Abstract: A redundant fieldbus redundant system includes two independent conditioned power modules which automatically detect cable faults, such as short or open circuits on both the host and field sides of the network. The power modules are interfaced directly on one side to the primary and backup H1 cards of the host system, and are directly interfaced on the other side to an automatically terminating network device coupler module which provides connections to field devices. The redundant fieldbus system provides power and communications in a parallel physical configuration between the host system and the field devices irrespective of any single point failure in the network. In case of a fault, the redundant fieldbus system automatically eliminates the faulty section of the network, switches power and communications to the healthy portion of the network and terminates the network for signal integrity.

Abstract: Certain exemplary embodiments comprise a method comprising a plurality of activities, comprising: via a CPE telephony device simultaneously connectable to a POTS connection and to a connection to a data network: facilitating, via the POTS connection, a PSTN call, and facilitating, via the data network connection, a display of data to a call participant of the PSTN call, the data provided the data network.

Abstract: A redundancy protection scheme comprises sending a protection packet from the primary network interface to the secondary network interface, the protection packet having a hardware address of the primary network interface as a source address and a hardware address of the secondary network interface as a destination address. The scheme further comprises determining whether the secondary network interface receives the protection packet from the primary network interface, operating the primary and secondary network interface as active and standby network interface in response to the secondary network interface receiving the protection packet, or operating both the primary and secondary network interface as active network interface in response to the secondary network interface not receiving the protection packet, and providing the hardware address of the active secondary network interface to devices coupled thereto.

Abstract: An optical network transmission channel failover switching device is proposed, which is designed for use in conjunction with an optical network for providing a transmission channel failover switching function, which is characterized by the provision of a two-to-two (2×2) type of optical switch, a one-to-two (1×2) type of optical switch, and a monitoring beam generating module for providing a backup channel monitoring function that can be used to activate the switching action. This feature allows the utilization of the optical network system to have enhanced reliability, serviceability, and security.

Abstract: The invention includes a method for processing messages at a component. One method includes receiving a message formed according to an embedded protocol or an external protocol, processing a portion of the received message for identifying the protocol used to form the message, and processing the received message using the identified protocol. The portion of the received message is formed using a comparison between at least one characteristic associated with the embedded protocol and at least one characteristic associated with the external protocol. Another method includes receiving, at a first type-one component, a message from one of a second type-one component or a type-two component, processing a portion of the message for identifying a protocol adapted for processing the received message, and processing the received message using the identified protocol.

Abstract: A wireless ad hoc communication system is provided in which in the case where an alternative route can not be discovered in a certain node, a restoration is attempted in an intermediate node instead of deleting all routes up to a transmission source. In order to do so, a route discovery process 20 discovers and sets a route when a corresponding route is not set at the time of data communication request 10. A link state management process 40 monitors a state of a link 30 on the route set by the route discovery process 20, and updates a link state in a route table of each wireless terminal. When the link quality deteriorates, a route information notification process 50 notifies the link state to urge a retention of transmission data. An alternative route search process 60 searches an alternative route when the link quality deteriorates, and traces back to a terminal on the transmission side in order to search further when the alternative route is not discovered.

Abstract: Systems and methods for establishing and/or routing wireless data and/or voice connections across a hybrid network based upon a user's selection or preference. Routing a wireless connection across a hybrid network includes allowing a user to select a routing preference, routing the wireless connection via a short-haul communications network if the routing preference indicates a short-haul communications network choice, and routing the wireless connection via a cellular network if the routing preference indicates a cellular network choice. In addition, a system and method for learning the user's data, cellular, and/or VoIP access habits in order, to optimize the user's experience and one that allows carriers to comply with CALEA and E911 rules by identifying the location of hybrid devices within the hybrid network are disclosed.

Abstract: Recovery time upon the failure of a link or switching system in an asynchronous data network can be minimized if downstream data switches provide upstream messages indicating to upstream switching system that the downstream traffic arrived in tact and was properly handled. Upon this loss or failure of the upstream status message to an upstream switching system, an upstream switching system can reroute data traffic around a failed link or failed switch with a minimal amount of lost data. The upstream status message is conveyed from a downstream switching system to an upstream switching system via a reverse notification tree data pathway.

