Patent Description:
Due to the advent of various multimedia services based on the Internet and the web, large amounts of data traffic are increasing, and with the advent of smart phones and a rapid increase in demand for data services, the need to increase transmission capacity has emerged in optical communication networks applied to radio access networks for mobile communication.

As a result, as the number of devices constituting an optical communication network increases as well as the complexity of the network structure significantly increases, efficient management of the network and maintenance of the devices have begun to emerge as important factors. In particular, there is a need for a way to improve the quality of service by detecting errors in devices of optical communication networks to prevent failure and to respond quickly to failures.

<CIT> discloses a distance calculating method between an apparatus and a remote unit, and a signal transmitting device applying the same within a station at a WDM mode optical network.

Provided are optical communication systems capable of efficiently monitoring connection states between optical communication devices constituting an optical communication system, and methods of monitoring the same.

According to the disclosure, there is an effect of efficiently monitoring connection states between optical communication devices.

Effects obtainable by the embodiments of the disclosure are not limited to the effects described above, and other effects not described herein may be clearly understood by one of ordinary skill in the art to which the inventive concept belongs from the following description.

Embodiments of the disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which:.

Since the disclosure may have diverse modified embodiments, preferred embodiments are illustrated in the drawings and are described in the detailed description. However, this is not intended to limit the disclosure to particular modes of practise.

In the description of the disclosure, certain detailed explanations of the related art are omitted when it is deemed that they may unnecessarily obscure the essence of the disclosure. In addition, numeral figures (e.g., first, second, and the like) used during describing the specification are just identification symbols for distinguishing one element from another element.

Further, in the specification, if it is described that one component "is connected to" or "accesses" the other component, it is understood that the one component may be directly connected to or may directly access the other component but unless explicitly described to the contrary, another component may be "connected" or "access" between the components.

In addition, terms including "unit," "er," "or," "module," and the like disclosed in the specification mean a unit that processes at least one function or operation and this may be implemented by hardware or software such as a processor, a micro processor, a micro controller, a central processing unit (CPU), a graphics processing unit (GPU), an accelerated Processing unit (APU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), and a field programmable gate array (FPGA) or a combination of hardware and software.

In addition, it is intended to clarify that the division of the components in the specification is only made for each main function that each component is responsible for. That is, two or more components to be described later below may be combined into one component, or one components may be divided into two or more components according to more subdivided functions. In addition, it goes without saying that each of the components to be described later below may additionally perform some or all of the functions of other components in addition to its own main function, and some of the main functions that each of the components is responsible for may be dedicated and performed by other components.

Hereinafter, various embodiments of the disclosure will be described in detail in order.

<FIG> is a configuration diagram of an optical communication system according to an embodiment.

Referring to <FIG>, an optical communication system <NUM> according to an embodiment may include a central office terminal (COT) <NUM> and n remote nodes (RNs) <NUM>-<NUM> to <NUM>-n (n is a natural number). Hereinafter, an application example of configuring an optical transport network, which is a subnetwork in which the COT and the n RNs <NUM>-<NUM> to <NUM>-n constitute a fronthaul segment of a radio access network architecture, will be described. However, the inventive concept of the disclosure is not limited thereto. It is apparent that the inventive concept of the disclosure may be applied to an optical transmission network such as midhaul and backhaul segments of the radio access network architecture, and further, an FTTx solution and an in-building solution.

The COT <NUM> and the n RNs <NUM>-<NUM> to <NUM>-n may be configured as an optical ring network in which they are connected to each other in a ring topology structure.

The connection structure will be described in more detail on the assumption that the optical communication system <NUM> according to an embodiment is constituted of the COT <NUM> and two RNs <NUM>-<NUM> and <NUM>-<NUM>. The COT <NUM> and the two RNs <NUM>-<NUM> and <NUM>-<NUM> may each include input/output ports for mutual connection. At this time, a first optical cable may be connected to a first input/output port of the COT <NUM>, and a second optical cable may be connected to a second input/output port of the COT <NUM>. Also, the first optical cable may be connected to a first input/output port of the first RN <NUM>-<NUM>, and a third optical cable may be connected to a second input/output port of the first RN <NUM>-<NUM>. In addition, the third optical cable may be connected to a first input/output port of the second RN <NUM>-<NUM>, and the second optical cable may be connected to a second input/output port of the second RN <NUM>-<NUM>. Here, the first to third optical cables may be a concept including not only a single optical cable but also a plurality of optical cables and their connection structures.

