Abstract: A unidirectional or bidirectional node for use in an optical communications network, a network consisting of such nodes and a method of maintaining a target loss around a ring. The node comprises one or more optical couplers as well as either or both of drop circuitry connected to an output port and add circuitry connected to an input port. This allows for changes to the wavelength plan without interruption of the ring traffic. If add circuitry is used, the wavelengths in the filtered add signal should be distinct from those of the incoming signal on the main optical path which is merged with the add signal. When separate fibers are used for transmitting and receiving data between a hub and nodes in a ring, the through loss of the couplers is reduced for upstream couplers, which increases the available loss to be assigned to the fiber. The method of maintaining a target loss around a ring relies on the known through loss of the coupler at each node to set the gain of an amplifier connected to the node.

Abstract: A method and apparatus for channel performance equalization in wavelength division multiplexed (WDM) systems is disclosed. Performance of the channels is estimated from optical power measurements of each signal transmitted by the channels. The measurements are taken at the inputs of optical amplifiers in the transmission path of the system. The channels are equalized by adjusting the optical power of the channel transmitters. The method is applicable to point-to-point networks as well as more complex network configurations such as those having an add-drop multiplexer (ADM) for inserting and extracting channels from the transmission path. The method can compensate for signals having different bit rates by applying an offset to the amount of optical power adjustment of the channel transmitters.

Abstract: A method for recovering an outgoing data signal from an incoming signal received over a transmission network. The method provides for preparing a bit error rate (BER) map for a data regenerator, determining, on the BER map, an optimal operation point for a provisioned BER.sub.prov value, and monitoring the data regenerator to function in the optimal operation point for providing a regenerated data signal. In addition, the errors in the regenerated data signal may be further corrected using current forward error correction circuitry. To prepare a BER map, the data regenerator operates in an error mapping mode, wherein the incoming signal is decoded using a slicing level V.sub.i and a phase shifted clock signal CL.sub.j. Each value BER.sub.i,j is measured over a preset period of time T.sub.prov for a pair V.sub.i, .phi..sub.j and stored in a memory. The BER maps may be prepared once a day or at any other suitable interval.

Abstract: A method for encoding a binary input sequence x(0,1) to obtain a duobinary output sequence y(+1,0,-1) is provided. The duobinary coding technique always provides an output bit y.sub.k =0 when the corresponding bit x.sub.k =0; bits y.sub.k alternatively assume a logical level "+1" and "-1" whenever an input bit x.sub.k-1 =0 changes to x.sub.k =1, and the output bit y.sub.k maintains the logical level "+1" or "-1" whenever the corresponding bit x.sub.k maintains the logical level "1". A coding device for encoding a binary input sequence x(0,1) to a duobinary output sequence y(+1,0,-1) is also provided, comprising a D-type flip-flop for generating a binary switch signal. A first AND circuit receives the input sequence and the switch signal, and provides a first binary sequence a(0,1), while a second AND circuit receives the input sequence and the complement of the switch signal and provides a second binary sequence b(0,1).

Abstract: A configuration for a SONET transport node comprises a pair of transparent mux/demuxs provided at two sites and connected over a high rate span. The T-Muxs provide continuity of all tribs and maintain a lower bit rate linear or ring system through the higher bit rate span. The lower bit rate linear or ring system operates as if it were directly connected without the higher bit rate midsection. For the forward direction of the traffic, the T-Mux comprises a multi-channel receiver for receiving the trib signals and providing for each trib signal a trib SPE and a trib OH. The trib SPEs are multiplexed into a supercarrier SPE and the trib OHs signals are processed to generate a supercarrier OH. A supercarrier transmitter maps the supercarrier SPE and the supercarrier OH into a supercarrier signal and transmits same over the high rate span. Reverse operations are effected for the reverse direction of traffic.