WO2015120895A1 - Method and apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged and a path computation device - Google Patents

Method and apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged and a path computation device Download PDF

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Publication number
WO2015120895A1
WO2015120895A1 PCT/EP2014/052847 EP2014052847W WO2015120895A1 WO 2015120895 A1 WO2015120895 A1 WO 2015120895A1 EP 2014052847 W EP2014052847 W EP 2014052847W WO 2015120895 A1 WO2015120895 A1 WO 2015120895A1
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WO
WIPO (PCT)
Prior art keywords
optical
power
disconnected
node
fibre
Prior art date
Application number
PCT/EP2014/052847
Other languages
French (fr)
Inventor
Francesco Fondelli
Giulio Bottari
Antonio D'errico
Original Assignee
Telefonaktiebolaget L M Ericsson (Publ)
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Application filed by Telefonaktiebolaget L M Ericsson (Publ) filed Critical Telefonaktiebolaget L M Ericsson (Publ)
Priority to PCT/EP2014/052847 priority Critical patent/WO2015120895A1/en
Publication of WO2015120895A1 publication Critical patent/WO2015120895A1/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/079Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
    • H04B10/0791Fault location on the transmission path
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/079Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
    • H04B10/0795Performance monitoring; Measurement of transmission parameters
    • H04B10/07955Monitoring or measuring power
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/079Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
    • H04B10/0797Monitoring line amplifier or line repeater equipment
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J14/00Optical multiplex systems
    • H04J14/02Wavelength-division multiplex systems
    • H04J14/0201Add-and-drop multiplexing
    • H04J14/0202Arrangements therefor
    • H04J14/021Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
    • H04J14/0212Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM] using optical switches or wavelength selective switches [WSS]

Definitions

  • the present invention relates to a method and apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged.
  • the present invention further relates to a method and path computation device for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network.
  • Optical communications networks comprise optical nodes interconnected by optical links, which typically comprise optical fibres.
  • optical links typically comprise optical fibres.
  • a path computation device determines a path for the optical traffic from the first optical node to the second optical node. The path may pass through a number of intermediate optical nodes / optical links.
  • Optical communications networks have failure recovery mechanisms, such that in the event that one of the optical links fails, e.g. the optical link is unplug, cut, or otherwise damaged, or one of the intermediate nodes fails, an alternative path for the optical traffic can be set up, which avoids the failed optical link.
  • FIG. 1 is a flow chart showing a known recovery procedure.
  • loss of signal LOS
  • an optical node on the path i.e. it is determined that the optical node is no longer receiving the optical traffic from the first optical node.
  • LOS loss of signal
  • step 102 it is then determined whether a failed optical link can be identified. If a failed optical link is identified, at step 103, an alternative path for the optical traffic is calculated and set up which detours around the failed optical link. This is referred to as a Fast Re-Route (FRR) recovery mechanism.
  • FRR Fast Re-Route
  • step 105 an alternative path for optical traffic from the first optical node to the second optical node is calculated and set up which is fully disjointed from the previous path (i.e. the alternative path does not include any of the optical links in the previous path). It is then determined, at step 106, whether there is still LOS at the optical node. Steps 105 and 106 are repeated, until the optical traffic is received at the optical node, or until no further alternative end-to-end path can be found.
  • optical fibre inside an optical node will be referred to as an "internal" optical fibre.
  • a probe or dummy signal generator is installed in the optical node which is configured to send an optical probe signal through an internal optical fibre to be monitored.
  • An optical power detector is arranged to detect whether the probe signal is output from the optical fibre. If the probe signal is not detected by the power detector, then it can be determined that the optical fibre must be disconnected or damaged.
  • an optical node may have many internal optical fibres (for example, a 4-way ROADM (reconfigurable add drop multiplexer) node may comprise twenty internal optical fibres), many probe signal generators would need to be installed in each optical node.
  • many probe signal generators would need to be installed in each optical node.
  • the optical node comprises an optical amplifier arranged to amplify optical traffic to be transmitted from a first end of the optical fibre through the optical fibre to a second end of the optical fibre.
  • the method comprises detecting the power of light received by an optical power detector arranged to detect light output from the second end of the optical fibre.
  • the method further comprises comparing the detected power to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier.
  • the method further comprises determining whether the optical fibre is disconnected or damaged based on the comparing, and outputting an indication of whether the optical fibre is disconnected or damaged based on the determining.
  • embodiments of the present invention enable a disconnected or damaged internal optical fibre to be detected, even if no optical traffic is supposed to be passing through the internal optical fibre, by making use of existing hardware in the optical node.
  • optical amplifiers are turned off when they receive no optical traffic, in order to save power.
  • the applicant has however appreciated that by configuring the optical node such that the optical amplifier stays on even if no optical traffic is received by the optical amplifier, or by sending a control signal to the optical amplifier to cause the optical amplifier to turn on, the optical noise which is emitted by the optical amplifier can be used, effectively, as a probe signal, even when no optical traffic is being transmitted by the optical amplifier.
  • determining whether the optical fibre is disconnected or damaged based on the comparing comprises determining that the optical fibre is disconnected or damaged if the detected power is lower than the power associated with the optical noise expected at the optical power detector.
  • determining whether the optical fibre is disconnected or damaged based on the comparing comprises determining that the optical fibre is not disconnected or damaged if the detected power is equal to or greater than the power associated with the optical noise expected at the optical power detector.
  • the method may further comprise sending a control signal to the optical amplifier to cause the optical amplifier to turn on and or to cause the gain of the optical amplifier to increase.
  • increasing the gain of the optical amplifier will increase the optical noise emitted by the optical amplifier, and therefore increasing the gain of the optical amplifier may lead to more accurate detection of whether the internal optical fibre is disconnected or damaged.
  • the method may further comprise determining that the optical amplifier is working properly based on an output from a monitoring point of the optical amplifier.
  • determining that the optical amplifier is working properly based on an output from a monitoring point of the optical amplifier.
  • the internal optical fibre may be monitored continuously. However, more preferably, to save processing power, the internal optical fibre is only monitored when it is suspected that the optical fibre might be disconnected or damaged.