Abstract: A wireless ad hoc communication system is provided in which in the case where an alternative route can not be discovered in a certain node, a restoration is attempted in an intermediate node instead of deleting all routes up to a transmission source. In order to do so, a route discovery process 20 discovers and sets a route when a corresponding route is not set at the time of data communication request 10. A link state management process 40 monitors a state of a link 30 on the route set by the route discovery process 20, and updates a link state in a route table of each wireless terminal. When the link quality deteriorates, a route information notification process 50 notifies the link state to urge a retention of transmission data. An alternative route search process 60 searches an alternative route when the link quality deteriorates, and traces back to a terminal on the transmission side in order to search further when the alternative route is not discovered.

Abstract: A network router initially communicates over a primary data path. Upon detection of an error condition associated with the primary data path, the network router initiates a layer 2 switch such that the communication occurring over the primary data path is switched to a backup data path. The layer 2 switch is preferably transparent to a layer 3 portion of the network router.

Abstract: Methods and apparatus for defining an alternate circuit path within a network given nodal diverse or link diverse constraints are disclosed. According to one aspect of the present invention, a device for computing circuit paths between a first node and a second node within a network that has a plurality of elements includes a route generator and a list mechanism. The route generator computes a primary circuit path between the first node and the second node such that the primary circuit path includes a first element. The list mechanism identifies the first element as being inaccessible to an alternate circuit path. Using the list mechanism, the route generator computes an alternate circuit path that does not include the first element identified by the list mechanism. In one embodiment, the first element is a link. In another embodiment, the first element is a node.

Abstract: A method and system provide capacity-efficient restoration within an optical fiber communication system. The system includes a plurality of nodes each interconnected by optical fibers. Each optical fiber connection between nodes includes at least three channel groups with different priority levels for restoration switching in response to a connection failure. The system maintains and restores full-capacity communication services by switching at least a portion of the channel groups from a first optical fiber connection to a second optical fiber connection system based on the priority levels assigned to the channel groups. Service reliability is effectively maintained without to incurring additional costs for dedicated spare optical fiber equipment by improving idle capacity utilization.

Abstract: A method for communication includes sending first data over a first communication link to a destination communication system at a first data rate, which can be varied. Second data, including at least a portion of the first data, is sent over a second communication link from the source communication system to the destination communication system at a second data rate, which can be varied. First and second data rates of the respective first and second communication links are dynamically set. At least the portion of the first data is selectively extracted from one of the first and second data at the destination communication system. In some embodiments, the first data equals the second data, and the data is extracted without data loss.

Abstract: Disclosed are a data transceiver and a method thereof in a wireless communication system, and particularly, is a data transceiver and method thereof using multiple routes in the wireless communication system. The data transmitting/receiving method using the multiple routes in the wireless communication system includes setting a direct route to a corresponding station and a relay route to a relay device, selecting one route from among the direct route and relay route, and transmitting/receiving data through the selected route.

Abstract: A technique dynamically creates and utilizes a plurality of multi-homed Virtual Private Network (VPN) tunnels from a client node of one spoke network to a client node of another spoke network in a computer network. According to the technique, a VPN client node, e.g., a “spoke,” creates at least one VPN tunnel with an enterprise network, e.g., a “hub.” Once the spoke-to-hub tunnel is established, the spoke may dynamically create a plurality of VPN tunnels with a peer spoke network, e.g., a “peer spoke.” The spoke designates (e.g., for a prefix) one of the tunnels as a primary tunnel and the other tunnels as secondary tunnels, and monitors the quality (e.g., loss, delay, reachability, etc.) of all of the dynamic tunnels, such as, e.g., by an Optimized Edge Routing (OER) process. The spoke may then dynamically re-designate any one of the secondary tunnels as the primary tunnel for a prefix based on the quality of the tunnels to the peer spoke.

Abstract: Recovery time upon the failure of a link or switching system in an asynchronous data network can be minimized if downstream data switches provide upstream messages indicating to upstream switching system that the downstream traffic arrived in tact and was properly handled. Upon this loss or failure of the upstream status message to an upstream switching system, an upstream switching system can reroute data traffic around a failed link or failed switch with a minimal amount of lost data. The upstream status message is conveyed from a downstream switching system to an upstream switching system via a reverse notification tree data pathway. The reverse notification pathway is established by using a messaging protocol between network switches by which the working and protection paths, among other things, are established.