Meanwhile, among the two RNs and the COT that are connected to each other, the COT may be connected to a portion that performs digital processing of a base station in the fronthaul segment of the radio access network architecture, for example, at least one digital unit (DU) (or baseband unit (BBU)), and each RN may be connected to a portion that performs wireless processing of the base station, for example, at least one radio unit (RU) (or remote radio head (RRH)). However, the disclosure is not limited thereto, and among the two RNs and the COT that are connected to each other, the COT may be connected to at least one macro cell RU, and each RN may be connected to at least one small cell RU. According to various fronthaul topologies of the radio access network architecture, a connection object and an interconnection structure of each of the COT and RTs may vary.

The COT <NUM> may be a device that multiplexes base station signals and transmits the base station signals to one or more connected RNs (at least one of <NUM>-<NUM> to <NUM>-n). For example, the COT <NUM> may receive a signal from a DU (not shown) and convert the signal into a WDM signal, and may transmit the WDM signal to one or more connected RNs (at least one of <NUM>-<NUM> to <NUM>-n) through an optical cable. That is, the COT <NUM> may receive a plurality of base station signals and convert them into optical signals of different wavelengths, and may transmit the optical signals to one or more RNs (at least one of <NUM>-<NUM> to <NUM>-n). The base station signal may be a baseband signal conforming to the standard of a fronthaul link such as Common Public Radio Interface (CPRI), Open Base Station Architecture Initiative (OBSAI), and Open Radio Equipment Interface (ORI).

In an example of <FIG>, the COT <NUM> may transmit the WDM signal to the first RN <NUM>-<NUM> in one direction of the ring network, that is, through the first optical cable, and may transmit the WDM signal to the nth RN <NUM>-n in the other direction of the ring network, that is, through the second optical cable.

Each of the RNs <NUM>-<NUM> to <NUM>-n is a device located on a cell site side in a remote location. Each of the RNs <NUM>-<NUM> to <NUM>-n is connected to the COT <NUM> and may transmit the WDM signal received from the COT <NUM> to at least one connected RU (not shown). That is, each of the RNs <NUM>-<NUM> to <NUM>-n may be a passive WDM device. On the other hand, each RN may be replaced with a remote terminal (RT). Various remote devices may be used according to an optical transmission network field to which the optical communication system <NUM> is applied.

The COT <NUM> according to an embodiment analyzes connection states between the COT <NUM> and the first RN <NUM>-<NUM> and between the COT <NUM> and the second RN <NUM>-<NUM> by using monitoring optical signals having distinct wavelengths (i.e., channels) from optical signals corresponding to the base station signal. For example, the COT <NUM> transmits the monitoring optical signals to the first RN <NUM>-<NUM> and/or the second RN <NUM>-<NUM>, and analyzes a monitoring optical signal, which is reflected by the first RN <NUM>-<NUM> and/or the second RN <NUM>-<NUM> and returns, to analyze connection states between the COT <NUM> and the first RN <NUM>-<NUM> and between the COT <NUM> and the second RN <NUM>-<NUM>.

Hereinafter, the operation of the COT <NUM> to analyze the connection states between the COT <NUM> and the first and second RNs <NUM>-<NUM> and <NUM>-<NUM> will be described in more detail.

<FIG> is a block diagram of a COT according to an embodiment, and <FIG> is a block diagram of an RN according to an embodiment. It is noted that <FIG> and <FIG> show main components for monitoring from among configurations of the COT and the RN for convenience of explanation.

The COT <NUM> according to an embodiment may include first to fourth optical signal-processing units <NUM> to <NUM>, a controller (MCU) <NUM>, and a first multiplexer/demultiplexer (MUX/DEMUX) <NUM> and a second MUX/DEMUX <NUM>. <FIG> illustrates an embodiment in which the COT <NUM> includes four optical signal-processing units and two MUX/DEMUXs, but the number of optical signal-processing units and MUX/DEMUXs may vary. For example, the number of optical signal-processing units may increase according to the number of RNs.

The first to fourth optical signal-processing units <NUM> to <NUM> may respectively generate monitoring optical signals under the control of the MCU <NUM>, and may output the generated optical signals to a corresponding MUX/DEMUX from among the first and second MUX/DEMUXs <NUM> and <NUM>.

The first optical signal-processing unit <NUM> may generate a first optical signal having a first wavelength λ1 and may output the first optical signal to the first MUX/DEMUX <NUM>. The second optical signal-processing unit <NUM> may generate a second optical signal having a second wavelength λ2 and may output the second optical signal to the second MUX/DEMUX <NUM>. The third optical signal-processing unit <NUM> may generate a third optical signal having a third wavelength λ3 and may output the third optical signal to the first MUX/DEMUX <NUM>. The fourth optical signal-processing unit <NUM> may generate a fourth optical signal having a fourth wavelength λ4 and may output the fourth optical signal to the second MUX/DEMUX <NUM>.

