Abstract:
A method for optically transmitting signaling and control information that aids in the monitoring and control of single- or multi-channel useful information in optical wavelength multiplex networks having at least one network element, the signaling and control information and the useful information being transmitted in the form of a digital signal, which is characterized in that the signal of the signaling and control information is transmitted using a code multiplex method (CDMA). Also described is a device for receiving signaling and control information, which is characterized in that the receiving device of the signaling and control information has assigned to it at least one monitor coupler one CDMA decoder, and one signaling device.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for optically transmitting signaling and control information and to a receiving device for signaling and control information. 
     BACKGROUND INFORMATION 
     For transmitting a signal carrying useful information, one or a plurality of optical frequencies (wavelengths) is used. If a plurality of optical frequencies is used, they can be considered separate channels. This method is characterized as wavelength multiplex or wavelength division multiplexing (WDM), access to individual channels being possible for at least two network elements. This is characterized as multiple access. 
     In the operation of optical wavelength multiplex networks, signaling and control information must be transmitted. This signaling and control information functions, on the one hand, for controlling and monitoring network elements and, on the other hand, network conditions can be thus represented and can be changed. A reference (Chawki, M. J. Tholey, V. Le Gac I: Management Protocol of a Reconfigurable WDM Ring,Network Using SDH Overhead Bytes; OFC 96 Technical Digest) describes the signaling and control information bring transmitted within the signal of the useful information (in-channel signaling). In addition, a reference (Draft Recommendation ITU-T G.MCS Geneva Jun. 1996) describes the signaling and control information being transmitted on an additional control channel, either on the same or a different medium. Finally, a reference (S. Johansson: Transport Network Involving a Reconfigurable WDM Layer, Journal of Lightwave Technology 14 (1996) 6, pp. 1341-1349) describes, in which the signaling and control information being transmitted with the assistance of so-called pilot tones. In this context, the pilot tones are transmitted in an electrical frequency range that is not used by the useful information. 
     In-channel signaling is disadvantageous in that the signaling and control information must be separated from the useful information signal by using additional electrical de-multiplexers and electrical multiplexers, it being necessary first to convert the optical signal in its entire bandwidth into an electrical signal. For processing the signaling and control information, a transceiver (transmitter/receiver) is additionally necessary at each network element. 
     For the use of additional control channels for the signaling and control information, the separation/addition of the control channels from the channels of the useful information using appropriate means is necessary. In addition, the use of a transceiver is required for the processing of the signaling and control information. Due to the multiple access, it is necessary to use a protocol, which controls the use of the transceiver, i.e., it determines what time the transceiver is to transmit or receive and/or which subscriber can use the transceiver. 
     The use of pilot tones in optical wavelength multiplex networks having varying hierarchical orders is difficult, since in optical wavelength multiplex networks information can be transmitted at varying transmission rates. Taking into account the entire network structure, no uniformly free frequency ranges for the transmission of pilot tones are generated in this way. 
     U.S. Pat. No. 5,619,492 describes an optical, local-area network (LAN) in which control information is transmitted in a data packet together with useful information. The entire data packet composed of control information and useful information is CDMA-coded. In a receiving part, the entire data packet is again CDMA decoded. 
     European Published Patent Application No. 0 367 452 describes an optical network in which information is transmitted in the CDMA method and in the wavelength multiplex method. 
     A reference (L. Nguyen et al.: “All-Optical CDMA with Bipolar Codes,” ELECTRONICS LETTERS, Vol. 31, No. 6, Mar. 16, 1995, pages 469-470) describes a CDMA method in optical networks, bipolar codes being used. 
     A reference (L. Giehman et al.: “The Application of Code Division Multiple Access for Transport Overhead Information in Transparent Optical Networks,” OPTICAL FIBER COMMUNICATION CONFERENCE AND EXHIBITION, Vol. 2, Feb. 22-27, optical networks, the CDMA-coded signaling and control information being impressed upon the signal of the useful information. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for optically transmitting signaling and control information in optical wavelength multiplex networks, requiring no free optical or electrical frequency range and not interfering with the useful information signal to be transmitted. 