Abstract: A redundant fieldbus system provides power and communications in a parallel physical configuration between the host system and attached field devices irrespective of any single point failure in the network. In case of a fault, the redundant fieldbus system automatically eliminates the faulty section of the network, switches power and communications to the healthy portion of the network and terminates the network for signal integrity. A device coupler for the system may include a fault detector coupled to an auto-termination circuit that terminates a fieldbus cable when a fault is detected. The device coupler may include fault detection and isolation coupled to each set of spur terminals used to connect field devices to the device coupler. A field device for the system may include circuitry for deselecting a faulty cable while maintaining connection to a healthy cable.

Abstract: A method of testing a digital mobile phone network such as a GPRS or 3G network comprises either using real traffic or creating test traffic using test mobile phone coupled to a computer, and using the computer to measure a parameter associated with the network's response to the traffic. The measurements made by the computer are themselves sent as traffic to create one or more data streams within the mobile phone network comprising the traffic, measurements relating to the traffic, and signalling relating to the traffic, whereby this data stream or these streams can be captured at interface points within the network and analysed to investigate the functioning of the network dynamically as the network is exercised with the traffic. Software and test equipment for performing the method are also described.

Abstract: This invention provides a tool for reliability evaluation and performance analysis of an IP backbone network by using the network packet loss ratio as the main measurement. A queuing model and algorithm is presented for calculating packet loss at congested interfaces or links. A reliability model is presented for considering network hardware component failures such as router failures, ATM switch failures, and physical link failures. Based on the measurement and models presented, a network reliability and performance (NetRAP) apparatus calculates IP network reliability and performance measurements. The NetRAP apparatus uses the network topology, a traffic matrix, and the reliability parameters of a network as inputs and calculates the network packet loss ratio and sigma score, and provides a list of heavily congested links under non-failure or different single failure conditions.

Abstract: An optical network transmission channel failover switching device is proposed, which is designed for use in conjunction with an optical network for providing a transmission channel failover switching function, which is characterized by the provision of a pair of two-to-two (2×2) optical switches and an optical transceiver module for providing a backup channel monitoring function that can be used to activate the failover switching action. This feature allows the utilization of the optical network system to have enhanced reliability, serviceability, and security.

Abstract: One embodiment of the present invention discloses a method and device for recovering a shared mesh network. The core idea of the method lies in that: a network ingress node of network connection service determines and saves routing information of a recovery path; after a working path is established successfully, a network management system controls resource reservation of the recovery path; and after the working path is interrupted, the network ingress node of the network connection service initiates an establishing procedure of the recovery path by using the reserved resources according to the saved routing information of the recovery path, and switches services on the working path to the recovery path for transmission. The technical solutions of the invention are easy to implement, and can be realized by using existing protocols; moreover, it can be well compatible with existing devices.

Abstract: The present invention provides a method and system for secure access to computer equipment. An embodiment includes a secure access controller connected to a link between a transceiver (such as a modem) and the computer equipment. Public and private keys are used by the secure access controller and a remote user. The keys are provided to the secure access controller by an authentication server. Once the transceiver establishes a communication link with the user, the access controller uses these keys to authenticate packets issued by the user to the computer equipment. If the packet is authenticated, the access controller passes the packet to the computer equipment. Otherwise, the packet is discarded. Another embodiment includes a secure access controller having a plurality of ports for connection to a plurality of different pieces of computer equipment. The secure access controller thus intermediates communications between the modem and the plurality of different pieces of computer equipment.

Abstract: One embodiment presented herein comprises a method of establishing at least two simultaneous forms of communication between at least two entities. The method can use a service to facilitate the communication or the entities can establish communications on their own (or one entity could be establishing multiple forms of communication with a service). One embodiment begins by connecting one of the entities to a service. The service is then used to establish an initial communication form between the entities. Alternatively, if a service is not used, the entities can establish the initial communication themselves. Next, a list of alternative communication forms that are possible between the entities is created. This list can be prioritized according to a number of different parameters. This list can be created using a previously established database maintained by the service or can be created by the entities themselves as they communicate over the initial communication channel.