The first to fourth wavelengths λ1 to λ4 may be different from wavelengths for transmission of base station signals. For example, the first to fourth wavelengths λ1 to λ4 may be different from a wavelength λRN1 of a base station signal transmitted to the first RN <NUM>-<NUM> and a wavelength λRN2 of a base station signal transmitted to the second RN <NUM>-<NUM>. In other words, in <FIG> and hereinafter, for convenience of description, a wavelength of a base station signal allocated to the first RN <NUM>-<NUM> and a wavelength of a base station signal allocated to the second RN <NUM>-<NUM> are each illustrated, but the wavelength of the base station signal allocated to each of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> may be plural.

The first wavelength λ1 and the second wavelength λ2, and the third wavelength λ3 and the fourth wavelength λ4 may be wavelengths of bands that are divided in the same band, respectively. For example, the first wavelength λ1 may be a wavelength in an L band of <NUM>, and the second wavelength λ2 may be a wavelength in an H band of <NUM>. In addition, the third wavelength λ3 may be a wavelength in the L band of <NUM>, and the fourth wavelength λ4 may be a wavelength in the H band of <NUM>.

In addition, the first wavelength λ1 and the second wavelength λ2 may be monitoring wavelengths allocated to the first RN <NUM>-<NUM>, and the third wavelength λ3 and the fourth wavelength λ4 may be monitoring wavelengths allocated to the second RN <NUM>-<NUM>. Such monitoring wavelengths may be wavelengths of such as a supervisory channel.

Each of the first to fourth optical signal-processing units <NUM> to <NUM> may include an optical transceiver (e.g., an XFP, SFP, QSFP, or CFP type optical transceiver, etc.), a signal coupler (e.g., a coupler), and a filter in order to generate an optical signal of a wavelength set according to the control of the controller <NUM> and may output the optical signal to a corresponding MUX/DEMUX from among the first and second MUX/DEMUXs <NUM> and <NUM>. In this case, the optical transceiver may be a wavelength tunable type optical transceiver, and may have a structure in which a transmission port and a reception port of the optical transceiver are connected to the signal coupler, the signal coupler is connected to the filter, and the filter is connected to a corresponding MUX/DEMUX.

Depending on the embodiment, the first to fourth optical signal-processing units <NUM> to <NUM> may be configured as filters for outputting an optical signal of a certain wavelength received from an external device to a corresponding MUX/DEMUX from among the first and second MUX/DEMUXs <NUM> and <NUM>.

The first MUX/DEMUX <NUM> may multiplex service optical signals corresponding to base station signals for the first and second RNs <NUM>-<NUM> and <NUM>-<NUM> and the first optical signal and the third optical signal to output a first WDM signal through a connected first optical cable. Hereinafter, a direction in which an optical signal is transmitted through the first MUX/DEMUX <NUM> is referred to as "E" (EAST).

The second MUX/DEMUX <NUM> may multiplex the service optical signals corresponding to the base station signals for the first and second RNs <NUM>-<NUM> and <NUM>-<NUM> and the second optical signal and the fourth optical signal to output a second WDM signal through a connected second optical cable. Hereinafter, a direction in which an optical signal is transmitted through the second MUX/DEMUX <NUM> is referred to as "W" (WEST).

The first MUX/DEMUX <NUM> may output reflected signal(s) received through the first optical cable to the controller <NUM> after transmitting the first WDM signal. In addition, the second MUX/DEMUX <NUM> may output reflected signal(s) received through the second optical cable to the controller <NUM> after transmitting the second WDM signal.

The controller <NUM> may control overall operations of the first to fourth optical signal-processing units <NUM> to <NUM> and/or the COT <NUM> as described above, and may analyze the reflected signal(s) input from the first MUX/DEMUX <NUM> and/or the second MUX/DEMUX <NUM> to analyze connection states of one or more RNs <NUM>-<NUM> to <NUM>-n constituting the optical communication system <NUM>.

Referring to <FIG>, the first RN <NUM>-<NUM> may include a first band filter <NUM>, a first wavelength filter <NUM>-<NUM>, a first signal reflector <NUM>-<NUM>, a second band filter <NUM>, a second wavelength filter <NUM>-<NUM>, a second signal reflector <NUM>-<NUM>, and a first RN MUX/DEMUX <NUM>-<NUM>. The second RN <NUM>-<NUM> may include a third band filter <NUM>, a third wavelength filter <NUM>-<NUM>, a third signal reflector <NUM>-<NUM>, a fourth band filter <NUM>, a fourth wavelength filter <NUM>-<NUM>, a fourth signal reflector <NUM>-<NUM>, and a second RN MUX/DEMUX <NUM>-<NUM>.

As the first band filter <NUM> and the second band filter <NUM> of the first RN <NUM>-<NUM> are connected to each other, the third band filter <NUM> and the fourth band filter <NUM> of the second RN <NUM>-<NUM> are connected to each other, and the second band filter <NUM> and the third band filter <NUM> are connected to each other, the COT <NUM> and the first and second RNs <NUM>-<NUM> and <NUM>-<NUM> may have a ring topology structure capable of transmitting and receiving optical signals in both directions.

