Abstract: A network element of a transport network has three fabrics housed within a single shelf of a telco rack, namely a packet fabric, an electrical fabric and an optical fabric. The shelf also includes inter-fabric circuitry, to bridge between the fabrics, e.g. packet-electrical and/or electrical-optical and/or packet-optical. The inter-fabric circuitries switchably transmit packets across fabrics in intermediate nodes of the transport network. The single shelf of some embodiments has a wall (“midplane”) between a rear region that holds the three fabrics and a front region that holds inter-fabric circuitry, and external interfaces to optical trunks and/or packet services and/or optical tributaries.

Abstract: A network component comprising at least one processor configured to implement a method comprising obtaining a wavelength availability information for a path, determining whether to implement a wavelength assignment based on the wavelength availability information, updating the wavelength availability information when the wavelength assignment is to be implemented, and forwarding the wavelength availability information. Also included is a method comprising obtaining a wavelength availability information, comparing a number of wavelengths in the wavelength availability information to a threshold, determining whether to implement wavelength conversion along a path when the number of available wavelengths is less than or about equal to the threshold, and resetting the wavelength availability information when wavelength conversion is to be implemented.

Abstract: A high capacity distributed switching system comprises electronic edge nodes connected to a balanced bufferless switch which may be electronic or optical. The balanced bufferless switch comprises a balanced connector and a switch fabric. The balanced connector comprises an array of temporally cyclic rotator units having graduated rotation shifts and each having a prime number of output ports. The switch fabric may be a mesh interconnection of switch modules. Due to the use of the balanced connector, establishing a path through the switch fabric requires at most a second-order time-slot matching process for a high proportion of connection requests with a much reduced need for a third-order time-slot matching process required in a conventional mesh structure.

Abstract: A method, apparatus and system for advertising a routing protocol message and calculating a route are provided which solve the problems that the time of connection establishment or rerouting in wavelength routing is too long and that wavelength utilization efficiency is low. The method for advertising the routing protocol message includes: obtaining node information and link information of a node, in which the node information contains port cross-connection capability information of the node, and the link information contains wavelength restriction information and wavelength status information of each link connected to the node; carrying the obtained node information and link information in a Type-Length-Value object of a routing protocol message, and advertising the routing protocol message in the network.

Abstract: A ring communication network according to an embodiment of the present invention includes a plurality of nodes in which a single one of the nodes is configured for full channel conversion and the remaining nodes, other than the single node, are configured for no channel conversion. Links with no more than W channels couple the nodes. The ring communication network also may include N nodes and links connecting the nodes for carrying data in W channels such that N?2 log2 W?1 where W is a power of 2. Each of the N nodes includes switches connected such that each channel of a first one of the links adjacent to any one of the N nodes can be switched to no more than W?1 channels of another one of the links adjacent any one node.

Abstract: An optical switch assembly comprising at least two optical amplifiers (10, 20), means for applying a first input signal to one end of both amplifiers (10, 20) and a second input signal to another end, and means for simultaneously driving one or other of the amplifiers into a saturated state whilst the other is unsaturated such that only the amplifier that is unsaturated provides any significant amplification to the input signals at each end, and means for feeding the amplified output signals from the amplifiers to at least two output nodes such that the two amplifiers (10, 20) are connected to the two output nodes in opposite connections.

Abstract: An optical node may include a plurality of optical input components operable to receive a plurality of signals communicated in an optical network and a plurality of optical output components operable to transmit a plurality of signals to be communicated in the optical network.

Abstract: The invention pertains to methods, apparatus, and systems optical of networking using tunable receivers, optical blocking elements selectively placed in the network, and optical routing elements comprised of passive elements, such as optical couplers and splitters. The routing elements have a plurality of ports and comprise passive elements such as couplers and splitters configured so that input light received at any port of the element is output from each of the other ports of the element, but not at port at which it was input.

Abstract: The present invention is directed to an optical node apparatus in which the number of light elements that propagates reference light is reduced, which includes pa input-side wavelength mux/demux elements, a switch module, pb output-side wavelength mux/demux elements, and a reference light source. Each of the input-side wavelength mux/demux element include at least two first port and at least two second port. One of the first ports included in each input-side wavelength mux/demux element is coupled to an input transmission path. The other of the first ports coupled to the reference light source, and each of the second ports is coupled to an input end of the switch module.