Abstract: When the routing function of router becomes disabled, a routing stop message is multicast to all terminals and another router in a LAN. If another router can provide the routing function, a routing start message is multicast to all terminals and the other router in the LAN. This method allows the terminals in the LAN to switch the default router at a predetermined timing according to both messages, thus minimizing the default router switching delay time and the packet loss.

Abstract: Extra traffic paths are provided in a communication network including at least two protection channels associated to respective transmission channels. Each protection channel admits an active state for carrying, in the presence of a failure in the associated transmission channel, traffic to be carried by the associated transmission channel, and a stand-by state, wherein the protection channel is adapted to carry extra traffic. The protection channels are run in a sub-network connection protection scheme, whereby one of the protection channels in its stand-by state is adapted to ensure recovery of extra traffic carried by the other protection channel while the other protection channel is switched to its active state or is subject to failure.

Abstract: A mobile ad-hoc network (MANET) communicates between a source node and destination node and includes a plurality of intermediate nodes. A main communication path is established between the source node through intermediate nodes to the destination node based on an underlying routing protocol. Alternative communication paths are established among neighboring nodes as standby nodes that are positioned an “n” hop distance from nodes of the main communication paths to form a tube of multiple communication paths from the source node to the destination node. The main communication path reconfigured within the tube of multiple communication paths to an alternative communication path using at least one standby node when the main communication path is broken.

Abstract: Protection and working routes are determined responsive to shared resources. The administrative weight value of a route can correspond to the physical distance associated with that route. Once the administrative weight values are assigned, that route having the lowest administrative weight value is designated the working route. The protect route is next identified by reassigning administrative weight values to the remaining routes in the network. Those routes that share resources, such as a fiber bundle or conduit, with the working route are assigned high administrative weight values, while those routes independent of the working route are assigned administrative weight values corresponding to the physical distance of each route. That route having the lowest administrative weight value after working route selection is designated the protect route.

Abstract: The synchronization of trunk failover between two FC-AL switches when a primary trunk failure occurs is disclosed. If primary trunk T1 should fail, S1 bypasses the cascade port and sends a MaRK (MRK) ordered set out over duplicate trunk T2 to switch S2. In response, S2 sends an acknowledgement MRK ordered set over T2 back to S1. S1 then reconfigures the switch to establish T2 as the primary trunk, and acts as a masters in the failover process and initiates LIP ordered sets which are communicated to all devices in the system to initialize them. Note that when S2 receives the MRK ordered set and acknowledges it by sending an acknowledgement MRK back to S1, it acts as a slave in the failover process and does not attempt to initiate LIPs, thereby eliminating the possibility of multiple Loop Initialization cycles and reducing the time in which data cannot be transmitted.

Abstract: Network traffic is sent via alternate paths in cases of network link or node failure. An alternate node responds to U-Turn traffic from a primary neighbor to select a further alternate. An algorithm for determining the alternate paths is provided to select loop-free neighbors.

Abstract: A security infrastructure and methods are presented that inhibit the ability of a malicious node from disrupting the normal operations of a peer-to-peer network. The methods of the invention allow both secure and insecure identities to be used by nodes by making them self-verifying. When necessary or opportunistic, ID ownership is validated by piggybacking the validation on existing messages. The probability of connecting initially to a malicious node is reduced by randomly selecting to which node to connect. Further, information from malicious nodes is identified and can be disregarded by maintaining information about prior communications that will require a future response. Denial of service attacks are inhibited by allowing the node to disregard requests when its resource utilization exceeds a predetermined limit. The ability for a malicious node to remove a valid node is reduced by requiring that revocation certificates be signed by the node to be removed.

Abstract: The initial transmission of data packets in a point-to-multipoint communication network may often be delayed when retransmissions of erroneously decoded data packets are required. According to an aspect of the present invention, point-to-multipoint data transmission and retransmission of erroneously decoded data from a transmitting station to a plurality of receiving stations is performed, where retransmitted data is sent via at least one communication channel, which is different from the one used for the initially transmitted data. Advantageously, due to this there may be no need for further communication between the transmitting station and the receiving stations. Furthermore, according to an aspect of the present invention, the initial transmission of data packets is not delayed by retransmissions.