Although not shown, outputs of the first band filter <NUM> and the second band filter <NUM> in the first RN <NUM>-<NUM> may be connected to a signal coupler (e.g., a coupler), and the signal coupler may couple the outputs of the first band filter <NUM> and the second band filter <NUM> and may output them to the first RN MUX/DEMUX <NUM>-<NUM>. Similarly, outputs of the third band filter <NUM> and the fourth band filter <NUM> in the second RN <NUM>-<NUM> may be connected to a signal coupler, and the signal coupler may couple the outputs of the third band filter <NUM> and the fourth band filter <NUM>-<NUM> and may output them to the second RN MUX/DEMUX <NUM>-<NUM>.

The first band filter <NUM> may include a band pass filter (BPF) capable of filtering a band including the wavelength λRN1, the first wavelength λ1, and the second wavelength λ2 of the base station signal allocated to the first RN <NUM>-<NUM>.

When the first WDM signal is received, the first band filter <NUM> may filter a service optical signal and the first optical signal allocated to the first RN <NUM>-<NUM> from the first WDM signal and may output the filtered service optical signal and first optical signal to the first wavelength filter <NUM>-<NUM> and the first RN MUX/DEMUX <NUM>-<NUM>.

Alternatively, when the second WDM signal is received, the first band filter <NUM> may filter the service optical signal and the second optical signal allocated to the first RN <NUM>-<NUM> from the second WDM signal and may output the filtered service optical signal and second optical signal to the first wavelength filter <NUM>-<NUM> and the first RN MUX/DEMUX <NUM>-<NUM>.

The first wavelength filter <NUM>-<NUM> may include a wavelength selection filter capable of filtering the first wavelength λ1 and the second wavelength λ2 bands. The first wavelength filter <NUM>-<NUM> may filter the first optical signal or the second optical signal from the output of the first band filter <NUM>, and may output the filtered first optical signal or the second optical signal to the first signal reflector <NUM>-<NUM>.

The first signal reflector <NUM>-<NUM> may reflect an optical signal output from the first wavelength filter <NUM>-<NUM> and may output the optical signal in the opposite direction. For example, the first signal reflector <NUM>-<NUM> may output a signal a signal obtained by reflecting the first optical signal (hereinafter referred to as a first reflected signal) or a signal obtained by reflecting the second optical signal (hereinafter referred to as a second reflected signal) to the first wavelength filter <NUM>-<NUM>.

The first wavelength filter <NUM>-<NUM> may output the first reflected signal or the second reflected signal to the first band filter <NUM>. The first band filter <NUM> may transmit the first reflected signal to the first MUX/DEMUX <NUM> of the COT <NUM> through a connected optical cable, and may transmit the second reflected signal to the second MUX/DEMUX <NUM> of the COT <NUM> through the second RN <NUM>-<NUM>.

Like the first band filter <NUM>, the second band filter <NUM> may include a BPF capable of filtering a band including the wavelength λRN1 of the base station signal allocated to the first RN <NUM>-<NUM>, and the first wavelength λ1 and the second wavelength λ2.

When the second WDM signal is received, the second band filter <NUM> may filter the service optical signal and the second optical signal allocated to the first RN <NUM>-<NUM> from the second WDM signal and may output the filtered service optical signal and second optical signal to the second wavelength filter <NUM>-<NUM> and the first RN MUX/DEMUX <NUM>-<NUM>.

Alternatively, when the first WDM signal is received, the second band filter <NUM> may filter a service optical signal and a first optical signal corresponding to the base station signal for the first RN <NUM>-<NUM> from the first WDM signal and may output the filtered service optical signal and first optical signal to the second wavelength filter <NUM>-<NUM> and the first RN MUX/DEMUX <NUM>-<NUM>.

The second band filter <NUM> may output an unfiltered wavelength band to the first band filter <NUM> or the third band filter <NUM> of the second RN <NUM>-<NUM>.

The second wavelength filter <NUM>-<NUM> may include a wavelength selection filter capable of filtering a band of the second wavelength λ2. The second wavelength filter <NUM>-<NUM> may filter the second optical signal from the output of the second band filter <NUM> and may output the filtered second optical signal to the second signal reflector <NUM>-<NUM>.

The second signal reflector <NUM>-<NUM> may reflect the optical signal output from the second wavelength filter <NUM>-<NUM> and may output the optical signal in the opposite direction. That is, the second signal reflector <NUM>-<NUM> may output the second reflected signal to the second wavelength filter <NUM>-<NUM>.

