  to the output module  24  can be detected and signaled.  
         [0045]    In order to implement an equipment protection, the output module  24  is comprised of a selecting circuit which receives the data signal of matrix  14  and the redundant data signal of matrix  16 . If the selecting circuit detects a squelched signal, it selects the redundant data signal for passing to the output.  
         [0046]    In view of the above, the main function of the detection and signaling means is to monitor an incoming data signal on defects and to squelch the signal to have a defined signal status which can be detected by subsequent stages/modules of the device.  
         [0047]    In FIG. 2, a portion of a cross-connect  12  is schematically shown. The cross-connect  12  comprises a CS matrix  31  constituted by two redundant matrices  33 ,  35 . The CS matrix  31  is for example part of the optical data unit  2  matrix (ODU  2  matrix).  
         [0048]    The CS matrix  31  is supplied with data signals by a number of input/output modules (I/O modules), two of which  37 ,  39  are shown. Each I/O module  37 ,  39  comprises a plurality of inputs  41  which are connected with input circuits  43 . The input circuits  43  process the received data signals in a certain manner and supply the signals to an IS matrix  45 . Each IS matrix  45  has a plurality of output ports, two of which are shown in FIG. 2 as connected with the CS matrix  31 .  
         [0049]    The IS matrix  45  provides a copy of each original data signal supplied to matrix  33 , whereas the copy of this data signal is supplied to the second matrix  35  of the CS matrix  31 . This is made for protection reasons as already described with reference to FIG. 1.  
         [0050]    The output ports of the CS matrix  31  are connected with an I/O module  47  which in turn comprises a matrix  49  and a number of output circuits  51 .  
         [0051]    As already mentioned before, the connection of two communication devices (network elements) within an optical network system is obtained by two transmission lines which are referred to as working line and protection line. Both lines transport identical data signals from one network element to another network element. This technique allows to react on any failure in one of the transmission lines.  
         [0052]    Due to this protection technique, the cross-connect  12  shown in FIG. 2 comprises input ports  41  connected with the working line and input ports  41  connected with the protection line. Particularly, the I/O module  37  is assigned to the working line and the I/O module  39  is assigned to the protection line.  
         [0053]    It is to be noted that the components and modules of the cross-connect  12  partially shown in FIG. 2 are distributed generally over several racks so that it is necessary to interconnect the modules and components via cables. In order to detect any cable problem, the cross-connect  12  comprises detection and signaling means as already described with reference to FIG. 1. Particularly, the input circuits  43  of the I/O modules  37 ,  39  comprise these detection and signaling means. Of course, every other module or component of the cross-connect may also comprise a detection and signaling means if required.  
         [0054]    The detection and signaling means is adapted to generate a squelched signal if the received data signal is defect. Such a squelched signal then passes for example the IS matrix  45 , the CS matrix  31  and arrives at the I/O module  47  and there at one of the output circuits  51 .  
         [0055]    In FIG. 2, the path of a signal transmitted via the protection line and the working line is indicated by broken lines  53 ,  55 . As apparent, both data signals come together in the output circuit  51 . Therein, a selecting circuit checks whether the working data signal is a squelched signal. If so, the selecting circuit selects the redundant data signal supplied via the protection line and the signal path indicated with reference numeral  55 . Hence, the output circuit  51  supplies the data signal of the protection line to its output port.  
         [0056]    It is to be noted that the squelched signal may pass every subsequent module or stage up to the output circuit  51  of the input/output module  47 .  
         [0057]    Hence, the use of the detection and signaling means allows to implement a very effective and transparent equipment protection in order to increase the reliability of the cross-connect  12 .  
         [0058]    In FIG. 3, two cross-connects  12  are schematically shown for describing the mentioned network protection technique. As mentioned before, each cross-connect  12  is fed with data signals via a working line W  61  and a copy of these data signals via a protection line P  63 . In the event that the working line  61  is defect, the I/O module of the cross-connect  12  connected with the working line  61  detects this defect and generates a squelched signal. This squelched signal passes through the modules of the cross-connect to the output circuit. There, it is detected as a squelched signal and in response thereto the redundant data signal supplied via the protection line  63  is selected as output signal.  
         [0059]    In FIG. 4, some possible protection schemes are shown. Since these are self-explanatory, it is refrained from a further detailed description thereof. Just briefly, the first scheme describes the equipment protection of normal connections which is generally achieved by transmitting two copies of a signal from one node to a destination note. Adjacent to this scheme, the so-called SNCP protection scheme is shown. This describes that two copies of a signal provided by two different nodes shall be transmitted to one destination node via two different paths. This scheme is implemented by providing a working line and a protection line, as described above.  
         [0060]    The present invention has been described on the basis of a cross-connect  12 . However, it is to be noted that the detection and signaling means may also be used in other communication devices. The present invention is not limited to cross-connects.