Transponder and optical transmission apparatus

A transponder among a plurality of transponders that are connected with a client device via a plurality of optical couplers, the transponder includes a protection timer configured to be activated when an alarm indication signal transmitted from the client device is received, and a controller configured to control transmission of an optical signal to one of the plurality of optical couplers when the protection timer times out, wherein a timeout value of the protection timer is set to a value different from a timeout value of a protection timer included in another transponder.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2013-056678, filed on Mar. 19, 2013, the entire contents of which are incorporated herein by reference.

FIELD

An embodiment discussed herein is related to a transponder and an optical transmission apparatus, for example, to a technology that is applicable to the optical transmission apparatuses having a redundant configuration using an optical coupler.

BACKGROUND

Wavelength division multiplexing (WDM) apparatuses have been used when constructing a backbone network with the significant increases in the capacity of networks.

In a WDM apparatus, a redundant configuration designed to increase reliability is employed for a network (see, for example, Japanese Laid-open Patent Publication Nos. 2001-77783 and 2004-96514). In order to select a redundant line (for example, an EAST line/WEST line), a switch (SW) unit having a switching function is used in the WDM apparatus. However, for the purpose of, for example, enhancing the efficiency of the WDM apparatus in terms of the number of lines it contains, the redundant configuration is sometimes implemented by using an optical coupler for connection with a subscriber (client) device, in place of mounting the SW unit in the WDM apparatus.

SUMMARY

According to an aspect of the invention, a transponder among a plurality of transponders that are connected with a client device via a plurality of optical couplers, the transponder includes a protection timer configured to be activated when an alarm indication signal transmitted from the client device is received, and a controller configured to control transmission of an optical signal to one of the plurality of optical couplers when the protection timer times out, wherein a timeout value of the protection timer is set to a value different from a timeout value of a protection timer included in another transponder.

DESCRIPTION OF EMBODIMENTS

A WDM apparatus having a redundant configuration using an optical coupler transmits an alarm signal to a client device when the WDM apparatus detects a failure having occurred in a client line. An example of the alarm signal is an alarm indication signal (AIS) or loss of signal (LOS).

When the client device receives the alarm signal, the client device transmits a remote defect indication (RDI), which is an example of an AIS, to the WDM apparatus. The RDI signal is split into two toward both of an East line and a West line by the optical coupler and received by transponders that are included in the WDM apparatus and respectively correspond to the East and West lines.

In this case, not switching performed by the client device but rather switching between transmission signals of the respective transponders has to be performed. However, switching control between optical transmission lines connected with the optical coupler, with which a two to one connection is made, is performed by using pieces of information from two different devices, that is, information on an optical transmission line failure detected by the client device and information on an output state of light subjected to switching control performed by the WDM apparatus. Thus, the switching control has been manually performed by using a device operation.

Embodiments of a transponder capable of performing, without using a device operation, switching control between optical lines that form a redundant configuration will be described below with reference to the drawings. Note that the embodiments to be described below are merely examples and it is not intended that application of various modifications or techniques that are not disclosed below be excluded. In the drawings used in the following embodiments, parts denoted by the same reference numerals are the same or similar parts, unless otherwise noted.

FIG. 1is a block diagram illustrating an example of an optical network (ring network) having a redundant configuration using WDM apparatuses. Each WDM apparatus is an example of an optical transmission apparatus. The optical network illustrated inFIG. 1includes, for example, subscriber (client) devices100and106, optical couplers101a,101b,105a, and105b, WDM apparatuses102and104, and relay nodes103aand103b.

The ring network has an East line and a West line. InFIG. 1, the East line is a transmission path that runs through the relay node103aand the West line is a transmission path that runs through the relay node103b.

The client device100is connected to the WDM apparatus102via the optical couplers101aand101b. Similarly, the client device106is connected to the WDM apparatus104via the optical couplers105aand105b.

A optical signal transmitted by the client device100(or106) is split into two by the optical coupler101a(or105a) and transmitted to the relay nodes103aand103bthrough transponders107aand107bthat are included in the WDM apparatus102(or104) and respectively correspond to the East line and the West line.

The optical signals of the East line and the West line that have been transmitted through the relay nodes103aand103bare received by the opposite WDM apparatus104(or102). The WDM apparatus104(or102) receives, from the relay nodes103aand103bof the East line and the West line, with the transponders107aand107brespectively corresponding to the East line and the West line, optical signals that are the same as the optical signals obtained by the optical coupler101a(or105a) splitting the optical signal into two.

The optical signals received by the transponders107aand107bare combined by the optical coupler105b(or101b) and transmitted to the client device106(or100).

