Abstract: A network system includes: a hub base that includes a first network device with a hub function, the first network device being connected to an information communication network; and a spoke base that includes a second network device without the hub function, the second network device being connected to the information communication network. Communication between a computer provided in the spoke base and an external device connected with the computer via Internet is performed such that intra-network loopback communication is performed between the first network device and the second network device in the information communication network without an internet service provider, and communication is performed between the first network device and the external device via the internet service provider.

Abstract: Apparatuses and methods enable connecting tunnels channeling data flow from a user terminal and to a mobile network through a virtual switch in a network device which is configured to provide a service by processing data in the data flow. A method performed by a device having one or more processors includes establishing a first tunnel between the device and a node of the mobile network, and a second tunnel between the device and another network device of the mobile network, the first tunnel and the second tunnel operating according to Internet protocols. The method further includes connecting the first tunnel to the second tunnel using a virtual switch running on the device, and connecting a virtual machine running on the device to the virtual switch, the virtual machine being configured to provide a service by processing data in the data flow.

Abstract: Described in detail herein are systems and methods for routing data in a distributed environment. A controller can maintain an inactive state. A terminal can receive a request associated with a physical object. The terminal can be communicatively coupled to a cloud computing system. The terminal can attempt to transmit the request to the cloud computing system. A router communicatively coupled to the controller and cloud computing system can attempt to initiate communication between the terminal and the cloud computing system in response to the terminal attempt to transmit the request to the cloud computing system. The router can route the request to the controller in response to failing to initiate communication between the terminal and the cloud computing system after specified amount of time. The controller can switch from an inactive state to an active state in response to receiving the request.

Abstract: The present disclosure generally discloses capabilities for supporting new network zones and associated services. The network zones and associated services may include a near-real-time (NRT) zone and associated NRT services, a real-time (RT) zone and associated RT services, or the like. The resilient network zones and associated resilient and non-resilient services may be configured to provide bounded latency guarantees for reliably supporting various types of applications (e.g., mobile fronthaul, cloud computing, Internet-of-Things (IoT), or the like). The network zones and associated services may be provided using a distance-constrained fiber and wavelength switching fabric design comprised of various network devices and using associated controllers, which may be configured to support service provisioning functions, service testing functions, wavelength switching functions, and so forth.

Abstract: A first information handling system may detect a reboot condition for the first information handling system. The first information handling system may transmit a first notification to a second information handling system, notifying the second information handling system that the first information handling system is going to reboot. The first information handling system may transmit a second notification to a third information handling system, instructing the third information handling system to age out old root information. The first information handling system may then reboot.

Abstract: A routing device receives a forwarding entry for forwarding a first flow and stores it locally. When the device is a key forwarding device of a first flow, the stored forwarding entry includes first and second forwarding entries. When the device is located in a primary forwarding path but is not the key forwarding device, the stored forwarding entry comprises one forwarding entry having a priority higher than a predefined minimum value. The device receives a first flow. When the stored forwarding entry comprises one forwarding entry having a priority higher than the minimum value and a link connected to an egress port in the forwarding entry has failed, the device sets the priority of the forwarding entry as the minimum value, and returns the first flow to the key forwarding device to trigger it to forward the first flow according to the second forwarding entry.

Abstract: A method for detecting communication loop in an ad hoc network is provided. The method may comprise: receiving, at a node of the ad hoc network, a message comprising a commutative value, wherein the node is associated with a node identifier and the commutative value pertains to node identifiers associated with one or more nodes along a path the message has been traversed along regardless of the order of the nodes; and determining, with aid of one or more processors, presence of a loop based on whether the commutative value is identical to a previously obtained commutative value.

Abstract: A packet processing method includes sending, by the first provider edge (PE) device, a Media Access Control (MAC) entry update packet to a third PE device when a port of a first PE device that is connected to a customer edge (CE) device is switched from an activated state to a deactivated state, wherein the MAC entry update packet is sent to trigger the third PE device to delete a first MAC entry whose packet forwarding destination address is the first PE device, generating, through learning, a second MAC entry whose packet forwarding destination address is a second PE device, and forwarding a packet based on the second MAC entry.

Abstract: Techniques for implementing application fault tolerance via battery-backed replication of volatile state are provided. In one set of embodiments, a primary host system can detect a failure that causes an application of the primary host system to stop running. In response to detecting the failure, the primary host system can replicate volatile state that is used by the application to a secondary host system, where the secondary host system maintains a copy of the application, and where execution of the application is failed over to the copy on the secondary host system using the replicated volatile state.