  • the optical fibre is monitored in response to a detection of a Loss of Signal (LOS) at the or another optical node.
  • LOS Loss of Signal
  • the optical node has a broadcast and select configuration whereby the same optical traffic is transmitted through each of a plurality of optical fibres inside the optical node.
  • the plurality of optical fibres includes the optical fibre.
  • the optical node further comprises a plurality of optical power detectors each arranged to detect the power of light output from a respective one of the plurality of optical fibres.
  • the method further comprises detecting the power of light received by each of the optical power detectors.
  • the method further comprises comparing the powers detected by the optical power detectors.
  • the method further comprises determining that the optical fibre might be disconnected or damaged based on the comparing of the powers detected by the optical power detectors.
  • the optical fibre is monitored in response to the determining that the optical fibre might be disconnected or damaged.
  • the apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged.
  • the optical node comprises an optical amplifier arranged to amplify optical traffic to be transmitted from a first end of the optical fibre through the optical fibre to a second end of the optical fibre.
  • the apparatus comprises an optical power detector arranged to detect the power of light output from the second end of the optical fibre.
  • the apparatus further comprises a processing unit adapted to compare the power detected by the optical power detector to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier.
  • the processing unit is further adapted to determine whether the optical fibre is disconnected or damaged based on the comparison and output an indication of whether the optical fibre is disconnected or damaged to apparatus based on the
  • a method for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network comprises receiving an indication that an optical fibre inside an optical node is disconnected or damaged.
  • the method further comprises retrieving information about the configuration of the optical node.
  • the method further comprises using the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
  • embodiments of the present invention facilitate the determination of an alternative path for optical traffic from a first optical node to a second optical node
  • the computer program configured to, when run on a computer, perform the method for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network.
  • the computer program may be stored on a computer readable medium.
  • the computer program may be in any form including a downloadable signal.
  • the path calculation device for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network.
  • the path calculation device comprises an interface adapted to receive an indication that an optical fibre inside an optical node is disconnected or damaged.
  • the path calculation device further comprises a processing unit adapted to retrieve information about the configuration of the optical node and to use the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
  • Figure 1 is a flow chart showing a recovery procedure known in the prior art
  • Figure 2 is a flow chart illustrating a method of detecting whether an optical fibre inside an optical node is disconnected or damaged according to an embodiment of the present invention
  • FIG. 3 illustrates apparatus in an optical node according to an embodiment of the present invention
  • Figure 4 shows the arrangement of an optical power detector according to an embodiment of the present invention
  • Figure 5 is a flow chart showing further method steps according to a preferred embodiment of the present invention.
  • Figure 6 is a schematic diagram of a path computation element according to an embodiment of the present invention.
  • Figure 7 is a flow chart showing steps which may be performed by the path computation element according to an embodiment of the present invention.
  • Figure 8 is a flow chart showing steps which may be performed by the path computation element according to a preferred embodiment of the present invention. Description
  • Figure 2 is a flow chart showing a method for detecting whether an optical fibre inside an optical node is disconnected or damaged according to an embodiment of the present invention.
  • the "damage" may be a cut through the optical fibre or any other type of damage which prevents at least partially an optical signal passing through the optical fibre.
  • a control signal may optionally be sent to an optical amplifier 20 arranged to amplify optical traffic to be transmitted from a first end of the internal optical fibre through the internal optical fibre to a second end of the internal optical fibre, to turn the optical amplifier 20 on and / or to increase the gain of the optical amplifier 20.
  • step 310 it may optionally be determined that the optical amplifier 20 is working properly based on an output from a monitoring point of the optical amplifier 20.
  • the power of light received by an optical power detector which is arranged to detect light output from the second end of the optical fibre, is detected.
  • the detected power is compared to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier.
  • an indication of whether the optical fibre is disconnected or damaged is output based on the determining.
  • step 340 may comprise, at step 342, determining that the optical fibre is disconnected or damaged, if the detected power is lower than the power associated with the optical noise expected at the optical power detector.
  • step 340 may also comprise, at step 342, determining that the optical fibre is not disconnected or damaged, if the detected power is equal to or greater than the power associated with the optical noise expected at the optical power detector.
  • optical node 10 comprising apparatus for detecting whether an optical fibre 12, 14 inside the optical node 10 is disconnected or damaged will now be described with reference to Figure 3 and Figure 4.
  • the optical node 10 is an n-way ROADM node which means that the optical node 10 comprises a plurality of output ports 16 each adapted for transmitting optical traffic over a respective optical link, and or a plurality of input ports 18 each adapted for receiving optical traffic from a respective optical link.
  • the optical node 10 has a broadcast and select configuration.
  • the optical node 10 may be an all-optical node or a packet-optical node.
  • the optical node 10 is a 4-way optical node 10 and comprises four output ports 16 and four input ports 18 (labelled N, S, E and W).
  • the optical node 10 further comprises a transmitter for transmitting optical traffic (add drop transponder 24) and a receiver for receiving optical traffic (add drop transponder 24).
  • add drop transponder 24 there are two add drop transponders 24 for redundancy purposes.
  • the optical traffic received at each input port 18 is passed to a respective optical amplifier 20 which amplifies the optical traffic and passes the amplified optical traffic to a power splitter 22.
  • the power splitter 22 splits the amplified optical traffic into a plurality of optical signals each comprising the optical traffic. In this example, the amplified optical traffic is split into five optical signals.
  • optical signals are transmitted through respective internal optical fibres 12 (which will be referred to as bypass fibre links) to respective output ports 16.
  • the other two signals are transmitted through respective internal optical fibres 14 (which will be referred to as add/drop fibre links) to respective receivers (add drop transponders 24).
  • each of the transmitters also comprises an optical amplifier 20, arranged to amplify optical traffic generated by the transmitter, and a power splitter (not shown).
  • the power splitter is arranged to receive the amplified optical traffic and split the amplified optical traffic into, in this example, four optical signals comprising the optical traffic.
