JP7713153B2 - OPTICAL TDM TRANSMISSION DEVICE, SYNCHRONIZATION METHOD, AND SYNCHRONIZATION PROGRAM - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. The lecture abstract and lecture paper (Document No. PN2022-6) will be published on the Institute of Electronics, Information and Communication Engineers' website (https://www.ieice.org/ken/paper/20220610BCka/) on June 3, 2022.

The present invention relates to an optical TDM transmission device, a synchronization method, and a synchronization program.

In order to achieve full-mesh optical connections between multiple communication stations in a transmission network, it is necessary to increase the number of optical paths. Optical time division multiplexing (TDM) is an effective technology for achieving this.

FIG. 19 is an explanatory diagram showing signals used in optical TDM transmission and signals used in a normal transmission network.
A signal 801 is a "continuous signal" in which a single signal occupies a transmission path of the same line and the same wavelength. A continuous signal is an optical signal used in existing link systems.
Signal 802 is a "burst signal" in which multiple signals are divided into fixed time intervals (time slots: TS) on the time axis on the same line and transmission path of the same wavelength. A burst signal is an intermittent optical signal on the time axis, and in TDM transmission, data is superimposed on this burst signal for transmission. Between burst signals, there is a non-signal interval (guard time: GT) where the optical power is almost zero.

In the data transfer method of optical TDM transmission, multiple nodes (transmission devices) connected to the same line send burst signals on the same wavelength with a time difference to avoid collisions between signals. The state in which burst signals can arrive at the destination receiving end without colliding with each other is called a synchronous state.

In optical TDM transmission, burst signal transmitting nodes are timed to achieve a synchronized state in which collisions do not occur between signals. To achieve this, each node must subtract the signal propagation delay time between nodes before transmitting and switching the direction of burst signals. Furthermore, the optical fiber that propagates the signals fluctuates over time in optical distance due to temperature changes. Therefore, to achieve high-precision synchronization for optical TDM transmission, each node must precisely time its signals while taking into account discrepancies in signal propagation delay time caused by fluctuations in optical distance over time.

The most common existing technology for synchronizing signals by considering their propagation delay and propagation delay variation is the optical TDM transmission method of PON (Passive Optical Network), which is widely used in current optical access networks. PON is a form of P2MP (Point to Multi-point) optical access system with a tree structure, in which a master node called OLT (Optical Line Terminal) placed in the telecommunications carrier's building and a node called ONU (Optical Network Unit) placed in each user's home are connected via a transmission path consisting of a passive optical splitter and optical fiber. The OLT measures the RTT (Round Trip Time) between each ONU in advance, calculates the timing when signals from each ONU will not collide, and notifies each ONU of this to synchronize the ONUs, and then the OLT instructs each ONU on the timing of signal transmission.

FIG. 15 is a diagram showing the configuration of a TDM-PON system described in Non-Patent Document 1.
In an optical transmission system, an OLT is connected to each ONU via optical fiber. The optical fiber from the OLT is branched to each ONU via an optical splitter SP. Hereinafter, the flow of signals from the OLT to the ONUs is referred to as "downstream signals," and the flow of signals from the ONUs to the OLT is referred to as "upstream signals."

FIG. 16 is a sequence diagram showing a signal flow in the TDM-PON system of FIG.
The OLT transmits a downstream continuous signal for measuring the RTT to the ONU at time t0. The destination ONU sets the time to t0 when it receives the downstream continuous signal from the OLT (S11). The ONU transmits an upstream burst signal for measuring the RTT at time t1 designated by the OLT. The OLT acquires the time t2 at which it receives the upstream burst signal (S12). The OLT then calculates the RTT between the ONU and the ONU based on the timestamps from t0 to t2.
The OLT notifies the ONU of the timing of transmitting the data signal using the burst light based on the calculated RTT (S13). The ONU transmits the data signal using the burst light based on the notified timing (S14).

FIG. 17 is a diagram showing the configuration of a TDM-PON system in a 1-to-N optical connection (P2MP optical connection) network described in Non-Patent Documents 1 and 2. In FIG.
In this configuration diagram, one OLT is connected to N ONUs (here, N=3). A downstream continuous signal P11 from the OLT to each ONU and a signal P13 in which upstream burst signals P12 from each ONU to the OLT are multiplexed are transmitted between the nodes.
The downstream signal P11 is, for example, the Sync signal (S11) and timing notification signal (S13) used in the RTT measurement in Fig. 16. The upstream signal P12 is, for example, the Sync signal (S12) and data signal (S14) addressed to another ONU in Fig. 16. The OLT achieves synchronization accuracy of about several tens to several hundreds [ns] by measuring the RTT every time each ONU transmits or receives a data signal (S14).