Abstract: Techniques for achieving application high availability via application-transparent battery-backed replication of persistent data are provided. In one set of embodiments, a computer system can detect a failure that causes an application of the computer system to stop running. In response to detecting the failure, the computer system can copy persistent data written by the application and maintained locally at the computer system to one or more remote destinations, where the copying is performed in a manner that is transparent to the application and while the computer system runs on battery power. The application can then be restarted on another computer system using the copied data.

Abstract: Techniques for achieving application high availability via crash-consistent asynchronous replication of persistent data are provided. In one set of embodiments, an application running on a computer system can, during runtime of the application: write persistent data to a local nonvolatile data store of the computer system, write one or more log entries comprising the persistent data to a local log region of the computer system, and asynchronously copy the one or more log entries to one or more remote destinations. Then, upon detecting a failure that prevents the application from continuing execution, the computer system can copy the local log region or a remaining portion thereof to the one or more remote destinations, where the copying is performed while the computer system runs on battery power and where the application is restarted on another computer system using a persistent state derived from the copied log entries.

Abstract: An information handling system such as a server, network switch, or virtual host collects electronic network topology data to identify topological redundancies between networked devices. Each topological redundancy indicates that a particular networked device has at least two physical cable connections to at least two other, separate devices. A topological redundancy to two network switches, for example, ensures that a networked device remains communicatively available should one of the network switches fail.

Abstract: The concepts and technologies disclosed herein provide high availability and high utilization cloud data center architecture for supporting telecommunications services. According to one aspect of the concepts and technologies disclosed herein, a 4-site model of application placement within the cloud computing environment provides 37.5% resource utilization with site availability of five 9s (99.999%) and virtual machine availability of five 9s. According to another aspect of the concepts and technologies disclosed herein, a 3-site model of application placement within the cloud computing environment provides 66% resource utilization with site availability of five 9s and virtual machine availability of five 9s. According to another aspect of the concepts and technologies disclosed herein, a 4-site model of application placement within the cloud computing environment provides 75% resource utilization with site availability of five 9s and virtual machine availability of five 9s.

Abstract: In some implementations, a method is provided. The method includes determining that a network device will perform a reboot. The method also includes saving state information. The state information comprises data used by the network device to process address resolution protocol (ARP) messages. The method further includes initiating the reboot of the network device. The method further includes initiating a first ARP service. The first ARP service is configured to process ARP messages during the reboot of the network device.

Abstract: The present invention relates to methods and apparatus for efficient handling of registration messages by network equipment.

Abstract: Various example embodiments for supporting communications for stream processing platforms are described. Various example embodiments for supporting communications in a stream processing platform may be configured to use micro-brokers to support communications in a stream processing platform by providing micro-brokers configured to support communications between operators of operator groups of the stream processing platform. Various example embodiments for supporting communications in a stream processing platform may be configured to use micro-brokers to support communications in the stream processing platform by providing micro-brokers configured to support communications between operators of operator groups of the stream processing platform using various communication modes (e.g.

Abstract: Systems and methods for providing full redundancy in a computing network using a single network interface controller (NIC) and a single NIC card within one or more computing devices (e.g., servers) are provided. Embodiments of the technology disclosed herein provide a NIC card with a processing device (e.g., a field-programmable gate array (FPGA)) having a first set of input pins associated with a primary network switch and a second set of input pins associated with a standby network switch. When a failure occurs on the primary network switch, the processing device of the NIC card is configured to perform a circuit switch action to switch the connection between a processing device output from the first set of input pins to the second set of input pins. Accordingly, the same NIC is capable of controlling the network interface of a computing device between to different network switches.

Abstract: A method for setting up communication links to redundantly operated controllers in an industrial automation system, in which a first controller is in an active operating state for controlling or regulating a technical process, and a second controller is in a reserve operating state, from which it is placeable into an active operating state in the event the first controller fails, where the first/second controllers respectively store a device identifier associated with the first/second controllers, information about associations between device names and communication network addresses of the first/second controllers is provided in accordance with a name service protocol within at least one subnetwork associated with the first/second controllers, and where retrieval of a piece of address or name information for one of the two controllers involves automatically providing the piece of address or name information to setup a communication link to the other controller based on the respective device identifier.