     The object is achieved in the present invention in that the Code Division Multiple Access (CDMA) signal of the signaling and control information is impressed using addition onto the signal of the useful information, the modulation range of the CDMA signal being less than the modulation range of the signal of the useful information. In this context, signaling and control information can be impressed on a multiplex signal existing on an optical fiber (LWL) or on individual channels. By using the code multiplex method, it is possible in an advantageous manner to transmit information selectively to individual network elements or to all network elements using the signaling and control information within an optical wavelength multiplex network. As a result of the fact that the modulation range of the CDMA signal is smaller than that of the useful information signal, influencing the signal of the useful information is substantially avoided. In addition, it is advantageous that the control signal is independent of synchronization with regard to the useful signal. This means that the CDMA signal can be transmitted at a different transmission rate than the useful information. For the detailed description of the CDMA method, two references are noted (R.C. Dixon: “Spread Spectrum Systems”; John Wiley and Sons, 1996 and A. J. Viterbi: “CDMA Principles of Spread Spectrum Communications”; Addison-Wesley, 1995). 
     Furthermore, it is advantageous that an identification (addressing) of a network element can take place via a specifiable code. This code can be unipolar or bipolar, or, if appropriate, also multi-step. In the use of the CDMA method, one bit of the signaling and control information to be transmitted is linked to a code word so that a code sequence arises which is composed of a plurality of chips. The individual bits of the code sequence are termed “chips” so as to avoid any confusion with the bits of the signaling and control information. By assigning the code words to individual network elements, the latter can be addressed. Thus, in an advantageous manner, it is possible to address individual network elements. For this purpose, a corresponding code word is to be clearly assigned using software to the network elements to be addressed. To be able to address a plurality of network elements of an optical wavelength multiplex network, a multiplicity of code words of this type may be employed in each case, however, at least one code word being clearly assigned to a network element. For example, it is nevertheless also possible to assign to code words to a network element representing, in this case, the information “0” or “1”. It is advantageous if the individual code words of the corresponding network elements are orthogonal to each other, a plurality of code words then constituting a so-called code family. By using a corresponding chip quantity (code word length), it is possible to be able to address virtually any number of network elements. 
     If a CDMA-coded bit of signaling and control information is transmitted to a network element that has a corresponding code word in its software, the bit can be identified in that, first, both code words are multiplied, with respect to chips, and then the individual multiplication results are added. Thus, for example, in a four-chip code word, the maximum sum possible is 4. As a result of transmission errors or noise, it is possible that individual chips are not clearly recognized or even are lost. The loss of a chip means that as the sum only the amount of 3 is calculated. However, here, too, the result is clear, since, for example, a multiplication with respect to chips and subsequent addition using a false code word that is orthogonal to the correct one, yields a result of 0. In this manner, a clear assignment of a bit of signaling and control information to a network element is possible. In addition, through the multiplication with respect to chips and subsequent addition, there results a so-called coding gain, since the original bit having the value of 1 receives the value 4 through the CDMA coding and the subsequent decoding. In this way, the signal-to-interference ratio is improved, i.e., a coding gain is achieved. In addition, it is possible in an advantageous manner by selecting a specifiable code to transmit in a particular manner particularly important signaling and control information. 
     In according to the present invention in impressing the signal of the signaling and control information on an envelope curve of the useful signal through intensity modulation, a small modulation index is selected. 
     In a further preferred embodiment of the method, provision is made that the CDMA-coded signal of the signaling and control information and the signal of the useful information are generated in a common network element as a summing signal. This means that both the CDMA-coded signal as well as the signal of the useful information are generated in a common transmitter (modulator). This happens as a result of the fact that the signals that are available at first as electrical pulses are converted into optical signals using an appropriate device, in the process the CDMA-coded signal being already impressed upon the signal of the useful information. Alternatively, provision can be made that the CDMA-coded signal of the signaling and control information is impressed on the signal of the useful information generated in a network element using a further network element. 