  • the four optical signals are transmitted through respective add/drop fibre links 14 to respective output ports 16.
  • the optical signals output from the internal optical fibres 12, 14 are received by a wavelength selective switch (WSS) 26, which may comprise a variable optical attenuator.
  • WSS wavelength selective switch
  • the WSS 26 blocks all of the optical channels (i.e. wavelengths) which are not to be transmitted from its associated output port 16 (or which are not to be received by its associated receiver), and passes only those which are.
  • the passed optical channels are amplified by an amplifier 20 and then transmitted from the associated output port 16 or received by the associated receiver.
  • the internal optical fibre 12, 14 to be monitored is the internal optical fibre indicated by a bold line, which connects a transmitter/receiver (add drop transponder B 24) to an output/input port 16, 18 (in this example the W output/input port 16, 18).
  • a transmitter/receiver add drop transponder B 24
  • an output/input port 16, 18 in this example the W output/input port 16, 18.
  • any of the other internal optical fibres 12, 14 in the optical node 10 could, in addition or alternatively, be monitored according to embodiments of the present invention.
  • an optical power detector 28 is arranged at the end of the internal optical fibre 14 associated with the output port 16.
  • the optical power detector 28 may be a photodiode or any other type of device suitable for detecting the power of received light.
  • the optical power detector 28 could instead be located at the other end of the internal optical fibre 14, the end which is associated with the receiver (add drop transponder B 24).
  • the optical power detector 28 is located between an internal port 30 adapted to receive an end of the internal optical fibre 14 and the WSS 26 arranged to receive an optical signal output from the internal optical fibre 14.
  • optical power detector 28 could for example be integrated within the WSS 26.
  • the apparatus further comprises a processing unit 30 which is coupled to the optical power detector 28, and optionally to the optical amplifier 20 arranged to amplify optical traffic to be transmitted through the internal optical fibre 12, 14.
  • the processing unit 30 may comprise one or more processors, which may be integrated to any degree.
  • the processing unit 30 may be configured to send a control signal to the optical amplifier 20 to cause the optical amplifier 20 to turn on and or to increase the gain of the optical amplifier 20.
  • the optical node 10 may instead be configured such that the optical amplifier 20 remains on, even if no optical traffic is being amplified by the optical amplifier 20.
  • the processing unit 30 may be configured to determine whether the optical amplifier 20 is working properly based on an output from a monitoring point of the optical amplifier 20.
  • the processing unit 30 is configured to compare the power of light detected by the optical power detector 28 to a power associated with optical noise expected at the optical power detector 28, the optical noise being emitted by the optical amplifier 20.
  • the processing unit 30 is further configured to determine whether the internal optical fibre 14 is disconnected or damaged based on the comparison, and to output an indication of whether the internal optical fibre 14 is disconnected or damaged based on the determination.
  • the power associated with the optical noise expected at the optical power detector 28 may be considered a threshold power.
  • the processing unit 30 may be configured to determine that the optical fibre 14 is not disconnected or damaged, if the detected power is equal to or greater than the threshold power (i.e. if at least the expected optical noise is received by the optical power detector 28). For example, in a 4-way ROADM node 10, the optical noise emitted by an optical amplifier 20 which is transmitted through each of the internal optical fibres 12, 14 may be -0.7dBm.
  • the processing unit 30 may also be configured to determine that the optical fibre 14 is disconnected or damaged, if the detected power is lower than the threshold power. For example, the optical fibre 14 is disconnected or damaged the power detected by the optical power detector may be -40dBm.
  • the status of each internal optical fibre 12, 14 may be monitored continuously.
  • the internal optical fibre 12, 14 may only be monitored in response, for example, to a detection of LOS at the optical node 10 or at another optical node 10 downstream of the optical node 10.
  • the optical node 10 has a broadcast and select configuration whereby the same optical traffic is transmitted through each of a plurality of optical fibres 12, 14 inside the optical node 10, as for example described above with respect to Figure 3 (e.g. each of the add drop fibre links from add drop transponder 24).
  • the apparatus further comprises a plurality of optical power detectors 28 (not shown) each arranged to detect the power of light output from a respective one of the plurality of optical fibres 12, 14.
  • the method comprises, at step 500, detecting the power of light received by each of the optical power detectors 28. At step 510, comparing the powers detected by the optical power detectors 28, and at step 520 determining whether one or more of the plurality of optical fibres 12, 14 might be disconnected or damaged based on the comparing of the powers detected by the optical power detectors 28.
  • the powers detected by one or more optical power detectors 28 are different from the powers detected by the other optical power detector(s) 28, this may indicate that one or more of the internal optical fibres 12, 14 might be disconnected or damaged.
  • the method for detecting whether an internal optical fibre 12, 14 is disconnected or damaged, as shown in Figure 2 may then be performed in response to a determination that the internal optical fibre 12, 14 might be disconnected or damaged.
  • the steps shown in Figure 6 may be performed by processing unit 30.
  • a disconnected or damaged internal optical fibre 12, 14 might be detected faster than if the detection is only performed after a LOS has been detected by another optical node 10.
  • the indication of whether an internal optical fibre 12, 14 is disconnected or damaged may be used by a path calculation device configured to determine an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network.
  • This path calculation device may be located within the optical node 10, or may be located remote from the optical node 10. In this latter case, the processing unit 30 may further be configured to send the indication to the path calculation device.
  • FIG. 6 shows a path calculation device 60 according to an embodiment of the present invention.
  • the path calculation device 60 comprises a receive interface 62 configured to receive an indication that an optical fibre inside an optical node 10 is disconnected or damaged, and a processing unit 64 which is configured to retrieve information about the configuration of the optical node and to use the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
  • the path calculation device 70 may further comprise a memory (not shown).
  • the processing unit 74 may comprise one or more processors, integrated to any degree.
  • an alternative path for the optical traffic may be set up, such that the optical traffic no longer passes through the internal optical fibre 12, 14.
  • the path calculation device 60 may determine that the optical traffic generated by add drop transponder 24 can still be transmitted by the optical node 10, but only from the other output ports 16 (N, S, E).
