Abstract: A method for fault protection in a bidirectional ring network includes transmitting first and second flows of packets around the bidirectional ring network while defining the first flow as a wrapping flow and the second flow as a non-wrapping flow. Upon detection by a node in the network that a segment of the network proximal to the node has failed, the packets in the first flow are wrapped at the node between clockwise and counterclockwise directions on the network so as to avoid the failed segment, while the packets in the second flow are not wrapped.

Abstract: Systems and methods for link discovery and verification technique that minimize the need for line termination resources that generate and interpret packets. Of two nodes verifying a link to one another, only one node need have any line termination capability. The node lacking line termination capability simply loops back packets generated by the other node thus verifying the link. Thus, an optical cross-connect can verify links to a wide variety of node types by employing a single line termination unit capable of terminating any suitable packet type. Alternatively, a router can verify connectivity to an optical cross-connect even when the optical cross-connect lacks any line termination capability at all. This saves greatly on implementation costs for optical networks.

Abstract: A node for use in a multi-source ring transmission system includes a controller and storage. Identifiers, such as ring addresses, for the relative first and relative last source nodes within the ring transmissions system are stored within the node's storage, in a squelch table for example. The node's relative first source node is the source node farthest upstream from the node and the node's relative last source node is the node that is farthest downstream from the node. The node blocks communications whenever both its relative first source node and its relative last source node fail.

Abstract: A shared mesh protection scheme defines an associated protection path when a working connection is established. Both global and local protection schemes are used to provide advantages similar to ring and span protection switching in ring networks. During the global protection path definition, the corresponding protection path information is sent down to a switch card of network elements making up the protection path. Upon detection of the failure, the network elements using an overhead byte message will inform the routing source network element of the connection of the failure in the working path The overhead bytes used are interrupt driven bytes located in the line and path overhead of network traffic The routing source node of the connection will then send the corresponding overhead byte messages down the protection path to provide for protection path establishment according to the preloaded data located at the switch card.

Abstract: A feedback-based adaptive network is described wherein at least a portion of the network elements report operating information relating to network conditions to a centralized data store. The information which is reported to the data store is analyzed by a policy engine which includes a plurality of application specific plug-in policies for analyzing selected information from the data store and for computing updated control information based upon the analysis of the information. The updated control information is fed back to selected network elements to thereby affect operation of the selected elements. Additionally the adaptive, feedback-based network of the present invention may include a network quality monitoring system for evaluating performance characteristics or other aspects of the network based upon predetermined standards or criteria.

Abstract: A digital information distribution system having a plurality of nodes that are connected to one another by counter-rotating data paths. Each node comprises a ring terminal that selects data packets from the data paths for use by the node and passes the remaining data packets to neighboring nodes. The data paths communicate data using asynchronous serial interface packets that transport video data or IP data.

Abstract: The present invention relates to a self-healing ring network and a method for fault handling in said network. Said network comprises two communication paths (1, 2) and at least two nodes (N1, N2, N3, N4, N5). A first node (N1) and a second node (N5) suppress transmission to and/or reception from a segment (IS) in the ring, called an inactive segment. In the case of an occurring fault, the inactive segment is moved to the fault. According to the invention the network comprises a separate supervisory channel (OSC) for transmitting information of the fault between the nodes (N1, N2, N3, N4, N5) of the network, in which supervisory channel (OSC) a fault flag (ASSERT_PSS) is provided for the indication of the fault.

Abstract: A system, method and computer program product are provided for analyzing a network utilizing an agent. Initially, a signal is sent from a computer to a host controller utilizing a network. Next, a response to the signal is received from the host controller. Information is then collected relating to network traffic involving the computer based on the response. The information is subsequently sent to the host controller on a periodic basis.

Abstract: A wireless analyzer device for an IEEE 802.11 Wireless LAN is programmed to perform both a per packet processing routine to obtain packet statistics, and a one second timer routine, followed by arranging the packet statistics in a logical manner for display on a computer monitor.

Abstract: A signal loopback device including a multiplexing/demultiplexing unit to carry out multiplexing/demultiplexing between a DS3 signal serving as a digital signal conforming to a DS3 C-bit parity system and a DS1 signal, a DS1 signal loopback storage unit to return the DS1 signal, a DS3 signal loopback storage unit to return the DS3 signal in an original input signal format, a selecting unit to select any one of DS3 loopback signals from the multiplexing/demultiplexing unit and the DS3 signal loopback storage unit, a protected detecting unit to output, when detecting loopback execution/cancellation information a plurality of times, a result of detection showing that loopback is to be executed or canceled, and a loopback control unit to make a control for loopback execution or loopback cancellation to the DS1 signal loopback storage unit, the DS3 signal loopback storage unit, and the selecting unit depending upon the result of detection.