     The summing signal that arises in this manner including the CDMA-coded signal and the signal of the useful information, can be received by a further network element. A plurality of summing signals may be combined into at least one wavelength multiplex signal. 
     In according to the present invention provision is made that at the input of a network element, for generating the summing signal or wavelength multiplex signal, a supplemental signal identical to it is generated. This occurs preferably using a so-called monitor coupler. The monitor coupler can be assigned to an optical fiber, which carries the wavelength multiplex signal. An optical filter element can be arranged advantageously downstream of the monitor coupler, the filter element then filtering out of the wavelength multiplex signal at least one summing signal of an optical channel. Alternatively, provision can be made that the monitor coupler be assigned to an optically selective element, in which the wavelength multiplex signal is divided into individual summing signals in accordance with the wavelengths employed. The monitor coupler is then assigned to at least one optical fiber that carries a summing signal. In this manner, it is possible to dispense with the filter element just described. This means that the summing signal can be relayed directly from the monitor coupler to a CDMA decoder. 
     The currently existing summing signal is detected by the CDMA decoder. For this purpose, the decoder is configured such that it only detects the signals of the signaling and control information. This is possible due to the fact that the useful information is transmitted at a significantly higher transmission rate (M-bit range) than the signaling and control information (k-bit range). In the CDMA decoder, the transmitted code words are compared with the code word stored in the CDMA decoder. In the event of agreement— as described above— the original bit sequence of the signaling and control information can be recovered, the latter being converted into the electrical area. In this manner, a processing is possible in a suitable downstream device. In this processing, on the one hand, control information for a network element is evaluated, whereas, on the other hand, it is possible that further signaling and control information can be generated so that further network elements can be controlled or monitored. Subsequently, this new signal of the signaling and control information may be again CDMA coded and may be impressed on the signal of the useful information. In an advantageous manner, the conversion of the useful information into the electrical range can be dispensed with, which leads to a simplification and cost reduction of the entire network. 
     In addition, the present invention relates to a device for receiving signaling and control information, which is characterized in that the receiving device of the signaling and control information has at least one monitor coupler and one signaling device. The monitor coupler, according to the present invention, generates a supplemental signal that is identical to the received signal that includes signaling and control information and useful information, the supplemental signal being fed to the CDMA decoder, which filters the signaling and control information from this signal and, subsequently, decodes it, and in that the decoded signaling and control information is fed to the signaling device, which controls the network element. In particular, as a result of the fact that the monitor coupler generates this supplemental signal from which in the CDMA decoder the control information is filtered out, it is possible to dispense with a recovery of the useful information, since the signaling and control information are impressed upon the useful signal and therefore can easily be separated from it. 
     In another embodiment the device according to the present invention, provision is made that the device have assigned to it a transmitting device including a code multiplex coder. In this way, it is possible to code once again the information generated in the signaling device so that it can subsequently be impressed on the signal of the useful information through addition using a modulator. 
    
    
     The invention will now be discussed in greater detail with reference to the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows in a cutaway view an optical wavelength multiplex network for transmitting useful information according to the present invention. 
     FIG. 2 shows a block diagram of a network element according to the present invention. 
     FIG. 3 shows a first embodiment of a receiving device according to the present invention of the network element as illustrated in FIG.  2 . 
     FIG. 4 shows a second embodiment of the receiving device according to the present invention. 
     FIG. 5 shows a third embodiment of the receiving device according to the present invention. 
     FIG. 6 a  shows a first embodiment of a transmitting device according to the present invention of the network element as illustrated in FIG.  2 . 
     FIG. 6 b  shows a refinement of the embodiment illustrated in FIG. 6 a.    