  • the path calculation device 60 may determine an alternative path from the optical node 10 to another optical node accordingly.
  • optical node 10 may be the first optical node, the second optical node or an intermediate node on a path between the first optical node and the second optical node.
  • Figure 7 is a flow chart showing steps for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network according to an embodiment of the present invention.
  • the method comprises receiving an indication that an optical fibre inside an optical node is disconnected or damaged.
  • the method further comprises retrieving information about the configuration of the optical node (e.g. from a memory) and, at step 720, the method comprises using the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
  • a LOS is detected at an optical node on a path for optical traffic from a first optical node to an optical second node in an optical communications network.
  • the LOS may be detected at the second node or at an intermediate node between the first optical node and the second optical node.
  • step 810 It may then be determined, where possible, at step 810, if there has been an "external" optical link failure. It may also be determined, in parallel, initially or subsequently, at step 830, whether there has been an internal link failure (i.e. a failure of an optical fibre inside an optical node along the path). This internal link failure may have occurred inside the first optical node, the second optical node or an intermediate node between the first optical node and the second optical node. This may be achieved by receiving an indication that an internal optical fibre inside one of the optical nodes is disconnected or damaged. Note that, at step 820, in this example, the path calculation device triggers the detection of whether the internal optical fibre is disconnected or damaged as described above. However, in other embodiments this trigger may not be necessary.
  • an internal link failure i.e. a failure of an optical fibre inside an optical node along the path. This internal link failure may have occurred inside the first optical node, the second optical node or an intermediate node between the first optical node and the second optical node. This
  • the path calculation device may, at step 840, search for, and set up, an alternative or protection path from the first optical node to the second optical node, which avoids the failed external link. It is then determined, at step 850, whether the LOS is still occurring. If the LOS is still occurring, then at step 860, the path calculation device repeatedly searches for, and sets up, an alternative end-to-end path between the first node and the second node (i.e. a fully disjointed path), until it is determined at step 870 that the LOS is no longer occurring, or no further alternative end-to- end path can be found.
  • the path calculation device repeatedly searches for and sets up an alternative end-to-end path between the first node and the second node, until it is determined at step 870 that the LOS is no longer active, or no further alternative end-to-end path can be found.
  • an alternative path may be determined, and set up, from the first optical node to the second optical node as described above with respect to Figure 7.
  • an alarm signal may be sent to the network operator indicating that the failed internal optical fibre should be reconnected / repaired.
  • an alternative end-to-end path is not repeatedly is not searched for, and set up, as described above. This may avoid wasting processing power, time and network resources.

Abstract

The present invention provides a method and apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged. The optical node comprises an optical amplifier arranged to amplify optical traffic to be transmitted from a first end of the optical fibre through the optical fibre to a second end of the optical fibre. The method comprises detecting the power of light received by an optical power detector arranged to detect light output from the second end of the optical fibre. The method further comprises comparing the detected power to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier. The method further comprises determining whether the optical fibre is disconnected or damaged based on the comparing, and outputting an indication of whether the optical fibre is disconnected or damaged based on the determining. There is also provided a method and path computation device for determining an alternative path for optical traffic from a first optical node to a second optical node in a communications network using the indication.

Description

METHOD AND APPARATUS FOR DETECTING WHETHER AN OPTICAL FIBRE INSIDE AN OPTICAL NODE IS DISCONNECTED OR DAMAGED AND A PATH
COMPUTATION DEVICE
Technical Field
The present invention relates to a method and apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged. The present invention further relates to a method and path computation device for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network.
Background
Optical communications networks comprise optical nodes interconnected by optical links, which typically comprise optical fibres. When optical traffic is to be transmitted from a first optical node to a second optical node, a path computation device determines a path for the optical traffic from the first optical node to the second optical node. The path may pass through a number of intermediate optical nodes / optical links.
Optical communications networks have failure recovery mechanisms, such that in the event that one of the optical links fails, e.g. the optical link is unplug, cut, or otherwise damaged, or one of the intermediate nodes fails, an alternative path for the optical traffic can be set up, which avoids the failed optical link.
Figure 1 is a flow chart showing a known recovery procedure. At step 101 , loss of signal (LOS) is detected at an optical node on the path (i.e. it is determined that the optical node is no longer receiving the optical traffic from the first optical node). If possible, at step 102, it is then determined whether a failed optical link can be identified. If a failed optical link is identified, at step 103, an alternative path for the optical traffic is calculated and set up which detours around the failed optical link. This is referred to as a Fast Re-Route (FRR) recovery mechanism.
If, however, a failed optical link cannot be identified, or if the alternative path set up at step 103 still results in LOS at the optical node, at step 105, an alternative path for optical traffic from the first optical node to the second optical node is calculated and set up which is fully disjointed from the previous path (i.e. the alternative path does not include any of the optical links in the previous path). It is then determined, at step 106, whether there is still LOS at the optical node. Steps 105 and 106 are repeated, until the optical traffic is received at the optical node, or until no further alternative end-to-end path can be found.
Summary
A problem with this recovery procedure however is that, if the fault is caused by a
disconnection of, or damage to, an optical fibre inside the optical node, it is possible that every re-route at step 105 will fail. Thus, processing power, time, and network resources may be wasted.
The applicant has appreciated that it would therefore be desirable to provide a method and apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged.
An optical fibre inside an optical node will be referred to as an "internal" optical fibre.
It is however not straightforward to detect whether an optical fibre inside an optical node is disconnected or damaged, even when no optical traffic is passing through the optical fibre.
In a known solution a probe or dummy signal generator is installed in the optical node which is configured to send an optical probe signal through an internal optical fibre to be monitored. An optical power detector is arranged to detect whether the probe signal is output from the optical fibre. If the probe signal is not detected by the power detector, then it can be determined that the optical fibre must be disconnected or damaged.
This solution is however expensive, since it requires a probe signal generator to be installed in the optical node. Given that an optical node may have many internal optical fibres (for example, a 4-way ROADM (reconfigurable add drop multiplexer) node may comprise twenty internal optical fibres), many probe signal generators would need to be installed in each optical node.
