JP2003069455A - Transmission line switching method in optical transmission network - Google Patents

Abstract

(57) [Problem] To provide a transmission line switching method in an optical transmission network in which nodes having optical amplifiers are connected by working and protection transmission lines, the signal instantaneous interruption time accompanying the transmission line switching is reduced by a command. Shorten to such a degree that the drop is not recognized. SOLUTION: In an optical transmission network in which nodes N1 to N4 are connected by working and protection transmission lines and each node N1 to N4 includes an optical amplifier A1 to A4, for example, a node N1 is provided. When switching the transmission path between N and N2, the control information of each optical module of the optical amplifier is held for the optical amplifiers A2 to A3 of all the nodes included in the downstream transmission path of the switching section, and the switching is performed. After a transition to the switching mode for operating each optical module based on the held control information later, the transmission path between the nodes N1 and N2 is switched by the optical switches SW1 and SW2. The command for transition to the switching mode is transferred using the optical supervisory channel (OSC).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission path switching method in an optical transmission network in which nodes having optical amplifiers are connected by a transmission path of a working system and a protection system, and more particularly, broadcasting by wavelength division multiplexing (WDM). TECHNICAL FIELD The present invention relates to a transmission path switching method for a network that transmits digital moving image data for use.

[0002]

2. Description of the Related Art FIG. 7 shows an example of the configuration of an optical transmission network having redundant optical transmission lines. As shown in the figure, in the optical transmission network, the transmission side terminal station node 7-1 and the reception side terminal station node 7-2 are connected via several relay nodes 7-3, and the respective nodes are connected to each other. They are connected by a redundant system transmission line composed of an active system optical transmission line 7-4 and a standby system optical transmission line 7-5.

A multiplexer 7-1 for wavelength-multiplexing and synthesizing a plurality of optical signals having different wavelengths is provided in the transmission side terminal station node 7-1.
1, a transmission optical amplifier 7-12 that collectively amplifies the combined optical signal, and an optical switch 7- that outputs the optical signal to either the working system or the standby system of the transmission path to the next node. 1
3 is provided.

In the relay node 7-3, an optical switch 7-31 for inputting an optical signal from the transmission path of the working system or the protection system
A relay optical amplifier 7-32 for amplifying the optical signal, and an optical switch 7-33 for outputting the optical signal to either the working system or the standby system of the optical transmission line to the next node.

An optical switch 7- for inputting an optical signal from the transmission path of the working system or the protection system into the terminal node 7-2 on the receiving side.
21 and a receiving optical amplifier 7-22 for amplifying the optical signal,
And a demultiplexer 7-23 for demultiplexing the wavelength-division-multiplexed optical signal into optical signals of respective wavelengths.

In the redundant optical transmission network as shown in FIG. 7, when the transmission path is switched in a certain span (transmission section between nodes), an instantaneous interruption of the optical signal occurs due to the switching operation of the optical switch. . At this time, the optical amplifier of the node on the downstream side path from this switching section detects the disconnection of the optical signal, and temporarily turns off the optical modules such as the pump laser, the variable optical attenuator, and the temperature adjustment element in the optical amplifier. Shut down.

After the completion of the switching of the optical switch, the optical amplifier detects the recovery of the input of the optical signal and starts the restarting operation control. However, it takes a lot of time to set the operation of each optical module. It takes several seconds for each optical amplifier stage to return the output optical signal level to the operating state before system switching.

FIG. 8 shows how the optical signal level rises according to the conventional system switching method. As shown in (a) of the figure, when the active system transmission line of a certain span is switched from the active system to the standby system transmission line by the optical switch 8-1, the node on the downstream side of the switching section is in operation. The optical signal level at the input point (point A) to the optical amplifier 8-3, in which the transmission lines of the system and the standby system are coupled to the optical coupler 8-2, has a switching time Ts as shown in (b) of FIG. A momentary interruption corresponding to the switching timing occurs.

The optical amplifier 8-3 is shut down by the detection of the optical signal input disconnection due to the switching of the optical switch 8-1, and even if the optical signal input level rises after the elapse of the switching time Ts, an optical module such as a pump laser or the like. Since the output level starts to recover after performing the setting control of (1), the output point (point B) of the optical amplifier 8-3 as shown in (c) of FIG.
It took a long time for the optical signal level to recover.