     FIG. 7 shows a second embodiment of the transmitting device according to the present invention. 
     FIG. 8 shows a third embodiment of the transmitting device according to the present invention. 
     FIG. 9 shows a fourth embodiment of the transmitting device according to the present invention. 
     FIG. 10 shows an embodiment of an optically selective element according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows in a cutaway view an optical wavelength multiplex network  1 , which includes network elements  2   a  through  2   g . Network elements  2   a  through  2   f  are also termed network nodes. Network element  2   g  is, for example, an optical intensifier  3 . Individual network elements  2   a  through  2   g  are connected by optical fibers (hereinafter designated as “LWL”)  4 . Network element  2   a  can be configured as power supply feeder  5 , which only contains a transmitting device for optical signals. 
     In FIG. 2, network element  2   e  is depicted. It is only connected to two optical fibers  4 , it being presumed in what follows purely by way of example, that network element  2   e  has an input  6  and output  7 , to which LWL  4  are connected. Network element  2   e  includes an optically selective element  8  as well as a signaling device  9 , which functions to evaluate and process the signaling and control information. It is discernible that signaling device  9  has an input  10  and output  11 . Network element  2   e  has assigned to it a receiving device  12 , which is arranged between element  8  and input  10  of signaling device  9 , (FIG.  3 ). 
     Receiving device  12  for signaling and control information includes a monitor coupler  13  (monitor branch), an optical wavelength selective element, in particular a filter  14 , a receiver  15 , which makes possible an optical/electrical conversion of a signal, and a CDMA decoder  16 . Receiving device  12  is connected to input  10  of signaling device  9 . Element  8  is— as was previously mentioned— coupled to an LWL  4  at input  6  and at output  7 , respectively. Monitor coupler  13  is assigned to input  6  of element  8 , and is connected via an LWL  4 ′ to filter  14 , which in turn is connected to receiver  15  via a further LWL  4 ′. Receiver  15  converts an optical signal into an electrical signal and feeds it to CDMA decoder  16  via a line  4 ″. CDMA decoder  16  is conductively connected to signaling device  9 . 
     In what follows, the mode of functioning of the receiving device is described in greater detail on the basis of FIG. 3, it being presupposed that a wavelength multiplex signal having wavelengths λ 1  through λ n  has been supplied at network element  2   a , it then being possible to pick off/tap off the wavelength multiplex signal at input  6  of optical element  8 . 
     Monitor coupler  13 , by way of example, using power division generates two wavelength multiplex signals, identical to each other, having wavelengths λ 1  through λ n , one part of the signal arriving at element  8  and the other part of the signal being supplied via LWL  4 ′ to filter  14 . Filter  14  is configured such that it advantageously filters out from the wavelength multiplex signal only one wavelength λ i . Thus at the output of filter  14 , a summing signal is present having wavelength λ i , the summing signal being fed via LWL  4 ′ to receiver  15 . Receiver  15  converts the summing signal into an electrical signal and feeds it via line  4 ″ to CDMA decoder  16 . CDMA decoder  16  is in particular configured such that it does not recognize the signal of the useful information, which, by way of example, can be achieved in that it contains a filter function using which it is possible to recognize from the summing signal only the CDMA-coded signal of the signaling and control information. This is possible due to the fact that the useful information is transmitted at a significantly higher transmission rate than the signaling and control information, so that here provision can be made for an electrical filter element. In this way, the transmission of signaling and control information takes place in an asynchronous manner in comparison to the useful signal. 
     In CDMA decoder  16 , a code word is stored using software, the code word functioning as a key for the signaling and control information provided for this network element  2   e , and the latter information can be decoded in this way. After the signaling and control information has been decoded, it is relayed to signaling device  9 . The device evaluates this information and controls, for example, network element  8 . Control of this type can be provided if network element  2   e  has a further output. Then it is possible to divide the wavelength multiplex signal downstream of input  6  into different partial signals, the partial signals being relayed to the outputs. Element  8  thus takes on a sort of switching function for the wavelength multiplex signal. The division of the wavelength multiplex signal, i.e., which wavelengths are made available at which output, controls signaling device  9  on the basis of the signaling and control information made available to it. 