Hiromichi Shinohara, All about Access Networks, Hirofumi Amano (ed.), Ohmsha, Tokyo, 2017. Yuanqiu Luo et al., “Time Synchronization over Ethernet Passive Optical Networks,” IEEE Communications Magazine, October 2012

Let us consider expanding the 1-to-N optical connection (P2MP optical connection) network of FIG. 17 to an N-to-M optical connection (MP2MP optical connection) network.
FIG. 18 is a diagram showing the configuration of a TDM-PON system in an N-to-M optical connection network.
In this configuration diagram, a group of N ONUs (here, N=3) located on the left side of the drawing is the transmitting side of the Metro network, and a group of M ONUs (here, M=3) located on the right side of the drawing is the receiving side of the Metro network. The left and right Metro networks are connected by a Core network, making a direct optical connection. The ONU on the transmitting side is equivalent to the ONU that is the source of the data signal P12. The ONU on the receiving side is equivalent to the ONU that receives the data signal P13.

There is also a data signal P14 transmitted (returned) from the receiving ONU to the transmitting ONU. This data signal P14 traveling from the receiving ONU to the transmitting ONU has the same direction as the downstream signal P11 in FIG. 17 traveling to the transmitting ONU. In existing PON systems, a Sync signal is added to the data signal by electrical processing in the OLT, and the downstream signal is transmitted to each ONU as a continuous signal. However, in an N-to-M optical connection network that does not include electrical termination between nodes, it is not possible to add a Sync signal to the data signal P14 at the OLT equivalent and transmit it as a continuous signal. Therefore, the conventional synchronization method used in existing TDM-PON systems cannot be directly applied to an N-to-M optical connection network.

FIG. 20 is a diagram illustrating a transmission period of TDM transmission.
The time slots are divided into periods T and assigned to each ONU. This period is called the TDM frame length. For example, a first ONU can transmit one data signal in the first period T, and another data signal in the next period T. The GT provided between the time slots serves to absorb signal deviations (synchronization errors).

FIG. 21 is an explanatory diagram of a signal collision of burst signals flowing from left to right.
In the reference numeral 811, a first data signal 811A, a second data signal 811B, and a third data signal 811C are superimposed in order on an optical fiber. Here, due to a large synchronization error between the ONUs, the time slot of the first data signal 811A and the time slot of the second data signal 811B partially overlap, causing a signal collision.
In the diagram 812, a first data signal 812A, a second data signal 812B, and a third data signal 812C are superimposed in order onto the optical fiber. Since the synchronization error between the ONUs is small, the time slots of the data signals do not overlap and can be correctly superimposed.

In other words, as shown by reference numeral 812, it is necessary to suppress the synchronization error between ONUs to an order that can be compensated for by GT.
On the other hand, existing synchronization methods based on RTT measurement have some synchronization errors due to delay fluctuations in signal processing associated with packet processing, making it difficult to dramatically improve the accuracy of synchronization. In addition, since electrical processing is not performed within the network, a separate wavelength is required for downstream signals from the OLT, and as the number of ONUs increases, the load is concentrated on the OLT that synchronizes with each of the multiple ONUs, and RTT measurement is required for each wavelength to achieve high-precision synchronization. In order to achieve high-precision synchronization for optical TDM transmission in an N-to-M optical connection network, it is necessary to establish a timing adjustment method that achieves high-precision synchronization that is not based on RTT measurement.

Therefore, the main objective of the present invention is to avoid collisions between data signals during multiplexing in an optical TDM transmission network with N-to-M optical connections, without measuring the RTT for each node.

In order to solve the above problems, an optical TDM transmission device according to the present invention has the following features.
The present invention relates to an optical TDM transmission system in which a plurality of optical TDM transmission devices transmit data signals in a state where the time slots between nodes are synchronized,
Each of the optical TDM transmission devices is
receiving a timing signal having a physical property different from that of the data signal, and storing a reception time and a reception cycle of the received timing signal as a reception timing of the timing signal;
The data signal transmitted from the transmitter is controlled so as to be superimposed on a time slot determined based on the stored reception timing.