Abstract: Systems, method, and computer program products for utilizing a spare lane for additional checkbits. Systems include computer, storage or communications systems with bitlanes for transferring error correcting code (ECC) words in packets over a bus in multiple cycles, a spare bitlane available to the bus, a spared mode and an initial mode. The spared mode is executed when the spare bitlane has been deployed as a replacement bitlane for carrying data for one of the other bitlanes. The initial mode is executed when the spare bitlane has not been deployed as a replacement bitlane. The initial mode includes utilizing the spare bitlane for carrying one or more additional ECC checkbits. The initial mode provides at least one of a more robust error detecting function for the bus than the spared mode and a more robust error correcting function for the bus than the spared mode.

Abstract: Methods and systems for identifying communication circuits are disclosed. In particular a communication circuit communicatively couples a first node to a second node. A virtual circuit identification is then obtained based on a first address associated with the first node and a second address associated with the second node. The communication circuit is then identified based on the virtual circuit identification.

Abstract: A method of advertising repair capability in a network repair scheme using network repair addresses for repairing around a repairable network component in a data communications network having, as components, nodes and links therebetween, comprises establishing whether an alternate repair path is available around a repairable component. If such a repair path is available, the method further comprises issuing a corresponding notification to nodes in the network.

Abstract: A method embodiment includes determining whether a communication received from a first processor connected to a network interface unit is intended for a second processor connected to the network interface unit. The method embodiment also includes selecting a first communication path between a route through a switch and a route directly to the second processor through which to route the communication from the network interface unit to the second processor. The method embodiment further includes routing the communication from the network interface unit to the second processor through the first communication path.

Abstract: A system comprising a computer including a plurality of network interface controllers (NICs), the plurality of NICs associated with an address. The system further comprises a switching apparatus coupled to the computer and an echo device coupled to the switching apparatus. The echo device is adapted to send a packet to the switching apparatus to verify connectivity with the plurality of NICs. The packet comprises the address. The switching apparatus compares the address with a data structure to locate a matching address. If no matching address is located, the switching apparatus sends copies of the packet to each of the plurality of NICs coupled to the switching apparatus.

Abstract: A method for determining primary and restoration paths for a new service in a mesh network involves (1) for each of a plurality of candidate primary/restoration path pairs for the new service, generating a path cost for each candidate pair, where the path cost for each restoration path is a function of the sum of the cost of links within the restoration path, and (2) selecting the primary and restoration paths for the new service from the plurality of candidate path pairs based on the path cost. If no sharing is possible, for low utilization links, the cost of links is a function of the administrative weight of the link, whereas for high utilization links, the link cost is a function of the inverse of the available capacity on the link. If sharing is possible, the cost is a function of the inverse of a sharing degree for the link.

Abstract: In one embodiment, a network comprises a plurality of nodes that are communicatively coupled to one another using bidirectional, half-duplex links. The network has a logical first channel over which data is propagated along the network in a first direction and a logical second channel over which data is propagated along the network in a second direction. For a given period of time, at least one of the plurality of nodes is scheduled to be a transmitting node that transmits data on both the first channel and the second channel. A first subset of the nodes not scheduled to transmit during the period are scheduled to relay data received from the first channel along the first channel. A second subset of the nodes not scheduled to transmit during the period are scheduled to relay data received from the second channel along the second channel.

Abstract: A method, computer readable medium and computer system for repairing a failed network connection between a client system and a network is disclosed. In a first aspect, the method preferably includes collecting real time connectivity information by the client system and utilizing the real time connectivity information by the client system to establish a connection with the network. In a second aspect, a computer system coupled to a network includes at least one network adapter for monitoring and collecting real time connectivity information from the network, memory for storing the real time connectivity information, and a processor coupled to the memory and to the at least one network adapter, where the processor is configured to execute program instructions for utilizing the real time connectivity information to repair a failed network connection between the computer system and the network.

Abstract: The present invention discloses a method for guaranteeing reliability of end-to-end QoS, including: a. detecting and determining whether there is a failure on a Label Switched Path (LSP); if there isn't, returning to the process of detecting; otherwise, determining whether there is a backup LSP for the failed LSP; if there is, an edge router or a transmit router switching service streams and corresponding resources from the failed LSP to the backup LSP based on a certain policy; otherwise, a resource control function (RCF) entity allocating a new LSP according to network topologies for the service streams born on the failed LSP, and switching the service streams from the failed LSP to the newly allocated LSP, and releasing the path resources formerly occupied by the service streams. The method can guarantee service continuity and reliability of QoS in a bearer network.

