Abstract: The design of telecommunication networks is such that there is provision of end-to-end path protection to multiple demands under a single link or node failure in the networks. Restoration routes are provided on Preconfigured Virtual Cycles (PVC's), where each demand is assigned one restoration route and specific restoration wavelengths on a segment of one cycle. Multiple demands may share restoration wavelengths, and the number of restoration wavelengths may vary among the PVC links. First, a plurality of candidate PVC's are generated where each demand may be assigned to multiple candidates. Assignment of demands with common failure scenarios are allowed, under certain conditions, to the same PVC. Next, a set of PVC's is selected from among the candidates, while minimizing total reserved restoration capacity and ensuring that all demands are protected. Next duplicate assignments are eliminated. Finally, conflicts of wavelength assignments are resolved. The invention focuses primarily on optical networks.

Abstract: A method for managing an optical network having a plurality of nodes interconnected by a plurality of fiber links includes installing one or more active reconfigurable optical add/drop multiplexer (ROADM) cards into a node and installing a spare ROADM card into the node. The one or more active ROADM cards are configured to pass optical traffic to and from the optical network. The installed spare ROADM card is remotely activated to pass optical traffic to and from the optical network, subsequent to configuring the one or more active ROADM cards, based on one of: an event or expiration of a time period.

Abstract: A method is provided for protection switching in an optical network. The method may include establishing a baseline power level for a channel. The method may further include receiving a signal associated with the channel via each of a first path of the optical network and a second path of the optical network. The method may also include monitoring a power intensity of the signal received via the first path. The method may additionally include protection switching from the signal received via the first path to the signal received via the second path in response to a determination that the baseline power level exceeds the power intensity of the signal received via the first path by a predetermined threshold.

Abstract: Systems and methods are described that provide a distributed restoration signaling protocol for shared mesh restoration with standbys for transparent optical networks.

Abstract: An optical communication network node apparatus is provided that considerably reduces the node apparatus in scale, especially, a switch device in scale relative to increase in the number of wavelength multiplexes.

Abstract: Schemes are provided for starting up optical transmission links where, after a link interruption, endpoints switch into a startup mode original detection state, and a query-transmit pulse goes out at both end points at given time intervals. In a “TRANSMITTED” handshake mode, in a loop to be passed through n times, and at least once, after the transmission of a transmit pulse, it is detected whether a received pulse is received within a given time span. If no received pulse is received, then the mode is ended and the system is returned to the original detection state. If a received pulse is received, it is answered with another transmit pulse. After the last transmit pulse, if another received pulse occurs within a given time span, the link is activated. If not, the “TRANSMITTED” handshake mode ends and the system enters the original detection state.

Abstract: An optical transmission system or its constituent repeater disposed optically between two terminals. The system includes at least two parallel optical paths between a first node and the repeater (one optical path being used as a backup for another), and another at least two parallel optical paths between a second node and the repeater (again, one optical path being used as a backup for another). The first nodes may, but need not, be terminals, but could also be repeaters, or other optical elements. For a signal traveling from the first terminal to the second terminal, the optical switching mechanism detects which of the at least two parallel optical paths an optical signal is being received from the first node, and channels the optical signal to at least one of the parallel optical paths leading from the repeater to the second node.

Abstract: Optical By-Pass (OBP) links may be created by adding wavelengths between nodes on the network. The OBP may extend between any pair of nodes on the network. Intermediate nodes on the OBP are transient nodes and simply forward traffic optically. An OBP extends between a pair of nodes and, unlike express links, is created in such a manner that it does not affect the previous allocation of resources on the network. This enables capacity to be added between pairs of nodes on the network to alleviate congestion at a portion of the network, without changing other traffic patterns on the network. This enables inclusion of an OBP to be deterministic and of linear impact on the network. The OBP links may be statically provisioned or created on demand. Optionally, the OBP links may be crated to coincide with PBB-TE tunnels on the network.

