Optical communications – Multiplex – Wavelength division or frequency division
Reexamination Certificate
2000-05-19
2003-10-21
Pascal, Leslie (Department: 2733)
Optical communications
Multiplex
Wavelength division or frequency division
C398S183000, C370S320000, C370S335000, C370S342000, C370S441000
Reexamination Certificate
active
06634809
ABSTRACT:
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
Gladisch Andreas
Ziemann Olaf
Deutsche Telekom AG
Kenyon & Kenyon
Pascal Leslie
Payne David C.
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