Arrangement at a remote node, a remote node, a central office and respective methods therein for supervision of a wavelength division multiplexed passive optical network

An arrangement at a Remote Node, a Remote Node, a Central Office, a WDM-PON and a method in an arrangement at a Remote Node, and a method in a Central Office are provided for supervision of the WDM-PON. The arrangement comprises at least one filter connected to the feeder fiber links and adapted to separate a data signal and an original OTDR signal received on either of the feeder fiber links. Further, the arrangement comprises a first splitter adapted to receive, from the at least one filter, the original OTDR signal, to split the original OTDR signal into a plurality of OTDR sub-signals and to output, to an N*M AWG, the plurality of OTDR sub-signals. The at least one filter is further adapted to output the original OTDR signal to the first splitter and to output the data signal to the AWG, thereby enabling supervision of the WDM-PON.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 35 U.S.C. §371 national stage application of PCT International Application No. PCT/SE2012/050337, filed on 28 Mar. 2012, the disclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to Wavelength Division Multiplexed Passive Optical Networks, WDM-PONs, and in particular to supervision of WDM-PONs.

BACKGROUND

Due to the trend towards higher bandwidth demand and advances in the Wavelength Division Multiplexing, WDM, device technology, the WDM Passive Optical Network, PON, is considered as a possible candidate for next-generation broadband access networks. In addition, the growing popularity of mobile data services is also places increasing demands on backhaul. WDM-PON is able to provide symmetrical ultra-high bandwidth to radio base stations and hence can easily address the growing bandwidth needs of mobile backhaul. On the other hand, to shorten the service provision down-time caused by a fibre-failure in a PON, an effective monitoring solution should be applied enabling fault detection and localization. Rapid troubleshooting becomes very important in mobile backhaul systems which support large amount of traffic to/from thousands of users. Centralized and automatic monitoring contributes to operational expenditures (OPEX) savings thanks to remote operation. No hardware upgrade on user side should be required (e.g. demarcation components) due to high hardware and manpower costs per drop link and PON monitoring functionality should be shared over the complete PON system to provide high sharing factor of the investment. Furthermore, the effective fibre-fault detection and localisation scheme should not affect data communication and be sensitive to as low power fluctuations as 1 dB.

Furthermore, operators need to guarantee the level of connection availability specified in the Service Level Agreement, SLA, in particular for business users and mobile backhauling. Protection mechanisms need to be provided in PONs to offer an acceptable reliability level. However, compared with core networks, access networks are very cost-sensitive due to the relatively low sharing factor for the cost associated with the deployment, management and technology upgrade. Therefore, it is important in PON deployment to minimise the cost of protection while maintaining the connection availability at an acceptable level. Furthermore, in order to reduce the affected number of users by single fault which has occurred in fibre access networks, the protection up to Remote Node, RN, needs to be provided in the first place, in particular in a large city with more than one million inhabitants. Due to the ultra dense population in the large city, for the most of access networks the required distance between RN and end user (i.e. the length of drop fibre, DF) is rather short. For instance, in Munich, Germany, the estimated average length of DF per user is less than 1 km (including suburban part). From the reliability point of view, the protection of the feeder fibre might be sufficient for the most cases.

SUMMARY

The object is to obviate at least some of the problems outlined above. In particular, it is an object to provide an arrangement at a Remote Node in a Wavelength Division Multiplexed Passive Optical Network, WDM-PON, a Remote Node in a WDM-PON, a Central Office in a WDM-PON and methods therein for supervision of the WDM-PON as well as a WDM-PON comprising a Remote Node and a Central Office as above, wherein the Central Office and the Remote Node are connected via two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link, having different geographical paths between the Central Office and the Remote Node. These objects and others may be obtained by providing an arrangement at a Remote Node, a Remote Node, a Central Office, a WDM-PON and a method in an arrangement at a Remote Node, and a method in a Central Office according to the independent claims attached below.

According to an aspect an arrangement at a Remote Node in a Wavelength Division Multiplexed Passive Optical Network, WDM-PON, configured for supervision of the WDM-PON is provided, wherein the Remote Node is connected to a Central Office by two individual feeder fibre links. The arrangement comprises at least one filter connected to the feeder fibre links and adapted to separate a data signal and an original Optical Time Domain Reflectometry, OTDR, signal received on either of the feeder fibre links. Further, the arrangement comprises a first splitter adapted to receive, from the at least one filter, the original OTDR signal, to split the original OTDR signal into a plurality of OTDR sub-signals and to output, to an N*M Arrayed Waveguide Grating, AWG, the plurality of OTDR sub-signals. The at least one filter further is adapted to output the original OTDR signal to the first splitter and to output the data signal to the AWG thereby enabling supervision of the WDM-PON without influencing the data signals.

According to an aspect, a Remote Node in a WDM-PON for supervision of the WDM-PON is provided, wherein the Remote Node is connected to a Central Office by two individual feeder fibre links. The Remote Node comprises an arrangement according to the aspect above and an N*M AWG, wherein N individual inputs of the AWG are connected to the arrangement such that the output of each of the at least one filter is connected to an input of the AWG and the outputs of the first splitter are connected to individual inputs of the AWG.