Abstract: A signal transmitter includes: a main transmission line-transmitting portion that transmits optical signals through main transmission lines; a backup transmission line-transmitting portion that transmits the optical signals through backup transmission lines paired with the main transmission lines; a selector that selects a transmission line to be used for transmitting the signals from any of the transmission lines through which the signals are transmitted by the main transmission line-transmitting portion and the backup transmission line-transmitting portion; and a controller that, when a fault occurs on at least one main transmission line, outputs a switching command to the selector based on information identifying the main transmission line with the fault, thus causing the main transmission line-transmitting portion to stop transmitting the signals to the main transmission line with the fault, while causing the backup transmission line-transmitting portion to transmit the signals being transmitted to the ma

Abstract: The invention discloses a system, a method and an apparatus for optical network protection. The system includes: an output control apparatus for obtaining protection mode information configured by a system and controlling an input signal to be output from a set line corresponding to said protection mode information; and a detection control apparatus for detecting powers of signals transmitted on an active line and on a standby line, if it is determined that said active line is abnormal and said standby line is normal according to detection results, then controlling said input signal to be output from a protection line corresponding to said protection mode information; if it is determined that said active line is normal, or that said active line and said standby line are abnormal according to the detection result, then controlling said input signal to be output from a set line corresponding to the protection mode information.

Abstract: A method and system for maximizing wavelength reuse in an optically protected wavelength-division-multiplexed (WDM) network, the WDM network supporting a plurality of service connections, includes associating service connections supported by non-overlapping paths to form respective service channel groups, and for each service channel group, assigning at least one common wavelength channel for establishing the service connections. In addition, for each of said groups, at least one common wavelength channel is assigned for establishing a shared protection path for the service connections of each of said groups. In addition, the wavelength channels assigned for establishing the shared protection paths for each of the groups may be used for providing service connections for the WDM network when not in use as shared protection paths. However such provisional service connections are dropped when the wavelength channels are needed to establish shared protection paths.

Abstract: A method is presented for supporting SNCP over a packet network connecting to two SDH sub-networks and transporting one or more SDH paths that are SNCP-protected in both SDH sub-networks. The packet network connects to each of two sub-network interconnection points by a working path and a protection path. The packet sub-network may provide the same type of path protection as an SDH sub-network using SNCP, while avoiding bandwidth duplication.

Abstract: Embodiments of the present invention disclose a method for implementing shared mesh protection includes: receiving, by a first node, a message of a second type sent by a second node, where the message of the second type carries a second positive incoming sublabel allocated by the second node for a protection path of a first service and the second positive incoming sublabel is used to indicate a specified feature of recovery information of the first service; allocating, by the first node, a first positive outgoing label for the protection path of the first service based on the second positive incoming sublabel, where the first positive outgoing label corresponds to the second positive incoming sublabel; and transmitting the recovery information of the first service to the second node based on an indication of the first positive outgoing sublabel when knowing that a working path of the first service is faulty.

Abstract: Passive optical networks can experience faults that are unrecoverable. An embodiments of the present invention is a hybrid passive optical network configured to protect a primary optical path employing a switch to transmit data from the primary path to a secondary path in a passive manner. In an event data flows through both the primary path and the secondary path, the optical switch may be configured to monitor the primary path. In such an embodiment, the optical switch is a protection optical switch that is sensitive to monitoring an optical signal that flows on the primary path. If the switch detects a loss of signal on the primary path, the optical switch automatically switches delivery of the optical signal from the primary path to the secondary path, via the optical switch to allow an optical line terminal to receive optical signals virtually uninterrupted.

Abstract: An optical transmission apparatus connected to an optical ring network stores identification information of an optical transmission apparatus as a communication partner predetermined on a communication path. Each optical transmission apparatus includes self identification information in header information of an optical signal having a working wavelength used in normal operation, and transmits the optical signal to one of the two optical ring networks transferring optical signals in mutually opposite directions. The optical transmission apparatus determines whether the identification information included in the header information of the received optical signal having the working wavelength matches pre-stored identification information. The optical transmission apparatus thus detects a fault that occurs by the communication path.

Abstract: Communication devices, systems, and methods for dynamic cell bonding (DCB) for Radio-over-Fiber (RoF)-based networks and communication systems are disclosed. In one embodiment, a method of operating an optical fiber-based wireless communication system is provided. The method includes determining a first plurality of remote units in a cloud bonded to a Radio-over-Fiber (RoF) communication session. The method also includes measuring a received signal strength from each of the first plurality of remote units. The method also includes measuring a received signal strength from each of a second plurality of remote units in the cloud not bonded to the RoF communication session. At least one of the second plurality of remote units is dynamically bonded to the RoF communication session if the measured received signal strength of the one of the second plurality of remote units is greater than the measured received signal strength of the first plurality of remote units.