According to the present invention there is provided method for detecting whether an optical fibre inside an optical node is disconnected or damaged. The optical node comprises an optical amplifier arranged to amplify optical traffic to be transmitted from a first end of the optical fibre through the optical fibre to a second end of the optical fibre. The method comprises detecting the power of light received by an optical power detector arranged to detect light output from the second end of the optical fibre. The method further comprises comparing the detected power to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier. The method further comprises determining whether the optical fibre is disconnected or damaged based on the comparing, and outputting an indication of whether the optical fibre is disconnected or damaged based on the determining.
Thus, advantageously, embodiments of the present invention enable a disconnected or damaged internal optical fibre to be detected, even if no optical traffic is supposed to be passing through the internal optical fibre, by making use of existing hardware in the optical node.
In existing optical nodes, optical amplifiers are turned off when they receive no optical traffic, in order to save power. The applicant has however appreciated that by configuring the optical node such that the optical amplifier stays on even if no optical traffic is received by the optical amplifier, or by sending a control signal to the optical amplifier to cause the optical amplifier to turn on, the optical noise which is emitted by the optical amplifier can be used, effectively, as a probe signal, even when no optical traffic is being transmitted by the optical amplifier.
In an embodiment of the present invention, determining whether the optical fibre is disconnected or damaged based on the comparing comprises determining that the optical fibre is disconnected or damaged if the detected power is lower than the power associated with the optical noise expected at the optical power detector.
In a further embodiment of the present invention, determining whether the optical fibre is disconnected or damaged based on the comparing comprises determining that the optical fibre is not disconnected or damaged if the detected power is equal to or greater than the power associated with the optical noise expected at the optical power detector.
The method may further comprise sending a control signal to the optical amplifier to cause the optical amplifier to turn on and or to cause the gain of the optical amplifier to increase. Advantageously, increasing the gain of the optical amplifier will increase the optical noise emitted by the optical amplifier, and therefore increasing the gain of the optical amplifier may lead to more accurate detection of whether the internal optical fibre is disconnected or damaged.
The method may further comprise determining that the optical amplifier is working properly based on an output from a monitoring point of the optical amplifier. Thus, advantageously, it can be determined that the detection is not affected by a faulty optical amplifier.
In some embodiments of the present invention the internal optical fibre may be monitored continuously. However, more preferably, to save processing power, the internal optical fibre is only monitored when it is suspected that the optical fibre might be disconnected or damaged.
In an embodiment of the present invention, the optical fibre is monitored in response to a detection of a Loss of Signal (LOS) at the or another optical node.
In another, preferred embodiment of the present invention, the optical node has a broadcast and select configuration whereby the same optical traffic is transmitted through each of a plurality of optical fibres inside the optical node. The plurality of optical fibres includes the optical fibre. The optical node further comprises a plurality of optical power detectors each arranged to detect the power of light output from a respective one of the plurality of optical fibres. The method further comprises detecting the power of light received by each of the optical power detectors. The method further comprises comparing the powers detected by the optical power detectors. The method further comprises determining that the optical fibre might be disconnected or damaged based on the comparing of the powers detected by the optical power detectors. In this preferred embodiment of the present invention, the optical fibre is monitored in response to the determining that the optical fibre might be disconnected or damaged.
Thus, for example, if the power detected by the optical power detector is different from the power(s) detected by the other optical power detector(s), this may indicate the optical fibre might be disconnected or damaged. Thus, advantageously, monitoring of the optical fibre may be triggered more quickly than waiting for an indication of LOS at another optical node. According to the present invention, there is further provided apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged. The optical node comprises an optical amplifier arranged to amplify optical traffic to be transmitted from a first end of the optical fibre through the optical fibre to a second end of the optical fibre. The apparatus comprises an optical power detector arranged to detect the power of light output from the second end of the optical fibre. The apparatus further comprises a processing unit adapted to compare the power detected by the optical power detector to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier. The processing unit is further adapted to determine whether the optical fibre is disconnected or damaged based on the comparison and output an indication of whether the optical fibre is disconnected or damaged to apparatus based on the
determination.
According to the present invention there is also provided a method for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network. The method comprises receiving an indication that an optical fibre inside an optical node is disconnected or damaged. The method further comprises retrieving information about the configuration of the optical node. The method further comprises using the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
Thus, advantageously, embodiments of the present invention facilitate the determination of an alternative path for optical traffic from a first optical node to a second optical node
There is also provided a computer program configured to, when run on a computer, perform the method for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network. The computer program may be stored on a computer readable medium. The computer program may be in any form including a downloadable signal.
There is also provided a path calculation device for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network. The path calculation device comprises an interface adapted to receive an indication that an optical fibre inside an optical node is disconnected or damaged. The path calculation device further comprises a processing unit adapted to retrieve information about the configuration of the optical node and to use the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
Description of the Drawings
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a flow chart showing a recovery procedure known in the prior art;
Figure 2 is a flow chart illustrating a method of detecting whether an optical fibre inside an optical node is disconnected or damaged according to an embodiment of the present invention;
Figure 3 illustrates apparatus in an optical node according to an embodiment of the present invention;
Figure 4 shows the arrangement of an optical power detector according to an embodiment of the present invention;
Figure 5 is a flow chart showing further method steps according to a preferred embodiment of the present invention;
Figure 6 is a schematic diagram of a path computation element according to an embodiment of the present invention;
Figure 7 is a flow chart showing steps which may be performed by the path computation element according to an embodiment of the present invention; and
Figure 8 is a flow chart showing steps which may be performed by the path computation element according to a preferred embodiment of the present invention. Description
Figure 2 is a flow chart showing a method for detecting whether an optical fibre inside an optical node is disconnected or damaged according to an embodiment of the present invention. The "damage" may be a cut through the optical fibre or any other type of damage which prevents at least partially an optical signal passing through the optical fibre.