According to still an aspect, a Central Office in a WDM-PON for supervision of the WDM-PON is provided, wherein the Central Office is connected to a Remote Node by two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link. The Central Office comprises at least one Optical Line Terminal, OLT, adapted to output data signals and an OTDR device adapted to output OTDR signals. The Central Office further comprises at least one filter adapted to receive data signals from the OLT and OTDR signals from the OTDR device and to multiplex the signals together and output the multiplexed signals towards the working feeder fibre link towards the Remote Node. The OTDR device is adapted to detect malfunction of the working feeder fibre link, wherein the Central Office is adapted to switch feeder fibre link so that the multiplexed signals are outputted on the protection feeder fibre link.

According to yet an aspect, a WDM-PON is provided. The WDM-PON comprises a Central Office and a Remote Node according to the respective aspects above, wherein the Central Office and the Remote Node are connected via two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link, having different geographical paths between the Central Office and the Remote Node.

According to an aspect, a method in an arrangement at a Remote Node in a WDM-PON for supervision of the WDM-PON is provided, wherein the Remote Node is connected to a Central Office by two individual feeder fibre links. The method comprises separating, in at least one filter connected to the feeder fibre links, a data signal and an original OTDR signal received on either of the feeder fibre links. The method also comprises receiving at a first splitter from the at least one filter, the original OTDR signal, and splitting the original OTDR signal into a plurality of OTDR sub-signals and outputting, to an N*M AWG the plurality of OTDR sub-signals. The at least one filter outputs the original OTDR signal to the first splitter and outputs the data signal to the AWG, thereby enabling supervision of the WDM-PON without influencing the data signals.

According to an aspect, a method in a Central Office in a WDM-PON for supervision of the WDM-PON is provided, wherein the Central Office is connected to a Remote Node by two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link. The method comprises outputting data signals from at least one OLT and outputting OTDR signals from an OTDR device. The method further comprises receiving, in at least one filter, the data signals from the OLT and the OTDR signals from the OTDR device and to multiplexing the signals together and outputting the multiplexed signals to the working feeder fibre link towards the RN. A malfunction of the working feeder fibre link is detected at the OTDR device, wherein the Central Office switches feeder fibre link so that the multiplexed signals are outputted on the protection feeder fibre link.

The arrangement at the Remote Node, the Remote Node, the Central Office, the WDM-PON and the method in the arrangement at the Remote Node, and the method in the Central Office have several advantages. They allows for two individual feeder fibre links to be connected between the CO and the RN, thereby increasing the reliability of operation of the WDN-PON. The arrangement supports a totally passive Optical Distribution Network. The arrangement may be upgraded to any WDM-PON topology based on AWG. It is further standard compliant.

DETAILED DESCRIPTION

Briefly described, exemplifying embodiments of an arrangement at a Remote Node, a Remote Node, a Central Office and respective methods therein as well as a Wavelength Division Multiplexed Passive Optical Network, WDM-PON, are provided for supervision of the WDM-PON, wherein the Remote Node is connected to a Central Office by two individual feeder fibre links. In normal operation, the Central Office and the Remote Node employs one of the feeder fibre links, referred to as the working feeder fibre link, for communication between the Central Office and the Remote Node. In case a malfunction of the feeder fibre link is detected at the Central Office, the Central Office switches to use the second feeder fibre link, referred to as the protection feeder fibre link, for communication between the Central Office and the Remote Node.

FIG. 1ais a schematic overview of an exemplifying network architecture of a WDM-PON. Generally, in a WDM-PON, a Central Office, CO,120is connected to a Remote Node, RN,100. The CO120is connected to the RN100avia a fibre link125which is generally referred to as a feeder fibre link. The CO120comprises an Optical Line Terminal, OLT,121which transmits data signals towards Optical Network Terminations, ONTs,130. When the OLT121transmits a data signal towards one of the ONTs130, the OLT121generates the data signal and injects the data signal into the feeder fibre link125to the RN100.

A WDM-PON generally comprises a system for supervision of the WDM-PON which comprises an OTDR device122. Generally in a WDM-PON, the OTDR device122is comprised in the CO120. The OTDR device122is adapted to generate OTDR signals of different wavelengths, wherein one OTDR signal has one specific wavelength. The OTDR device122transmits the generated OTDR signals to a filter123. The filter123also receives the data signals from the OLT121and multiplexes the signals together and injects, or transmits, the multiplexed signals to the RN100for forwarding to one or more of the ONTs130. It shall be pointed out that a feeder fibre generally carries data signals. The OTDR may, in alternative solutions, be connected by separate fibre link between the CO120and the RN100. However, in such solutions, the separate fibre link carrying only OTDR signals is not a feeder fibre link.

It shall further be pointed out that the possible wavelengths of the OTDR signals are different from the possible wavelengths of the data signals. In one example, the wavelengths of the OTDR signals are within a specified or predetermined range, or bandwidth, and the wavelengths of the data signals are within a different specified or predetermined range, or bandwidth. The two different bandwidths or ranges are spaced apart wavelength-wise such that they do not overlap. For example, the two bandwidths are spaced apart wavelength-wise by a multiple of a Free Spectral Range, FSR. For Example, with 32 individual ONTs connected to the RN, the data signal may comprise up to 32 wavelengths, λ1, λ2, . . . λ32, and the OTDR signal has a wavelength of λ1i+n*FSR, where FSR is a Free Spectral Range of the AWG, i is an integer from 1 to 32 and n is an integer value.