Abstract: According to an embodiment of the present disclosure, a bidirectional communications system includes a first non-blocking network including a bidirectional optical switch, a plurality of nodes, a plurality of optical transceivers connected between the bidirectional optical switch and the plurality of nodes, each optical transceiver including a transmitter, a receiver and an optical combiner, and a second network connected to at least one of the nodes and the at least one at least one bidirectional optical switch for control of a crossconnect.

Abstract: An optical communications network node (10) comprising an optical transmitter module (16), an optical receiver module (12), an electrical cross-point switch (20) and control apparatus (24, 26). The optical transmitter module (16) comprises optical sources (18) each having a different operating wavelength and each being selectively assignable as an optical circuit switching channel source or an optical burst switching channel source. The optical receiver module (12) comprises a said plurality of optical detectors each operable at one of said operating wavelengths. The electrical cross-point switch (20) comprises switch paths (22) and is configurable to allocate a first set of switch paths for optical circuit switching and a second set of switch paths for optical burst switching.

Abstract: Provided is an apparatus for transferring optical data in an optical switching system using time synchronization. The apparatus performs time synchronization on optical data to input the optical data at regular intervals through fiber delay line for time synchronization respectively disposed on input ports. Therefore, the apparatus can efficiently reduce a data blocking rate in comparison with a conventional optical switching system using an asynchronous electric buffer without a synchronous process, and achieve the same performance as conventional asynchronous technology despite using fewer wavelength converters and buffers, thus reducing system cost. In addition, using dynamic time synchronization modules, the apparatus performs time synchronization for minute time variation due to an environment such as temperature.

Abstract: A wavelength selective light cross connect device 1A is configured of a route selector 10A including route selection elements 11-1 to 11-N, wavelength selector 20A, route selector 40A including route selection elements 41-1 to 41-M and controller 50A. The route selection elements 11-1 to 11-N select routes for WDM signals of N channels inputted to input routes Rin1 to RinN, and directs the WDM signals to the wavelength selector 20A. The wavelength selector 20A performs a selection operation to (N×M) WDM signals according to their wavelength, and outputs the signals. Wavelength selection elements 40-1 to 40-M receives different outputs obtained from the respective route selection elements via the wavelength selector 20A, selects routes and outputs the signals from output routes Rout1 to RoutM.

Abstract: An optical add-drop multiplexer having first and second routes includes: an optical cross connect; a first multiplexer optically coupled to a plurality of output ports of the optical cross connect; a second multiplexer optically coupled to a plurality of other output ports of the optical cross connect; a first wavelength selective switch to generate a first WDM optical signal including an optical signal output from the first multiplexer and to guide the first WDM optical signal to the first route; and a second wavelength selective switch to generate a second WDM optical signal including optical signal output from the second multiplexer and to guide the second WDM optical signal to the second route.

Abstract: A multiple input/output wavelength selective switch device 1 is configured of an N×M optical cross connect switch 10, wavelength selector 20 and controller 40. The N×M optical cross connect switch 10 turns WDM signals of N channels inputted to input routes Rin1 to RinN into M WDM signals. The wavelength selector 20 can perform a selection operation with respect to each of the M WDM signals according to their wavelengths and output the signals from output routes Rout1 to RoutM.

Abstract: An optical transmission system 100 includes a plurality of transmission devices 110 to 150 each configured to be capable of transmitting and receiving an optical signal at each of a plurality of different wavelengths and thereby transmitting and receiving a plurality of optical signals simultaneously. The transmission device 120 transmits an optical signal received at a transmission wavelength to each of the transmission device 130 and the transmission device 140. The optical transmission system transmits the optical signal at the transmission wavelength from the transmission device 110 to the transmission device 150 via each of a plurality of paths that partly overlap. The optical transmission system estimates, for each of the paths, a line quality representing the degree of coincidence between an optical signal transmitted by the transmission device 110 and an optical signal received by the transmission device 150.

Abstract: A photonic cross-connect includes a plurality of ingress WS-switches with drop outputs outputting WDM drop signals including odd channels and a plurality of egress WS-switches for receiving WDM add signals including add channels. Wavelength selective elements in a drop path and in an add path comply with a double frequency spacing and about a double bandwidth of the ingress WS-switches or egress WS-switches. If both odd and even channels are dropped and added, separate add and drop paths are provided for the odd and for the even channels.