Abstract: A switch architecture includes an ingress module, ingress fabric interface module, and a switch fabric. The switch fabric communicates with egress fabric interface modules and egress modules. The architecture implements multiple layers of congestion management. The congestion management may include fast acting link level flow control and more slowly acting end-to-end flow control. The switch architecture simultaneously provides high scalability, with low latency and low frame loss.

Abstract: An information transmission, sending, and acquisition method and device. A method includes: using a master and slave relay terminal in an information relay terminal pair at the head of an information relay terminal pair queue to synchronously receive information sent by a sending terminal, and using the master relay terminal to transmit information to a receiving terminal; when a fault occurs in the master or slave relay terminal at the head of the queue, stopping using the master and slave relay terminals to receive information, and deleting the information relay terminal pair from the queue; after the slave or master relay terminal in the deleted terminal pair transmits all the information to the receiving terminal and the fault of the master or slave relay terminal is removed, inserting the terminal pair to the tail of the queue; and meanwhile, when the fault occurs in the master or slave relay terminal, using the next adjacent terminal pair to continue receiving the information.

Abstract: Example method includes: defining, by a network device, a source virtual local area network (VLAN), wherein the source VLAN is common for at least a first switch and a second switch, and wherein the source VLAN is dedicated to a particular link between the first switch and the second switch; and using an Internet Protocol (IP) address corresponding to the defined source VLAN as a source address for peer-to-peer traffic transmitted between the first switch and the second switch, wherein no peer-to-peer traffic between the first switch and the second switch is transmitted over a link other than the particular link.

Abstract: A method for transmitting control commands in a computer system, which includes components at least in the form of nodes, actuators and communication systems, wherein the control commands are communicated over the communication systems from the nodes to the actuators, and wherein one or more of the components may fail to operate according their specification. For consistently accepting control commands at the actuators, the nodes and their control commands are assigned priorities, wherein a node and its control commands have the same priority, wherein at least two priorities are used, wherein a high priority node produces high priority control commands and a low priority node produces low priority control commands, and wherein a high priority node is configured to communicate its control commands over at least two communication systems to the actuators and a low priority node is configured to communicate its low priority control commands over at least one communication system to the actuators.

Abstract: A method for withdrawing programmed routes in network devices. The method includes receiving instructions to withdraw at least one route of a set of programmed routes, where the set of programmed routes is stored in a forwarding information base (FIB), removing the at least one route from a set of routes stored in a routing information base (RIB), notifying at least one peer network device of a set of peer network devices about the at least one route to be withdrawn, initializing a timer with a timeout value and starting the timer, before the time expires, processing a packet that uses the at least one route to be withdrawn, and after the timer expires, removing the at least one route from the FIB.

Abstract: The described technology provides a capability for web applications from different domains to interact within one application environment. For example, an enterprise web application executing on a client terminal is provided the capability to monitor a second web application from a third party vendor even when the second web application is independently executing within an iframe or the like within the enterprise web applications container or context. In some example embodiments, the communication is enabled by a composite cookie or key that incorporates portions of an enterprise web application cookie or key and also portions of a vendor web application cookie or key.

Abstract: A method and apparatus to bring up a network controller in a network of multiple network elements is described. In an exemplary embodiment, the network controller receives an indication that the network controller is booting up. The network controller is coupled to a plurality of network elements in a network, where the network controller maintains a controller database that supports a network-wide service used by the plurality of network elements. The network controller further receives state information from the plurality of network elements. In addition, the network controller builds the controller database from the state information. Furthermore, the network controller sends updates from the controller database to each of the plurality of network elements, where each of the plurality of network elements incorporates these updates into a respective network element database and the network element database is used to perform the network-wide service.

Abstract: A layer-2 switch, forming a communication network along with a communication terminal, includes a plurality of communication ports, frame identification units to identify a specific frame that is regularly transmitted from the communication terminal in the communication network, a setting unit to set a monitoring cycle and a reception threshold for detecting a loop path in the communication network, a monitoring unit to identify, for each of the communication ports, a plurality of communication terminals that are a source of the specific frame, and to count the number of the specific frames received from each of the communication terminals within the monitoring cycle, and a determination unit to determine whether a loop path is detected for each of the communication ports by comparing a counter value, which indicates the number of the specific frames, with the reception threshold, and to execute control to stop transmission and reception of the frame at the communication port at which a loop path is detected.