According to an exemplifying embodiment of a WDM-PON, the CO and the RN are connected by two individual feeder fibre links, which have different geographical paths between the CO and the RN. The two feeder fibre links are referred to as a working feeder fibre link and a protection feeder fibre link. In normal operation of the WDM-PON, the CO employs the working feeder fibre link for transmitting data signals multiplexed with OTDR signals to the RN. In case a malfunction of the working feeder fibre link occurs and is detected at the CO, the CO switches to start using the protection feeder fibre link for transmitting data signals multiplexed with OTDR signals to the RN.

An exemplifying embodiment of an arrangement at a RN in a WDM-PON, configured for supervision of the WDM-PON wherein the RN is connected to a CO by two individual feeder fibre links, will now be described with reference toFIGS. 2 and 3.

FIGS. 2 and 3are block diagrams of two exemplifying embodiments of an arrangement at a Remote Node for supervision of the WDM-PON wherein the RN is connected to a CO by two individual feeder fibre links.

BothFIGS. 2 and 3discloses the arrangement210,310comprising at least one filter212,312a,312bconnected to the feeder fibre links and adapted to separate a data signal and an original Optical Time Domain Reflectometry, OTDR, signal received on either of the feeder fibre links. Further, the arrangement210,310comprises a first splitter211,311adapted to receive, from the at least one filter212,312a,312b, the original OTDR signal, to split the original OTDR signal into a plurality of OTDR sub-signals and to output, to an N*M Arrayed Waveguide Grating220,320, AWG, the plurality of OTDR sub-signals. The at least one filter212,312a,312bis further adapted to output the original OTDR signal to the first splitter211,311and to output the data signal to the AWG220,320, thereby enabling supervision of the WDM-PON without influencing the data signals.

Starting withFIG. 2, the arrangement210comprises at least one filter212which is connected to the feeder fibre links, Feeder1and Feeder2, and adapted to separate a data signal and an original OTDR signal received on either of the feeder fibre links, the data signal and the original OTDR signal being multiplexed together when received by the filter212. As can be seen inFIG. 2, there are two feeder fibre links, Feeder1and Feeder2, connected to the arrangement210. The filter212receives a multiplexed signal which comprises a data signal and an OTDR signal. The filter212is adapted to separate the OTDR signal and the data signal and to output the OTDR signal to the first splitter211. The first splitter211has N−1 outputs. The first splitter211receives the OTDR signal and splits the OTDR signal into N−1 OTDR sub-signals. The OTDR sub-signals have the same wavelength as the original OTDR signal which inputted into the first splitter, but the amplitude or optical power of the OTDR sub-signals is (N−1):th of the original OTDR signal. Merely as an example, assume that N=9, then the amplitude or optical power of the OTDR sub-signals is 1/(9−1)=⅛ of the amplitude or optical power of the original OTDR signal. The first splitter211is further adapted to output the N−1 OTDR sub-signals to the N*M AWG220. The at least one filter212, which is adapted to separate the received multiplexed signal, is further adapted to output the data signal to the AWG220. The AWG220receives the data signal and the OTDR sub-signals and forwards the signals to appropriate ONTs depending on the wavelengths of the data signal and the OTDR sub-signals. The ONTs are connected to the RN by individual fibre links which are also referred to as drop links. InFIG. 2this is illustrates as Drop1, Drop2, . . . , Drop M.

It shall be pointed out that the data signal may comprises up to M different wavelengths, wherein in each wavelength is dedicated a specific ONT. In this manner, the data signal may comprise up to M individual signals, one signal for each ONT.

The N−1 OTDR sub-signals will travel down in a respective drop link and due to Rayleigh scattering, portions of the OTDR sub-signals will back scatter towards the CO and the OTDR device. The back scattered light at the OTDR device is referred to as a trace, which may then be analysed to identify and analyse a possible fault which has occurred on one or more of the drop links between the RN and the ONTs. By one single OTDR wavelength, N−1 individual drop links may be supervised or monitored due to the splitting of the original OTDR signal into the N−1 OTDR sub-signals.