Abstract: Protection transmission unit allocation, such as STS# in a SONET/SDH network utilizing time slot interchange on the working path, may be determined by disseminating connection information, connection identification information, and a prioritization scheme, to nodes on the network and allowing them to deterministically allocate protection transmission units to connections on the protection cycle. Network elements forming physical or logical rings may thus ascertain the location on protection for a given connection without requiring protection unit allocation to be disseminated from a central controller. Since each node is starting with the same connection information and running the same priority determination, each will end up with the same result and will know where to place and find connections on protection.

Abstract: For alternate operation of a terminal (EG1) at at least two communication nodes (GK1, GK2), the terminal (EG1) is first registered with a first of the communication nodes (GK1). In this case, registration is followed by there being a logical connection between the terminal (EG1) and the first communication node (GK1). The obtainability of the first communication node (GK1) is monitored, and in the event of the first communication node (GK1) being unobtainable a status information item relating to the unobtainability is produced, and the status information item is taken as a basis for setting up a logical connection between the terminal (EG1) and the second communication node (GK2). The terminal (EG1) is then automatically operated at the second communication node (GK2).

Abstract: Mechanisms for measuring network availability are described. A first network element produces a first knowledge digest encoding the first set of forwarding policy indicators associated with a set of packets into a fixed length bit array. The first network element periodically sends probe messages containing the knowledge digest to a second network element. The second network element produces a second knowledge digest encoding a second set of forwarding policy indicators into a fixed length bit array. The second network element compares the first knowledge digest to the second knowledge digest to determine whether the first set of forwarding policy indicators is a subset of the second set of forwarding policy indicators. The second network element indicates the availability of the path as long as probe messages are received from the first network element.

Abstract: A communication network comprising at least one first terminal, at least one second terminal, a plurality of links, and at least first and second nodes. The first node is bidirectionally coupled to the first terminal through at least a first one of the links, and also is bidirectionally coupled to the second terminal through at least a second link and the second node. Preferably, the first node comprises a plurality of communication paths, each of which is coupled at a first end thereof to at least one corresponding first link. Second ends of the communication paths are all coupled to the second link, through a multiplexing device, and route signals between the first and second links. The first node also preferably comprises at least one alternate communication path having a first end coupled through the multiplexing device to the second link, at least one switch that is coupled to the alternate communication path, and a detector for detecting a failure in at least one of the communication paths.

Abstract: For establishing a multimedia session with a remote user's terminal, a terminal starts a signaling intended to establish the multimedia session addressed to the remote user's terminal. Predetermined acknowledgement messages indicate to the terminal and to the remote terminal that the multimedia session is established. The terminal and/or the remote terminal run at least a module of a multimedia application before reception of the predetermined acknowledgement messages.

Abstract: A method of protecting a protected link is disclosed. The method includes connecting traffic from a service module to a first physical module having a link layer framer that is connected to a protected egress link. The traffic is connected through the first physical module through a pooling switch to a second physical module that is connected to an alternate egress link.

Abstract: A port shutdown protocol coordinates among various components involved in the process of administratively bringing down a link at both ends of a link connecting two switches. Execution of the protocol avoids or reduces frame drops and/or reordering. In this protocol, peer switches perform various actions when bringing down an ISL in a synchronized manner. In one implementation, this protocol uses the Exchange Peer Protocol (EPP) as the underlying transport to carry the port shutdown protocol frames.

Abstract: The invention provides a method and system for coupling a SONET/SDH network to a routing network that does not have a single point of failure. Multiple routers are coupled between the SONET/SDH network and the routing network, one for each data path; for example, a first router for the working data path and a second router for the protection data path. The routers intercommunicate to force APS to switch data paths bidirectionally, so as to allow only a single router for each data path.

Abstract: A method for automatically managing a virtual output queuing system in a switching fabric. The method includes detecting if a link is one of a non-operational-link and an operational-link. The link enables communication between a first-switching-unit and a second-switching-unit. If the link is the non-operational-link, the method further includes discarding at least one packet destined for the link. The discarding step further includes either dropping of the at least one packet or scheduling the at least one packet.

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