[0010]

As described above, in the optical transmission network having the transmission lines of the working system and the protection system, it takes a long time for the output level of the optical amplifier to be recovered when the transmission lines are switched. For this reason, if the transmission path is switched while transmitting digital moving image data for broadcasting or the like, a video failure such as frame drop occurs. A first object of the present invention is to shorten the signal interruption time associated with transmission path switching to the extent that dropped frames are not recognized (on the order of milliseconds).

It is desirable that the transmission line be switched as quickly as possible. However, if the transmission line is immediately switched to recover the optical input while the energy accumulated in the optical amplifier remains, the optical amplifier will recover. Light surge will occur. This optical surge is amplified and increased as it progresses to the amplifier in the subsequent stage, which causes a failure in the optical amplifier in the subsequent stage such as the receiving side terminal node.

A second object of the present invention is to suppress the optical surge caused by the energy stored in the amplification medium of the optical amplifier at the time of switching the transmission line and prevent the failure of the optical amplifier. Furthermore, after switching the transmission line, A third object is to prevent continuation of an optical signal abnormality due to a defective transmission path at the switching destination.

[0013]

The transmission line switching method in an optical transmission network according to the present invention comprises: (1) an optical amplifier that amplifies an optical signal to each node by connecting the nodes with a working transmission line and a protection transmission line. In the equipped optical transmission network,
When switching the transmission path between the nodes, hold the control information of each optical module of the optical amplifier with respect to the optical amplifiers of all the nodes included in the downstream transmission path of the switching section,
After the switching, the transmission mode of the switching section is switched after switching to a switching mode for operating each optical module based on the held control information.

(2) Optical switches are provided at both transmitting and receiving ends of the transmission line between the nodes, the switching timing of the optical switches at the transmitting and receiving ends is controlled, and the optical amplifier of the downstream side transmission route accompanying the switching of the transmission line is transmitted to the optical amplifier. It is characterized in that the transmission timing is switched by adjusting the switching timing so that the optical input signal disconnection time is a time in which the energy accumulated in the optical amplification medium of the optical amplifier is sufficiently released.

Further, (3) after switching the transmission line between the nodes, when an input light level abnormality in a downstream node of the switching section is continuously detected for a predetermined time, before switching the transmission line in the switching section. It is characterized by switching back.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A transmission line switching method for shortening a signal interruption time according to the present invention includes a method for switching all optical signals included in a switching section from a downstream relay node to a receiving terminal station node before switching a transmission line. The amplifier (that is, all the optical amplifiers affected by the switching of the transmission line) is switched to a special operation mode (hereinafter referred to as a switching mode).

The switching mode referred to here is a mode in which the output light level of the optical amplifier rises immediately when the input light to the optical amplifier recovers, and the pump laser of the optical amplifier before switching, the variable optical attenuator, By holding the control information of each optical module such as the temperature adjustment element and operating each optical module based on the held control information after switching, the output light level of the optical amplifier rises instantly and the signal interruption time Can be significantly reduced.

A command for switching all the optical amplifiers included in the relay node on the downstream side of the transmission path switching section to the receiving side terminal node to the switching mode and a command for switching the transmission path are the optical supervisory channel (OSC: Optical Supervisory). Ch
annel) or DCN (Data Communication Network)
It is possible to notify by using a data communication network for remote monitoring control such as.

The optical supervisory channel (OSC) is a channel used for exchanging supervisory control information between nodes, and is a channel that is wavelength division multiplexed on a transmission line by using a wavelength different from that for transmitting user information. Is. Further, when a data communication network (DCN) composed of a LAN (Local Area Network) or the like capable of accessing each communication node from a remote monitoring control terminal is constructed, this communication network is used. A command for switching mode can be notified.

FIG. 1 shows an embodiment of the present invention in which a transition to a switching mode is notified by an optical supervisory channel (OSC).
This embodiment shows an example in a wavelength division multiplexing transmission network composed of four nodes (3 spans), and each node exchanges supervisory control information with an adjacent node by an optical supervisory channel (OSC).

The terminal nodes (nodes N1 and N4) have a pair of transmission / reception optical monitoring channels (OSC), and the relay nodes (nodes N2, N3) have transmission / reception two pairs of optical monitoring channels (OSC). . Further, optical switches (SW1, SW2) are provided at both ends of transmission and reception of the transmission path. When the working transmission line of the span S1 between the node N1 and the node N2 is switched to the protection transmission line, it is switched according to the following procedure.

