JP4557647B2 - Optical transmission system - Google Patents

Description

  The present invention relates to an optical transmission system that includes a plurality of nodes and transparently transmits optical signals to electrical signals at each node without regenerative conversion. This type of system is also called an all-optical network. Examples of the node include an OADM (Optical Add / Drop Multiplexer), a PXC (Photonic Cross Connect) device, and a WDM (Wavelength Division Multiplexer) device.

  Many nodes provided in an information transmission system have a function of issuing an alarm when a signal arriving at an input end is interrupted. However, in an all-optical network, when an input signal is interrupted at the input end of a certain node due to a fiber cut or the like, the optical signal to all the downstream nodes is interrupted. Therefore, it is very difficult to identify a fault location because an input signal disconnection is cascaded to downstream nodes, and even if there is only one fault location, an alarm is issued from a plurality of nodes.

  Further, in many cases, an optical signal does not flow through an unopened wavelength path or a wavelength path for a protection line. Therefore, a node detects an input signal disconnection even if there is no failure for these paths. In order to verify the presence / absence of a failure, it is essential to open a wavelength path or to perform a switching process to a protection line.

The related technology is disclosed in Patent Document 1 below. The technique described in this document is intended to facilitate the identification of a fault location.
Japanese Patent Laid-Open No. 11-252049

  As described above, the all-optical network has a problem that it is difficult to identify a fault location. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical transmission system capable of easily identifying a fault location.

In order to achieve the above object, according to an aspect of the present invention, in an optical transmission system in which a plurality of nodes that transmit optical signals transparently are connected via a link that can multiplex a plurality of wavelength paths, Each of the nodes monitors an optical signal received via the link and detects the disconnection of the link, and when the disconnection of the link is detected by the input disconnection detection unit, the link A dummy light corresponding to the wavelength of the wavelength path is inserted into an optical switch that switches an optical signal to a plurality of wavelength paths that reach the downstream side via the dummy, and the dummy light is connected to the path to the downstream link. An optical insertion unit, and the dummy optical insertion unit includes a wavelength-switching light source that sequentially generates wavelength light corresponding to each of the plurality of wavelength paths in a time-division manner. The optical transmission system according to claim bets is provided.

  By taking such means, a dummy optical signal replacing the optical signal is inserted downstream of the wavelength path when an input signal disconnection is detected. As a result, it is possible to prevent the input interruption alarm from spreading to the downstream side, so that it is easy to identify the fault location. In particular, in a wavelength division multiplexing transmission system, the optical signals of all wavelength paths are lost when the link is disconnected. Therefore, in the present invention, by using the wavelength switching type light source, it is possible to cover all wavelength paths with one or a small number of light sources.

  ADVANTAGE OF THE INVENTION According to this invention, the optical transmission system which can identify a fault location easily can be provided.

  FIG. 1 is a schematic diagram showing an optical transmission system assumed in the present invention. This system includes a plurality of nodes 11 to 16, and the nodes 11 to 16 are connected in a mesh form via links L. Each link L is an optical fiber and transmits wavelength multiplexed light. Each node 11-16 transmits the optical signal of each wavelength transparently to an adjacent node.

  In FIG. 1, for example, when a failure occurs in the link L between the nodes 11 and 12, this failure is detected at the node 12. In response to this, the node 12 issues a LOS (Loss of Signal) alarm. Further, since the optical signal does not reach the nodes 13, 14 and 15 due to this failure, any of these nodes will issue a LOS alarm. As described above, in the all-optical network, it is known that the link failure successively spreads to the downstream links, so that it becomes difficult to identify the failure location. Embodiments that can avoid such a situation are disclosed below.

[First Embodiment]
FIG. 2 is a functional block diagram showing a first embodiment of a node provided in the optical transmission system of the present invention. This node includes a plurality of input ports connected to the link L in FIG. 1, and includes wavelength separation units (WDM) 21 to 2n for each port. Each of the wavelength demultiplexing units 21 to 2n demultiplexes the wavelength multiplexed light that arrives via the link L into individual wavelength light and inputs it to the optical switch unit (optical SW) 30. The optical switch 30 switches the path of each wavelength light and then inputs it to the wavelength multiplexing units (WDM) 41 to 4n. The wavelength multiplexing units 41 to 4n multiplex the wavelength light after switching and send it to the downstream link.

  By the way, the node in FIG. 2 includes input signal disconnection detection units 51 to 5n, a control unit 60, a dummy light generation unit 70, and optical switches 81 to 8n. Input signal disconnection detectors 51 to 5n are provided for each upstream link, and monitor the state of wavelength multiplexed light for each link to detect the presence or absence of input disconnection. The dummy light generating unit 70 generates light (hereinafter referred to as dummy light) that can be distinguished from the transmitted optical signal. The dummy light is input to optical switches 81 to 8n provided for each upstream link. When the control unit 60 detects an input interruption in any of the upstream links, the controller 60 controls the optical switch of the corresponding link to connect the dummy light. As a result, dummy light is inserted downstream of the link where the input interruption is detected.