Abstract: A network component comprising at least one processor configured to implement a method comprising transmitting a request to compute a routing assignment, a wavelength assignment, or both, wherein the request comprises a lightpath constraint indicator is disclosed. Also disclosed is an apparatus comprising a Path Computation Client (PCC) configured to transmit a request to and receive a reply from a Path Computation Element (PCE), wherein the request comprises a lightpath constraint, and wherein the reply comprises a routing assignment, a wavelength assignment, an error message, a no-path indication, or combinations thereof. Included is a method comprising receiving a request comprising a request parameter (RP) object comprising a lightpath constraint, sending a reply comprising a routing assignment, a wavelength assignment, an error message, a no-path indicator, or combinations thereof, wherein the request is received and the reply is sent using path computation element protocol (PCEP).

Abstract: A switch matrix for selectively connecting at least one of N signal inputs to at least one of M signal outputs, N and M being integers greater than two, includes a cluster of N input switches arranged about each of the M signal outputs resulting in at least M clusters of N input switches, each input switch having a switch input and a switch output, the switch outputs being connected to respective signal outputs, the clusters and the input switches in the clusters being arranged to permit adjacent switch inputs of adjacent clusters to be connected to form input switch nodes; and a steering switch for each of the signal inputs. The steering switch selectably connects a signal input to an input switch node, wherein the combination of the steering switches and the input switches are operable to connect a desired signal input to a desired signal output.

Abstract: A passive optical network (PON) system comprising a plurality of optical network units (ONUs) having one downstream receiver and one upstream transmitter, an optical line terminal (OLT) having a downstream transmitter and a plurality of upstream receivers, wherein each upstream receiver is associated with a subset of the ONUs, and an optical distribution network (ODN) that connects the OLT to the ONUs is disclosed. An OLT for a PON, comprising a downstream transmitter, and a plurality of upstream receivers, wherein a downstream transmitter bandwidth is greater than each upstream receiver bandwidth is also disclosed. A network component comprising a processor configured to implement a method comprising determining a downstream bandwidth and an upstream bandwidth for a PON, and increasing a number of upstream channels per downstream channel for the PON when asymmetry between the downstream bandwidth and the upstream bandwidth is greater than a threshold amount is also disclosed.

Abstract: A multi-chassis network device includes a plurality of nodes that operate as a single device within the network and a switch fabric that forwards data plane packets between the plurality of nodes. The switch fabric includes a set of multiplexed optical interconnects coupling the nodes. For example, a multi-chassis router includes a plurality of routing nodes that operate as a single router within a network and a switch fabric that forwards packets between the plurality of routing nodes. The switch fabric includes at least one multiplexed optical interconnect coupling the routing nodes. The nodes of the multi-chassis router may direct portions of the optical signal over the multiplexed optical interconnect to different each other using wave-division multiplexing.

Abstract: A M×N wavelength selective optical switch (WSS) for switching K wavelength channels is disclosed. The WSS has two MEMS micromirror arrays, a M×K array and a 1×N array, for switching any wavelength channel from any input port to any output port, provided that any output port receives optical signals from only one input port. The WSS can be used to build fully reconfigurable, colorless and directionless node of an agile optical network.

Abstract: In order to insert a regenerator into a wavelength cross-connect equipment, there is provided at least one port that demultiplexes one wavelength among the wavelength multiplexed signals that are input to a wavelength selective switch. An output of the port that demultiplexes one wavelength is input to the regenerator, and an output of the regenerator is again input to the WSS. The wavelength output from the regenerator is converted into another wavelength different from the wavelength that is input to the regenerator and can be processed by the WSS in advance. The output from the regenerator is input to the WSS through an optical coupler or another input port of the WSS.

Abstract: The present invention relates to controlling wavelength switching in a plurality of nodes that are provided to increase the distance of signal transmission in inverse MUX transmission in which a high-speed line is divided into a plurality of low-speed lines for transmission. A maximum skew occurring between adjacent nodes is measured, and switching of wavelength channels is performed in one or a plurality of nodes on the basis of the measured maximum skew to keep the skew of the entire inverse MUX transmission system at or below a prescribed value. The optical communication device is provided with an NNI functional block to which high-speed lines on the transmission channel side are connected, and a UNI functional block to which low-speed lines on the client side are connected.