Abstract: A method and corresponding network element configuration for delivering communications services between first and second survivable rings, each comprising a respective plurality of network elements, at least two of which are common to both rings. For each particular service, one of the common network elements is designated as a primary gateway node and another as a secondary gateway node. A primary inter-ring connection is established for the particular service by a switch at the primary gateway node, but no inter-ring connection is established at the secondary gateway node. The secondary gateway node comprises a controller for monitoring the status of the primary gateway node and establishing a new inter-ring connection for delivery of said service upon detecting a failure of the primary gateway node. This provides survivable inter-ring traffic which is bandwidth-efficient and with a low switching delay.

Abstract: A digital information distribution system having a plurality of nodes that are connected to one another by counter-rotating data paths. Each node comprises a ring terminal that selects data packets from the data paths for use by the node and passes the remaining data packets to neighboring nodes. The data paths communicate data using asynchronous serial interface packets that transport video data or IP data.

Abstract: A method for reconfiguring a ring of nodes connected by a working fiber and a protection fiber upon disruption of the signal in either the working fiber or the protection fiber includes signaling the other nodes. Each node determines whether it is a node adjacent to the disruption. Those nodes that are not adjacent to the disruption undergo no change in their operation. A receiving node adjacent to the disruption forms a bridge isolating the disruption and sends an acknowledgement signal back to a signaling node. Upon receipt of the acknowledgement signal, the signaling node also forms a bridge. This results in the isolation of that portion of the ring having a disruption and the formation of a new ring.

Abstract: A communication system comprising a first communication device configured to receive an audio based transaction, wherein the first communication device supplies formatted transaction data to a network through an associated communication link. Additionally, a plurality of alternate communication devices are coupled to the network through respective communication links associated with each of the alternate communication devices. At least one alternate communication device is configured to receive the formatted transaction data from the network through the associated respective communication link.

Abstract: A system and method for path protection switching in ring networks is provided in which the path protection switch occurs at the transmitter node that initiated a particular virtual channel of data packets onto the ring network. A failure in one of the data communication-paths of the ring network is detected by the network nodes on either side of the failure. These network nodes then initiate a wrap mechanism that embeds a special feedback wrap indicator flag into packets received at the two nodes, and then wraps (or transmits back) these packets (with the feedback indicator) in the opposite direction towards the transmitter node that initiated the packets onto the ring. Each transmitter node detects whether received packets are associated with virtual channels that it initiated onto the ring and if so detected, then determine whether the feedback indicator flag is set.

Abstract: A configurable interconnect for use with high-speed electronic system components. The interconnect uses a lightweight protocol with control characters embedded into the data stream. The control characters define events such as end of packet, end of packet with error, transmit on, transmit off, synchronizing codes, and pass-through status. In one described embodiment, the protocol is used in an internetworking device node in which a pair of high-speed counter rotating rings transport data packets. The high-speed interconnect permits data packets to pass through the node without the delays which might otherwise be experienced with time division multiplex bus structures and the like.

Abstract: A communications network comprising at least two nodes is disclosed. The network has two communication paths that carry traffic in opposite directions and work as a bi-directional bus. The network has a first inactive segment that carries no traffic and is arranged to allow the first inactive segment to be made active and another segment to be made inactive, especially in the case of fault in the other segment. The activation and inactivation logically “move” the first inactive segment. Additional protection paths are provided between the nodes.

Abstract: An exchange equipment using STM able to achieve an improvement of an efficiency of use and an improvement of ease of increase of terminal cards, that is, an STM type exchange, including a time switch, for performing exchange processing of time division multiplexed data, wherein a ring highway is connected via a terminal common unit to an upstream highway and a downstream highway coupled to this time switch via a highway interface unit or directly and wherein a plurality of terminal cards are connected to this ring highway. Each terminal card is provided with an add/drop unit which drops and adds the data from and to an assigned time slot on the ring highway according to control information indicating time slot assignment information determined by the control unit and adds the data and with a card control unit which controls the add/drop unit.