Abstract: In accordance with embodiments of the present disclosure, a method may include for each particular working demand in a communication network, calculating a dedicated backup path for a working path of the particular working demand such that each particular backup path does not include links present in the working path. The method may also include, for each particular working demand: (i) assigning to the backup path a wavelength associated with the particular working demand; and (ii) assign to the backup path a transponder at each of the source and destination of the backup path associated with the wavelength; such that the backup path for at least one particular working demand is assigned a transponder that is also assigned to the backup path for at least one other particular working demand.

Abstract: The present disclosure provides systems and methods for rapid circuit provisioning in Optical Transport Networks (OTN) using signaling and routing protocols thereby enabling fast mesh restoration. The present invention utilizes a shim layer between OTN messaging (e.g., GCC or High-Level Data Link Control (HDLC)) and the associated signaling and routing protocol (e.g., OSRP, GMPLS, etc.). If an ODUk Connection CTP or TTP needs to be created, the shim layer runs a fast “OTN Setup” protocol, while buffering out going OTN messages. Incoming messages are still processed and do not require additional buffering. The purpose of the OTN Setup protocol is to allow the OTUk to re-frame on its client ODUk, while buffering out-going messages. When re-framing completes, buffers are released and the OTN messaging resumes without dropping any of the signaling frames.

Abstract: In an optical transmission system, a first monitoring section configured to monitor a first optical signal on a first optical transmission line to detect a first failure. A modulating section generates a second optical signal obtained through modulation of a signal corresponding to the first optical signal based on the first failure, to transmit the second optical signal onto a second optical transmission line which is connected with the first optical transmission line and a terminal unit. A second monitoring section monitors the second optical signal on the second optical transmission line to detect a second failure, and a detecting section detects the first failure from the second optical signal on the second optical transmission line.

Abstract: There is described an optical terminal for use in a passive optical network. The optical terminal comprises an optical I/O module for sending and receiving optical data packets along an optical fibre, an electrical I/O module for sending and receiving electrical data packets via an electrical connection, a signal converter operatively connected to the optical and electrical I/O modules for converting the data packets between optical and electrical formats, a controller for controlling the operation of the I/O modules and the signal converter. The controller is configured to detect a failure of a primary data path in the optical network, initiate an automatic protection switch to a secondary data path for optical data packets, and generate traffic flow update messages to be sent upstream. Each traffic flow update message contains, as a source address, a MAC address of a client device downstream of the terminal.

Abstract: A method of processing data for computing alternative paths in an optical network (10, 40) including making a list of groups (12, 14, 16, 18, 20, 22, 24, 26) that comprise links wherein the links in a group share a risk of being affected by the same fault, comparing each group (12, 14, 16, 18, 20, 22, 24, 26) with other groups (12, 14, 16, 18, 20, 22, 24, 26) in the list to determine whether each group includes the same links as another group, and deleting the groups (16, 26, 20, 22) that comprise links which are a subset of the links in another group.

Abstract: A method for channel protection switching of an optical network device, an Optical Transport Network (OTN) device, and a Passive Optical Network (PON) device is provided. The method includes detecting, by the PON device, whether an OTN alarm indication signal is received after discovering a fault. If the OTN alarm indication signal is received, the alarm generated by the PON device is suppressed so that the PON device does not perform channel protection switching. The PON device detects whether an OTN alarm indication signal is received, and suppresses the alarm generated by the PON device so that the PON does not generate futile alarms or lead to futile switching when the OTN fails but the PON works normally.

Abstract: A method is provided for protection switching in an optical network.

Abstract: Optical network protection devices and protection methods including: a working line; a protection line; a determination module configured to determine the protection type of optical network; a first judgment module configured to judge whether the working line is normal according to performance parameter values of service signal in the working line and switching conditions configured for multiplexing section protection when the protection type of optical network is the multiplexing section protection; a second judgment module, configured to judge whether the working line is normal according to performance parameter values of service signal in the working line and switching conditions configured for channel section protection when the protection type of optical network is the channel section protection; a switching module, configured to take the service signal in the protection line as an output signal when working line is abnormal.