Abstract: A system and method for allowing legacy devices to be discovered on a DotDot network is disclosed. The system includes a gateway device to interface between DotDot devices and legacy devices. In some embodiments, the gateway device has a plurality of network interfaces to communicate with these legacy devices. The gateway device discovers the legacy devices that it can communicate with. The gateway device then presents information about these legacy devices in a Resource Directory. In some embodiments, the Resource Directory is maintained within the gateway device. In other embodiments, the gateway device utilizes a Resource Directory that exists on the DotDot network.

Abstract: A system for optimizing network traffic is described. The system includes a primary appliance having a first handoff engine in an active state. The primary appliance is configured to receive from a first switch one of first data or a copy of first data to be provided to a second switch. The system also includes a secondary appliance having a second handoff engine in a passive state, where the secondary appliance is configured to receive from the first switch the other of the first data or the copy of the first data. The second handoff engine is configured to monitor state data provided by the first handoff engine, determine a condition of the first handoff engine using the state data and the other of the first data or the copy of first data, and based on the determination, provide instructions for the secondary appliance to provide the other of the first data or the copy of the first data to the second switch.

Abstract: Embodiments are directed to a process and system for recovering from data link failure in a network, by retaining, in a first provider edge device, path information for a first host coupled to a second host over the network in a control plane, upon indication of withdrawal of the first host from a second provider edge device, starting a timer controlling a period of re-advertisement and re-routing to the first host, removing, in the first provider edge device, the first host from a data plane, and generating, in the first provider edge device, a new route to advertise the first host address to cause other provider edge devices to receive the new route and adjust their respective control plane routes prior to expiration of the timer.

Abstract: Examples disclosed herein relate to selection of a master controller in a software defined network (SDN). In an example, a master controller may monitor a parameter on each SDN controller in a team of SDN controllers comprising the master controller, wherein the master controller performs a role of master over a group of network devices. In response to a determination that a value of the parameter on the master controller is above a pre-defined limit, master controller may select another SDN controller from the team. Master controller may assign the role of master over network devices in the group to the selected SDN controller based on a ranking of the network devices, wherein the network devices may be assigned in succession until a limit defined for a value of the parameter on the selected SDN controller is reached.

Abstract: Provided is a software updating apparatus that can flexibly respond to various situations, including update capacity and use cases of each ECU, in a case of updating control information of a plurality of ECUs. Update control information necessary for update processing, including update data to be newly applied to an ECU, is received from a server and control of the update processing is performed based on the received update control information.

Abstract: In one embodiment, Ethernet Virtual Private Network (EVPN) is implemented using Internet Protocol Version 6 (IPv6) Segment Routing (SRv6) underlay network and SRv6-enhanced Border Gateway Protocol (BGP) signaling. A particular route associated with a particular Internet Protocol Version 6 (IPv6) Segment Routing (SRv6) Segment Identifier (SID) is advertised in a particular route advertisement message of a routing protocol (e.g., BGP). The SID includes a locator of a particular router and a function encoding representing a particular EVPN end function of the particular router, with the particular SID including a routable prefix to the particular router. The particular router receives a particular packet including the particular SID; and in response, the particular router performs the particular EVPN end function on the particular packet. In one embodiment, the particular packet includes a Segment Routing Header (SRH) including the particular SID as the currently active SID.

Abstract: One embodiment of the present invention provides a switch. The switch includes a link aggregation module and a link management module. The link aggregation module establishes a virtual link aggregation group comprising a plurality of links coupled to the switch and one or more other switches. The plurality of links includes a first and a second sets of links coupling a first and a second end devices, respectively. The link management module determines a current mode which indicates which of the sets of links is currently active, and operates the first and the second sets of links as active and standby links, respectively, for the virtual link aggregation group based on the current mode and a port role for a port participating in the virtual link aggregation group. The port role indicates whether the port is coupled to an active link or a backup link.

Abstract: The disclosure relates to technology for supporting a virtual switch to change data plane providers on a framework supporting multiple data plane providers. A processing device receives a request to change a first data plane provider, where the virtual switch is configured with a topology on the first data plane provider to use a flow management protocol. The virtual switch includes network interfaces connected to ports to enable communication among entities attached to the network interfaces by forwarding data packets within a first datapath of the first data plane. In response to the change, the network interfaces are disconnected, the first datapath is removed and a second datapath is created. The virtual switch is then configured to operate with the second datapath while retaining the flow management protocol and the topology, such that the entities communicate by forwarding data packets within the second datapath on the second data plane.