According to the present invention, it is possible to avoid collisions between data signals during multiplexing in a network with N-to-M optical connections without measuring the RTT for each node.

FIG. 1 is a configuration diagram of an optical TDM transmission system in an N-to-M optical connection network according to an embodiment of the present invention. FIG. 2 is a configuration diagram in which the N-to-M optically connected network of FIG. 1 according to the present embodiment is applied to a network having a ring topology. FIG. 2 is an explanatory diagram of a T transmitter according to the present embodiment. FIG. 4 is an explanatory diagram of time slots constituting the burst signal of FIG. 3 according to the present embodiment. FIG. 2 is a configuration diagram of a T transmitter according to the present embodiment. FIG. 2 is a time slot diagram illustrating a method of extracting a timing signal according to the present embodiment. FIG. 7 is an enlarged time slot diagram of a part of FIG. 6 according to the present embodiment. FIG. 2 is a configuration diagram of a node according to the present embodiment. FIG. 9 is a sequence diagram showing the operation of the node in FIG. 8 according to the present embodiment. FIG. 2 is a time slot diagram illustrating a method of extracting a timing signal according to the present embodiment. FIG. 11 is an enlarged time slot diagram of a portion of FIG. 10 according to the present embodiment. FIG. 2 is a configuration diagram of a node according to the present embodiment. FIG. 13 is a sequence diagram showing the operation of the node in FIG. 12 according to the present embodiment. FIG. 13 is a hardware configuration diagram of an optical TDM transmission device (the node in FIG. 8 and the node in FIG. 12) according to the present embodiment. FIG. 1 is a diagram showing the configuration of a TDM-PON system described in Non-Patent Document 1. 16 is a sequence diagram showing a signal flow in the TDM-PON system of FIG. 15. FIG. 1 is a configuration diagram of a TDM-PON system in a 1-to-N optical connection (P2MP optical connection) network described in Non-Patent Documents 1 and 2. FIG. 1 is a diagram illustrating the configuration of a TDM-PON system in an N-to-M optical connection network. 1 is an explanatory diagram showing signals used in optical TDM transmission and signals used in a normal transmission network. FIG. 2 is an explanatory diagram of a transmission period of TDM transmission. FIG. 1 is an explanatory diagram of a signal collision of burst signals flowing from left to right.

Below, one embodiment of the present invention is described in detail with reference to the drawings.

1 is a diagram showing the configuration of an optical TDM transmission system in an N-to-M optical connection network. This TDM transmission system is an example of an optical TDM system in which a plurality of nodes transmit data signals with time slots synchronized between the nodes.
The TDM transmission system of Fig. 1 includes a T (Timing) transmitter 30 instead of the OLT (two-way synchronization processing) that measures the RTT between each ONU on the transmitting side of Fig. 18. The T transmitter 30 transmits a timing signal P15 to each node on the transmitting side using one time slot on the same wavelength as the data signal. Each node on the transmitting side receives the timing signal P15 and stores the reception time and reception cycle of the received timing signal P15 as the reception timing. By each node knowing the reception timing of the timing signal, it is possible to know with high accuracy the time slot on which the data signal is superimposed (one-way synchronization processing).

The T transmitter 30 transmits a timing signal P15, and each node stores the received timing signal P15 as the reception timing. By receiving the timing signal P15 for each wavelength at which multiple nodes transmit data signals, a time slot synchronization state is achieved between the nodes indirectly compensating for the propagation delay time for each wavelength.

Here, in order to allow each node to distinguish between the timing signal P15 and the data signal P12, the T transmitter 30 transmits a timing signal P15 having different physical properties, such as intensity and time slot width, from the data signal P12. The timing signal P15 having different physical properties is a signal exemplified below.
A timing signal P15 whose optical power (intensity) is different from that of the data signal P12
A timing signal P15 whose time slot width (TS width) is different from that of the data signal P12

Each node receives a timing signal P15 having physical properties different from those of the data signal P12, and stores the reception time and reception period of the received timing signal P15 as the reception timing of the timing signal P15.
Furthermore, each node controls so that the data signal P12 transmitted from itself is superimposed on the time slot determined based on the stored reception timing.
Furthermore, even after the reception timing is stored, each node receives the timing signal P15 transmitted to that node, and corrects the stored reception timing based on the received timing signal P15.

