Abstract:
A wavelength division multiplexing transmission device includes a multiplexer part which multiplexes a plurality of first signals having a first bit rate and different wavelengths into a second signal having a second bit rate higher than the first bit rate and inserts wavelength data information concerning the different wavelengths into the second signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wavelength discriminating function, and more particularly to a wavelength division multiplexing transmission device and method having a wavelength discriminating function applicable to a wavelength division multiplexing transmission system in an optical communication system. 
     Recently, there has been considerable activity of increasing communication channels due to an abrupt demand for communications in optical transmission systems. However, an extension work of optical fiber cables needs a huge amount of cost. Hence, a wavelength division multiplexing transmission system is positioned as a key scheme because such a system efficiently utilizes the existing optical fiber cables and can increase the channel capacity by increasing the degree of multiplexing. Nowadays, four-wave multiplexing, eight-wave multiplexing, 16-wave multiplexing and 32-wave multiplexing have been used in practice in the wavelength division multiplexing transmission system. 
     2. Description of the Related Art 
     FIG. 1 is a block diagram of a conventional wavelength division multiplexing transmission system (four-wave multiplexing). Line terminal equipment LTE receives four data signals STM-M of a relatively low bit rate and multiplexes the data signals into an optical signal STM-N of a relatively high bit rate having a given wavelength by a method which will be described with reference to FIG.  2 . 
     A line terminal equipment (LTE)  11  multiplexes  1  multiplexes four data signals STM-M# 1 -# 4  of a relatively low bit rate into a single optical signal STM-N of a relatively high bit rate having a wavelength λ 1  to an optical coupler  15 . Similarly, line terminal equipment LTE  12 ,  13  and  14  respectively output multiplexed optical signals STM-N having wavelengths λ 2 , λ 3  and λ 4  and supply them to the optical coupler  15 , which has a wavelength multiplexing function (MUX). 
     The wavelengths λ 1 -λ 4  are arranged as shown in FIG.  3 . As shown in FIG. 3, the wavelengths λ 1 -λ 4  are respectively set equal to 1548.51 nm, 1551.72 nm, 1554.94 nm and 1558.17 nm. With this arrangement, the wavelength division multiplexing can be realized. Further, 8-wave multiplexing and 16-wave multiplexing can be realized as shown in FIG.  3 . 
     Turning to FIG. 1 again, the optical coupler  15  combines the four high-bit-rate optical signals STM-N having the different wavelengths from the line terminal equipment  11 - 14 , and outputs a combined, namely, multiplexed optical signal to an optical coupler  17  via an optical fiber cable  16 . 
     The optical coupler  17 , which has a wavelength demultiplexing function (DMUX), demultiplexes the multiplexed STM-N signal received from the optical fiber cable  15  into four optical signals STM-N having the different wavelengths. Then, the optical coupler  17  outputs the optical signal STM-N of the wavelength λ 1  to line terminal equipment LTE  18 . Similarly, the optical coupler  17  outputs the optical signals STM-N of the wavelengths λ 2 -λ 4  to line terminal equipment LTE  19 - 21 , respectively. 
     The line terminal equipment  18  is supplied with the high-bit-rate optical signal STM-N of the wavelength λ 1  and demultiplexes it into four low-bit-rate data signals STM-M by a method which will be described later with reference to FIG.  2 . Similarly, the line terminal equipment  19 ,  20  and  21  are respectively supplied with the high-bit-rate optical signals STM-N of the wavelengths λ 2 -λ 4  and demultiplex them into four low-bit-rate data signals STM-M. 
     The line terminal equipment LTE will be described with reference to FIG. 2, which is a block diagram thereof. The line terminal equipment  11  receives the four low-bit-rate data signals STM-M# 1 -STM-M# 4  from an external device, and outputs these signals to a multiplexer (MUX)  29  via interface parts  25 - 28 , respectively. The multiplexer  29  inserts OHBs (Over Head Bit or Over Head Byte), which are used to transfer maintenance information between communication devices. 