Looking atFIG. 3, the arrangement310comprises at least one filter312a,312bconnected to the feeder fibre links, Feeder1and Feeder2. The at least one filter312a,312bis adapted to separate a data signal and an original OTDR signal received on either of the feeder fibre links. As can be seen inFIG. 3, there are two feeder fibre links, Feeder1and Feeder2, connected to the arrangement310. The filter312a,312breceives a multiplexed signal which comprises a data signal and an OTDR signal. The filter312a,312bis adapted to separate the OTDR signal and the data signal and to output the OTDR signal to the first splitter311. The first splitter311has N−2 outputs. The first splitter311receives the OTDR signal and splits the OTDR signal into N−2 OTDR sub-signals. The OTDR sub-signals have the same wavelength as the original OTDR signal which is inputted into the first splitter, but the amplitude or optical power of the OTDR sub-signals is (N−2):th of the original OTDR signal. Merely as an example, assume that N=10, then the amplitude or optical power of the OTDR sub-signals is 1/(10−2)=⅛ of the amplitude or optical power of the original OTDR signal. The first splitter311is further adapted to output the N−2 OTDR sub-signals to the N*M AWG320. The at least one filter312a,312b, which is adapted to separate the received multiplexed signal, is further adapted to output the data signal to the AWG320. The AWG320receives the data signal and the OTDR sub-signals and forwards the signals to appropriate ONTs depending on the wavelengths of the data signal and the OTDR sub-signals. The ONTs are connected to the RN by individual fibre links which are also referred to as drop links. InFIG. 3this is illustrates as Drop1, Drop2, . . . , Drop M.

The N−2 OTDR sub-signals will travel down in a respective drop link and due to Rayleigh scattering, portions of the OTDR sub-signals will back scatter towards the CO and the OTDR device. The back scattered light at the OTDR device is referred to as a trace, which may then be analysed to identify and analyse a possible fault which has occurred on one or more of the drop links between the RN and the ONTs. By one single OTDR wavelength, N−2 individual drop links may be supervised or monitored due to the splitting of the original OTDR signal into the N−2 OTDR sub-signals.

It shall be pointed out that the data signal may comprises up to M different wavelengths, wherein in each wavelength is dedicated a specific ONT. In this manner, the data signal may comprise up to M individual signals, one signal for each ONT.

The arrangement has several advantages. The arrangement allows for two individual feeder fibre links to be connected between the CO and the RN, thereby increasing the reliability of operation of the WDN-PON. The arrangement supports a totally passive Optical Distribution Network. The arrangement may be upgraded to any WDM-PON topology based on AWG. It is further standard compliant.

In an example, wherein the arrangement comprises one filter212, the arrangement210further comprises a second splitter213with two inputs connected to the two feeder fibre links respectively for receiving the data signal and the OTDR signal on either of the feeder fibre links and an output for outputting the received data signal and the OTDR signal to the filter212.

Looking atFIG. 2, the arrangement210comprises one filter212as described above. The arrangement210in this example further comprises a second splitter213. The second splitter has two inputs and each input is connected to an individual feeder fibre link. The arrangement210receives the multiplexed signal or signals on one of the feeder fibre links, illustrated inFIG. 2as Feeder1and Feeder2. The second splitter213does not need to know on which feeder fibre link the multiplexed signal is received since the second splitter213will forward the received multiplexed signal to the filter212in order for the filter212to separate the data signal and the original OTDR signal. The CO will employ one of the feeder fibre links as the working feeder fibre link and the other feeder fibre link; the protective feeder fibre link will not be used in normal operation. Only in case the CO detects a malfunction of the working feeder fibre link, the CO will switch to use the protection feeder fibre link. But as can be seen inFIG. 2, the second splitter213of the arrangement210does not need to know which feeder fibre is the working feeder fibre link and which is the protective feeder fibre link.

In an example, the first splitter211is adapted to split the received OTDR signal into N−1 OTDR sub-signals and to output the N−1 OTDR sub-signals to the AWG220on respective N−1 connections between the first splitter211and the AWG220.

Again looking atFIG. 2, the AWG has N inputs and M outputs. Since there is only one filter212in this example which outputs a received data signal to the AWG, there are N−1 inputs which may be used for OTDR sub-signals. Therefore, the first splitter211splits a received original OTDR signal into N−1 OTDR sub-signals and outputs the N−1 OTDR sub-signals to respective N−1 inputs of the AWG220. The inputs of the AWG220are also referred to as monitoring ports.

According to another example, the arrangement comprises two filters312a,312b, wherein each of the two filters is connected to an individual respective feeder fibre link, wherein the first splitter311is further adapted to receive the original OTDR signal from either of the two filters312a,312band to output N−2 OTDR sub-signals, to the N*M AWG320.

Looking atFIG. 3, the arrangement310comprises two filters312aand filters312b. The arrangement310in this example also has two feeder fibre links, Feeder1and Feeder2connected to it. One of the feeder fibre links, Feeder1, is connected to one of the filters312a, and the other feeder fibre link, Feeder2, is connected to the other filter312b. Both filters312aand312bare adapted to receive a multiplexed signal comprising both a data signal and an original OTDR signal. Both filters312aand312bare adapted to separate the data signal and the original OTDR signal and to output the data signal to an N*M AWG320and to output the original OTDR signal the first splitter311. In other words, the filters312aand312bhave the same functionality as filter212described in conjunction withFIG. 2. The first splitter311is further adapted to receive the original OTDR signal from either of the two filters312a,312b, to split the original OTDR signal into N−2 OTDR sub-signals and to output the N−2 OTDR sub-signals, to the N*M AWG320. Also in this example, the arrangement310does not need to know on which feeder fibre link the multiplexed signal is received since both filters312aand312bwill separate the data signal and the original OTDR signal. The CO will employ one of the feeder fibre links as the working feeder fibre link and the other feeder fibre link; the protective feeder fibre link will not be used in normal operation. Only in case the CO detects a malfunction of the working feeder fibre link, the CO will switch to use the protection feeder fibre link. But as can be seen inFIG. 3, irrespective of which feeder fibre link the multiplexed signal is received on, the multiplexed signal will be separated, the data signal will be forwarded to the AWG320and the original OTDR signal will be splitted into N−2 OTDR signals which will be forwarded to the AWG320. The inputs of the AWG320are also referred to as monitoring ports.