This allows each node to extract signals with different physical properties as the timing signal P15. This means that each node can grasp accidental deviations in the timing signal P15 at the physical layer and correct the deviations. Therefore, by having each node detect the timing signal P15 superimposed on the optical path for transmitting and receiving signals at the physical layer, even if the synchronization state of the time slots between nodes is broken for some reason, it is possible to re-establish a highly accurate synchronization state by simply receiving the timing signal P15 again.
In addition, a burst signal P13 in which the timing signal P15 and the data signal P12 are superimposed at the same wavelength flows on the optical path. Each receiving node can extract the desired data signal P13 while discarding the timing signal by referring to the physical properties of the received burst signal P13.

FIG. 2 is a diagram showing a configuration in which the N-to-M optically connected network of FIG. 1 is applied to a network having a ring topology.
In FIG. 1, three nodes are arranged on the left side of the drawing as transmitting nodes, and three nodes are arranged on the right side of the drawing as receiving nodes.
In FIG. 2, four nodes are arranged on the left side of the drawing as transmitting nodes, and five nodes are arranged on the right side of the drawing as receiving nodes.
The T transmitter 30 transmits a timing signal T to the four nodes on the transmitting side. That is, the starting point of the timing signal T is the T transmitter 30 in both Fig. 1 and Fig. 2. The four nodes on the transmitting side superimpose a data signal D on the timing signal T. The five nodes on the receiving side receive the timing signal T and the data signal D.

FIG. 3 is an explanatory diagram of the T transmitter 30.
The T transmitter 30 transmits a timing signal P15 to the node A. The node A receives the timing signal P15 and transmits a data signal transmitted from the node A using the same wavelength as the timing signal P15.
Node B extracts only the timing signal P15 from among the timing signal P15 and the data signal transmitted from node A, and transmits the data signal transmitted from node B using the same wavelength as that of the timing signal P15.
Node C extracts only timing signal P15 from among timing signal P15 and the data signals transmitted from nodes A and B, and transmits the data signal transmitted from node C using the same wavelength as timing signal P15.
As a result, the timing signal P15 and the data signals P12 transmitted from the nodes A, B, and C are multiplexed as a signal P13.

FIG. 4 is an explanatory diagram of the time slots constituting the burst signal P13 of FIG.
Reference numeral 101 denotes a time slot of wavelength λ1 at the time when the T transmitter 30 first transmits a timing signal T. Each node receives the timing signal T. The timing signal T is inserted periodically according to a signal-specific pattern shown by reference numeral 103, and the other time slots are empty slots.
Reference numeral 102 denotes a time slot of wavelength λ1 at the time when a certain node transmits (superimposes) a data signal as a burst signal (burst light) into the empty slot of reference numeral 101.

FIG. 5 is a diagram showing the configuration of the T transmitter 30. As shown in FIG.
The T transmitter 30 includes a clock unit 31, a counter management unit 32, a control unit 33, and a timing signal transmission unit .
The clock unit 31 supplies a clock to the counter management unit 32. Based on the clock from the clock unit 31, the counter management unit 32 counts the time from when a timing signal is transmitted to when the next timing signal is transmitted, as a counter value.
The control unit 33 controls the timing signal transmission unit 34 to transmit a timing signal based on the counter value notified by the counter management unit 32. The timing signal transmission unit 34 transmits the timing signal under the control of the control unit 33.

6 to 9, the processing of timing signals with different optical powers will be described as an example of physical properties different from those of data signals. The processing of timing signals with different optical powers is summarized as follows (Process 1A) to (Process 3A).
(Process 1A) During a preparation period, the T transmitter 30 transmits a timing signal having a power different from that of a data signal to each node, thereby causing each node to store the power threshold of the timing signal.
(Process 2A) During the operation period, the T transmitter 30 transmits the same timing signal as during the preparation period to each node. Each node can distinguish whether the received signal is a data signal or a timing signal by using the stored power threshold as a clue. The reception timing of the received timing signal is used as a reference for the data signal to be transmitted (on which TS it is superimposed).
(Process 3A) During the operation period, each node corrects the reference (reception timing) of the data signal (Process 2A) based on the received timing signal.