  Thereby, in this embodiment, when a failure occurs in any of the links L, dummy light is inserted into all the wavelength paths on the downstream side. As a result, even if a LOS failure occurs in a certain link, the optical signal of the link on the downstream side is not lost, so that the failure can be prevented from spreading downstream. As a result, it is possible to limit the fault location to only one, and it is possible to easily identify the location where the failure occurred.

[Second Embodiment]
FIG. 3 is a functional block diagram showing a second embodiment of a node provided in the optical transmission system of the present invention. In FIG. 3, parts common to FIG. 2 are given the same reference numerals, and only different parts will be described here. The node in FIG. 3 includes a dummy light generation unit 90 that is directly connected to one port of the optical switch 30. The dummy light generation unit 90 includes a wavelength switching type light source, and generates dummy light whose wavelength changes in a time division manner.

  In FIG. 3, when an input interruption is detected in any of the links, the control unit 60 immediately controls the optical switch 30 to connect the dummy light to the path to the downstream link. Since the wavelength of the dummy light changes in a time division manner, as a result, the dummy light is sequentially inserted into all downstream wavelength paths. Even if it does in this way, the effect similar to 1st Embodiment can be acquired. In addition, in the present embodiment, it is not necessary to provide a dummy light generation unit for each wavelength, so that the number of dummy light generation units can be reduced and the configuration of the node can be simplified. In particular, if a light source capable of outputting all wavelengths is used, only one dummy light generator 90 is required, which can greatly contribute to simplification of the configuration.

  Furthermore, in this embodiment, a broadband light source may be used instead of the wavelength switching light source. That is, if a light source capable of generating a dummy light having a spectrum covering the band from the longest wavelength to the shortest wavelength among all the wavelength paths is used, the dummy light can be simultaneously inserted into all the downstream wavelength paths. . This also contributes to the simplification of the configuration in addition to the effects of the first embodiment.

[Third Embodiment]
FIG. 4 is a functional block diagram showing a third embodiment of a node provided in the optical transmission system of the present invention. 4 that are the same as those in FIG. 2 are denoted by the same reference numerals, and only different parts will be described here. In FIG. 4, input signal disconnection detectors 111 to 11p and 1n1 to 1nq are provided for each wavelength light after being separated by the wavelength separators 21 to 2n. When the input interruption of any wavelength light is detected, the control unit 60 controls the optical switch to connect the dummy light to the downstream signal path.

  With such a configuration, the presence or absence of an optical signal can be monitored for each wavelength path, and dummy light insertion can be performed individually for each wavelength path. As a result, dummy light is inserted into an unopened wavelength path where the optical signal is not propagating, or a wavelength path secured as a protection line, and an input signal disconnection alarm is monitored at the opposite node to cut the fiber, etc. It becomes possible to detect the failure. This eliminates the need to perform operations such as actually opening a wavelength path or switching to a protection line in order to detect failure. Therefore, it is possible not only to easily identify the location where the failure has occurred, but also to improve the convenience of network operation.

  The present invention is not limited to the above embodiment. For example, an optical coupler may be used instead of the optical switches 81 to 8n in FIG. Further, the present invention can be embodied by modifying the constituent elements without departing from the spirit of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The schematic diagram which shows the optical transmission system assumed in this invention. The functional block diagram which shows 1st Embodiment of the node with which the optical transmission system of this invention is equipped. The functional block diagram which shows 2nd Embodiment of the node with which the optical transmission system of this invention is equipped. The functional block diagram which shows 3rd Embodiment of the node with which the optical transmission system of this invention is provided.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11-16 ... Node, L ... Link, 21-2n ... Wavelength separation part, 30 ... Optical switch, 41-4n ... Wavelength multiplexing part, 51-5n ... Input signal interruption | blocking detection part, 60 ... Control part, 70, 90 ... Dummy light generation unit, 81-8n ... optical switch, 111-11p, 1n1-1nq ... input signal disconnection detection unit

Claims (1)

In an optical transmission system in which a plurality of nodes that transmit optical signals transparently are connected via a link that can multiplex a plurality of wavelength paths,
Each of the plurality of nodes is
An input disconnection detecting means for monitoring an optical signal received via the link and detecting the disconnection of the link;
When the link disconnection is detected by the input disconnection detecting means, a dummy corresponding to the wavelength of the wavelength path is connected to an optical switch that switches optical signals to a plurality of wavelength paths that reach the downstream side via the link. A dummy light insertion means for inserting light and connecting the dummy light to a path to a downstream link ;
The dummy light inserting means includes a wavelength-switching light source that sequentially generates time-division wavelength light corresponding to each of the plurality of wavelength paths.

Images