In an example, wherein arrangement comprises two filters312aand312b, each of the two filters312aand312bis adapted to output the data signal on an individual and respective connection to the AWG320.

In yet an example, the first splitter211,311is further adapted to split the received original OTDR signal to eight outputs of the first splitter211,311.

In other words, the first splitter211,311receives the original OTDR signal from the filter212,312aor312band splits it into 8 OTDR sub-signals and outputs each of the 8 OTDR sub-signals on 8 individual outputs of the first splitter211,311to be inputted on 8 inputs of the AWG220,330. As described above, the 8 OTDR sub-signals have the same wavelength but a reduced amplitude or power. By these 8 OTDR sub-signals, it is possible to supervise or monitor8individual drop links connecting the RN with 8 ONTs.

Embodiments herein also relate to a RN in a WDM-PON, for supervision of the WDM-PON, wherein the RN is connected to a CO by two individual feeder fibre links.

The RN comprises an arrangement210,310according to any of the examples described above and an N*M AWG220,320, wherein N individual inputs of the AWG220,320are connected to the arrangement210,310such that the output of each of the at least one filter212,312a,312bis connected to an input of the AWG220,320and the outputs of the first splitter211,311are connected to individual inputs of the AWG220,320.

Looking atFIG. 2, the arrangement210is illustrated being comprised in the RN200. The arrangement comprises as least one filter212which separates the data signal and the original OTDR signal as described above. The data signal is outputted from the filter212to one input of the AWG220. The splitter211receives the original OTDR signal, splits it into N−1 OTDR sub-signals and outputs the N−1 OTDR sub-signals to respective N−1 inputs, or monitoring ports, of the AWG220. Thereby, the arrangement210has a total of N outputs connected to N respective inputs of the N*M AWG220.

Looking atFIG. 3, the arrangement310is illustrates being comprised in the RN300. The arrangement comprises two filters312a,312bwhich separate the data signal and the original OTDR signal as described above. The data signal is outputted from the either of the filters312a,312bto respective inputs of the AWG320. The splitter311receives the original OTDR signal, splits it into N−2 OTDR sub-signals and outputs the N−2 OTDR sub-signals to respective N−2 inputs of the AWG320. Thereby, the arrangement310has a total of N outputs connected to N respective inputs of the N*M AWG320. Since there are two filters312aand312bin this example, two of the N outputs from the arrangement310are dedicated for data signals and N−2 outputs from the arrangement310are dedicated for monitoring, or OTDR sub-signals.

The RN comprising the arrangement has the same advantages as the arrangement itself. The RN allows for two individual feeder fibre links to be connected between the CO and the RN, thereby increasing the reliability of operation of the WDN-PON. The arrangement supports a totally passive Optical Distribution Network. The arrangement may be upgraded to any WDM-PON topology based on AWG. It is further standard compliant.

In an example, the arrangement210comprises one filter212which has an output connected to an input to the AWG220and the first splitter211has N−1 outputs connected to a respective input of the N*M AWG220.

In an example when the arrangement210comprises one filter212, N=9 and M=32.

In other words, the arrangement210has 9 outputs, one output is dedicated for data signals and 8 outputs are dedicated for monitoring, or OTDR sub-signals. In this manner, 8 individual drop links may be monitored or supervised using one OTDR signal of a specific wavelength. The AWG220has 32 outputs, which implies that the AWG220, and hence the RN200, may have up to 32 ONTs connected to it. Since one OTDR wavelength may be used to monitor or supervise 8 ONTs, only 4 different wavelengths of the OTDR signal are required to supervise the 32 ONTs.

In another example, the arrangement310comprises two filters312a,312bwhich have a respective output connected to a respective input to the AWG320and the first splitter311has N−2 outputs connected to a respective input of the N*M AWG320.

In an example when the arrangement310comprises two filters312a,312b, N=10 and M=32.

The arrangement310in this example comprises 10 outputs, whereof 2 outputs are dedicated for data signals and 8 outputs are dedicated for monitoring, or OTDR sub-signals. In this manner, 8 individual drop links may be monitored or supervised using one OTDR signal of a specific wavelength. The AWG320has 32 outputs, which implies that the AWG320, and hence the RN300, may have up to 32 ONTs connected to it. Since one OTDR wavelength may be used to monitor or supervise 8 ONTs, only four different wavelengths of the OTDR signal are required to supervise the 32 ONTs.

Embodiments herein also relate to a CO in a WDM-PON for supervision of the WDM-PON, wherein the CO is connected to a RN by two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link.

Exemplifying embodiments of such a CO will now be described with reference toFIGS. 4 and 5which are block diagrams of exemplifying embodiments of a CO for supervision of the WDM-PON wherein the CO is connected to a RN by two individual feeder fibre links.