Abstract: The present invention encompasses a method for 1+1 protection of an optical transmission path comprising a working path and a protection path that connect a first and second terminal node. In a working mode, an optical transmission signal is transmitted via the working path from the first to the second terminal node. At the second terminal node, the optical transmission signal is split into two optical sub-signals, and one of the optical sub-signals is sent via the protection path to a protection-path connection node as a working-path control signal. In the case of an interruption of the signal transmission via the working path, the protection-path connection node detects the absence of the working-path control signal and switches the system from the working mode to a protection mode in which signal transmission is conducted via a separate protection path.

Abstract: The present application provides a method for time division multiplex service protection. The method includes: on an OLT in a passive optical network, a working uplink port and a protection uplink port are set for a time division multiplex service and a protection group is created for the working uplink port and the protection uplink port; when a service flow protection for the time division multiplex service is triggered, the time division multiplex service flow is switched from the working uplink port to the protection uplink port, therefore realizing the protection for the time division multiplex service flow. The present application provides an uplink channel protection mechanism for important services in an access system, such as the time division multiplex service, which needs no protection switching protocol, and makes the service recovery time stand within 50 ms, thereby realizing fast and nondestructive recovery of the time division multiplex service.

Abstract: A network component comprising at least one control plane controller configured to implement a method comprising transmitting a message to at least one adjacent control plane controller, wherein the message comprises a Type-Length-Value (TLV) indicating Routing and Wavelength Assignment (RWA) information. Included is a method comprising communicating a message comprising a TLV to a control plane controller, wherein the TLV indicates RWA information. Also included is an apparatus comprising a control plane controller configured to communicate a TLV to at least one adjacent control plane controller, wherein the TLV indicates RWA information.

Abstract: A network may include fiber optic lines and fiber distribution panels connected by the one or more fiber optic lines. At least one of the fiber distribution panels may include an optical fiber connector designated as a connector that is for emergency use. The network may further include a plurality of optical network terminals located at premises of subscribers to the network.

Abstract: The invention discloses a network protection method and device, the method comprises: initiating a protection configuration request through a control plane of an automatically switched optical network (ASON); and realizing a protection configuration on each node of the network according to the protection configuration request. A safe and reliable recovery capability; a reliable efficiency guarantee and an effective guarantee of the coordination of the switching and recovery are provided.

Abstract: A reflector assembly is disclosed that may include a housing; a fiber stud disposed within the housing; a filter lens having an OTDR reflective layer, the filter lens located downstream from the fiber stud and receiving light energy from the fiber stud, and configured to be transparent for light within a communication wavelength band and reflective within a diagnostic wavelength band.

Abstract: A joint switching method for an aggregation node, an aggregation node, and an optical network protection system including an aggregation node are provided. By monitoring information transferred between an active optical line terminal (OLT) and a broadband network gateway (BNG), the aggregation node finds a fault in time according to the monitored information and when a fault occurs, the aggregation node starts a local protection solution, enables a corresponding backup port connected to a backup OLT corresponding to the active OLT, and disables an active port connected to the active OLT. Through the method, when the active OLT is switched to the backup OLT, the aggregation node performs joint switching, which ensures normal communication.

Abstract: Systems and methods for optical path protection for distributed antenna systems are provided. In one embodiment, a system comprises a hub and at least one node located remotely from the hub. The hub is coupled to the node by first and second fiber paths, the first fiber path comprising an uplink fiber and a downlink fiber, the second fiber path comprising an uplink fiber and a downlink fiber. The node is coupled to the downlink fibers of the first and second fiber paths via an optical combiner, and is further coupled to the uplink fibers of the first and second fiber paths via an optical splitter. The node further monitors a signal quality of a downlink optical signal and communicates to the hub information indicative of the signal quality. The hub switches communications between the hub and the node from the first to second fiber path based on the information.

Abstract: The present invention is intended to provide an optical transmission system which is applicable not only to a known signal but also to an unknown signal, and has a high reliability at a low cost. A branching device branches an optical transmission output of a transmitter, and transmits the branched signals through different optical transmission channels. A polarization mode dispersion monitor monitors the degree of polarization mode dispersion from the optical transmission channels at the receiving end. A switch control circuit and a switch select a signal which is less affected by a deterioration in quality due to polarization mode dispersion, and outputs the selected signal to receiver 8. In this way, the probability of a deterioration in the quality of a signal due to polarization mode dispersion can be reduced for a transmission signal.