Abstract: A ring-ordered dynamically reconfigurable computer network utilizing an existing communications system. The network comprises a plurality of nodes. Each node is coupled to the existing communications system by two data channels and a control channel. The network is established by each data channel of each node connecting operably to a data channel of another node. All the nodes are ordered in a ring. The control channel of each node is operably connected to the switch of the existing communications system. The network also comprises a network manager to establish the network, facilitate communication among the nodes, and dynamically reconfigure the network without disturbing communication among the nodes. Optionally, each node connects to the network only when it actually needs to communicate with another node.

Abstract: A transmission unit and a failure recovery method with failure recover functions, which use limited network resources efficiently. A label table manager manages a label table which associates incoming labels related to incoming transmission data with outgoing labels related to outgoing transmission data. Based on the label table, a transmission controller performs label-switching of transmission data. A path set-up unit establishes a loopshaped protection path that includes a part or whole of transmission links of an existing working path and would allow transmission data to flow in the opposite direction to that of the working path. When a failure occurs, a failure recovery controller changes the association between the incoming and outgoing labels stored in the label table and switches the failed part of the working path to the loop-shaped protection path, thereby restoring the label-switched network.

Abstract: A system for selectively routing data within a fiber channel arbitrated loop, including an intra-loop router configured to be coupled between a first segment and a second segment of the fiber channel arbitrated loop. The intra-loop router includes a router controller configured to be coupled with the first and second segments, and a processing system coupled with the router controller. The processing system is configured to receive fiber channel frames and cause those frames to be re-transmitted onto a selected one of the first and second segments of the fiber channel arbitrated loop.

Abstract: An optical communications system employs a plurality of optical nodes interconnected in a ring configuration by at least two optical transmission media, for example, optical fiber. The at least two optical transmission media, in this example, provide optical service transmission capacity and optical protection transmission capacity. Efficient restoration of optical communications between optical nodes in the ring, after an optical transmission media failure, is realized by employing a relatively simple and efficient optical switch matrix having a first number of possible switching states and, then, by utilizing only a second number of the switching states fewer than the first number to switch optically from the optical service transmission capacity of the failed or faulted optical transmission media to the optical protection transmission capacity of another optical transmission media.

Abstract: The network monitoring system includes a monitor device coupling to a network switch through a mirror port interface of the network switch. The network switch supports a number of regular port interfaces connected to different network components and the mirror port connected to the monitor device. The mirror port mirrors all network traffic of any selected regular port interfaces of the network switch. When the monitor device receives a data packet from the network switch, the monitor device extracts the network address information from such as the source and destination address from the data packet. The monitor device then examines internal lookup tables to determine whether there are corresponding physical port interface for the network address information. If the corresponding physical port interfaces for the network address information are not available in the lookup table, the monitor device interrogates the network switch for the corresponding physical port interface.

Abstract: A process for ring bundling reduces the number of add/drop multiplexers required for a ring deployed in a telecommunications network. The input into the process is a list of all the time slots for a ring and the offices of the ring where each of the time slots adds or drops traffic. The process groups together time slots having many add/drops in common to maximize the number of offices where all the time slots pass through without adding or dropping traffic. OC-3 time slots are initially grouped in pairs, then in fours, then in eights, and finally in groups of sixteen to form one or more OC-48 optical signals transported in the ring.

Abstract: A method of and a circuit arrangement for data transfer between a master means and slave means, in which bit sequences are transferred each having an address field for addressing the respective slave means to be controlled, a control field for control information, and a data field. The data bit number of the data field may be different depending on the addressed slave means. The bit sequences transmitted from the master means are read back directly to the master means, so that the occurrence of corrupt bits in the bit sequence is recognized and a transfer of the bit sequence recognized as corrupt to the addressed slave means can be prevented.

Abstract: A method of managing the change of time slot allocation in classical MS-SP ring networks. In two-fiber rings, the criterion for choosing the low priority AU-4 to be used for the protection in case of simple failure can be summarized as follows: given an STM-n ring line signal, where “n” is the overall number of the handled channels, there results that LP AU-4#XLP=AU-4#(XHP+n/2), where X is the HP AU-4 index in the failured span. In four-fiber rings, AU-4 LP=AU-4#X HP. Should two or more failures occur, criteria are provided for selecting one of the failured spans and tracing the problem back to the case of single two/four fiber ring failure.