     A system controller  30  performs various control procedures in accordance with information and data supplied from a local terminal  33  and/or a remote terminal  23  such as a workstation (WS) connected to a network management system (NMS)  22 . The remote terminal  23  enables a remote maintenance work. 
     The multiplexer  29  multiplexes the four data signals STM-M supplied thereto into a single high-bit-rate data signal, and adds OHB data thereto. Then, the multiplexer  29  supplies an electro-optic converter (E/O)  34  with the multiplexed data signal with the OHB data added thereto. 
     The electro-optic converter  34  converts the received electric signal into a corresponding optical signal. Although not shown in FIG. 2, the optical signal outgoing from the electro-optic converter  34  is supplied to the optical coupler  15  shown in FIG. 1, which coupler multiplexes other optical signals generated similarly. Then, the multiplexed optical signal is output from the optical coupler  15  to the optical coupler  17  via the optical fiber cable  16 . 
     An opto-electric (O/E) converter  36  receives the multiplexed optical signal from the optical fiber cable  16 . The converter  36  converts the received optical signal into a corresponding electric signal, which is supplied to a demultiplexer (DMUX)  37 . The demultiplexer  37  demultiplexes the received signal into the data signals STM-M# 1 -STM-M# 4  and the OHB data. The data signals STM-M# 1 -STM-M# 4  are respectively supplied to devices of the next stage via interface parts  43 - 46 . The OHB data is supplied to a system controller  38 , which performs various controls in accordance with instructions supplied from a local terminal  42  or the aforementioned remote terminal  23 . 
     A description will now be given of a transfer of the maintenance information between the communication devices using the OHB data. The wavelength division multiplexing transmission is used in an SDH (Synchronous Digital Hierarchy) optical communication system which conforms to the international standard of synchronous multiplexing recommended by ITU-T. In the SDH optical communication system, the maintenance information is transferred between the communication devices using the OHB data provided in the STM-N frame which is the unit for multiplexing. The way of using the OHB data is defined. 
     The minimum management interval between the communication devices in the SDH optical communication system is called “section”, and the OHB data for managing the section is called RSOH (Reg. Section Over Head). Conventionally, the RSOH has a section trace function of performing the inter-section management, called J 0  byte. The section tracing function using the J 0  byte shows from where the signal being transferred comes. 
     The section trace function will be described with reference to FIG. 4. A station (A)  50  is now located on the transmission side. The optical coupler  15  of the station  50  combines the optical signals respectively having the wavelengths λ 1 -λ 4  generated by the line terminal equipment  11 - 14 , and sends the multiplexed signal to a station (B)  51  located on the reception side. The interval between the stations  50  and  51  is the section, and the section trace function using the J 0  byte manages information on the section including the country number, the name of the station and the name of the transmitter device 
     However, in the wavelength division multiplexing transmission system, the J 0  bytes of all the wavelength-division-multiplexed signals having different wavelength have the same value because the J 0  bytes show from which the respective signals come from (station  50  in the case shown in FIG.  4 ). Hence, it is impossible to check each of the wavelength-division-multiplexed signals having the different wavelengths by referring to the respective J 0  bytes. Conventionally, a spectrum analyzer is used to measure the wavelengths of the wavelength-division-multiplexed signals and check each of them. The above work by the maintenance person is very cumbersome. 
     In the wavelength division multiplexing transmission system, as an increased number of wavelengths, the adjacent wavelengths become closer to each other. Thus, if a wavelength connection fails, the signals cannot be received correctly or signals other than the target signals may be received. Furthermore, an increased number of wavelengths which are multiplexed and transferred over a single optical fiber needs a more complex management work directed to, for example, getting information on the states of channels. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide a wavelength division multiplexing transmission device and method and a wavelength division multiplexing system, in which the above disadvantages are eliminated. 