Abstract: The present invention relates to an optical fiber access network and a communication protection method thereof. The optical fiber access network comprises an optical fiber communication system, a wireless communication system, a communication service switch device, a second optical network unit and a protection optical fiber. The wireless communication system is introduced to protect the optical fiber between the optical branching divider and the optical network unit in the optical fiber communication system. The protection optical fiber or the wireless communication system is used to protect the communication service respectively when there is a broken failure between the optical line terminal and the optical network unit in the optical fiber communication system. This invention overcomes the limit of the resource, protects communication service of the optical fiber communication system and improves the bandwidth utility of the communication system.

Abstract: A method of protection switching between first and second transceivers where dispersion compensation is effected electrically in the transmitters. The method includes detecting, at the second transceiver, a signal failure of a signal transmitted from the first transceiver and, upon detecting the signal failure, signalling the first transceiver to change its compensation function. The signalling can be done by encoding overhead bits in a signal transmitted from the second to the first transceiver. Another method of protection switching includes both transceivers toggling alternate reception paths upon detecting a signal failure and changing their dispersion compensation function to that of their respective alternate path.

Abstract: In a fiber-optic communications system, a backup or redundant optical link is provided at the central office in parallel with the primary one in use. Parameters associated with the backup link, including its signal delay, its attenuation, etc. are stored at the time of installation. Upon failure of the primary link, switchover can be automatic, and the stored parameters are used to make adjustments necessary for the differences between the primary link and the backup link. In addition, having information on the differences between the two links, the central office is able to send control information downstream which is used at the remote site to control changes that must be made for upstream signals. For example, customer equipment can be signaled to adjust its timing for the next time slot or interface amplifiers can be adjusted to account for the change in attenuation.

Abstract: A system and method for responding to a failure in a communications network. The failure is detected by a router, which then transmits data from the protection port. A signal is sent from the router to a optical cross-connect system indicating the failure and causing the optical cross-connect system to connect the protection port of the router to a working port of the OXC.

Abstract: In accordance with an embodiment, a method for sparing channels in a wavelength division multiplexing (WDM) transponder comprises transmitting network traffic, over a plurality of active channels, wherein each active channel is associated with an active transmitter. Determining that one or more active transmitters have failed and switching traffic from the channels associated with the failed transmitters to first spare channels, wherein the first spare channels are associated with a plurality of first spare transmitters included in a first spare WDM module. Switching traffic from the channels associated with the failed transmitters to second spare channels. The second spare channels are associated with a plurality of second spare transmitters included in a second spare WDM module to allow for a plurality of active transmitters to fail before requiring immediate replacement of an active WDM module with at least one failed transmitter.

Abstract: Systems and methods are described for restoring wavelength services in mesh networks using pre-configured, standby lightpaths. The standby lightpaths are pre-cross-connected lightpaths that provide connectivity between switching nodes having a fiber link of degree-2 or higher. The restoration method overcomes the problem of optical impairments for long haul connections, avoids wavelength power balancing delays, provides wavelength conversion for capacity efficiency, and allows sharing of links across nonsimultaneous failures.

Abstract: The rapid switching of optical fiber communication between one or two working optical amplifiers and one protect optical amplifier is accomplished using fast optical fiber switching and alarm detection circuits that protects the loss of communication due to amplifier failure.

Abstract: A solution for detecting and recovering from a failure in a protected single-fiber passive optical network. A detector is used to detect the degradation in power level of optical signals. Furthermore, the invention discloses a variable symmetric split ratio approach to improve the number of splits (e.g. the number of ONUs). A single-fiber passive optical network is disclosed that uses a plurality of passive nodes connected in the optical fiber between the interfaces, wherein in the passive nodes 2-by-2 splitters/combiners are used to couple optical power from and into the optical fiber at a predetermined split ratio.

Abstract: The embodiments of the invention provide a method of routing convergence in a control plane of an intelligent optical network, which includes: a function unit perceiving a service link state transmitting an alarm notification message indicating a failure in a service link to a routing protocol unit when the service link is in failure; the routing protocol unit confirming a service link failure in the control plane according to the alarm notification message. The embodiments of the invention also provide an apparatus of routing convergence in a control plane of an intelligent optical network. According to the embodiments of the invention, the establishment of a new service or re-routing may be implemented within several seconds or even hundreds of milliseconds after the service link failure in the control plane occurs.