According to an exemplifying embodiment, the CO400,500comprises at least one Optical Line Terminal, OLT,401a,401b,501adapted to output data signals and an OTDR device420,520adapted to output OTDR signals. The CO400,500further comprises at least one filter410a,410b,510adapted to receive data signals from the OLT401a,401b,501and OTDR signals from the OTDR device420,520and to multiplex the signals together and output the multiplexed signals towards the working feeder fibre link towards the Remote Node200,300. The OTDR device420,520is adapted to detect malfunction of the working feeder fibre link, wherein the Central Office is adapted to switch feeder fibre link so that the multiplexed signals are outputted on the protection feeder fibre link.

Starting withFIG. 4, the CO400is illustrated to comprise at least one OLT401a,401badapted to output data signals.FIG. 4further illustrates the CO400comprising an OTDR device420adapted to output OTDR signals. The CO400also comprises at least one filter410a,410badapted to receive data signals from the OLT401a,401band OTDR signals from the OTDR device420and to multiplex the signals together and output the multiplexed signals towards the working feeder fibre link towards the Remote Node200,300. The CO400further comprises a switch430which is adapted to receive OTDR signals from the OTDR device420and to direct the OTDR signals to the at least one filter410a,410bso that the at least one filter410a,410bis able to multiplex the OTDR signal with data signals from at least one OLT401a,401b.

Looking atFIG. 5, the CO500is illustrated to comprise at least one OLT501adapted to output data signals.FIG. 5further illustrates the CO500comprising an OTDR device520adapted to output OTDR signals. The CO500also comprises at least one filter510adapted to receive data signals from the OLT501and OTDR signals from the OTDR device520and to multiplex the signals together and output the multiplexed signals towards the working feeder fibre link towards the Remote Node200,300. The CO500further comprises a switch550which is adapted to receive multiplexed signals from the at least one filter510and to direct the received multiplexed signals to the RN200,300on one of the feeder fibre links. In normal operation, the switch550transmits the received multiplexed signals to the RN200,300on the working feeder fibre link and in case of a malfunction of the working feeder fibre link; the switch550transmits the received multiplexed signals to the RN200,300on the protection feeder fibre link.

The OTDR device420,520is in an example connected to a control unit (not shown). The control unit is adapted to analyse the back-scattered light from the drop link in order to detect any possible fault which has occurred in a drop link. The control unit may further be connected to the CO400,500to control the switch430,550and the at least one OLT401a,401bso that in case a malfunction of the working feeder fibre link is detected, the control unit controls the switch (and the OLTs in case of more than one) such that the protection feeder fibre link is used to transmit signals (data signals multiplexed with OTDR signals) to the RN200,300.

It shall be pointed out that the CO400,500is illustrated comprising an External Wavelength Adaptation Module, EWAM,430,540. The EWAM430,540is a module which receives the OTDR signal from the OTDR device420,520and modulates the wavelength of the received OTDR signal. As described above, one specific wavelength of one OTDR signal may be used to supervise, or monitor, a plurality of ONTs, but possibly not all. In order to monitor all ONTs in the WDM-PON, several OTDR signals of different wavelengths may be needed. One way to generate OTDR signals of different wavelengths is by means of a tuneable OTDR device, T-OTDR. Another means for generating OTDR signals of different wavelengths is to employ an OTDR device capable of generating only one wavelength and combine such an OTDR device with an EWAM, wherein the different OTDR signals of different wavelengths are obtained by the OTDR device and the EWAM together.

The CO has the several advantages. The CO allows for two individual feeder fibre links to be connected between the CO and the RN, thereby increasing the reliability of operation of the WDN-PON. The arrangement supports a totally passive Optical Distribution Network. The arrangement may be upgraded to any WDM-PON topology based on AWG. It is further standard compliant.

According to an example, the CO400comprises a first and a second OLT401a,401b, a first and a second filter410a,410band a switch430. The switch430has an input connected to an output of the OTDR device420and is adapted to receive OTDR signals. The switch430further has two outputs, each connected to a respective filter410a,410b, wherein each respective filter410a,410bfurther is connected to a respective OLT401a,401band a respective feeder fibre link and is adapted to receive data signals from the respective OLT401a,401band OTDR signals from the OTDR device420and to multiplex the signals together and output the multiplexed signals on respective feeder fibre link.

In yet an example, when the CO400comprises a first and a second OLT401a,401b, the first OLT401ais connected to the working fibre link by means of the first filter410a, the first OLT401abeing a serving OLT and the second OLT401bbeing a backup OLT, wherein upon detection of malfunction of the working feeder fibre link, the switching of feeder fibre links to the protection feeder fibre link comprises switching OLT such that the backup OLT401bbecomes the serving OLT.