At step 300, a control signal may optionally be sent to an optical amplifier 20 arranged to amplify optical traffic to be transmitted from a first end of the internal optical fibre through the internal optical fibre to a second end of the internal optical fibre, to turn the optical amplifier 20 on and / or to increase the gain of the optical amplifier 20.
Then, at step 310, it may optionally be determined that the optical amplifier 20 is working properly based on an output from a monitoring point of the optical amplifier 20.
Then, at step 320, the power of light received by an optical power detector, which is arranged to detect light output from the second end of the optical fibre, is detected. At step 330, the detected power is compared to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier. At step 340, it is determined whether the optical fibre is disconnected or damaged based on the comparing. Then, at step 350, an indication of whether the optical fibre is disconnected or damaged is output based on the determining.
In a preferred embodiment of the present invention, step 340 may comprise, at step 342, determining that the optical fibre is disconnected or damaged, if the detected power is lower than the power associated with the optical noise expected at the optical power detector. Step 340 may also comprise, at step 342, determining that the optical fibre is not disconnected or damaged, if the detected power is equal to or greater than the power associated with the optical noise expected at the optical power detector.
An example of an optical node 10 comprising apparatus for detecting whether an optical fibre 12, 14 inside the optical node 10 is disconnected or damaged will now be described with reference to Figure 3 and Figure 4.
In this example, the optical node 10 is an n-way ROADM node which means that the optical node 10 comprises a plurality of output ports 16 each adapted for transmitting optical traffic over a respective optical link, and or a plurality of input ports 18 each adapted for receiving optical traffic from a respective optical link. In this example, the optical node 10 has a broadcast and select configuration. The optical node 10 may be an all-optical node or a packet-optical node.
In this example, the optical node 10 is a 4-way optical node 10 and comprises four output ports 16 and four input ports 18 (labelled N, S, E and W). The optical node 10 further comprises a transmitter for transmitting optical traffic (add drop transponder 24) and a receiver for receiving optical traffic (add drop transponder 24). In this example, there are two add drop transponders 24 for redundancy purposes.
The optical traffic received at each input port 18 is passed to a respective optical amplifier 20 which amplifies the optical traffic and passes the amplified optical traffic to a power splitter 22. The power splitter 22 splits the amplified optical traffic into a plurality of optical signals each comprising the optical traffic. In this example, the amplified optical traffic is split into five optical signals.
Three of the optical signals are transmitted through respective internal optical fibres 12 (which will be referred to as bypass fibre links) to respective output ports 16. The other two signals are transmitted through respective internal optical fibres 14 (which will be referred to as add/drop fibre links) to respective receivers (add drop transponders 24).
Note that each of the transmitters (add drop transponders 24) also comprises an optical amplifier 20, arranged to amplify optical traffic generated by the transmitter, and a power splitter (not shown). The power splitter is arranged to receive the amplified optical traffic and split the amplified optical traffic into, in this example, four optical signals comprising the optical traffic. The four optical signals are transmitted through respective add/drop fibre links 14 to respective output ports 16.
At each of the output ports 16, and each of the receivers (add drop transponders 24), the optical signals output from the internal optical fibres 12, 14 are received by a wavelength selective switch (WSS) 26, which may comprise a variable optical attenuator. The WSS 26 blocks all of the optical channels (i.e. wavelengths) which are not to be transmitted from its associated output port 16 (or which are not to be received by its associated receiver), and passes only those which are. The passed optical channels are amplified by an amplifier 20 and then transmitted from the associated output port 16 or received by the associated receiver.
In this example, the internal optical fibre 12, 14 to be monitored is the internal optical fibre indicated by a bold line, which connects a transmitter/receiver (add drop transponder B 24) to an output/input port 16, 18 (in this example the W output/input port 16, 18). However, any of the other internal optical fibres 12, 14 in the optical node 10 could, in addition or alternatively, be monitored according to embodiments of the present invention.
In this example, an optical power detector 28 is arranged at the end of the internal optical fibre 14 associated with the output port 16. The optical power detector 28 may be a photodiode or any other type of device suitable for detecting the power of received light. However, the optical power detector 28 could instead be located at the other end of the internal optical fibre 14, the end which is associated with the receiver (add drop transponder B 24).
In particular, in this example, as shown in Figure 4, the optical power detector 28 is located between an internal port 30 adapted to receive an end of the internal optical fibre 14 and the WSS 26 arranged to receive an optical signal output from the internal optical fibre 14.
However, in alternative arrangements, the optical power detector 28 could for example be integrated within the WSS 26.
The apparatus further comprises a processing unit 30 which is coupled to the optical power detector 28, and optionally to the optical amplifier 20 arranged to amplify optical traffic to be transmitted through the internal optical fibre 12, 14. The processing unit 30 may comprise one or more processors, which may be integrated to any degree.
In preferred embodiments of the present invention, the processing unit 30 may be configured to send a control signal to the optical amplifier 20 to cause the optical amplifier 20 to turn on and or to increase the gain of the optical amplifier 20. However, in alternative embodiments, the optical node 10 may instead be configured such that the optical amplifier 20 remains on, even if no optical traffic is being amplified by the optical amplifier 20.
Further, the processing unit 30 may be configured to determine whether the optical amplifier 20 is working properly based on an output from a monitoring point of the optical amplifier 20. The processing unit 30 is configured to compare the power of light detected by the optical power detector 28 to a power associated with optical noise expected at the optical power detector 28, the optical noise being emitted by the optical amplifier 20. The processing unit 30 is further configured to determine whether the internal optical fibre 14 is disconnected or damaged based on the comparison, and to output an indication of whether the internal optical fibre 14 is disconnected or damaged based on the determination.
The power associated with the optical noise expected at the optical power detector 28 may be considered a threshold power. The processing unit 30 may be configured to determine that the optical fibre 14 is not disconnected or damaged, if the detected power is equal to or greater than the threshold power (i.e. if at least the expected optical noise is received by the optical power detector 28). For example, in a 4-way ROADM node 10, the optical noise emitted by an optical amplifier 20 which is transmitted through each of the internal optical fibres 12, 14 may be -0.7dBm. The processing unit 30 may also be configured to determine that the optical fibre 14 is disconnected or damaged, if the detected power is lower than the threshold power. For example, the optical fibre 14 is disconnected or damaged the power detected by the optical power detector may be -40dBm.
