The present invention proposes a new method for solving the problem of fault tolerance. This new approach obtains all secondary routes assigned to each possible connection (user). The secondary routes replace the main routes when these are affected by at least one fault, which keeps the users connected as long as, for each connection, there is at least one route with operative links for reaching the destination nodes thereof. This new approach solves the general case of an arbitrary set of simultaneous link failures. The method also assesses the number of wavelengths for each link of the network, so that the probability of any connection request from a determined user c being blocked is less than a predefined threshold β.sub.c, despite the possible occurrence of the fault scenario.

In an optical communication system, an optical communication device and a plurality of optical transmission devices are loop-connected via transmission line. An optical signal transmission unit of the optical communication device, when no communication interruption occurs in the transmission line, outputs an optical signal addressed to a communication destination device that communicates with the own device to a transmission line connected to either one of two neighboring optical transmission devices. The optical signal transmission unit outputs, at the time of communication interruption occurring in the transmission line, an optical signal addressed to the communication destination device to both of transmission lines connected to respective two neighboring optical transmission devices. A branch unit of the optical transmission device branches the optical signal input from a neighboring device, and outputs branched optical signals to another neighboring device and a subordinate communication destination device of the own device.

An example system includes a first network device having first circuitry. The first network device is configured to perform operations including receiving data to be transmitted to a second network device over an optical communications network, and transmitting first information and second information to the second device. The first information is indicative of the data, and is transmitted using a first communications link of the optical communications network and using a first subset of optical subcarriers. The second information is indicative of the data, and is transmitted using a second communications link of the optical communications network and using a second subset of optical subcarriers. The first subset of optical subcarriers is different from the second subset of optical subcarriers.

An example system includes a first network device having first circuitry. The first network device is configured to perform operations including receiving data to be transmitted to a second network device over an optical communications network, and transmitting first information and second information to the second device. The first information is indicative of the data, and is transmitted using a first communications link of the optical communications network and using a first subset of optical subcarriers. The second information is indicative of the data, and is transmitted using a second communications link of the optical communications network and using a second subset of optical subcarriers. The first subset of optical subcarriers is different from the second subset of optical subcarriers.

Systems, methods, and computer-readable media are provided for signaling the presence of a fault in a multi-band optical network or other communication system. In response to a detected fault in a multi-band communication system impacting a specific band of the multi-band communication system, a method, according to one implementation, may include a step of creating a fault signal corresponding to the detected fault. The method may also include the step of conveying the fault signal to at least one of an upstream controller and a downstream controller of the multi-band communication system to trigger an action for handling the fault on the specific band. The action may be handled independently of other actions associated with one or more other bands of the multi-band communication system.

An example system includes a first network device having first circuitry. The first network device is configured to perform operations including receiving data to be transmitted to a second network device over an optical communications network, and transmitting first information and second information to the second device. The first information is indicative of the data, and is transmitted using a first communications link of the optical communications network and using a first subset of optical subcarriers. The second information is indicative of the data, and is transmitted using a second communications link of the optical communications network and using a second subset of optical subcarriers. The first subset of optical subcarriers is different from the second subset of optical subcarriers.

An optical branching/coupling device includes: a first optical branching unit that splits first light with a first and a second wavelength, and outputs second light and third light; a wavelength selector that receives the second light, receives fourth light with a third wavelength, output fifth and sixth light, one of the fifth light and the sixth light including an optical signal of the first wavelength of the second light and including the fourth light, and the other including an optical signal of the second wavelength; a first light switch that receives the fifth light and the sixth light, output one of the fifth light and the sixth light as seventh light, and output the other as eighth light; and a second light switch that receives the third light, receives the eighth light, and outputs the third or the eighth light that have been input as ninth light.

Systems and methods include receiving first power snapshot from a receiving end of a foreign controlled link of the one or more foreign controlled optical links when there are no faults thereon; responsive to obtaining second power snapshot from the receiving end of the foreign controlled link, detecting a fault on one of at least one channel and part of the spectrum traversing the foreign controlled link; correlating the second power snapshot with the first power snapshots; and raising an indication of fault for the foreign controlled link based on the correlating.

A transport network, a node, and a method are disclosed. The transport network, the node, and the method detect a failure of a super channel originating from a sliceable light source that is routed through the transport network, by detecting an optical loss of signal by an optical power monitoring device, in presence or absence of an optical loss of signal of the complete band by at least one photo detector. This information is analyzed with a fault detection algorithm using a patch cable network configuration to determine a fault indication for a failure within the first node. The fault signal indicative of the fault indication is then passed to another node on the first path.

A method and an apparatus for spectrum defragmentation, where the method includes: obtaining, by a transmit end, a target data stream; sending the target data stream on one line using a to-be-adjusted frequency band; adjusting, on another line, an occupied frequency band of the target data stream from the to-be-adjusted frequency band to a target frequency band; switching the target data stream to the other line; and transmitting the target data stream using the target frequency band.