In this way, in the ring network illustrated inFIG. 1, an optical signal transmitted from the client device100(or106) is split into two by the optical coupler101a(or105a) and transmitted to the opposite WDM apparatus104(or102) through the East line and the West line. Subsequently, optical signals of the East line and the West line are combined by the optical coupler105b(or101b) and received by the opposite client device106(or100).

InFIG. 1, the reference numerals108aand108brespectively denote multiplexing/demultiplexing (MUX/DMUX) units corresponding to the East line and the West line. The reference numerals109aand109brespectively denote optical amplifiers corresponding to the East line and the West line.

Next,FIG. 2illustrates an example of the configuration of the transponders107aand107bdescribed above. The transponders107aand107billustrated inFIG. 2each include, for example, an optical-to-electrical conversion unit (O/E)201, an SDH processor202, a DW (OTU) processor203, and an electrical-to-optical conversion unit (E/O)204, which serve as a transmission system toward the relay node103a(or103b) (a reception system from the client device100(or106)) as an example.

In addition, the transponders107aand107beach include, for example, an optical-to-electrical conversion unit (O/E)211, a DW (OTU) processor212, an SDH processor213, and an electrical-to-optical conversion unit (E/O)214, which serve as a reception system from the relay node103a(or103b) (a transmission system toward the client device100(or106)) as an example.

Furthermore, the transponders107aand107beach include, for example, an RDI detector221, a T1 timer222for protecting optical transmission, a T2 timer223for waiting for recovery from an RDI state, and an optical transmission controller224, which serve as a control system as an example.

The O/E201converts an optical signal input from the optical coupler101a(105a) into an electrical signal.

The SDH processor202converts the signal (client signal) which has been converted into the electrical signal by the O/E201into a frame format of a synchronous digital signal for a synchronous digital hierarchy (SDH) or synchronous optical network (SONET). That is, the client signal is mapped into a payload of an SDH or SONET frame.

The DW (OTU) processor203converts, by using a digital wrapper (DW) technique, the synchronous digital signal (frame signal for the SDH or SONET) obtained by the SDH processor202into a frame format for an optical channel transport unit (OTU). That is, the synchronous digital signal is wrapped by the OTU and transmitted.

The E/O204converts the electrical signal of the OTU frame obtained by the DW (OTU) processor203into an optical signal and transmits the optical signal to a network (the relay node103aor103b).

The O/E211converts an optical signal received from the network into an electrical signal.

The DW (OTU) processor212extracts, from an OTU frame of the electrical signal received from the O/E211, a frame signal (SDH or SONET frame) mapped in the OTU frame.

The SDH processor213terminates the frame signal obtained by the DW (OTU) processor212and extracts a client signal mapped in the frame signal.

The E/O214converts the client signal obtained by the SDH processor213into an optical signal and transmits the optical signal to the client device100(or106) (the optical coupler101b(105b)).

The RDI detector221detects an RDI obtained in format conversion performed by the SDH processor202. That is, when an RDI is transmitted from the client device100(or106) having received an alarm signal, such as a LOS, the RDI detector221detects the RDI.

The T1 timer222is activated when an RDI is detected by the RDI detector221, and measures a first timer period (T1).

The T2 timer223is activated when the T1 timer222ends (times out), and measures a second timer period which is different from the first timer period.

When the T1 timer222times out, the optical transmission controller224controls optical transmission performed by the E/O214, that is, the E/O214for transmitting an optical signal is controlled by the optical transmission controller224. For example, the optical transmission controller224stops optical transmission performed by the E/O214when the E/O214is in a state in which an optical signal is able to be transmitted, and starts optical transmission performed by the E/O214when the E/O214is in an optical transmission stop state that is a state in which the E/O214is controlled to stop transmitting the optical signal. In addition, in the case where an RDI is continuously detected (an RDI is not cancelled) even when the T2 timer223times out, the optical transmission controller224determines that a failure has occurred. At this time, a failure notification may be made to, for example, a network management system (NMS).

FIG. 3illustrates an example of a state transition of the transponder107a(107b) according to the above control performed by the optical transmission controller224.

As illustrated inFIG. 3, when an RDI transmitted from the client device100(or106) is detected (state transition309) while the transponder107aor107bis transmitting light to the client device100(or106) (state303), the T1 timer222is activated (state304).

When cancellation of an RDI is detected (state transition308) while the T1 timer222is running, the optical transmission controller224determines that transmission is normal, and continues a current optical output state of the E/O214(state303).