The second wavelength filter <NUM>-<NUM> may output the second reflected signal to the second band filter <NUM>. The second band filter <NUM> may transmit the second reflected signal to the second MUX/DMX <NUM> of the COT <NUM> through a connected optical cable and the second RN <NUM>-<NUM>.

As such, unlike the first wavelength filter <NUM>-<NUM>, the second wavelength filter <NUM>-<NUM> may filter only a signal having a specific wavelength, that is, the second optical signal. Accordingly, when the second band filter <NUM> is connected to the first MUX/DEMUX <NUM> of the COT <NUM> through an optical cable to receive the first WDM signal without being connected to the second MUX/DMX <NUM> of the COT <NUM> through an optical cable and the second RN <NUM>-<NUM> to receive the second WDM signal, no reflected signal is generated by the second wavelength filter <NUM>-<NUM> and the second signal reflector <NUM>-<NUM>. Based on these characteristics, the COT <NUM> may detect a change in a connection state of the first RN <NUM>-<NUM>.

Meanwhile, the first RN MUX/DEMUX <NUM>-<NUM> may multiplex a service optical signal output from the first band filter <NUM> and/or the second band filter <NUM> and may transmit the multiplexed service optical signal to at least one connected RU (not shown). In this case, the first optical signal or the second optical signal may be filtered by the first RN MUX/DEMUX <NUM>-<NUM> and may not be transmitted to the RU.

The second RN <NUM>-<NUM> has a configuration corresponding to the above-described first RN <NUM>-<NUM> and may operate similarly.

In particular, the second RN <NUM>-<NUM> may be configured such that the fourth wavelength filter <NUM>-<NUM> filters a third optical signal and a fourth optical signal respectively corresponding to the third wavelength λ3 and the fourth wavelength λ4, and the third wavelength filter <NUM>-<NUM> filters only the third optical signal corresponding to the third wavelength λ3. When a connection state between the COT <NUM> and the second RN <NUM>-<NUM> is reversed, no reflected signal is generated in a specific direction.

In other words, when the third band filter <NUM> is connected to the second MUX/DEMUX <NUM> of the COT <NUM> through an optical cable to receive the second WDM signal without being connected to the first MUX/DMX <NUM> of the COT <NUM> through an optical cable and the first RN <NUM>-<NUM> to receive the first WDM signal, no reflected signal is generated by the third wavelength filter <NUM>-<NUM> and the third signal reflector <NUM>-<NUM>. Based on these characteristics, the COT <NUM> may detect a change in the connection state between the COT <NUM> and the second RN <NUM>-<NUM>.

The controller <NUM> may analyze connection states between the COT <NUM> and the first RN <NUM>-<NUM> and between the COT <NUM> and the second RN <NUM>-<NUM> by analyzing reflected signal(s) received from among the first to fourth reflected signals.

For example, the controller <NUM> may determine whether the first RN <NUM>-<NUM> is normally connected (e.g., a connection direction, etc.), the distance to the second RN <NUM>-<NUM>, and the like by analyzing whether the first optical signal and/or the second optical signal are/is transmitted from the COT <NUM> in different directions, and then the corresponding first and/or second reflected signals are/is received, and the time until reception.

In addition, the controller <NUM> may determine whether the second RN <NUM>-<NUM> is normally connected (e.g., a connection direction, etc.), the distance to the second RN <NUM>-<NUM>, and the like by analyzing whether the third optical signal and/or the fourth optical signal are/is transmitted from the COT <NUM> in different directions, and then the corresponding third and/or fourth reflected signals are/is received, and the time until reception.

Operations of analyzing connection states of the RNs <NUM> of the controller <NUM> will be described in detail with reference to <FIG>.

<FIG> are views illustrating a first connection state (CASE <NUM>) to a tenth connection state (CASE <NUM>) of an optical communication system, and <FIG> is a view of a connection state monitoring table according to an embodiment.

First, referring to <FIG>, a case in which direction 'E' of the COT <NUM> is connected to direction 'W' of the first RN <NUM>-<NUM> and direction 'W' of the COT <NUM> is connected to direction 'E' of the second RN <NUM>-<NUM> is illustrated (CASE <NUM>). In this case, the COT <NUM> and the first RN <NUM>-<NUM> may be connected to each other through a first optical cable, the COT <NUM> and the second RN <NUM>-<NUM> may be connected to each other through a second optical cable, and the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> may be connected to each other through a third optical cable.

As the first band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'W' as illustrated in <FIG>, a first WDM signal may be input to the first band filter <NUM> of the first RN <NUM>-<NUM>. In this case, a first reflected signal may be generated through the first band filter <NUM>, the first wavelength filter <NUM>-<NUM>, and the first signal reflector <NUM>-<NUM>, and the generated first reflected signal may be output to the first band filter <NUM> and transmitted to the COT <NUM> through the first optical cable.