FIG. 6 is a time slot diagram illustrating how the timing signals are derived.
Fig. 7 is a time slot diagram showing an enlarged portion of Fig. 6. The painted pattern of each signal is the same as that of reference numeral 103 in Fig. 4.
The T transmitter 30 transmits a timing signal having optical power greater than that of a data signal (longer in the upward direction in the drawing) at every predetermined timing T0.
Each node compares the power of each signal received on the same wavelength with a predetermined power threshold, and regards a signal that exceeds the predetermined power threshold as a new timing signal and a signal that is below the predetermined power threshold as a data signal. Each node then sets a standard (reception timing) for superimposing a data signal based on the new timing signal.

Therefore, it is desirable that each node receives only the timing signal from the T transmitter 30 during a preparation period before transmitting or receiving a data signal, and sets the power (or the average value) of the received timing signal as a predetermined power threshold. Alternatively, each node may directly receive the predetermined power threshold as setting data from an administrator or the like. This threshold setting process during the preparation period can be applied to setting not only the threshold for optical power, but also thresholds for other physical properties such as the threshold for TS width.
Furthermore, during an operation period in which data signals are transmitted and received, each node may modify the criteria for superimposing a data signal when the node receives a new timing signal that exceeds a predetermined power threshold.

Fig. 8 is a configuration diagram of a node 50. The node 50 is, for example, one of three transmitting nodes arranged on the left side of Fig. 1, or one of four transmitting nodes arranged on the left side of Fig. 2.
The node 50 includes a burst optical receiving unit 51, a TIA (trans impedance amplifier) 52, a voltage detection circuit unit 53, a control unit 54, a TS (Time Slot) control unit 55, a counter management unit 56, a clock unit 57, and a burst optical transmitting unit 58.
The burst light receiving unit 51 receives a burst light (burst signal) including a timing signal.
The TIA 52 converts the current value of the burst signal into a voltage value.
The voltage detection circuit unit 53 monitors the waveform level of the converted voltage value and notifies the control unit 54 of a signal that exceeds a predetermined power threshold as a timing signal, and notifies the control unit 54 of a signal that is below the predetermined power threshold as a data signal.

The control unit 54 receives the timing signal of the preparation period and sets a predetermined power threshold calculated from the timing signal in the voltage detection circuit unit 53. Then, the control unit 54 notifies the TS control unit 55 and the counter management unit 56 of the reception timing obtained from the timing signal notified during the operation period. Furthermore, the control unit 54 may receive a new timing signal and correct the reception timing stored up to the previous time.
Based on the reception timing notified by the control unit 54, the TS control unit 55 controls the time slot in which the signal transmitted by the own device is superimposed so as not to collide with other signals.
The counter management section 56 notifies the counter value to the control section 54 and the TS control section 55. The counter value indicates the time from when a timing signal is transmitted until when the next timing signal is transmitted, as described in FIG.
The clock unit 57 supplies a clock to the counter management unit 56 .
The burst light transmitting unit 58 superimposes an arbitrary signal on the TS specified by the TS control unit 55 and transmits the data signal.

FIG. 9 is a sequence diagram showing the operation of the node 50 in FIG.
In the preparation period, the burst light receiving unit 51 receives the burst light and converts it into an electrical signal (O/E conversion: Optical/Electrical conversion) (S111).
The TIA 52 converts the current value of the electrical signal into a voltage value (S121). The voltage detection circuit unit 53 notifies the control unit 54 of the time response of the voltage value (S131).
The control unit 54 grasps the voltage value of the timing signal (S141). The control unit 54 determines a voltage value that is to be a threshold value, and notifies the voltage detection circuit unit 53 of the voltage value (S142).

During the operation period, the burst light receiving unit 51 receives the burst light and converts it into an electrical signal (O/E conversion) (S112).
The TIA 52 converts the current value of the electrical signal into a voltage value (S122).
The voltage detection circuit unit 53 notifies the control unit 54 of a time response (timing signal) of the voltage value exceeding the threshold value (S132).
The control unit 54 notifies the counter management unit 56 of the timing of receiving the timing signal (S143).
The clock unit 57 supplies a clock (S161). The counter management unit 56 starts the counter (S151).

The control unit 54 notifies the TS control unit 55 of the time slot reference (reception timing) (S144).
The counter management section 56 notifies the TS control section 55 of the counter value indicating the time from when a timing signal is received until when the next timing signal is received (S152).
The TS control unit 55 determines a TS (time slot) into which a Data signal is to be superimposed (S171).
The burst light transmitting unit 58 superimposes an arbitrary signal on the TS specified by the TS control unit 55 and transmits the data signal (S181).