When cancellation of an RDI is not detected before the T1 timer222times out (state transition310), the optical transmission controller224stops optical output performed by the E/O214, that is, the optical transmission controller224controls the E/O214to not transmit an optical signal. Subsequently, the T2 timer223is activated (state301), resulting in a state of waiting for RDI cancellation due to optical output performed by another system. If the transponder107a(107b) is positioned as its own system, optical output performed by the other system refers to optical output performed by the E/O214of the other transponder107b(107a).

Next, there will be described a state transition made when a system whose optical transmission has been stopped (hereinafter also referred to as an “optical stop system”) performs switching control.

When an RDI is detected (state transition305) in an optical stop state (state301), the T1 timer222is activated (state302). When an RDI is cancelled (state transition306) while the T1 timer222is running, the optical transmission controller224determines that optical output performed by the other system is normal, and continues a current optical output state (optical stop) (state301).

When an RDI is not cancelled before the T1 timer222times out (state transition307), the optical transmission controller224starts optical output performed by the E/O214, that is, the optical transmission controller224controls the E/O214to start transmitting an optical signal (state303). Also, the T2 timer223is activated (state303), resulting in a state of waiting for RDI cancellation due to optical output performed by the other system.

InFIG. 3, T1 denotes a count value of the T1 timer222, T1s denotes a timeout value of the T1 timer222, T2 denotes a count value of the T2 timer223, and T2s denotes a timeout value of the T2 timer223. “T1≦T1s” represents that a state transition does not occur while the T1 timer222has not timed out. Similarly, “T2≦T2s” represents that a state transition does not occur while the T2 timer223has not timed out.

Next,FIGS. 4A and 4Billustrate examples of flowcharts of the above optical transmission control (switching process) performed by the optical transmission controller224.

The reference numeral401denotes a processing flow for an initial setting of the T1 timer222. The initial setting process is performed when the transponder107a(or107b) is activated, and an optical transmission stop process in a redundant system and a T1 timer initial setting are performed.

That is, in an optical transmission stop state that is a state in which an optical signal is not transmitted (operation401-1), the optical transmission controllers224of the transponders107aand107brespectively check whether or not the transponders107aand107bthemselves are configured for an East system (E system) (operation401-2). When the transponder107a(107b) itself is configured for the E system (YES in operation401-2), the optical transmission controller224sets a variable N=2 ms and a variable M=4 ms (operation401-3), initializes the count value T1 of the T1 timer222to 0, and also sets the timeout value T1s of the T1 timer222to N (=2 ms) (operation401-5).

On the other hand, when the transponder107a(107b) itself is configured for a West system (W system) (NO in operation401-2), the optical transmission controller224sets the variables N and M to values different from those in the E system (N=5 ms and M=3 ms) (operation401-4), initializes the count value T1 of the T1 timer222to 0, and also sets the timeout value T1s of the T1 timer222to N (=5 ms).

Next, inFIG. 4A, the reference numeral402denotes a processing flow performed by the T1 timer222. The optical transmission controller224monitors whether or not an RDI is detected by the RDI detector221(a NO route in operation402-1). When an RDI is detected (YES in operation402-1), the optical transmission controller224activates the T1 timer222(operation402-2).

Subsequently, the optical transmission controller224monitors whether or not the T1 timer222has timed out (the relationship of T1>T1s has been satisfied) (operation402-3). When the T1 timer222has not timed out (NO in operation402-3), the count value T1 is updated (operation402-4), and the optical transmission controller224checks whether or not an RDI has been cancelled (operation402-5).

When an RDI has been cancelled (YES in operation402-5), the optical transmission controller224stops the T1 timer222(operation402-6), returns to the operation402-1, and monitors whether or not an RDI is detected. When an RDI has not been cancelled (NO in operation402-5), the optical transmission controller224returns to the operation402-3and monitors whether or not the T1 timer222has timed out (the relationship of T1>T1s has been satisfied).

Next, inFIG. 4A, the reference numeral421denotes an optical output control flow. When the T1 timer222has timed out (T1>T1s: YES in operation402-3), the optical transmission controller224checks whether its own system is an optical output system which is in an optical output state or an optical stop system which is in an optical output stop state (operation421-1).

When its own system is an optical stop system (YES in operation421-1), the optical transmission controller224controls the E/O214so as to start optical output (operation421-2). On the other hand, when its own system is an optical output system (NO in operation421-1), the optical transmission controller224controls the E/O214so as to stop optical output (operation421-3).

Next, inFIG. 4B, the reference numeral411denotes an RDI recovery-waiting processing flow. This process411is executed after the optical output control process421ends. That is, when the optical output control process ends, the T2 timer223is activated (operation4114), and the optical transmission controller224monitors whether or not the T2 timer223has timed out (for example, the relationship of the count value T2>10 ms has been satisfied) (operation411-2).