Abstract: Switching architectures for WDM mesh and ring network nodes are presented. In mesh networks, the switching architectures have multiple levels—a network level having wavelength routers for add, drop and pass-through functions, an intermediate level having device units which handle add and drop signals, and a local level having port units for receiving signals dropped from the network and transmitting signals to be added to the network. The intermediate level device units are selected and arranged for performance and cost considerations. The multilevel architecture also permits the design of reconfigurable optical add/drop multiplexers for ring network nodes, the easy expansion of ring networks into mesh networks, and the accommodation of protection mechanisms in ring networks.

Abstract: A wavelength division multiplexer terminal with a multiplexer arrangement with a first switching matrix, and a demultiplexer arrangement with a second switching matrix allows flexibility for connection transceivers to ports of the wavelength division multiplexer and wavelength division demultiplexer respectively. Optical monitoring receivers are connected upstream the wavelength division multiplexer and downstream the wavelength division demultiplexer for managing and supervising connections.

Abstract: Modular WSS-based Communications system with colorless and network-port transparent add/drop interfaces is described herein. According to certain aspects of the invention, equipment architecture is provided that enables a linear, ring, and mesh optical network. The embodiments of the invention are primarily on how to add and drop signals at a node of the network. The embodiments of the invention are based on the use a wavelength selective switch (WSS), which is an emerging component technology. Other methods and apparatuses are also described.

Abstract: A communication apparatus includes at least one input port, multiple output ports, at least one Serial-to-Parallel (S/P) converter and at least one Parallel-to-Serial (P/S) converter. The S/P converter is operative to receive from the input port an input data stream that is to be cross-connected to a destination output port, and to separate the input data stream into multiple sub-streams. Each of the switching planes includes at least one input for receiving a respective sub-stream from the S/P converter; multiple outputs, each output associated with a respective one of the output ports; and switching circuitry, which is configured to switch the respective sub-stream to the output that is associated with the destination output port. The P/S converter is coupled to the outputs of the switching planes so as to combine the multiple sub-streams switched by the switching circuitry into a combined output data stream at the destination output port.

Abstract: In a Wavelength Division Multiplexed (WDM) all-optical network having optical nodes linked together by optical fibers carrying communication channels of separate wave-lengths, a method is applied in order to extend the size of the all-optical network. According to the method, a model is set up for the all-optical network in which a wavelength graph containing vertices and edges represents the physical effects of the nodes and links. After identifying a set of demand, an objective function is calculated expressing the total routing cost and total signal power demand of the channels. The minimum of the objective function returns the signal powers for each channel to be tuned.

Abstract: An optimally-sized optical cross-connect that switches optical signal paths with a minimum number of wavelength selective switches and their interconnections. To switch optical signals of N routes (N=1, 2, . . . ), an optical cross-connect includes a 2×N (2-input, N-output) wavelength selective switch for each of N input routes and a N×2 (N-input, 2-output) wavelength selective switch for each of N output routes. One input port of each 2×N wavelength selective switch receives an optical signal from a corresponding input route, while the other input port of the same receives an optical add signal from a corresponding add route. One output port of each N×2 wavelength selective switch outputs an optical signal to a corresponding output route, while the other output port outputs an optical drop signal to a corresponding drop route.

Abstract: A system for communicating cross-connection information within an optical network by use of wavelength information is provided. Cross-connection information in Wavelength Division Multiplexing (WDM) devices is abstracted, to produce wavelength reachability information and wavelength occupation status information for each node within the optical network. Cross-connection information is distributed from one node to all other nodes or a Path Calculation Equipment (PCE), through extended routing protocols, providing a base for calculating service paths.

Abstract: A time-shared network comprising edge nodes and optical core nodes may be dynamically divided into several embedded networks, each of which covering selected edge nodes. At least one of the edge nodes may host an embedded-network controller operable to form multiple-source flow-rate allocation requests each of the requests specifying flow-rate allocations to a plurality of paths from several source nodes to several sink nodes. A core node may also host an embedded-network controller or several embedded-network controllers. The time-shared network may use both time-division multiplexing and burst switching.

Abstract: The present invention provides an information processing system, comprising a plurality of calculation nodes with an optical transmitter, which individually outputs a plurality of optical signals each having a different wavelength, and an optical receiver, which individually receives a plurality of optical signals each having a different wavelength, an optical transmission path connecting a plurality of the calculation nodes to each other, and optical pathway switching unit, lying in the optical transmission path, for transmitting the optical signal to the specific calculation node in accordance with a wavelength of the optical signal output from one of the calculation nodes.