The processing of timing signals having different optical powers as an example of physical properties different from those of data signals has been described above with reference to FIGS.
10 to 13, the processing of timing signals with different TS widths will be described as an example of physical properties different from those of data signals. The processing of timing signals with different TS widths is outlined below as (Process 1B) to (Process 3B).
(Process 1B) During the preparation period, the timing transmitter 30 transmits a timing signal having a TS width different from that of the data signal to each node, thereby causing each node to store the TS width of the timing signal.
(Process 2B) During the operation period, the T transmitter 30 transmits the same timing signal as during the preparation period to each node. Each node can distinguish whether the received signal is a data signal or a timing signal by using the stored TS width as a clue. The reception timing of the received timing signal is used as a reference for the data signal to be transmitted (on which TS it is superimposed).
(Process 3B) During the operation period, each node corrects the reference (reception timing) of the data signal (Process 2B) based on the received timing signal.

FIG. 10 is a time slot diagram illustrating how the timing signals are derived.
Fig. 11 is a time slot diagram showing an enlarged portion of Fig. 10. The painted pattern of each signal is the same as that of reference numeral 103 in Fig. 4.
The T transmitter 30 transmits a timing signal having a narrower TS width than the data signal (shorter in the left and right time axis directions in the figure) at every predetermined timing T0. Also, each node superimposes the data signal with a certain guard time (GT) therebetween.
Each node compares the TS width of each signal received on the same wavelength with a predetermined TS width threshold, and regards a signal below the predetermined TS width threshold as a new timing signal and a signal above the predetermined TS width threshold as a data signal. Each node then sets a standard for superimposing a data signal based on the new timing signal.

FIG. 12 is a configuration diagram of the node 50B.
Compared with the node 50 in FIG. 8, the voltage detection circuit unit 53 of the node 50B is replaced with a TS width detection circuit unit 53B.
The TS width detection circuit unit 53B monitors the TS width of the converted voltage value, and notifies the control unit 54 of a signal that falls below a predetermined TS width (pulse width) threshold as a timing signal, and notifies the control unit 54 of a signal that is above the predetermined TS width threshold as a data signal.
The control unit 54 receives the timing signal of the preparation period and sets a predetermined TS width threshold value calculated from the timing signal in the TS width detection circuit unit 53B.
The processing contents of the other processing units are as described with reference to FIG.

FIG. 13 is a sequence diagram showing the operation of the node 50B in FIG.
In the preparation period, the burst light receiving unit 51 receives the burst light and converts it into an electrical signal (O/E conversion: Optical/Electrical conversion) (S211).
The TIA 52 converts the current value of the electrical signal into a voltage value (S221). The clock unit 57 supplies a clock to the TS width detection circuit unit 53B (S261). The TS width detection circuit unit 53B measures the TS width based on the time response of the voltage value, and notifies the control unit 54 of the measurement result (S231).
The control unit 54 grasps the TS width value of the timing signal (S241).The control unit 54 determines the TS width that will be a trigger, and notifies the TS width detection circuit unit 53B (S242).

During the operation period, the burst light receiving unit 51 receives the burst light and converts it into an electrical signal (O/E conversion) (S212).
The TIA 52 converts the current value of the electrical signal into a voltage value (S222).
The TS width detection circuit unit 53B extracts a signal (timing signal) having a width equal to or less than the specified TS width, and notifies the control unit 54 of the timing signal (S232).
The control unit 54 grasps the reception time (reception timing) of the timing signal, and notifies the counter management unit 56 of the reception time (S243).
The clock unit 57 supplies a clock to the counter management unit 56 (S262). The counter management unit 56 starts the counter (S251).

The control unit 54 notifies the TS control unit 55 of the reception timing (S244).
The counter management section 56 notifies the TS control section 55 of the counter value indicating the time from when a timing signal is received until when the next timing signal is received (S252).
The TS control unit 55 determines a TS (time slot) in which the Data signal is to be superimposed (S271).
The burst light transmitting unit 58 superimposes an arbitrary signal on the TS specified by the TS control unit 55 and transmits the data signal (S281).