(1) Switching span S from control terminal CNT
A transmission line switching command is issued to the downstream node N2 of No. 1. The node N2 shifts each optical module of the optical amplifier A2 to the switching mode, and then, the optical supervisory channel (OS
C) is used to transmit the switching mode request signal to the node N3 at the subsequent stage. (2) The node N3 transfers each switching module request signal to the node N4 using the optical supervisory channel (OSC) after switching each optical module of the optical amplifier A3 to the switching mode similarly to the node N2. (3) The node N4 (reception terminal station) transitions each optical module of the optical amplifier A4 to the switching mode, and then uses the optical supervisory channel (OSC) to send a switching mode transition completion signal (ACK) to the node N3. Send. (4) The node N3 receives the switching mode transition completion signal (AC
When K) is received, the switching mode transition completion signal (ACK) is transferred to the node N2 using the optical supervisory channel (OSC). (5) The node N2 receives the switching mode transition completion signal (AC
K) is received, the transmission path of the span S1 is switched to the optical switch S.
After switching to the standby system side by W2, a transmission line switching signal is transmitted to the node N1 using the optical supervisory channel (OSC). (6) The node N1 receives the transmission line switching signal from the node N2, and switches the transmission line of the span S1 to the standby system side by the optical switch SW1.

FIG. 2 shows an embodiment of the present invention in which a transition to the switching mode is notified by the data communication network (DCN). This embodiment also shows an example of a wavelength division multiplex transmission network composed of four nodes (3 spans), and in the wavelength division multiplex transmission network, optical switches (SW1, SW2) are provided at both ends of transmission and reception of a transmission line between each node. .

Each node is notified of the monitor control information from the remote monitor controller RCNT via the data communication network (DCN). When the working transmission line of the span S1 between the node N1 and the node N2 is switched to the protection transmission line, it is switched according to the following procedure.

(1) A switching mode request signal is transmitted from the remote control terminal RCNT to the node N2 via the data communication network (DCN). (2) Upon receiving the switching mode request signal, the node N2 transitions each optical module of the optical amplifier A2 to the switching mode, and then transmits the switching mode transition completion signal to the remote monitoring control terminal RCNT via the data communication network (DCN). Send to. (3) As for the node N3 and the node N4, the above (2)
The optical amplifiers A3 and A4 are transited to the switching mode in the same procedure as. (4) A transmission line switching signal is transmitted from the remote monitoring control terminal RCNT to the node N1. (5) The node N1 switches the transmission path of the span S1 to the standby system side by the optical switch SW1 and then transmits a switching completion signal to the remote monitoring control terminal RCNT via the data communication network (DCN). (6) The remote monitoring control terminal RCNT sends the node N2
A transmission path switching signal is transmitted via a data communication network (DCN). (7) The node N2 connects the transmission path of the span S1 to the optical switch S.
After switching to the standby system side by W2, the data communication network (D
CN) to send a switching completion signal to the remote monitoring control terminal RC
Send to NT.

Next, with reference to FIG. 3, an embodiment of suppressing an optical surge at the time of switching a transmission line according to the present invention will be described. In this embodiment, as shown in FIG. 3A, two optical switches SW1 and SW are provided at both transmitting and receiving ends of a transmission line in a switching section.
2 is provided, and by controlling the switching timing of the two optical switches SW1 and SW2, the light input interruption time accompanying the optical switch switching operation is made variable.

FIG. 3B shows the optical switch SW1 at the transmitting end.
Shows the output light level when the active system is switched to the standby system, and (c) in the figure shows the output light level when the optical switch SW2 at the receiving end is switched from the active system to the standby system. As shown in (b) and (c) of FIG.
By providing a time difference between the switching timing of W1 and the switching timing of the receiving end optical switch SW2 and adjusting the time difference, the optical input of the downstream side optical amplifier 3-1 in the switching section as shown in FIG. Disconnection time (that is, from the switching start point of the transmitting end optical switch SW1 to the receiving end optical switch SW
The time until the switching completion point of 2) is adjustable (variable).

Then, the light input interruption time of the downstream side optical amplifier 3-1 in the switching section is adjusted so that the energy accumulated in the optical amplifying medium is sufficiently discharged, and the energy accumulated in the optical amplifying medium is adjusted. By recovering the optical signal input level of the optical amplifier 3-1 after the emission, it is possible to suppress the occurrence of the optical surge in the optical amplifier in the subsequent stage.

In the embodiment shown in FIG. 3, the transmission end optical switch SW1 is first switched and then the reception end optical switch SW2 is switched to adjust the optical input interruption time. It is also possible to adopt an embodiment in which the receiving end optical switch SW2 is switched and then the transmitting end optical switch SW1 is switched to adjust the optical input interruption time.