Abstract: A wavelength-division-multiplexed based photonic burst switched (PBS) network, which includes edge and switching nodes, optically communicate information formatted into PBS control and data burst frames. Each PBS data burst frame is associated with a PBS control burst frame. A PBS burst frame includes a PBS burst header and burst payload having fields to indicate whether: (a) the PBS burst frame is a PBS control burst; (b) the control burst is transmitted on a wavelength different from that of the associated PBS data burst; and (c) the PBS burst frame has a label for use in a generalized multi-protocol label swapping (GMPLS)-based control system. The PBS burst payload frame includes fields to indicate (a) specific PBS payload information; (b) PBS data payload; and (c) an optional PBS payload frame check sequence (FCS) for error detection.

Abstract: Undirected cross connects are provided based on wavelength-selective switches. A undirected Cantor network is disclosed where the switch nodes are wavelength selective switches. A undirected Clos cross connect is also disclosed where one or more undirected switches are undirected Cantor networks having at least one wavelength selective switch.

Abstract: The invention relates to an optical circuit structure for realizing a higher-order node in an optical transmission network with a number N of bidirectional remote ports, wherein an optical receive wavelength division multiplexed signal with a set of optical receive channels can be fed to each remote port and wherein an optical transmit wavelength division multiplexed signal with a set of optical transmit channels can be output from each remote. The optical drop channel means and the optical add and cross-connect means include exclusively optical splitter units, optical demultiplexing units, and optical add units, wherein for generating each transmit wavelength division multiplexed signal for a certain remote port, the receive wavelength division multiplexed signals of several or all of the other remote ports are guided as cross-connect wavelength division multiplexed signals toward the certain remote port.

Abstract: In a wavelength division multiplex (WDM) optical communications network having a plurality of nodes, each of which comprises a wavelength selective optical cross-connect having a plurality of switching matrices, each switching matrix being provided for switching wavelength channels of a specific wavelength, a method of transmitting information from a start node to a target node includes the steps of applying to respective inputs of switching matrices of the start cross-connect, at least two wavelength channels (working an protection channels) having different wavelengths but which are modulated with the same information; transmitting the working and protection channels to the target cross-connect; and dropping the working and protection channels at outputs of different switching matrices provided for different wavelengths of the target cross-connect.

Abstract: A modular wavelength cross connect node for use in a dense wavelength division multiplexing network exhibiting low cost and improved performance by employing a bidirectional wavelength selective switch in a main optical path and using optical circulators to share any common ports.

Abstract: Bidirectional wavelength cross connects include a plurality of ports, each configured to receive an input optical signals, each input optical signal having a plurality of spectral bands. At least one of the plurality of ports is disposed to simultaneously transmit an output optical signal having at least one of the spectral bands. A plurality of wavelength routing elements are configured to selectively route input optical signal spectral bands to output optical signals.

Abstract: A wavelength path switching node apparatus is provided that improves the utilization efficiency of wavelength resources by allocating wavelength paths by following traffic variations in packet units. A node apparatus on the wavelength path start point side includes: a packet distributing section that stores input packets in a buffer, fetches the packets from the buffer and distributes to an initial path and additional paths; a control section that allocates the additional paths based on distribution states of the packet units; and an optical switch that switches wavelength paths based on this control. A node apparatus on the wavelength path end point side includes: a monitoring section that monitors packets distributed to the initial path and the additional paths; a control section that allocates the additional paths based on distribution states of the packet units obtained by this monitoring; and an optical switch that switches wavelength paths based on this control.

Abstract: A core unit arranged in a transmission path includes a through path for causing an input signal to an input port to pass through to an output port, a drop-side port 25a that drops the input signal having a predetermined wavelength, and an add-side port 25b that adds channel having a predetermined wavelength to the input light.

Abstract: A drive circuit is provided for a semiconductor optical amplifier type gate switch includes a first transmission path and a second transmission path. The first transmission path includes a common first sub-path between a signal source and a first node; and an individual second sub-path for each of a plurality of operational amplifiers between the first node and a corresponding one of the operational amplifiers. The second transmission path includes an individual third sub-path between each of the operational amplifiers and a second node; and a common fourth sub-path between the second node and the semiconductor optical amplifier type gate switches. Transmission delay times of all the individual second sub-paths are equal, and transmission delay times of all the individual third sub-paths are equal.