FIG. 14 is a hardware configuration diagram of an optical TDM transmission device (the node 50 in FIG. 8 and the node 50B in FIG. 12).
The optical TDM transmission device is configured as a computer 900 having a CPU 901, a RAM 902, a ROM 903, a HDD 904, a communication I/F 905, an input/output I/F 906, and a media I/F 907. The T transmitter 30 in FIG.
The communication I/F 905 is connected to an external communication device 915. The input/output I/F 906 is connected to an input/output device 916. The media I/F 907 reads and writes data from a recording medium 917. Furthermore, the CPU 901 controls each unit by executing a program (also called an application or its abbreviation, an app) loaded into the RAM 902. This program can be distributed via a communication line, or can be recorded on a recording medium 917 such as a CD-ROM and distributed.

[effect]
The present invention relates to an optical TDM transmission system in which a plurality of nodes 50 transmit data signals in a state where the time slots between the nodes are synchronized,
Each node 50:
receiving a timing signal having physical properties different from those of the data signal, and storing the reception time and reception cycle of the received timing signal as reception timing of the timing signal;
The present invention is characterized by controlling so that the data signal transmitted from the transmitter itself is superimposed on a time slot grasped based on the stored reception timing.

This allows each node 50 to determine whether the received signal is a data signal or a timing signal by measuring the physical properties of the signal. Therefore, each transmitting node stores the period and reception time of the received timing signal as reception timing, thereby synchronizing with other nodes (one-way synchronization processing).
Therefore, in a network with N to M optical connections, collisions between signals during multiplexing can be avoided without measuring the RTT for each individual node.

The present invention is characterized in that each node 50 receives a timing signal having different physical properties from the data signal, and whose optical power is different from that of the data signal.

This allows each node 50 to quickly determine whether or not a timing signal is present by measuring the power of the physical layer without referring to the signal contents of the timing signal.

The present invention is characterized in that each node 50 receives a timing signal having different physical properties from the data signal and a time slot width different from that of the data signal.

This allows each node 50 to quickly determine whether or not a timing signal is present by measuring the time slot width of the physical layer without referring to the signal contents of the timing signal.

The present invention is characterized in that each node 50 receives a timing signal transmitted to each node 50 even after the reception timing has been stored, and corrects the stored reception timing based on the received timing signal.

This makes it possible to maintain highly accurate time slot synchronization between nodes even in the event of accidental timing signal misalignment by autonomously extracting the timing signal.

30 T transmitter 31 Clock unit 32 Counter management unit 33 Control unit 34 Timing signal transmission unit 50, 50B Node (optical TDM transmission device)
51 Burst optical receiver 52 TIA
53 Voltage detection circuit section 53B TS width detection circuit section 54 Control section 55 TS control section 56 Counter management section 57 Clock section 58 Burst optical transmission section

Claims (6)

In an optical TDM transmission system in which a plurality of optical TDM transmission devices transmit data signals in a state where time slots between nodes are synchronized,
Each of the optical TDM transmission devices is
receiving a timing signal having a physical property different from that of the data signal, and storing a reception time and a reception cycle of the received timing signal as a reception timing of the timing signal;
An optical TDM transmission device, characterized in that the optical TDM transmission device performs control so that the data signal transmitted from the optical TDM transmission device itself is superimposed on a time slot grasped based on the stored reception timing. 2. The optical TDM transmission device according to claim 1, wherein each of the optical TDM transmission devices receives, as the timing signal having the different physical property from the data signal, a timing signal having an optical power different from that of the data signal. 2. The optical TDM transmission device according to claim 1, wherein each of said optical TDM transmission devices receives said timing signal having a time slot width different from that of said data signal as said timing signal having said physical property different from that of said data signal. The optical TDM transmission device according to claim 1, wherein even after the reception timing is stored, each of the optical TDM transmission devices receives the timing signal transmitted to the optical TDM transmission device, and corrects the stored reception timing based on the received timing signal. A synchronization method implemented in an optical TDM transmission system in which a plurality of optical TDM transmission devices transmit data signals in a state in which time slots between nodes are synchronized, comprising the steps of:
Each of the optical TDM transmission devices is
receiving a timing signal having a physical property different from that of the data signal, and storing a reception time and a reception cycle of the received timing signal as a reception timing of the timing signal;
A synchronization method comprising: controlling so that the data signal transmitted from the own station is superimposed on a time slot grasped based on the stored reception timing. A synchronization program for causing a computer to function as an optical TDM transmission device as described in any one of claims 1 to 4.