FIG. 4 shows a flow of a switching operation example for suppressing an optical surge at the time of switching a transmission line according to the present invention. An example of this operation is the span 1 in the optical transmission network shown in FIG.
This is an operation example in which the transmission path is switched after the downstream side optical amplifier has been switched to the switching mode as described above, and is executed by the following procedure.

The node N2 on the downstream side of the switching section transmits a switching request signal for the optical switch SW1 to the upstream node N1 using the optical supervisory channel (OSC) (step 4-1). Next, the node N1 switches the optical switch SW1 to the backup transmission line side (step 4-2).

Next, the node N2 waits for a fixed time (adjustable time for releasing the energy), and then switches the optical switch SW2 to the backup system transmission line side (step 4-
3). The node N2 transmits a polling signal to the node N1 to notify that the transmission path has been switched to the standby system (step 4-4). The node N1 transmits a response signal to the notification to the node N2 (step 4-5).

Next, with reference to FIG. 5, an embodiment for preventing continuation of an optical signal abnormality after transmission line switching according to the present invention will be described. A transition to the aforementioned switching mode according to the invention,
Furthermore, after adjusting the optical input disconnection time and switching the transmission line to the standby system, the abnormal state continuation time of the input optical level is measured at the downstream side node of the switching section, and the abnormal state continues even after the lapse of a predetermined time. In this case, a switching request signal for switching the transmission path again is transmitted to the opposite node on the upstream side to switch back the transmission path.

The abnormal state of the input optical level after switching the transmission line is detected as shown in FIG. 5A when the input optical signal level of the optical amplifier 5-1 at the downstream side node of the switching section is not restored. Alternatively, as shown in (b) of the same figure, it can be determined by detecting that the input optical level of the optical supervisory channel (OSC) in the downstream node of the switching section is not restored. By switching back the transmission line, it is possible to prevent the continuation of the signal failure state after the transmission line is switched.

FIG. 6 shows a flow chart of an example of the switchback operation when the abnormal state continues after the transmission line switching according to the present invention. In this operation example, in the span between the node N1 and the node N2,
After switching the optical amplifier to the switching mode as described above, and further adjusting the optical input interruption time to switch the transmission path from the working system to the protection system (step 6-1), the receiving side node N2 in the switching section. In the above step, if a predetermined time elapses without recovering the input level of the optical amplifier or the optical supervisory channel (OSC), the optical switch SW2 is switched back (step 6-
2) Send a request for switching the optical switch SW1 to the node N1 using the optical supervisory channel (OSC) line (step 6-3).

Upon receiving the switching request, the node N1 switches back the optical switch SW1 (step 6-4) and transmits a switching notice to the node N2 using the optical supervisory channel (OSC) line (step 6). -5). Upon receiving the switching notification, the node N2 transmits a switchback completion notification to the monitoring control terminal (step 6-6).

(Supplementary Note 1) When switching transmission lines between nodes in an optical transmission network including an optical amplifier for amplifying an optical signal in each node by connecting the active transmission line and the protection transmission line between the nodes Control information of each optical module of the optical amplifier is held for the optical amplifiers of all nodes included in the downstream transmission path of the section, and each optical module is operated based on the held control information after switching. A transmission line switching method, characterized in that after switching to a switching mode, the transmission lines in the switching section are switched. (Additional remark 2) The transition of the switching mode to the optical amplifier of each node and the switching of the transmission path are performed by the transfer of the command using the optical management channel in the optical transmission network. Transmission line switching method. (Supplementary Note 3) The transition of the switching mode to the optical amplifier of each node and the switching of the transmission path are performed by using a data communication network different from the optical transmission network according to an instruction from a remote monitoring control device. The transmission line switching method according to appendix 1. (Supplementary Note 4) Optical switches are provided at both transmission and reception ends of the transmission line between the nodes, switching timings of the optical switches at the transmission and reception ends are controlled, and an optical input signal interruption to an optical amplifier of a downstream side transmission route due to transmission line switching 4. The transmission path is switched by adjusting the switching timing so that the time is a time at which the energy stored in the optical amplification medium of the optical amplifier is sufficiently released. Transmission line switching method. (Supplementary Note 5) After switching the transmission path between the nodes, when an input optical level abnormality in a downstream node of the switching section is continuously detected for a predetermined time, the transmission path of the switching section is switched back before switching. 5. The transmission path switching method according to any one of appendices 1 to 4, which is characterized.