Abstract: In case of a trouble in any unit network of a communications network system which comprises a plurality of unit networks, communications are relieved and reliability of communications is improved. The respective unit networks are connected through internetwork connection circuits, and communications are normally made on each unit network by a communication path formed by performing loopback of remote communication devices at both ends of the individual unit network. If a trouble such as a disconnection fault occurred in a certain unit network, the loopback of the internetwork connection circuit of the remote communication devices at both ends of the unit network having the trouble is relieved to form an alternate communication path, and this alternate communication path is used to keep the communications between local communication terminals adjacent to the troubled spot.

Abstract: A system and method for sharing a spare channel among two or more optical ring networks that have a common span. A first optical cross-connect switch (OCCS) and a first OCCS controller are placed at one end of the span and a second OCCS and OCCS controller are placed at the other end of the span. The first OCCS and the first OCCS controller are coupled to a first ADM from each optical ring, and the second OCCS and the second OCCS controller are coupled to a second ADM from each optical ring. The first OCCS controller receives alarm indications from each ADM that it is coupled to that senses a ring failure. The second OCCS controller receives alarm indications from each ADM that it is coupled to that senses a ring failure.

Abstract: A transmission unit which transports digital signals between different network systems, effectively converting the signals to resolve their differences in the specifications. A first signal interface transmits and receives first network signals. A second signal interface transmits and receives second network signals. A downward converter produces lower-level signals by converting received first and second network signals to a lower hierarchical level at which the first and second network systems are compatible with each other in terms of logical signal structure. An upward converter produces a higher-level signal by converting each given lower-level signal to an upper hierarchical level which complies with the first or second network system. A loopback unit provides loopback paths to route the lower-level signals from the downward converter to the upward converter, so that the first and second network signal will be converted in both directions.

Abstract: In a redundancy method for Ethernet communication between a plurality of nodes constituting a distributed control system, the nodes are connected to each other in a duplex state through first and second Ethernet communication lines which are independent of each other. A node on the transmission side transmits identical data to both the first and second Ethernet communication lines. A node on the reception side determines one of the identical data received from the node on the transmission side through the first and second Ethernet communication lines which has arrived first as reception data.

Abstract: A local area network with a plurality of nodes for transmitting cells in the asynchronous transfer mode over a ring system having two opposite direction rings. In the event of a defect in a transmitting line from a node, or a defect in a neighboring node, a loop is formed in this node to reroute messages from one ring to the other. First, a node detecting a defect transmits a message of a first type to all other involved nodes, identifying the location of the detected defect. This information is entered in a respective status table in each node. After evaluating the information in its status table, a node which should form a loop does so, and sends a message of a second type identifying the loop to any nodes which do not already have this information.

Abstract: An optical communications system employs a plurality of optical nodes interconnected in an optical ring transmission configuration by at least two optical transmission media, for example, optical fiber. The at least two optical transmission media, in this example, provide optical service transmission capacity and optical protection transmission capacity. Efficient restoration of optical communications between optical nodes in the optical ring transmission configuration, after an optical transmission media failure, is realized by employing an autonomous optical restoration arrangement and technique. To this end, each node autonomously controls an optical switch matrix in the node in effecting the desired restoration without the need of switch control signals transmitted from any other node in the ring, from a main controller or from a central controller.

Abstract: The channel protection facility in a two-fiber bi-directional line switched ring network may be significantly enhanced by protecting the service channels in one of the fibers with corresponding protection channels in the other fiber and vice-versa. Thus, if a failure occurs such that the content of the service channels cannot be forwarded to an upstream point, then, without having to perform a wavelength conversion function, the service channels may be substituted for the protection channels in the other fiber and forwarded to the upstream point in the opposite direction via the ring network.

Abstract: A restoration procedure for use in bidirectional multiplex section-switched ring transmission systems re-establishes a connection path by using a loopback connection at nodes bordering the failure and by then establishing a jumpered connection path, for each active tributary affected by the failure. The jumpered connection path at affected node eliminates any unnecessary loop formed in the re-established connection path caused by the loopback connection at the border nodes. There is stored in memory at each node (1) the provisioned connection path, (2) the jumpered path, and (3) a jumper flag is set indicating that a jumper connection exists. When the failure is cleared the (1) jumpered path is removed and its record erase from memory, (2) the provisioned connection path is restored, and (3) the jumper flag is reset. Advantageously, the this operation can be programmed into existing node controllers and is compatible with existing restoration procedures.