As the second band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'E' as illustrated in <FIG>, a second WDM signal may be input to the second band filter <NUM> of the first RN <NUM>-<NUM>. In this case, a second reflected signal may be generated through the second band filter <NUM>, the second wavelength filter <NUM>-<NUM>, and the second signal reflector <NUM>-<NUM>, and the generated second reflected signal may be output to the second band filter <NUM>. The second reflected signal may be transmitted to the COT <NUM> through a third optical cable, the second RN <NUM>-<NUM>, and a second optical cable.

As the third band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'W' as illustrated in <FIG>, the first WDM signal may be input to the third band filter <NUM> of the second RN <NUM>-<NUM>. In this case, a third reflected signal may be generated through the third band filter <NUM>, the third wavelength filter <NUM>-<NUM>, and the third signal reflector <NUM>-<NUM>, and the generated third reflected signal may be output to the third band filter <NUM>. The third reflected signal may be transmitted to the COT <NUM> through the third optical cable, the first RN <NUM>-<NUM>, and the first optical cable.

As the fourth band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'E' as illustrated in <FIG>, the second WDM signal may be input to the fourth band filter <NUM> of the second RN <NUM>-<NUM>. In this case, a fourth reflected signal may be generated through the fourth band filter <NUM>, the fourth wavelength filter <NUM>-<NUM>, and the fourth signal reflector <NUM>-<NUM>, and the generated fourth reflected signal may be output to the fourth band filter <NUM> and transmitted to the COT <NUM> through the second optical cable.

The controller <NUM> may determine connection states of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> by comparing a received reflected signal with a preset connection state monitoring table.

In the example shown in <FIG>, the controller <NUM> may receive all of the first to fourth reflected signals, and in this case, may determine that both the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> are normally connected to the COT <NUM>.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'W' of the second RN <NUM>-<NUM> and the direction 'W' of the COT <NUM> is connected to the direction 'E' of the first RN <NUM>-<NUM> is illustrated (CASE <NUM>). In this case, the COT <NUM> and the second RN <NUM>-<NUM> may be connected to each other through a first optical cable, the COT <NUM> and the first RN <NUM>-<NUM> may be connected to each other through a second optical cable, and the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> may be connected to each other through a third optical cable.

As the first band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'W' as illustrated in <FIG>, the first WDM signal may be input to the first band filter <NUM> of the first RN <NUM>-<NUM>. In this case, a first reflected signal may be generated through the first band filter <NUM>, the first wavelength filter <NUM>-<NUM>, and the first signal reflector <NUM>-<NUM>, and the generated first reflected signal may be output to a third optical cable of the first band filter <NUM>. The first reflected signal transmitted to the third optical cable may be transmitted to the COT <NUM> through the second RN <NUM>-<NUM> and the first optical cable.

As the second band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'E' as illustrated in <FIG>, the second WDM signal may be input to the second band filter <NUM> of the first RN <NUM>-<NUM>. In this case, a second reflected signal may be generated through the second band filter <NUM>, the second wavelength filter <NUM>-<NUM>, and the second signal reflector <NUM>-<NUM>, and the generated second reflected signal may be transmitted to the COT <NUM> through the second optical cable of the second band filter <NUM>.

As the third band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'W' as illustrated in <FIG>, the first WDM signal may be input to the third band filter <NUM> of the second RN <NUM>-<NUM>. In this case, a third reflected signal may be generated through the third band filter <NUM>, the third wavelength filter <NUM>-<NUM>, and the third signal reflector <NUM>-<NUM>, and the generated third reflected signal may be transmitted to the COT <NUM> through the first optical cable of the third band filter <NUM>.

As the fourth band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'E' as illustrated in <FIG>, the second WDM signal may be input to the fourth band filter <NUM> of the second RN <NUM>-<NUM>. In this case, a fourth reflected signal may be generated through the fourth band filter <NUM>, the fourth wavelength filter <NUM>-<NUM>, and the fourth signal reflector <NUM>-<NUM>, and the generated fourth reflected signal may be output to a third optical cable of the fourth band filter <NUM>. The fourth reflected signal output to the third optical cable may be transmitted to the COT <NUM> through the first RN <NUM>-<NUM> and the second optical cable.

Even in this case, the controller <NUM> may receive all of the first to fourth reflected signals, and may determine that the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> are normally connected.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'W' of the first RN <NUM>-<NUM> is illustrated (CASE <NUM>). In this case, the COT <NUM> and the first RN <NUM>-<NUM> may be connected to each other through a first optical cable and a second optical cable, and the COT <NUM> and the second RN <NUM>-<NUM> are not connected to each other.

As the first band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'W' as illustrated in <FIG>, when the first WDM signal is input to the first band filter <NUM> of the first RN <NUM>-<NUM>, a first reflected signal may be generated and transmitted to the COT <NUM> through the first optical cable.