In some embodiments of the present invention, the status of each internal optical fibre 12, 14 may be monitored continuously.
However, in alternative embodiments of the present invention, the internal optical fibre 12, 14 may only be monitored in response, for example, to a detection of LOS at the optical node 10 or at another optical node 10 downstream of the optical node 10.
A further preferred embodiment of the present invention is shown in the flow chart of Figure 5. In this embodiment, the optical node 10 has a broadcast and select configuration whereby the same optical traffic is transmitted through each of a plurality of optical fibres 12, 14 inside the optical node 10, as for example described above with respect to Figure 3 (e.g. each of the add drop fibre links from add drop transponder 24). The apparatus further comprises a plurality of optical power detectors 28 (not shown) each arranged to detect the power of light output from a respective one of the plurality of optical fibres 12, 14.
The method comprises, at step 500, detecting the power of light received by each of the optical power detectors 28. At step 510, comparing the powers detected by the optical power detectors 28, and at step 520 determining whether one or more of the plurality of optical fibres 12, 14 might be disconnected or damaged based on the comparing of the powers detected by the optical power detectors 28.
Thus, if for example, the powers detected by one or more optical power detectors 28 are different from the powers detected by the other optical power detector(s) 28, this may indicate that one or more of the internal optical fibres 12, 14 might be disconnected or damaged. The method for detecting whether an internal optical fibre 12, 14 is disconnected or damaged, as shown in Figure 2, may then be performed in response to a determination that the internal optical fibre 12, 14 might be disconnected or damaged. The steps shown in Figure 6 may be performed by processing unit 30. Thus, advantageously, a disconnected or damaged internal optical fibre 12, 14 might be detected faster than if the detection is only performed after a LOS has been detected by another optical node 10.
The indication of whether an internal optical fibre 12, 14 is disconnected or damaged may be used by a path calculation device configured to determine an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network. This path calculation device may be located within the optical node 10, or may be located remote from the optical node 10. In this latter case, the processing unit 30 may further be configured to send the indication to the path calculation device.
Figure 6 shows a path calculation device 60 according to an embodiment of the present invention. The path calculation device 60 comprises a receive interface 62 configured to receive an indication that an optical fibre inside an optical node 10 is disconnected or damaged, and a processing unit 64 which is configured to retrieve information about the configuration of the optical node and to use the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
The path calculation device 70 may further comprise a memory (not shown). The processing unit 74 may comprise one or more processors, integrated to any degree.
Thus, an alternative path for the optical traffic may be set up, such that the optical traffic no longer passes through the internal optical fibre 12, 14. By way of example, with reference to Figure 3, if it is determined that the internal optical fibre 14 coupling add drop transponder 24 and output / input port 16, 17 W is disconnected or damaged, the path calculation device 60 may determine that the optical traffic generated by add drop transponder 24 can still be transmitted by the optical node 10, but only from the other output ports 16 (N, S, E). Thus, advantageously, the path calculation device 60 may determine an alternative path from the optical node 10 to another optical node accordingly.
Note that the optical node 10 may be the first optical node, the second optical node or an intermediate node on a path between the first optical node and the second optical node.
Figure 7 is a flow chart showing steps for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network according to an embodiment of the present invention.
At step 700, the method comprises receiving an indication that an optical fibre inside an optical node is disconnected or damaged. At step 710, the method further comprises retrieving information about the configuration of the optical node (e.g. from a memory) and, at step 720, the method comprises using the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
An example of a protection procedure according to a preferred embodiment of the present invention is shown in Figure 8.
In this procedure, at step 800, a LOS is detected at an optical node on a path for optical traffic from a first optical node to an optical second node in an optical communications network. The LOS may be detected at the second node or at an intermediate node between the first optical node and the second optical node.
It may then be determined, where possible, at step 810, if there has been an "external" optical link failure. It may also be determined, in parallel, initially or subsequently, at step 830, whether there has been an internal link failure (i.e. a failure of an optical fibre inside an optical node along the path). This internal link failure may have occurred inside the first optical node, the second optical node or an intermediate node between the first optical node and the second optical node. This may be achieved by receiving an indication that an internal optical fibre inside one of the optical nodes is disconnected or damaged. Note that, at step 820, in this example, the path calculation device triggers the detection of whether the internal optical fibre is disconnected or damaged as described above. However, in other embodiments this trigger may not be necessary. If, at step 810, an external link failure is identified, then the path calculation device may, at step 840, search for, and set up, an alternative or protection path from the first optical node to the second optical node, which avoids the failed external link. It is then determined, at step 850, whether the LOS is still occurring. If the LOS is still occurring, then at step 860, the path calculation device repeatedly searches for, and sets up, an alternative end-to-end path between the first node and the second node (i.e. a fully disjointed path), until it is determined at step 870 that the LOS is no longer occurring, or no further alternative end-to- end path can be found.
Similarly, if no internal link failure is detected at step 830 then, at step 860, the path calculation device repeatedly searches for and sets up an alternative end-to-end path between the first node and the second node, until it is determined at step 870 that the LOS is no longer active, or no further alternative end-to-end path can be found.
However, if an internal optical fibre failure is identified, at step 880, an alternative path may be determined, and set up, from the first optical node to the second optical node as described above with respect to Figure 7. In addition, or alternatively, an alarm signal may be sent to the network operator indicating that the failed internal optical fibre should be reconnected / repaired.
Furthermore, advantageously, an alternative end-to-end path is not repeatedly is not searched for, and set up, as described above. This may avoid wasting processing power, time and network resources.

Claims

1 . A method for detecting whether an optical fibre inside an optical node is
disconnected or damaged, the optical node comprising an optical amplifier arranged to amplify optical traffic to be transmitted from a first end of the optical fibre through the optical fibre to a second end of the optical fibre, the method comprising:
detecting the power of light received by an optical power detector arranged to detect light output from the second end of the optical fibre;
comparing the detected power to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier;
determining whether the optical fibre is disconnected or damaged based on the comparing; and
outputting an indication of whether the optical fibre is disconnected or damaged based on the determining.