     In FIG. 4, for a further embodiment of the receiving device, according to the present invention network element  2   b  is considered, purely by way of example. It has an element  8 ′, which includes an input  6  as well as two outputs  7  and  7 ′. At input  6 , the wavelength multiplex signal having wavelengths λ 1  through λ n  is available. Element  8 ′ divides this wavelength multiplex signal, for example, such that at output  7  only one signal is applied, which has only one wavelength λ i . Therefore, here there already exists one single summing signal, which in turn is divided by monitor coupler  13  into two identical partial signals. A partial signal reaches receiver  15  via LWL  4 ′, the receiver in turn undertaking a conversion from the optical area into the electrical area, and the electrical signal is relayed to CDMA decoder  16 . CDMA decoder— as was already described— is conductively connected to signaling device  9 . The other partial signal is fed to network element  2   g  at output  7 ′ via LWL  4 , being intensified in network element  2   g  and transferred to network node  2   d.    
     The signaling and control information is decoded, in the embodiment illustrated in FIG. 4, in the same manner as in the embodiment illustrated in FIG. 3, it being possible to dispense with only filter  14 , since no wavelength multiplex signal is available at monitor coupler  13 , rather it being useful to pick off a summing signal. 
     Furthermore, is obvious in FIG. 4, network element  2   g  is connected to signaling element  9 . This can take place either via the already available LWL or using a radio connection or an electrical line. As was already mentioned, network element  2   g  is an optical intensifier  3 , which can intensify an optical signal which has been weakened by losses in the optical fiber. For example, the degree of intensification of intensifier  3  can be regulated using signaling device  9 , although it is also possible to relay error messages of amplifier  3  to signaling device  9 . These error messages can then be advantageously retrieved at the location of network element  2   b , so that repair measures or maintenance work can be begun. Signaling device  9  as illustrated with FIG.  4 — as was described above — controls optically selective element  8 ′. 
     This embodiment according to the present invention as illustrated in FIG. 5 depicts an element  8 ″, to whose input  6  the wavelength multiplex signal is fed. Element  8 ″ includes an optical/electrical converter unit  17 , which converts the wavelength multiplex signal into an electrical signal. Output  7  of element  8 ″, in this context, is an electrical line  18 , from which a branch  19  is conductively connected to CDMA decoder  16 . CDMA decoder  16  operates in the same manner as described above, so that reference may be made to the corresponding description passages. 
     Downstream of branch  19 , electrical line  18  leads to a modulator (not depicted), which converts the electrical signal again into an optical signal. 
     A modulator  20  of this type is depicted in FIG. 6 a . After signaling device  9  has received the signaling and control information, has evaluated it, and possibly generated new signaling and control information, the latter is fed at output  11  of signaling device  9  to a transmitting device  25  via an electrical connecting line  22 , transmitting device  25  having a CDMA coder  21 . CDMA coder  21  links the individual bits of the signaling and control information to a code word, so that the information can be assigned to a further network element. After the CDMA coding, a transfer takes place via electrical connecting line  22 ′ to a junction  23 , so that a summing signal can be fed in electrical form to modulator  20 . Modulator  20  contains an electrical/optical converter unit  24 , which converts the electrical summing signal into an optical signal. The signal of the signaling and control information is already impressed on this summing signal. It is fed to network  1  via LWL  4 . 
     Alternatively, provision can be made— as is depicted in FIG. 6 b — that, in place of modulator  20 , an element  8 ′″ is provided for which on the input side has an electrical connection. Inside element  8 ′″ there takes place the electrical/optical conversion into a signal that is fed then to network  1  via an LWL  4 . Reference is made to FIG. 6 a  for the description of transmitting device  25 . 