Abstract: Some embodiments provide a method for maintaining a cluster topology for a cluster of application instances operating across several datacenters. On a particular machine at which a particular one of the application instances operates, the method maintains a cluster topology that identifies, for each application instance of the cluster, the datacenter in which the application instance operates. From the particular application instance, the method receives a query request for at least a portion of the cluster topology through a programmatic interface. The method provides the requested portion of the cluster topology to the particular application instance. The particular application instance uses the cluster topology for processing application data based on the locations of a set of application instances within the several datacenters.

Abstract: A method of dynamically updating DNS information in an IP network. A first entity of the IP network, distinct from DNS servers of the IP network, receives a request from a second entity of the network, likewise distinct from the DNS servers but possessing a copy of DNS information, constituting a record in at least one DNS server of the IP network. The first entity responds to the request by sending a message to the second entity, including an indication about the need to modify the copy. On receiving the message, the second entity determines whether the indication includes at least one additional instruction. If so, the second entity: performs a DNS interrogation, and on receiving a response, modifies its copy of the DNS information based the response and the additional instruction; or modifies its copy of the DNS information based on the additional instruction without performing a DNS interrogation.

Abstract: A method of determining the state of each peer node in a pair of first and second peer nodes is provided. The first node is configured as a confirmed active node and the second node is configured as a standby node. The second node transitions into a tentative active mode when a predetermined number of heartbeat messages are lost between the pair nodes while the first and second nodes remain functional. The second node receives a first message from the first node after the heartbeat messages are established between the peer nodes. The first message indicates that the first node is in the confirmed active mode. In response to the first message, the second node transitions from the tentative active mode into the standby mode and sends a second message from the second node to the first node indicating that the second node is in the standby mode.

Abstract: A method for providing network connectivity to at least one client device includes: connecting the at least one client device to an access gateway device to create a local area network of the access gateway device; and connecting the access gateway device to an internet protocol edge function. The at least one client device is connected to a telecommunications network via the access gateway device and the internet protocol edge function. In order to provide the network connectivity to the at least one client device, a network connectivity link is provided, the network connectivity link comprising: a local area network-segment between the at least one client device and the access gateway device, and a wide area network-segment between the access gateway device and the internet protocol edge function.

Abstract: A method for forwarding a data flow of multiple data packets according to a protocol adapted for locally-managed data forwarding in a software-defined networking (SDN) architecture includes entering each data packet of the data flow of multiple data packets to a data communication forwarding entity (FE). At the forwarding entity, the next destination of the data packet is selected by applying state machine logic to at least one field of the data packet and to state information tracked by the forwarding entity before the data packet is received. The state machine logic includes rules for forwarding the data packet.

Abstract: A device may determine that a route is inactive. Information identifying the route may be stored in a forwarding plane portion of a forwarding table and a control plane portion of the forwarding table. The route may be associated with directing network traffic toward an endpoint network device. The device may remove the information identifying the route from the forwarding plane portion of the forwarding table without removing the information identifying the route from the control plane portion of the forwarding table based on determining that the route is inactive. The device may route network traffic based on the forwarding table after removing the information identifying the route from the forwarding plane portion of the forwarding table without removing the information identifying the route from the control plane portion of the forwarding table.

Abstract: Provided is a network relay apparatus of a gateway redundancy system, including: a storage unit configured to store, as an internal status, a redundancy status for indicating whether the network relay apparatus operates as an active system or a standby system for each subscriber terminal or subscriber terminal group, and a subscriber status for indicating a list of used address information for each subscriber terminal; and a management unit configured to: monitor communication between another network relay apparatus in a redundancy configuration and a subscriber terminal group; record, into the storage unit, used address information assigned by the another network relay apparatus to a subscriber terminal as a part of the subscriber status; and notify or advertise the sequentially recorded internal status to a notification destination sequentially at a predetermined timing.

Abstract: A method and a transmitting node for redirecting of a flow of data packets to a path of alternative paths, and a method and a receiving node for enabling redirection of a flow of data packets to a path of alternative paths, where data packets are marked with a value indicating the importance of the data packets. The method for directing directs one or more flows of data packets for the alternative paths, wherein data packets marked with a higher value are prioritized over data packets marked with a lower value. Based on feedback information, the transmitting node redirects a flow of data packets to a second path of the alternative paths, if the metric of congestion indicates a higher congestion on the first path than on the second path.