Also, as the second band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'E' as illustrated in <FIG>, when the second WDM signal is input to the second band filter <NUM> of the first RN <NUM>-<NUM>, a second reflected signal may be generated and transmitted to the COT <NUM> through the second optical cable.

In this case, the controller <NUM> may receive the first and second reflected signals, and may not receive the third and fourth reflected signals. Accordingly, the controller <NUM> may determine that the first RN <NUM>-<NUM> is normally connected and the second RN <NUM>-<NUM> does not exist.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'W' of the second RN <NUM>-<NUM> is illustrated (CASE <NUM>). In this case, the COT <NUM> and the second RN <NUM>-<NUM> may be connected to each other through a first optical cable and a second optical cable, and the COT <NUM> and the first RN <NUM>-<NUM> are not connected to each other.

As the third band filter <NUM> of the second RN <NUM>-<NUM> is connected in the direction 'W' of the second RN <NUM>-<NUM> as illustrated in <FIG>, when the first WDM signal is input to the third band filter <NUM> of the second RN <NUM>-<NUM>, a third reflected signal may be generated and transmitted to the COT <NUM> through the first optical cable.

Also, as the fourth band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'E', when the second WDM signal is input to the fourth band filter <NUM> of the second RN <NUM>-<NUM>, a fourth reflected signal may be generated and transmitted to the COT <NUM> through the second optical cable.

In this case, the controller <NUM> may receive the third and fourth reflected signals, and may not receive the first and second reflected signals. Accordingly, the controller <NUM> may determine that the second RN <NUM>-<NUM> is normally connected and the first RN <NUM>-<NUM> does not exist.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'W' of the first RN <NUM>-<NUM> and the direction 'W' of the COT <NUM> is connected to the direction 'E' of the second RN <NUM>-<NUM> is illustrated (CASE <NUM>). In this case, the COT <NUM> and the first RN <NUM>-<NUM> may be connected to each other through a first optical cable, the COT <NUM> and the second RN <NUM>-<NUM> may be connected to each other through a second optical cable, and the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> may be connected to each other through a third optical cable.

As the second band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'E', when the first WDM signal is input to the second band filter <NUM> of the first RN <NUM>-<NUM>, no reflected signal is generated. In a case of the second wavelength filter <NUM>-<NUM> at the rear end of the second band filter <NUM>, only a second optical signal may be filtered, so that a first or third optical signal of the first WDM signal cannot be filtered. Accordingly, no reflected signal is generated.

Meanwhile, as the first band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'W', when the second WDM signal is input to the first band filter <NUM> of the first RN <NUM>-<NUM>, a second reflected signal may be generated by the first wavelength filter <NUM>-<NUM> at the rear end of the first band filter <NUM> and the first signal reflector <NUM>-<NUM>. This is because the first wavelength filter <NUM>-<NUM> may selectively filter the first or second optical signal. The generated second reflected signal may be transmitted to the COT <NUM> through the third optical cable, the second RN <NUM>-<NUM>, and the second optical cable.

As described with reference to <FIG>, as the third band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'W' and the fourth band filter <NUM> is connected to the second RN <NUM>-<NUM> in the direction 'E', a third reflected signal and a fourth reflected signal may be generated and transmitted to the COT <NUM>.

Accordingly, the controller <NUM> will not be able to receive only the first reflected signal from among the first to fourth reflected signals. In this case, the controller <NUM> may determine that there is an error in the connection direction of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> is normally connected.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'W' of the second RN <NUM>-<NUM>, and the direction 'W' of the COT <NUM> is connected to the direction 'W' of the first RN <NUM>-<NUM> (CASE <NUM>) is illustrated.

In this case, because only a connection order of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> is changed in the example of <FIG>, the controller <NUM> will not be able to receive only the first reflected signal from among the first to fourth reflected signals. Accordingly, the controller <NUM> may determine that there is an error in the connection direction of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> is normally connected.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'W' of the first RN <NUM>-<NUM> and the direction 'W' of the COT <NUM> is connected to the direction 'E' of the second RN <NUM>-<NUM> is illustrated (CASE <NUM>). In this case, the COT <NUM> and the first RN <NUM>-<NUM> may be connected to each other through a first optical cable, and the COT <NUM> and the second RN <NUM>-<NUM> may be connected to each other through a second optical cable.

As described with reference to <FIG>, as the first band filter <NUM> of the first RN <NUM>-<NUM> is connected to the first RN <NUM>-<NUM> in the direction 'W' and the second band filter <NUM> is connected to the first RN <NUM>-<NUM> in the direction 'E', a first reflected signal and a second reflected signal may be generated and transmitted to the COT <NUM>.