Looking atFIG. 4, the CO400comprises two OLTs, a first401aOLT and a second OLT401b. The CO400further comprises two filters, a first filter410aand a second filter410b. The CO further comprises a switch430. The switch430receives an OTDR signal from the OTDR, optionally via the EWAM440, and depending on which feeder fibre link is the working feeder fibre link, the switch430forwards the received OTDR signal to one of the two filters410a,410b. In case Feeder1is the working feeder fibre, the switch430forwards the OTDR signal to the first filter410a. If Feeder1is the working feeder fibre link, the first OLT401ais a serving OLT. The filter410areceives the OTDR signals from the switch430and data signals from the first OLT401a. The first filter410amultiplexes the received data signals and the OTDR signals together and transmits, or outputs, the multiplexed signals on the working feeder fibre link, Feeder1, towards the RN200,300.

In case of a malfunction of the working feeder fibre link, Feeder1, the switch430outputs the received OTDR signal to the second filter410b. The second OLT401bbecomes the serving OLT, meaning that the first OLT401abecomes a standby or back-up OLT. The standby OLT does not transmit any data signals, but may run in parallel to the serving OLT. The now serving OLT, i.e. the second OLT401btransmits a data signal to the second filter410b, which multiplexes the data signal and the OTDR signal together and outputs, or transmits, the multiplexed signal on the protection feeder fibre link, Feeder2, towards the RN200,300.

In another example, the CO500comprises one OLT501, one filter510and a switch550, the switch550having an input connected to an output of the filter510and adapted to receive the multiplexed signals, the switch550further having two outputs each connected to a respective feeder fibre link.

In still an example, when the CO500comprises one OLT501, one filter510and a switch550, wherein the switch550in normal condition connects the output of the filter510to the working feeder fibre link, wherein upon detection of malfunction of the working feeder fibre link, the switching of feeder fibre links to the protection feeder fibre link comprises the switch550connecting the output of the filter510to the protection feeder fibre link.

Looking atFIG. 5, the CO500comprises one OLT501which is connected to one filter510. The OLT501generates a data signal which the OLT transmits to the filter510. The CO also comprises an OTDR device520. The OTDR device generates an OTDR signal which the OTDR device520transmits to the filter510. The filter510thus receives both the data signal and the OTDR signal which the filter510multiplexes together to a multiplexed signal which the filter510outputs, or transmits, to a switch550. The switch550receives the multiplexed signal and outputs, or transmits, the multiplexed signal to the RN200,300on one of the feeder fibre links, Feeder1or Feeder2. For example, assume the Feeder1is the working feeder fibre link and the Feeder2is the protective feeder fibre link, then the switch550outputs, or transmits, the multiplexed signal to the RN200,300on Feeder1.

In case of a malfunction of the working feeder fibre link, Feeder1, the switch550outputs, or transmits, the multiplexed signal to the RN200,300on Feeder2, i.e. the protection feeder fibre link. As described above, the CO500may comprise, or being connected to, a control unit (not shown), which will either detect the malfunction of the working feeder fibre link or receive a notification that a malfunction of the working feeder fibre has occurred. In such a case, the control unit will control the switch550to switch from outputting, or transmitting, a received multiplexed signal on the working feeder fibre link to the protection feeder fibre link.

In this manner, the operation of the feeder fibres connecting the CO400,500and the RN200,300are assured.

It shall be pointed out that the CO400,500may be used together with any of the examples of the RN200,300described above.

Embodiments herein also relate to a WDM-PON, comprising a CO400,500according to any of the examples described above and a RN200,300according to any of the examples described above, wherein the CO400,500and the RN200,300are connected via two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link, having different geographical paths between the CO400,500and the RN200,300.

Looking atFIG. 6, a schematic overview of an exemplifying embodiment of a WDM-PON comprising a CO400,500and a RN200,300connected by two individual feeder fibre links is illustrated.FIG. 6illustrates that the CO400,500may be any of the examples described above of a CO being adapted to be connected to the RN200,300by means of two feeder fibre links, one working feeder fibre link650wand one protection feeder fibre link650p.FIG. 6further illustrates that the RN may be any of the examples described above of a RN being adapted to be connected to the CO400,500by means of two feeder fibre links, one working feeder fibre link650wand one protection feeder fibre link650p. Further,FIG. 6illustrates the CO400,500being connected to the RN200,300by means of two feeder fibre links, one working feeder fibre link650wand one protection feeder fibre link650phaving different geographical paths between the CO400,500and the RN200,300.

The WDM-PON has several advantages. The WDM-PON allows for two individual feeder fibre links to be connected between the CO and the RN, thereby increasing the reliability of operation of the WDN-PON. The arrangement supports a totally passive Optical Distribution Network. The arrangement may be upgraded to any WDM-PON topology based on AWG. It is further standard compliant.

Embodiments herein also relate to a method in an arrangement at a RN in a WDM-PON for supervision of the WDM-PON, wherein the RN is connected to a CO by two individual feeder fibre links. Such a method will now be described with reference toFIG. 7. The method has the same objectives, technical features and advantages as the arrangement described above. The method will be described in brief in order to avoid unnecessary repetition.

FIG. 7is a flowchart of an exemplifying embodiment of a method in an arrangement at a remote node for supervision of a WDM-PON.