Abstract: A WDM optical cross-connect has input and output channels for through traffic. A first group of matrices connects the input channels to the output channels. Each input channel is connected to an input of a matrix of the first group and each output channel is connected to an output of the matrix. Input/output channels are provided for adding/dropping traffic. Each add/drop channel is connected to an input/output of a second group of matrices. The outputs/inputs of the second group of matrices are connected to inputs of a third group of matrices or outputs of a fourth group of matrices and the outputs/inputs of the third/fourth group of matrices are connected to inputs/outputs of the first group of matrices such that the matrices of the second, third and first groups of the first, fourth and second groups each form a Clos network.

Abstract: An apparatus and method for effectively transmitting a packet data and a control data of path information about the packet data in an optical packet data switching network. The method includes grouping a plurality of wavelengths into at least two wavelength bandwidths, each wavelength bandwidth being composed of neighboring wavelengths, and transmitting the optical packet data and the control data with wavelengths of different wavelength bandwidths respectively. Since the wavelength to transmit the optical packet data and the wavelength to transmit the control data has a difference from each other, a node receiving optical data easily divides the packet data and the control data.

Abstract: A circuit structure for a transmission network node for transmitting high bit-rate, IP-based time division-multiplexed signals, especially for an optical Multi-Gigabit Ethernet. The structure includes a bidirectional remote ports at two sides, each receiving and transmitting time-division multiplexed signals. Each time division-multiplexed signal has a frame structure with a number of virtual time slots each transporting certain contents. The path-switch unit is constructed to execute switching functions for realizing a drop function, a pass-through function, and a drop-and-continue function. Channel cards and network structures are also provided.

Abstract: An optical apparatus is disclosed wherein increase of the number of wavelength selective switches provided for a standby system can be suppressed. The optical apparatus includes a plurality of upstream side optical devices and a plurality of downstream side optical devices configured such that a plurality of output ports to be set as output destinations of light from a plurality of input ports can be changed over for each wavelength. An upstream side standby switch connected at a plurality of inputs thereof individually to the input ports and can change over an output of light from the inputs for each wavelength. A downstream side standby switch is connected at an input thereof to the output of the upstream side standby switch and at a plurality of outputs thereof individually to the output ports and can output light from the input to the plural outputs thereof.

Abstract: A method that changes the selection of a 2:1 multiplexer that receives a first output signal from a first framer and a second output signal from a second framer. The first output signal is the same as the second output signal. An apparatus having a framer and a 2:1 multiplexer that receives an inbound signal from the framer. A first multiplexer receives at least one signal from another framer and the 2:1 multiplexer has an input coupled to an output from the first multiplexer. A second multiplexer receives at least one signal from the other framer and the second multiplexer has an output coupled to an input of the framer for an outbound signal.

Abstract: Methods and systems for using a wavelength as an address in an optical network are disclosed. In particular, methods for selecting a wavelength for a particular node in an optical network, resolving a wavelength for a destination node in an optical network from a network address, and receiving and transmitting data packets at particular wavelengths are disclosed. A resulting system implementing such methods may significantly reduce space, weight and power measurements while transferring data at high rates for a data network.

Abstract: A Centralized Resource Management (CRM) system that supports the sharing of all the transponders in a WXC node, i.e., any spare transponder can be reconfigured to accommodate any drop channel, regardless of wavelength or input port. Consequently, network restoration in case of network failures is supported as well as the ability to reconfigure as a result of dynamic traffic requirements in the network. CRM advantageously is applied to conventional WXC node as well as WSS-based WXC nodes in the WDM networks. Three CTM schemes which manage the transponders in the WSS-based WXC node are described along with reconfiguration algorithms for an optical switchless CRM solution.

Abstract: The control of the transmission of useful optical signals on different line paths of an optical transmission device is accomplished via at least one of the following features: using signal sources and signal sinks, the useful optical signals are coupled into the line paths, or are coupled out of them; at least one portion of the optical line paths is configured as normal line paths having coupling nodes via which a switchover to an alternative line path can be undertaken if a normal line path is disturbed; in addition to the useful optical signals, test signals, whose evaluation is used for the switchover between the line paths, are transmitted bidirectionally section-by-section; at least two types of test signals can be transmitted, of which a first type is used as an indicator for an intact line path and a second type as an indicator for a disturbed line path; and any switchover to an alternative line path is only undertaken if, before the detection of the disturbance, a test signal of the first type has be