As the third band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'E', when the second WDM signal is input to the third band filter <NUM>, no reflected signal is generated. In a case of the third wavelength filter <NUM>-<NUM> at the rear end of the third band filter <NUM>, only a third optical signal may be filtered, so that a second or fourth optical signal of the second WDM signal cannot be filtered. Accordingly, no reflected signal is generated.

Meanwhile, as the fourth band filter <NUM> of the second RN <NUM>-<NUM> is connected to the second RN <NUM>-<NUM> in the direction 'W', when the first WDM signal is input to the fourth band filter <NUM>, a third reflected signal may be generated by the fourth wavelength filter <NUM>-<NUM> at the rear end of the fourth band filter <NUM> and the fourth signal reflector <NUM>-<NUM>. This is because the fourth wavelength filter <NUM>-<NUM> may selectively filter the third or fourth optical signal. The generated third reflected signal may be transmitted to the COT <NUM> through the third optical cable, the first RN <NUM>-<NUM>, and the first optical cable.

As such, the controller <NUM> cannot receive only the fourth reflected signal from among the first to fourth reflected signals. Accordingly, the controller <NUM> may determine that the first RN <NUM>-<NUM> is normally connected and only the second RN <NUM>-<NUM> has a connection direction error.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'W' of the second RN <NUM>-<NUM>, and the direction 'W' of the COT <NUM> is connected to the direction 'E' of the first RN <NUM>-<NUM> (CASE <NUM>) is illustrated.

In this case, because only a connection order of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> is changed in the example of <FIG>, the controller <NUM> will not be able to receive only the fourth reflected signal from among the first to fourth reflected signals even in this example. Accordingly, the controller <NUM> may determine that the first RN <NUM>-<NUM> is normally connected and only the second RN <NUM>-<NUM> has a connection direction error.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'E' of the first RN <NUM>-<NUM>, and the direction 'W' of the COT <NUM> is connected to the direction 'W' of the second RN <NUM>-<NUM> (CASE <NUM>) is illustrated.

In this example, as in the embodiments described with reference to <FIG> and <FIG>, connection directions of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> are all reversed. Accordingly, the first and fourth reflection signals may not be generated, but only the second and third reflection signals may be generated.

Accordingly, the controller <NUM> may determine that both the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> have a connection direction error.

Referring to <FIG>, a case in which the direction 'E' of the COT <NUM> is connected to the direction 'E' of the second RN <NUM>-<NUM>, and the direction 'W' of the COT <NUM> is connected to the direction 'W' of the first RN <NUM>-<NUM> (CASE <NUM>) is illustrated.

In this case, because only a connection order of the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> is changed in the example of <FIG>, the controller <NUM> will be able to receive only the second and third reflected signals from among the first to fourth reflected signals even in this example. Accordingly, the controller <NUM> may determine that both the first RN <NUM>-<NUM> and the second RN <NUM>-<NUM> have a connection direction error.

A monitoring table in which results for CASE <NUM> to CASE <NUM> described above are arranged in advance (see <FIG>) may be stored in advance in a storage space (not shown) provided in the controller <NUM>. The controller <NUM> may monitor connection states of the RN(s) <NUM>-<NUM> to <NUM>-n connected to the COT <NUM> by comparing the received reflected signal(s) with the monitoring table.

Accordingly, according to the disclosure, connection states between optical communication devices (i.e., the COT <NUM> and the RNs <NUM>-<NUM> to <NUM>-n) may be effectively monitored from a remote location without an administrator's on-site visit.

While the embodiments have been particularly shown and described, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the disclosure as defined by the appended claims.

Claim 1:
An optical communication device (<NUM>) of an optical ring network (<NUM>), the optical communication device (<NUM>) comprising:
a first optical signal-processing unit (<NUM>) configured to output a first optical signal having a first wavelength;
a first multiplexer/demultiplexer, MUX/DEMUX, (<NUM>) configured to output the first optical signal in a first direction, and receiving and outputting a first reflected signal which is a reflected signal of the first optical signal;
a second optical signal-processing unit (<NUM>) configured to output a second optical signal of a second wavelength;
a second MUX/DEMUX (<NUM>) configured to output the second optical signal in a second direction opposite to the first direction, and receiving and outputting a second reflected signal which is a reflected signal of the second optical signal; and
a controller (<NUM>) configured to analyze a connection state of a first remote optical communication device (<NUM>-<NUM>) to which the first and second optical signals are allocated, based on the first and second reflected signals - the first remote optical communication device (<NUM>-<NUM>) is connected to the optical communication device (<NUM>) through the optical ring network (<NUM>),
wherein the first reflected signal is generated by the first remote optical communication device (<NUM>-<NUM>) only when the first optical signal is received in a preset direction from among the first and second directions, and
wherein the second reflected signal is generated by the first remote optical communication device (<NUM>-<NUM>) only when the second optical signal is received in another preset direction from among the first and second directions.