[0038]

As described above, according to the present invention,
Before switching the redundant transmission line in the optical transmission network, control information of each optical module is held in advance for all the optical amplifiers affected by the input optical level fluctuation due to the switching, and the retained control is performed after switching. By switching to the switching mode that operates each optical module based on the information and then switching the transmission path, the output optical level of the optical amplifier can be raised in a short time. It is possible to greatly reduce the disconnection time.

Further, in an optical transmission network having optical switches at both ends of the transmission line, when switching the transmission lines, the switching timing of the optical switches at both ends of the transmission line is shifted, and the light input to the optical amplifier on the downstream side of the transmission line is shifted. By adjusting the timing at which the signal level recovers to be approximately the same as the emission time of the energy accumulated in the optical amplification medium of the optical amplifier, it is possible to suppress the occurrence of an optical surge in the optical amplifier.

After switching the transmission lines, if it is detected that the optical amplifier input or the optical supervisory channel (OSC) input does not recover to the normal level even after a certain time elapses at the receiving side node of the switching span, the original transmission line is restored. By switching back, it is possible to prevent continuation of a signal defect after switching the transmission path.

Since the optical amplifier has already transitioned to the switching mode in this switchback, the output light level of the optical amplifier can be raised in a short time, and the optical switches at both ends of the transmission line can be turned on. By adjusting the switching timing of, it is possible to suppress the occurrence of optical surge and switch back.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention in which a transition to a switching mode is notified by an optical supervisory channel (OSC).

FIG. 2 is a diagram showing an embodiment of the present invention in which a transition to a switching mode is notified by a data communication network (DCN).

FIG. 3 is an explanatory diagram of an embodiment of suppressing an optical surge at the time of switching a transmission line according to the present invention.

FIG. 4 is a diagram showing a flow of a switching operation example of suppressing an optical surge at the time of switching a transmission line according to the present invention.

FIG. 5 is an explanatory diagram of an embodiment for preventing continuation of an optical signal abnormality after switching a transmission line according to the present invention.

FIG. 6 is a diagram showing a flow of an example of a switchback operation when an abnormal state continues after switching a transmission line according to the present invention.

FIG. 7 is a diagram showing a configuration example of an optical transmission network having a redundant optical transmission line.

FIG. 8 is a diagram showing how an optical signal level rises according to a conventional system switching method.

[Explanation of symbols]

N1, N2, N3, N4 nodes S1, S2, S3 span (transmission section between nodes) SW1, SW2 Optical switch OSC optical monitoring channel CNT control terminal

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichi Tsuchiya             2-3-9 Shin-Yokohama, Kohoku-ku, Yokohama-shi, Kanagawa             Issue Fujitsu Digital Technology Stock Association             In-house (72) Inventor Makoto Takakuwa             4-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa             No. 1 within Fujitsu Limited (72) Inventor Akio Morimoto             4-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa             No. 1 within Fujitsu Limited (72) Inventor Toru Matsumoto             4-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa             No. 1 within Fujitsu Limited (72) Inventor Takeo Kato             4-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa             No. 1 within Fujitsu Limited (72) Inventor Atsushi Sudo             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Akihide Sano             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Takeo Tode             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Yoshinori Koike             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Kazuhiro Oda             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 5K002 AA01 AA03 AA06 BA06 CA13                       DA02 DA05 EA03 EA33 FA01                       GA01                 5K014 AA01 CA06 HA10                 5K021 AA04 BB01 CC01 CC03 CC08                       CC11 DD02 FF04 FF11

Claims (3)

[Claims] 1. In an optical transmission network having an optical amplifier that amplifies an optical signal in each node by connecting the nodes with a working transmission line and a protection transmission line, the switching section when switching the transmission line between nodes. For the optical amplifiers of all the nodes included in the downstream transmission path of, hold the control information of each optical module of the optical amplifier,
A transmission line switching method, characterized in that after switching, a transition is made to a switching mode for operating each optical module based on the held control information, and then the transmission line in the switching section is switched. 2. An optical input signal to an optical amplifier on a downstream transmission path, which is provided with optical switches at both transmission and reception ends of a transmission path between the nodes, controls switching timing of the optical switches at both transmission and reception ends, 2. The transmission path switching according to claim 1, wherein the switching timing is adjusted to switch the transmission path so that the disconnection time is a time when the energy accumulated in the optical amplification medium of the optical amplifier is sufficiently released. Method. 3. After switching the transmission path between the nodes, when an input optical level abnormality in a downstream node of the switching section is continuously detected for a predetermined time, the transmission path in the switching section is switched back before switching. The transmission line switching method according to claim 1 or 2.