     A more specific object of the present invention is to provide a wavelength division multiplexing transmission device, method and system in which each of wavelengths multiplexed and transferred over an optical fiber in the wavelength division multiplexing system can be checked and the wavelength management can be facilitated. 
     The above objects of the present invention are achieved by a wavelength division multiplexing transmission device comprising: a multiplexer part which multiplexes a plurality of first signals having a first bit rate and different wavelengths into a second signal having a second bit rate higher than the first bit rate and inserts wavelength data information concerning the different wavelengths into the second signal. With the above structure, it is possible to notify a remote device of information indicative of the wavelengths included in the second signal. 
     The above objects of the present invention are also achieved by a wavelength division multiplexing transmission device comprising: a plurality of multiplexer parts, each of which multiplexes a plurality of first signals having a first bit rate and different wavelengths into a second signal having a second bit rate higher than the first bit rate and inserts wavelength data information concerning the different wavelengths into the second signal; and an optical coupler which combines second signals from the plurality of multiplexer parts and outputs a resultant optical signal. 
     The above objects of the present invention are also achieved by a wavelength division multiplexing transmission device comprising: a demultiplexer part which demultiplexes a second signal having a second bit rate into first signals having a first bit rate lower than the second bit rate and having different wavelengths and wavelength value data concerning the different wavelengths. With the above structure, it is possible to recognize, on a reception side, which wavelengths are included in the second signal. 
     The above-mentioned objects of the present invention are achieved by a wavelength division multiplexing transmission device comprising: an optical coupler which separates an optical signal transferred over an optical fiber cable into second signals; and a plurality of demultiplexer parts, each of which demultiplexes one of the second signals having a second bit rate into first signals having a first bit rate lower than the second bit rate and having different wavelengths and wavelength value data concerning the different wavelengths. 
     The above-mentioned objects of the present invention are also achieved by a wavelength division multiplexing transmission system comprising: a first wavelength division multiplexing transmission device; a second wavelength division multiplexing transmission device; and an optical fiber cable. The first and second wavelength division multiplexing transmission devices are configured as described above. 
     The above-mentioned objects of the present invention are also achieved by a wavelength division multiplexing transmission method comprising the steps of: multiplexing a plurality of first signals having a first bit rate and different wavelengths into a second signal having a second bit rate higher than the first bit rate; and inserting wavelength data information concerning the different wavelengths into the second signal. 
     The above-mentioned objects of the present invention are also achieved by a wavelength division multiplexing transmission method comprising the steps of: receiving a second signal; and demultiplexing a second signal having a second bit rate into first signals having a first bit rate lower than the second bit rate and having different wavelengths and wavelength value data concerning the different wavelengths. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a conventional wavelength division multiplexing transmission system; 
     FIG. 2 is a block diagram of line terminal equipment shown in FIG. 1; 
     FIG. 3 is a diagram showing a table of an arrangement of wavelengths in the wavelength division multiplexing transmission system; 
     FIG. 4 is a diagram showing a section trace function; 
     FIG. 5 is a diagram of a line terminal equipment according to an embodiment of the present invention; 
     FIGS. 6A and 6B are diagrams of an arrangement in which wavelength value data is inserted into a section trace; 
     FIG. 7 is a diagram of a section overhead (SOH) of STM- 1  frame structure; 
     FIGS. 8A and 8B are diagrams of an arrangement in which the wavelength value data is inserted into the section overhead. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given of an embodiment of the present invention related to a wavelength division multiplexing transmission device and method and a wavelength division multiplexing transmission device having a wavelength discriminating function. 
     FIG. 5 is a block diagram of line terminal equipment LTE having a wavelength discriminating function according to an embodiment of the present invention. A line terminal equipment  61  receives four data signals STM-M# 1 -STM-M# 4  of a relatively low bit rate from an outside thereof, and sends these signals to a multiplexer (MUX)  66  via interface parts  62 - 65 , respectively. In addition to the above signals, the multiplexer  66  is supplied with OHB data for transferring maintenance information between communication devices. In the present invention, wavelength value data indicative of the wavelengths transferred in the wavelength division multiplexing. 