Abstract: The known alternate circuiting of ATM cells is efficiently controlled upon employment of linear structures. In order to also be able to transfer these structures to ring-shaped architectures, a ring-shaped structure is inventively formed of linear structures in that further linear structures are linked into the transmission section of a linear structure and the switching equipment of the original linear structure are brought together or merged. Further, a plurality of protection entities share a transmission capacity that is reserved in common.

Abstract: The present invention relates to an arrangement and a method for detecting faults in an optical fiber network, comprising at least two nodes arranged with at least two optical fibers to a bus with the end nodes connected via two spare fibers. Every node comprising a central module (50), at least two protection switches (60,61) and optical amplifiers (21,22,23,24) and said central module comprising at least one central processor (51), at least one logical unit (52), at least one protection signal transmitter (53) and at least one protection signal monitor (54). The end nodes of the bus transmit a protection signal in at least one direction of the bus and said end nodes can detect the own protection signal and the protection signal transmitted from the other end node. All nodes in the bus can detect Optical Power Loss, OPL. The bus will reshape into new end nodes in case of a fault.

Abstract: A control network has a bus to which is connected a master node and a plurality of slave nodes in a loop configuration. Each of the master node and slave nodes has a transceiver connected to the bus through a shunt circuit. The shunt circuit comprises a switch (such as a relay) in parallel circuit configuration with an impedance element (such as resistor). The switch is operated under control of the node and under normal conditions remains closed, thereby allowing signals to be carried freely over the bus. When a fault occurs, each of the nodes opens its switch, causing the separate portions of the bus to become isolated. The master node then instructs each slave node, starting with the closest slave node, to close its switch. When a slave node fails to respond, the fault location has been detected. The master node repeats the process for the opposite direction of the loop. Operation then continues, with the slave node nearest the fault remaining isolated.

Abstract: A technique for reducing the computational complexity for discriminating the existence of a communication path in a lattice communication network control system includes the steps of: checking for an existence of an alternate path between the two terminal nodes of a link, when a failure occurs in a link; and in the presence of the alternate path, setting the link to a failure state based on a consideration that there is a substitute path for the link, or in the absence of the alternate path, setting the link to an unconfirmable state out of the control of a management node, considering that a network is divided into two separate parts.

Abstract: An add drop multiplexing (ADM) apparatus has a simple and compact structure. The ADM apparatus has high-order interfaces connected to a high-order network, path setting units each for setting a path for a signal according to path data and inserting or dropping the signal to or from the high-order network, a first path protection switch for selecting one of the signals dropped by the path setting units, low-order interfaces each for receiving the selected signal and transmitting the same to a low-order network, and a second path protection switch for receiving low-order signals from the low-order interfaces and transferring one of them to the path setting units so that the path setting units may insert the signal into the high-order network.

Abstract: A communication arrangement for use in a communication network and comprises a number of pieces of communication equipment or nodes arranged in a ring configuration of first and second ring paths operated in respective first and second opposite directions so as to provide path protection within the ring. A selected piece of equipment provides a head end for the ring. The ring is configured via said switching circuits provided in the pieces of equipment so as to provide a virtual break in a ring section adjacent the head end piece of equipment. In response to detection of a fault in a ring section the switching circuits to reconfigure the ring so as to move the virtual break from the ring section adjacent the head end piece of equipment to the ring section in which the fault has been detected so as to maintain path protection by forming two loops extending from the virtual break in the ring configuration in opposite directions to the head end.

Abstract: A wavelength-switching, mesh-based restoration method among a network of optical cross-connects (OXCs) is disclosed. The method is defined as "quasi-centralized" in that the network is first partitioned into a plurality of subnetworks, then a single "restoration controller" is defined for each separate subnetwork. The subnetwork partitioning is defined as being either "minimally overlapping", meaning that the OXCs are "clustered" in their network topology, with only a few links required to join the various, autonomous subnetworks, or "highly overlapping", meaning that the OXCs are defined as being included in more than one subnetwork. Each subnetwork restoration controller (SRC) includes a network graph and is therefore responsible for providing restoration around faults recognized in its own subnetwork.

Abstract: The delineation and quick invocation of protection switching is achieved by generating a protection indicator having an initial state at the point that a transmission facility failure is detected and passing the indicator downstream. A switch that receives the indicator either increments or decrements the indicator in accordance with predetermined rules. However, a switch that receives the indicator when it reaches an active state immediately invokes protection switching if that switch is at the sink end of an associated protection path.