When the T2 timer223has not timed out (NO in operation411-2), the count value T2 of the T2 timer223is updated (operation411-6), and the optical transmission controller224checks whether or not an RDI has been cancelled (operation411-7).

When an RDI has not been cancelled (NO in operation411-7), the optical transmission controller224returns to the operation411-2and monitors whether or not the T2 timer223has timed out. When an RDI has been cancelled (YES in operation411-7) while the T2 timer223is running, the optical transmission controller224determines that normal communication using an optical output has been performed in either its own system or the other system, and stops the T2 timer223(operation411-8).

On the other hand, when the T2 timer223has timed out (YES in operation411-2), the optical transmission controller224checks whether its own system is an optical output system or an optical stop system (operation411-3). When its own system is an optical output system (YES in operation411-3), the optical transmission controller224determines that a failure has occurred, and makes a failure notification (operation411-4). On the other hand, when its own system is an optical stop system (NO in operation411-3), the optical transmission controller224monitors whether or not an RDI has been cancelled.

Subsequently, the optical transmission controller224monitors whether or not an RDI has been cancelled (NO in operation411-5). When an RDI has been cancelled (YES in operation411-5), the optical transmission controller224stops the T2 timer223(operation411-8).

Next, inFIG. 4B, the reference numeral403denotes a processing flow subsequent to the process performed by the T1 timer222for protecting optical transmission. The processing flow403subsequent to the T1 timer process is executed at a point in time when the T2 timer223is stopped. That is, when the T2 timer223is stopped, the optical transmission controller224checks whether its own system is an optical output system or an optical stop system (operation403-1).

When its own system is an optical output system (YES in operation403-1), the optical transmission controller224checks whether or not a failure notification has been made (operation403-2). When a failure notification has been made (YES in operation403-2), the optical transmission controller224makes a recovery notification (operation403-3).

In addition, the optical transmission controller224resets the count value T1 of the T1 timer222to 0, and also sets the timeout value T1s of the T1 timer222to M (operation403-4). When a failure notification has not been made (NO in operation403-2), the optical transmission controller224does not make a recovery notification, but updates the count value T1 and the timeout value T1s of the T1 timer222(operation403-4).

When its own system is an optical stop system (NO in operation403-1), the optical transmission controller224resets the count value T1 of the T1 timer222to 0, and also sets the timeout value T1s of the T1 timer222to N (operation403-5).

In the above example, two redundant lines are provided; alternatively, even in the case where three or more redundant lines are provided, when the timeout value of the T1 timer222is defined for each line, operations equivalent to those illustrated inFIGS. 4A and 4Bmay be performed.FIGS. 5A and 5Billustrate such an example (the case of three lines). InFIG. 5A, the optical transmission controller224determines which of redundant systems its own system is (operation401-2a), and sets variables M and N corresponding to a determined redundant system (operations401-3a,401-3b, and401-3c). After that, operations equivalent to those illustrated inFIGS. 4A and 4Bare performed.

As described above, the transponders107aand107baccording to the foregoing embodiments each include the T1 timer222that is activated upon detection of a change in the state of an RDI transmitted from the client device100(106), and the optical transmission controller224that performs optical output control upon timeout of the T1 timer222.

This enables switching between transmission lines connected with the optical coupler101a(105a) without another notification device being provided between the client device100(106) and the WDM apparatus102(104), and between the transponders107aand107bof the WDM apparatus102(104). In other words, redundant configuration switching using the optical coupler101a(105a) is able to be performed without a change being made to the client device100(106) and also without control using a device operation being performed.

Additionally, a timeout value is set in the T1 timer222differently depending on an optical transmission state, and thus control may be performed so that both the transponders107aand107bconnected to an input of the optical coupler101a(105a) are not simultaneously put into a state in which an optical signal is able to be transmitted. This control is able to be performed independent of an optical output state of another system forming a redundant configuration. Hence, the fact that optical outputs from the different transponders107aand107bare mixed in the optical coupler101b(105b) may be avoided with a simple mechanism.

Furthermore, the T2 timer223that monitors detection of an RDI for a certain period regardless of an optical output state is provided, and thus it may be determined that a failure has occurred in an optical transmission line or the optical couplers101aand101b(105aand105b).

As illustrated inFIG. 5A, a timeout value is defined differently depending on the number of redundant lines, and thus the embodiment is adaptable to a redundant configuration having three or more lines.

When a WDM line failure occurs, switching of a largest number of contained lines (40 lines in the case of a WDM apparatus for 40 waves) is performed. In this case, switching control is able to be performed on each line individually and independently, and a switching time period depending on the number of contained lines is not increased.