Abstract: Provided is a bidirectional wavelength division multiplexed passive optical network (WDM-PON) which includes a central office (CO) that transmits and receives multiplexed optical signals, a remote node (RN) that communicates with the CO, receives a multiplexed optical signal to demultiplex, and receives a demultiplexed optical signal to multiplex, an optical network unit (ONU) that transmits and receives demultiplexed optical signals to and from the RN, operational and protective backbone optical fibers that connect the CO to the RN, and operational and protective distribution optical fibers that connect the RN to the ONU.

Abstract: Systems and methods for optical path protection for distributed antenna systems are provided. In one embodiment, a method is provided. The method comprises receiving an electrical uplink radio frequency signal; generating an uplink optical signal derived from the electrical uplink radio frequency signal; splitting the uplink optical signal for transmission on a primary uplink optical fiber and a secondary uplink optical fiber; combining any downlink optical signal received on a primary downlink optical communication medium and any downlink optical signal received on a second downlink optical communication medium in order to output a downlink optical signal; and generating a downlink radio frequency signal derived from the downlink optical signal.

Abstract: The present invention provides a method and apparatus for implementing trunk optical fiber protection in EPON. According to the technical scheme of the present invention, activating an optical module at a master PON port, deactivating an optical module at a standby PON port, configuring a service for the master PON port, and synchronizing static data and dynamic data to the standby PON port; synchronizing and adjusting a value of an MPCP counter at the standby PON port according to a value of an MPCP counter at the master PON port; and carrying out fault detection, transmitting an operating state to the standby PON port when the fault occurs, and performing a master-standby switch of the PON ports.

Abstract: An optical switch including a first reversible optical circulator and a second reversible optical circulator is provided. Each of the first reversible optical circulator and the second reversible optical circulator respectively has four I/O ports, wherein the four I/O ports are respectively a first terminal, a second terminal, a third terminal, and a fourth terminal, the four terminals sequentially transmit an optical signal in a forward circulation or a backward circulation according to a control signal, and an open end is formed between the first terminal and the adjacent fourth terminal. The open ends of the first reversible optical circulator and the second reversible optical circulator are coupled with each other.

Abstract: An optoelectronic integrated apparatus, including a plurality of working optical source links, at least one spare optical source link, at least one spare data channel, and a protection control unit for detecting whether there is any working optical source link faulty. When detecting that a working optical source link is faulty, controlling a spare optical source link whose emission wavelength is the same as the faulty working optical source link to fulfill the functions of the faulty working optical source link and switching a data signal from the working data channel to a spare data channel. The spare optical source link is adapted to modulate the optical signal using the data signal from the spare data channel, and transmits the modulated optical signal. Reliability of the optoelectronic integrated apparatus is enhanced without increasing the maintenance cost.

Abstract: The present invention discloses a method and system for group optical channel shared protection. In the invention, when a failure occurs, operations are performed on an optical wavelength group, and four actions are accomplished at the time of switching: switching the affected optical wavelength group on the working fiber to a backup fiber (Steer); switching the optical wavelength group whose destination node is the current node on the backup fiber to the working fiber (Copy); making the optical wavelength group whose destination node is not the current node on the backup fiber transparently pass through the current node (Pass Through); and blocking or stripping the backup wavelength group transferred on the backup fiber (Strip). In addition, the invention further discloses a plurality of node structures for realizing the above operations.

Abstract: The optical communication system of the present invention is constructed with a data plane and a control plane, and includes a first monitor for monitoring a path alarm on the data plane, a second monitor for monitoring a path alarm on the control plane, and an alarm comparator for comparing alarm statuses of the optical paths that the first monitor and the second monitor preserve, wherein an optical communication apparatus, of which the first monitor and the second monitor both are in a status of having detected the alarm, operate so as to start an operation of avoiding a fault. Such a configuration makes it possible to make a detour only around an appropriate section including a fault location without performing an erroneous operation when a fault has occurred in an optical path, in which a plurality of detour sections, in an all-optical communication system.

Abstract: An optical transmission apparatus that protects different types of signals with a common backup transponder. The optical transmission apparatus includes working transponder units that relay respective optical signals on corresponding working transmission lines to or from external client devices, a backup transponder unit that can relay optical signals of different interface types, a 3:1 optical switch unit and a 1:3 optical switch unit that connect the external client devices and the working transponder units, and can connect the external client device and the backup transponder unit, and a monitor control unit that monitors occurrence of a failure in the working transponder units and the backup transponder unit, and controls switching of the transmission lines upon detection of a failure.