Abstract: A communication system capable of reliably recovering its communication functions on its own when a fault occurs, and which can be used to construct a highly flexible network. This communication system is configured so that a plurality of node devices (12) supporting data generating sources are connected via communication paths (13) that use ATM technology to a plurality of center devices (11), just as if it possessed distributed ATM switch functions. When the communication paths (13) between two (2) node devices (12-2 and 12-3) are cut, the center device (11-2) detects the fault point, and autonomously recovers communication functions by transferring the node device (12-2) originally under its control to the control of the center device (11-1). When this happens, the center device 11-2) cannot communicate via the communication paths (13) due to the fault, and must use a local communication means such as a wide area network (16) to communicate with the center device (11-1).

Abstract: An engineering order wire arrangement is provided for a synchronous telecommunications network comprising a plurality of nodes interconnected via transmission paths, each path accommodating a plurality of transmission channels. Engineering voice traffic is carried on a first overhead channel having a defined network route topology. A second overhead channel is used to define a model network having a a route topology identical to that of the first overhead channel. The model network is tested to determine its integrity, i.e. the absence of loops. If the model network is found to be defective, both networks are reconfigured.

Abstract: The dynamic synchronous transfer mode dual ring topology has two rings with opposite fiber directions. The dual rings may have a plurality of common nodes. A first channel may be established in a first segment extending between a first and second nodes. Tokens associated with the first channel may be provided. In this way, time slots may be transmitted in the first channel from the first node to the second node. If a fiber failure occurs in the first segment, the second node is likely to first detect the fiber failure and transmit a fiber failure message. It is then determined if the first channel extends across the fiber failure. If the first channel is affected by the fiber failure then a channel failure message is transmitted and the first channel is terminated and all the tokens associated with the first segment are removed. If the first channel is not affected then time slots are continued to be transmitted on the first channel.

Abstract: The optical node comprises two working directional switches (22,27) connected serially in a primary ring line (2), respectively ahead of and after an extracting and/or inserting unit (11), and further connected serially in a secondary ring line (3), which are adapted to controllably switch the optical signal path between the primary ring line (2) and the secondary ring line (3), and to the extracting and/or inserting unit (11). The node further comprises two backup directional switches associated with the working directional switches and connected operatively in the primary (2) and secondary (3) ring lines to restore the optical node (10) to proper operation on the occurrence of a failure at the working directional switches.

Abstract: A circuit and technique whereby loopback testing is performed in a serial communications device by concurrently transmitting from and receiving data into a single FIFO storage unit. The circuit includes a transmitter, a receiver, a single FIFO, operatively connected to both the transmitter and the receiver, for storing both transmitted and received data at the end of a loopback test. The circuit may be part of a transceiver which may in turn be part of an infrared communications controller installed in a personal computer.

Abstract: The present invention relates generally to protection of asynchronous transfer mode (ATM) traffic against Synchronous Optical Network (SONET) fiber cuts or other types of transmission media failures in a SONET Ring. The nodes of the Synchronous Optical Network protect the asynchronous transmission mode cells for immediate failures in the Synchronous Optical Network by establishing a table indicating the topology of the nodes in the Synchronous Optical Network. Each node is capable of detecting a loss of header error check synchronization and generating a protection payload data unit, which is egressed to the plurality of nodes. In addition, each node is capable of ingressing protection payload data units from neighboring nodes and for switching the transmission of asynchronous transmission mode cells within the node so that the cells being transmitted in the network are protected.

Abstract: The present invention allows a data packet to reach its destination by automatically routing the data packet around failed components by means of a simple and efficient routing algorithms. The present invention is directed to a method and apparatus for routing a data packet through a series of ring stations, a series of mid-switch routing elements, and end-switch routing elements. An apparatus according to the invention includes a first series of ring stations and routing elements that are adapted to communicate with each other, and formed in a ring. Each ring is paired with another ring that includes a second series of ring stations and routing elements that are also adapted to communicate with each other as described above to form a second ring, and thus the two rings forming a ring pair. Each routing element, mid-switch and end-switch, is adapted to switch the path of the data packet between the two rings.

Abstract: A method for controlling bidirectional line protection switching by using a remote defect indication signal. The method includes the following steps of: inserting and transmitting a remote defect indication signal through the opposite directional link, in case the receiving end of working line detects a defect while a traffic is transmitted via a bidirectional link, and then switching to a back-up line by controlling the selector of the receiving station; and switching to the protection line by controlling the selector of the transmitting station, in case the remote defect indication signal is detected via the opposite directional link.