2. A method according to claim 1 , wherein determining whether the optical fibre is
disconnected or damaged based on the comparing comprises determining that the optical fibre is disconnected or damaged if the detected power is lower than the power associated with the optical noise expected at the optical power detector.
3. A method according to claim 1 or 2, wherein determining whether the optical fibre is disconnected or damaged based on the comparing comprises determining that the optical fibre is not disconnected or damaged if the detected power is equal to or greater than the power associated with the optical noise expected at the optical power detector.
4. A method according to claim 1 , 2 or 3, further comprising sending a control signal to the optical amplifier to turn the optical amplifier on and/or to increase the gain of the optical amplifier.
5. A method according to any preceding claim, further comprising determining that the optical amplifier is working properly based on an output from a monitoring point of the optical amplifier.
6. A method according to any preceding claim, wherein the steps of detecting the power of light received by an optical power detector arranged to detect light output from the second end of the optical fibre; comparing the detected power to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier; determining whether the optical fibre is disconnected or damaged based on the comparing; and outputting an indication of whether the optical fibre is disconnected or damaged based on the determining are performed in response to a detection of Loss of Signal (LOS) at the or another optical node.
7. A method according to any of claims 1 to 6, wherein the optical node has a broadcast and select configuration whereby the same optical traffic is transmitted through each of a plurality of optical fibres inside the optical node, wherein the plurality of optical fibres includes the optical fibre, and the optical node further comprises a plurality of optical power detectors each arranged to detect the power of light output from a respective one of the plurality of optical fibres, the method further comprising:
detecting the power of light received by each of the optical power detectors; comparing the powers detected by the optical power detectors;
determining that the optical fibre might be disconnected or damaged based on the comparing of the powers detected by the optical power detectors; and
wherein the steps of detecting the power of light received by an optical power detector arranged to detect light output from the second end of the optical fibre; comparing the detected power to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier; determining whether the optical fibre is disconnected or damaged based on the comparing; and outputting an indication of whether the optical fibre is disconnected or damaged based on the determining are performed in response to the determining that the optical fibre might be disconnected or damaged.
8. Apparatus for detecting whether an optical fibre inside an optical node is
disconnected or damaged, the optical node comprising an optical amplifier arranged to amplify optical traffic to be transmitted from a first end of the optical fibre through the optical fibre to a second end of the optical fibre, the apparatus comprising:
an optical power detector arranged to detect the power of light output from the second end of the optical fibre; and
a processing unit adapted to: compare the power detected by the optical power detector to a power associated with optical noise expected at the optical power detector, the optical noise being emitted by the optical amplifier;
determine whether the optical fibre is disconnected or damaged based on the comparison; and
output an indication of whether the optical fibre is disconnected or damaged to apparatus based on the determination.
9. Apparatus according to claim 8, wherein the processing unit is adapted to determine that the optical fibre is disconnected or damaged if the detected power is lower than the power associated with the optical noise expected at the optical power detector.
10. Apparatus according to claim 8 or 9, wherein the processing unit is adapted to
determine that the optical fibre is not disconnected or damaged if the detected power is equal to or greater than the power associated with the optical noise expected at the optical power detector.
1 1 . Apparatus according to claim 8, 9 or 10, wherein the apparatus is further adapted to send a control signal to the optical amplifier to turn the optical amplifier on and/or to increase the gain of the optical amplifier.
12. Apparatus according to any of claims 8 to 1 1 , wherein the processing unit is further adapted to
determine that the optical amplifier is working properly based on an output from a monitoring point of the optical amplifier.
13. Apparatus according to any of claims 8 to 12, wherein the processing unit is adapted to compare the power detected by the optical power detector to the power associated with optical noise expected at the optical power detector, determine whether the internal optical fibre is disconnected or damaged based on the comparison and output an indication of whether the internal optical fibre is disconnected or damaged to apparatus based on the determination in response to a detection of a Loss of Signal (LOS) at the or another optical node.
14. Apparatus according to any of claims 8 to 12, wherein the optical node has a
broadcast and select configuration whereby the same optical traffic is transmitted through each of a plurality of optical fibres, wherein the plurality of optical fibres includes the optical fibre, the apparatus further comprising
a plurality of optical power detectors each arranged to detect the power of light output from a respective one of the plurality of optical fibres, and wherein
the processing unit is further adapted to:
compare the powers detected by the optical power detectors;
determine that the optical fibre might be disconnected or damaged based on the comparison of the detected powers; and, wherein
the processing unit is adapted to compare the power detected by the optical power detector to the power associated with optical noise expected at the optical power detector, determine whether the internal optical fibre is disconnected or damaged based on the comparison and output an indication of whether the internal optical fibre is disconnected or damaged to apparatus based on the determination in response to the determination that the optical fibre might be disconnected or damaged.
15. An optical node for an optical communications network, the optical node comprising:
an optical fibre having a first end and a second end;
an optical amplifier arranged to amplify optical traffic to be transmitted from the first end of the optical fibre through the optical fibre to the second end of the optical fibre; and
apparatus according to any of claims 8 to 14.
16. A method for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network, the method comprising:
receiving an indication that an optical fibre inside an optical node is disconnected or damaged;
retrieving information about the configuration of the optical node; and using the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
17. A computer program configured to, when run on a computer, perform the method according to claim 16.
18. A path calculation device for determining an alternative path for optical traffic from a first optical node to a second optical node in an optical communications network, the path calculation device comprising:
an interface adapted to receive an indication that an optical fibre inside an optical node is disconnected or damaged;
a processing unit adapted to retrieve information about the configuration of the optical node and to use the indication and the information about the configuration of the optical node to determine an alternative path for optical traffic from the first optical node to the second optical node.
PCT/EP2014/052847 2014-02-13 2014-02-13 Method and apparatus for detecting whether an optical fibre inside an optical node is disconnected or damaged and a path computation device WO2015120895A1 (en)

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