     FIG. 7 depicts a modulator  20 ′, using which it is possible using addition to impress onto an optical signal a signal having signaling and control information, emitted by transmitting device  25 , the former signal being made available to the latter signal via LWL  4 . Using this signal, the useful information is transmitted. Through addition of the two signals, there arises at output  26  of the modulator a summing signal which is fed via input  6  to element  8 . At its output  7 , the summing signal is again fed to network  1  via LWL  4 . 
     A further embodiment of a transmitting device  25  is depicted in FIG.  8 . Transmitting device  25  has an optical source  27 , which converts the CDMA-coded information from signaling device  9 , or from CDMA coder  21 , into optical signals. Via an LWL  4 ′, the signaling and control information is coupled via a coupler  28  into LWL  4 . In this manner, a summing signal can already be relayed to element  8 , the summing signal containing the useful information and the signaling and control information. 
     Alternatively, with respect to FIG. 8, provision can be made that downstream of an element  8  a modulator  20 ″ is arranged which functions subsequently to impress CDMA-coded signaling and control information from transmitting device  25  onto the useful signal, so that the useful signal can be fed via LWL  4  to network  1  as a summing signal (see FIG. 9 ). Identical or identically functioning parts such as were mentioned in the preceding description sections are provided with the same reference numerals. In this regard, reference is made to the corresponding explanations. 
     FIG. 10 depicts an optically selective element  8   a , which, in contrast to optically selective element  8 , has two inputs  6  and two outputs  7 . At one input  6 , for example, via LWL  4  a wavelength multiplex signal having wavelengths λ 1  through λ n  is applied. At other input  6 , a further wavelength multiplex signal having wavelengths λ n+1  through λ m  is available. For the following description, the assumption is made, purely by way of example, for reasons of simplicity, that at each input  6  of element  8   a  a wavelength multiplex signal is available which is composed only of two different wavelengths. For example, these can be wavelengths λ 1  and λ 2  as well as wavelengths λ 3  and λ 4 . 
     The wavelength multiplex signal (λ 1 ,λ 2 ) can be picked off via a monitor coupler  13 . Monitor coupler  13  is preferably connected to filter  14  as illustrated in FIG.  3 . In this regard, for the processing of this signal reference is made to the corresponding description. 
     Element  8   a  functions to separate and/or to exchange individual channels of wavelength multiplex signals from/among each other. For this purpose, element  8   a  has at inputs  6  in each case a device  29 , which is provided for making available in separated form the individual wavelengths of a multiplex signal. A coupling device  30  arranged downstream of device  29  makes it possible once again to divide the individual channels — in accordance with the control specifications— from the signaling and control information. This means that after the multiplex signals have been divided into individual summing signals, a wavelength conversion of the desired summing signals takes place in coupling device  30 . In this way, it is possible that a wavelength multiplex signal is available at the outputs which has wavelengths λ 1  and λ 2  and a further wavelength multiplex signal has wavelengths λ 3  and λ 4 , although, for example, the information of input-side wavelength λ 3  is contained in output-side wavelength Ala. Output-side wavelength λ 3 a then contains preferably the information of input-side wavelength λ 1 . 
     In addition, element  8   a  has designed to it a further monitor coupler  31 , which purely by way of example, is here assigned to the electrical line of wavelength λ 4 . A monitor coupler  31  of this type can also be assigned to a plurality of electrical lines within element  8   a . 
     It is also obviously possible to furnish element  8   a  with more than two inputs and outputs, the number of inputs preferably corresponding to the number of outputs. 
     Element  8   a  illustrated in FIG. 10 may be modified in accordance with the preceding explanations. For example, it can have an electrical input and an optical output or vice versa, so that this element  8   a  can be applied in all of the embodiments described above. 
     Finally, it should be noted that all of the receiving devices and transmitting devices can be combined with each other in any way desired, after the appropriate modification.