FIG. 7illustrates the method700in an arrangement at a RN in a WDM-PON for supervision of the WDM-PON, wherein the RN is connected to a CO by two individual feeder fibre links comprising separating710, in at least one filter connected to the feeder fibre links, a data signal and an original OTDR signal received on either of the feeder fibre links. The method700also comprises receiving720at a first splitter from the at least one filter, the original OTDR signal, and splitting the original OTDR signal into a plurality of OTDR sub-signals and outputting, to an N*M AWG the plurality of OTDR sub-signals. The at least one filter outputs the original OTDR signal to the first splitter and outputs the data signal to the AWG, thereby enabling supervision of the WDM-PON without influencing the data signals.

The method in the arrangement at the RN has several advantages, as described above. The method in the arrangement allows for two individual feeder fibre links to be connected between the CO and the RN, thereby increasing the reliability of operation of the WDN-PON. The arrangement supports a totally passive Optical Distribution Network. The arrangement may be upgraded to any WDM-PON topology based on AWG. It is further standard compliant.

In an example, the arrangement comprises one filter, wherein the method further comprises receiving, at a second splitter with two inputs connected to the two feeder fibre links, the data signal and the OTDR signal on either of the feeder fibre links and outputting the received data signal and the OTDR signal to the filter.

In yet an example, the received OTDR signal is splitted, in the first splitter, into N−1 OTDR sub-signals and the N−1 OTDR sub-signals are outputted on respective N−1 connections between the first splitter and the AWG.

In another example, the arrangement comprises two filters, wherein each of the two filters is connected to an individual respective feeder fibre link, wherein the method comprises receiving, at the first splitter, the original OTDR signal from either of the two filters and outputting N−2 QTDR sub-signals, to the N*M AWG.

According to an example, the data signal is outputted, from any of the two filters, on an individual and respective connection to the AWG.

In still an example, the received OTDR signal is splitted, in the first splitter to eight outputs of the first splitter.

Embodiment herein also relate to a method in a CO in a WDM-PON for supervision of the WDM-PON, wherein the CO is connected to a RN by two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link. Such a method will now be described with reference toFIG. 8. The method has the same objectives, technical features and advantages as the CO described above. The method will be described in brief in order to avoid unnecessary repetition.

FIG. 8is a flowchart of an exemplifying embodiment of a method in a CO for supervision of a WDM-PON.

FIG. 8illustrates the method800in the CO in a WDM-PON for supervision of the WDM-PON, wherein the CO is connected to a RN by two individual feeder fibre links, one working feeder fibre link and one protection feeder fibre link, comprising outputting810data signals from at least one OLT and outputting820OTDR signals from an OTDR device. The method further comprises receiving830, in at least one filter, the data signals from the OLT and the OTDR signals from the OTDR device and to multiplexing the signals together and outputting the multiplexed signals to the working feeder fibre link towards the RN. A malfunction of the working feeder fibre link is detected at the OTDR device, wherein the Central Office switches feeder fibre link so that the multiplexed signals are outputted on the protection feeder fibre link.

The method in the CO has several advantages. The method allows for two individual feeder fibre links to be connected between the CO and the RN, thereby increasing the reliability of operation of the WDN-PON. The arrangement supports a totally passive Optical Distribution Network. The arrangement may be upgraded to any WDM-PON topology based on AWG. It is further standard compliant.

In an example, the Central Office comprises a first and a second OLT, a first and a second filter and a switch, the switch having an input connected to an output of the OTDR device and two outputs each connected to a respective filter, wherein each respective filter further is connected to a respective OLT and a respective feeder fibre link. The method comprises receiving the OTDR signals from the OTDR device at the switch and outputting the OTDR signals to one of the filters. The method further comprising receiving, at any of the respective filter, the OTDR signals from the switch and data signals from the respective OLT, the method further comprising multiplexing, at any of the respective filter, the signals together and outputting the multiplexed signals on respective feeder fibre link.

In yet an example, the first OLT is connected to the working fibre link by means of the first filter, the first OLT is a serving OLT and the second OLT is a backup OLT. The method comprises, when detecting a malfunction of the working feeder fibre link: switching feeder fibre links to the protection feeder fibre link by switching OLT such that the backup OLT becomes the serving OLT.

In still an example, the Central Office comprises one OLT, one filter and a switch, the switch having an input connected to an output of the filter and two outputs each connected to a respective feeder fibre link. The method comprises receiving the multiplexed signals at the switch and outputting the received multiplexed signal to one of the feeder fibre links.

According to an example, the method comprises connecting, at the switch, the output of the filter to the working feeder fibre link in normal operation, and upon detection of malfunction of the working feeder fibre link, switching of feeder fibre links to connect the output of the filter to the protection feeder fibre link.

The above described supervision of fibre links connecting the RN200,300with ONTs may further be performed together with Optical Transceiver Monitoring, OTM, wherein measurable parameters are provided, which may be measured by the ONTs. The ONTs may then report the measurement results to the CO400,500. An example of a measurable parameter is transmitted/received power of signals sent between the OLT401a,401b,501in the CO400,500and the ONTs.

While the embodiments have been described in terms of several embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent upon reading of the specifications and study of the drawings. It is therefore intended that the following appended claims include such alternatives, modifications, permutations and equivalents as fall within the scope of the embodiments and defined by the pending claims.