Abstract: In one embodiment, a method comprises creating, in a computing network, a loop-free routing topology comprising a plurality of routing arcs for reaching a destination device, each routing arc comprising a first network device as a first end of the routing arc, a second network device as a second end of the routing arc, and at least a third network device configured for routing any network traffic along the routing arc toward the destination device via any one of the first or second ends of the routing arc; and causing the network traffic to be forwarded along at least one of the routing arcs to the destination device.

Abstract: Systems, methods, and apparatuses are disclosed herein for identifying a topology of a MoChi system prior to a boot-up of an operating system. A master SoC may detect, prior to boot-up of an operating system that uses the master SoC, an initialization command, and may, in response to detecting the initialization command, assign a first chip identifier to the master SoC. The master SoC may transmit a discovery communication from the master SoC to a slave SoC that is one hop away from the master SoC. The slave SoC may determine whether the slave SoC is a last hop SoC, and, in response to determining that the slave SoC is a last hop SoC, the slave SoC may transmit a reply communication to the master SoC. The master SoC may then assign, based on the reply communication, a second chip identifier to the slave SoC.

Abstract: A method and system of portable and flexible deployment of dedicated and virtual servers. A user input of an order requesting the deployment of a dedicated or virtual server at a specified data center location is received at a user interface. A user input of a selection of a server image pertaining to the server to be deployed is received at a first screen at the user interface. A second screen is presented to the user at the user interface, which enables the user to select one or more geographic locations of two or more distinct geographic locations, from a menu displayed on the second screen, for storing and deploying the selected server image in a data center at each selected geographic location. The server is selected according to the user input of the selected server image. The selected server is deployed.

Abstract: A system for providing small cell backhaul communication includes a small cell backhaul network including a plurality of small cell network nodes. A software defined network (SDN) controller controls link configuration between the plurality of small cell network nodes of the small cell backhaul network. The SDN controller communicates control channel information with the plurality of small cell network backhaul nodes over a control channel using a communications protocol that enables software defined networking.

Abstract: Coexistence and migration of legacy and VXLAN networks may be provided. A first anchor leaf switch and a second anchor leaf switch may detect that they can reach each other over a Virtual Extensible Local Area Network (VXLAN) overlay layer 2 network. In response to detecting that they can reach each other over the VXLAN, the second anchor leaf switch may block VLANs mapped to the VXLAN's VXLAN Network Identifier (VNI) on the second anchor leaf switch's ports connecting to spine routers. In addition, the first anchor leaf switch and the second anchor leaf switch may detect that they can reach each other over a physical layer 2 network. In response to detecting that they can reach each other over a physical layer 2 network, the second anchor leaf switch may block Virtual Extensible Local Area Network (VXLAN) segments at the second anchor leaf switch.

Abstract: In an example, a VTEP device may store first routing information acquired by the VTEP device, wherein the first routing information may be routing information of a host device connected with the VTEP device. The VTEP stores second routing information sent from other VTEP devices in a VXLAN, wherein the second routing information may be routing information of a host device connected with the other VTEP devices. The VTEP receives an address resolution request from a source host device, wherein the address resolution request comprises an IP address of a target host device, and a VXLAN identifier of a VXLAN to which the target host device belongs. and in response to a determination that routing information of the target host device may be stored locally, the VTEP sends an address resolution response comprising a MAC address of the target host device to the source host device.

Abstract: A storage controller comprising a first server and a second server is maintained. Data of the first server is stored in a first storage cloud, and data of the second server is stored in a second storage cloud. In response to a failure of the second server, the first server performs operations of the second server by using the stored data of the first server in the first storage cloud.

Abstract: A transmission system includes: a first transmission device that receives a first signal from the work path; a second transmission device, coupled to a protection path in a redundant configuration with respect to the work path, that receives a second signal from the protection path; and a first communication device coupled to the first and second transmission devices, wherein the first communication device, when detecting switching information from the first transmission device, notifies the first transmission device of first switching notification information and notifies the second transmission device of second switching notification information, the first transmission device stops relaying the first signal to the first communication device in response to the first switching notification information from the first communication device, and the second transmission device starts to relay the second signal to the first communication device in response to the second switching notification information from the f