     A description will now be given of a method of inserting the wavelength value data into the OHB data supplied from a system controller  67  to the multiplexer  66 . 
     FIGS. 6A and 6B show byte arrangements in which the wavelength value data is inserted into the section trace (J 0  byte). More particularly, FIG. 6A shows a byte arrangement in which the wavelength value data is not inserted into the section trace, and FIG. 6B shows a byte arrangement in which the wavelength value data is inserted into the section trace. 
     The section trace (J 0  byte) transfers an S-APIs (Section Access Point Identifier) in order to discriminate a mutual connection between the transmission-side device and the reception-side device. As is known, there are two types of the section access point identifier. By way of example, a description will be given of a case where the wavelength value data is inserted into continuous transmission of a message formed of a 16-byte frame. 
     As shown in FIGS. 6A and 6B, when the start identifier consists of one byte and the country number consists of three bytes, the arrangement shown in FIG. 6A utilizes 12 bytes for section discrimination. The arrangement shown in FIG. 6B uses 7 bytes for the wavelength value data, and is allowed to use only 4 bytes for section discrimination. Hence, the original information to be sent using the section trace (J 0  byte) is restricted by inserting the wavelength value data and a problem may occur. 
     With the above in mind, the present embodiment employs another way to transfer the wavelength value data. 
     FIG. 7 shows an example of the OHB data. As shown in FIG. 7, the OHB data consists of 9 bytes×9 columns, and includes undefined (unused) bytes indicated by “x”. The wavelength value data is inserted into undefined bytes. In the following description, the wavelength value data is inserted into two undefined bytes  85  and  86  next to the J 0  byte. 
     FIG. 8 shows a method of inserting the wavelength value data into the two undefined bytes  85  and  86 . More particularly, FIG. 8A shows a method of encoding the wavelength value data, and FIG. 8B shows a bit arrangement in which the encoded wavelength value data is inserted in the OHB data. A case will be considered where a signal source for wavelength division multiplexing is a laser source of the 1.55 μm band. The values of the wavelengths can be discriminated from each other by the four lower digits thereof. When the four lower digits (any of 0-9) are respectively denoted as a, b, c and d, the wavelength value data can be represented as follows: 
     
       
           λn= 15 ab.cd  (nm)  (1) 
       
     
     When the four lower digits are expressed in binary notation, each of the digits can be expressed by four bits, and the four lower digits can be expressed by 16 bits. As shown in FIG. 8B, the encoded wavelength value data a and b are inserted into byte # 2  corresponding to the undefined byte  85 , and the encoded wavelength value data c and d are inserted into byte # 3  corresponding to the undefined byte  86 . In the above manner, the wavelength value data is inserted into the OHB data. 
     Turning to FIG. 5 again, the wavelength value data is supplied to a transmission-side wavelength value setting part  68  from the local terminal  69 . The transmission-side wavelength value setting part  68  encodes the wavelength value data as described above, and supplies the encoded wavelength value data to the system controller  67 . The system controller  67  supplies the OHB data including the wavelength value data to the multiplexer  66 . The system controller  67  performs various controls in accordance with the instructions from the local terminal  69 . 
     The multiplexer  66  multiplexes the four low-bit-rate data signals STM-M# 1  - STM-M# 4  into a high-bit-rate data signal, and adds the OHB data thereto. Then, the multiplexer  66  supplies the high-bit-rate data signal with the OHB data added thereto to an electro-optic converter  70 . 
     The elecro-optic converter  70  converts the supplied high-bit-rate data signal into an optical signal STM-N. Although not illustrated in FIG. 5, the optical signal STM-N output by the electro-optic converter  70  is supplied to the optical coupler  15  shown in FIG. 1, which coupler multiplexes other optical signals generated similarly. Then, the multiplexed optical signal is output from the optical coupler  15  to the optical coupler  17  via the optical fiber cable  16 . 
     An opto-electric (O/E) converter  72  receives the multiplexed optical signal from the optical fiber cable  16 . The converter  72  converts the received optical signal into a corresponding electric signal, which is supplied to a demultiplexer (DMUX)  73 . The demultiplexer  73  demultiplexes the received signal into the data signals STM-M# 1 -STM-M# 4  and the OHB data. The data signals STM-M# 1 -STM-M# 4  are respectively supplied to devices of the next stage via interface parts  78 - 81 . The OHB data is supplied to a system controller  74 , which performs various controls in accordance with instructions supplied from a local terminal  77 . 
     The system controller  74  detects the encoded wavelength value data from the supplied OHB data, and supplies it to a reception-side wavelength monitor part  75  and a wavelength value expected value check part  76 . The parts  75  and  76  subject the encoded wavelength data to a process reverse to that of the transmission-side line terminal equipment  61 , so that the wavelength value data is reproduced. 
     The reception-side wavelength value monitor part  75  notifies the local terminal  77  of the wavelength value data. The wavelength value expected value check part  76  compares expected values of the wavelength value data of the received signals prepared in the local terminal  77  beforehand with the notified wavelength value data, and determines whether the target signals are duly connected. 
     The system controller  74  is notified of the result of the above determination from the check part  76 . If it is determined that the target signals are not duly connected, the system controller  74  performs an abnormality procedure by which a given alarm process and a transfer of an alarm to the outside of the line terminal equipment  71  are performed. 
     The above-mentioned embodiment has the transmission-side wavelength data setting part  68 , the reception-side wavelength value monitor part  75  and the wavelength value expected value check part  76  separately from the system controllers  67  and  74 . Alternatively, the embodiment may be modified so that the system controller  67  and  74  perform the processes of the transmission-side wavelength data setting part  68 , the reception-side wavelength value monitor part  75  and the wavelength value expected value check part  76 . 
     According to the present invention, it is possible to check the connection between the line terminal equipment and the optical fiber by comparing, in the wavelength value expected value check part  76 , the expected values of the wavelength value data with the wavelength value data transferred and extracted on the receive side. 
     The reception-side wavelength value monitor part  75  is capable of notifying an external device such as the local terminal  77  of the reproduced wavelength value data. Hence, the work of installing and extending channels and optical fiber lines can be facilitated. 
     It is possible to easily process and manage the information by transferring the OHB data including the wavelength value data separate from the OHB data including the section trace (J 0  byte). This is advantageous to a network in which a wavelength division multiplexing transmission system and a single-wavelength transmission system coexist. In such a network, the section information common to both the systems is transferred by the section trace, while the wavelength information required for only the wavelength division multiplexing transmission system is transferred by the separate OHB data. If there is no need for the wavelength information, a wavelength undefined code may be inserted into the OHB data. 
     In practice, the section trace (J 0  byte) is expressed in different fashions. For example, different carriers used in different countries or companies express the section trace in different fashions. In contrast, the use of the undefined bytes for transferring the wavelength value data makes it easy to cope with an increase in the number of wavelengths to be multiplexed and the number of optical fiber cables. 
     If a future technical advance makes it possible to replace an optical coupler by an electronic device, the target wavelength can easily be selected by using the wavelength value data used in the present invention, so that there is no need to change the connections of optical fiber cables. 
     It is possible to provide a transmission device includes the configurations of the line terminal equipment  61  and the line terminal equipment  71 . 
     The present invention includes another embodiment in which only the wavelength of a signal in the wavelength division multiplexing transmission device is converted into another wavelength. In this case, the wavelength data information concerning the converted wavelength is inserted into or added to the signal. 
     The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application no. 10-206780 filed on Jul. 22, 1998, the entire contents of which are hereby incorporated by reference.