Optical TDM Transmission Device, Synchronization Method, and Synchronization Program

Abstract

An optical time-division-multiplexing (TDM) transmission system in which a plurality of nodes (50) transmit data signals in a state in which time slots between the nodes are synchronized, wherein each of the nodes (50) receives a timing signal that differs in physical characteristics from the data signals, stores the reception time and reception cycle of the received timing signal as a reception timing of the timing signal, and performs control such that a data signal transmitted from the node itself is superimposed in a time slot that is ascertained with reference to the stored reception timing.

Description

Technical Field

[0001] The present invention relates to an optical TDM transmission device, a synchronization method, and a synchronization program.

Background Art

[0002] In order to perform full-mesh optical connection between a plurality of communication stations in a transmission network, an increase in the number of optical paths is required. As one technique for realizing an increase in the number of optical paths, optical time-division multiplexing (TDM) is effective.

[0003] FIG. 19 is an explanatory diagram showing signals used in optical TDM transmission and signals used in a normal transmission network. Signal 801 is a "continuous signal" in which a single signal occupies a transmission path of the same line and the same wavelength. The continuous signal is an optical signal used in an existing link system. Signal 802 is a "burst signal" in which a plurality of signals are divided by a fixed time width (time slot: TS) divided on the time axis on a transmission path of the same line and the same wavelength. The burst signal is an intermittent optical signal on the time axis, and in TDM transmission, data is superimposed on this burst signal for transmission. There is a signal-free section (guard time: GT) with almost zero optical power between burst signals.

[0004] In the data transfer method of optical TDM transmission, a plurality of nodes (transmission devices) connected to the same line transmit burst signals on the same wavelength with a time difference from each other to avoid signal collisions. A state in which burst signals can reach the destination receiving end without colliding with each other is called a synchronized state.

[0005] In optical TDM transmission, by synchronizing the timing between the transmission nodes of burst signals, a synchronous state where signals do not collide is achieved. For this purpose, it is necessary for each node to transmit and switch the burst signal path after subtracting the signal propagation delay time between the nodes. In addition, the optical fiber that propagates the signal has an optical distance that varies temporally due to temperature changes. Therefore, in order to achieve high-precision synchronization for optical TDM transmission, each node needs to synchronize the timing with high precision while also considering the deviation of the signal propagation delay time caused by the temporal variation of the optical distance.

[0006] As one of the most common existing technologies for synchronization considering signal propagation delay and propagation delay variation, there is the optical TDM transmission method of PON (Passive Optical Network) that is widespread in the current optical access network. In PON, it is a form of a P2MP (Point to Multi-point) type optical access system with a tree structure, in which a master node called an OLT (Optical Line Terminal) placed in the building of the communication carrier and nodes called ONUs (Optical Network Unit) placed in each user's home are connected via a transmission path composed of an optical splitter and an optical fiber, which are passive components. The OLT measures the RTT (Round Trip Time) with each ONU in advance, calculates the timing at which signals from each ONU do not collide, notifies each ONU, and thereby synchronizes between the ONUs. On top of that, the OLT instructs each ONU of the signal transmission timing.

[0007] FIG. 15 is a configuration diagram of a TDM-PON system described in Non-Patent Document 1. In the optical transmission system, the OLT is connected to each ONU by an optical fiber. The optical fiber from the OLT is branched to each ONU via an optical splitter SP. Hereinafter, the signal flow from the OLT to the ONU is referred to as a "downlink signal", and the signal flow from the ONU to the OLT is referred to as an "uplink signal".

[0008] FIG. 16 is a sequence diagram showing the signal flow in the TDM-PON system of FIG. 15. The OLT transmits a downstream continuous signal for RTT measurement to the ONU at time t0. The destination ONU sets the time to t0 at the timing when it receives the downstream continuous signal from the OLT (S11). When the time t1 specified by the OLT arrives, the ONU transmits an upstream burst signal for RTT measurement. The OLT acquires the time t2 when it receives the upstream burst signal (S12). Thereby, the OLT calculates the RTT with the ONU based on the timestamps from time t0 to t2. Based on the calculated RTT, the OLT transmits the transmission timing of the data signal using burst light to the ONU (S13). The ONU transmits the data signal using burst light based on the notified timing (S14).

[0009] FIG. 17 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. In this configuration diagram, one OLT and N ONUs (here N = 3) are connected. A downstream continuous signal P11 from the OLT to each ONU and a signal P13 in which an upstream burst signal P12 from each ONU to the OLT is multiplexed propagate between nodes. The downstream signal P11 is, for example, the Sync (synchronization) signal (S11) and the timing notification signal (S13) used in the RTT measurement of FIG. 16. The upstream signal P12 is, for example, the Sync signal (S12) and the data signal for other ONUs (S14) in FIG. 16. The OLT achieves a synchronization accuracy of about several tens to several hundreds [ns] by measuring the RTT every time each ONU transmits and receives a data signal (S14).

Prior Art Documents

Non-Patent Documents

[0010]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] Consider expanding the above-described one-to-N optical connection (P2MP optical connection) network in FIG. 17 to an N-to-M optical connection (MP2MP optical connection) network. FIG. 18 is a configuration diagram of a TDM-PON system in an N-to-M optical connection network. In this configuration diagram, a set of N ONUs (here N = 3) arranged on the left side of the drawing is regarded as the transmission side of the Metro network, and a set of M ONUs (here M = 3) arranged on the right side of the drawing is regarded as the reception side of the Metro network. Then, the left and right Metro networks are connected by the Core network to form a direct optical connection. Note that the ONU on the transmission side indicates the equivalent of the ONU that is the source of the data signal P12. The ONU on the reception side indicates the equivalent of the ONU that receives the data signal P13.

[0012] There is also a data signal P14 transmitted (returned) from the ONU on the reception side to the ONU on the transmission side. This data signal P14 from the ONU on the reception side to the ONU on the transmission side has the same direction as the downstream signal P11 in FIG. 17 going towards the ONU on the transmission side. In the existing PON system, 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 without electrical termination between nodes, a Sync signal cannot be added to the data signal P14 at the equivalent of the OLT and transmitted as a continuous signal. Therefore, the conventional synchronization method used in the existing TDM-PON system cannot be directly applied to an N-to-M optical connection network.

[0013] FIG. 20 is an explanatory diagram of the transmission cycle of TDM transmission. Time slots are segmented every period T and assigned to each ONU. This period is called the TDM frame length. For example, the 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 time slots serves to absorb signal deviation (synchronization error).

[0014] FIG. 21 is an explanatory diagram of signal collision of a burst signal flowing from left to right. In reference numeral 811, the first data signal 811A, the second data signal 811B, and the third data signal 811C are sequentially superimposed on the optical fiber. Here, due to a large synchronization error between ONUs, the time slots of the first data signal 811A and the second data signal 811B partially overlap, resulting in signal collision. In reference numeral 812, the first data signal 812A, the second data signal 812B, and the third data signal 812C are sequentially superimposed on the optical fiber. Here, since the synchronization error between ONUs is small, the time slots of each data signal can be correctly superimposed without overlapping.

[0015] That is, as shown in reference numeral 812, it is necessary to suppress the synchronization error between ONUs to an order that can be compensated by GT. On the other hand, in the existing synchronization method based on RTT measurement, since synchronization errors due to signal processing delay fluctuations associated with packet processing occur to a certain extent, it is difficult to achieve a dramatic improvement in synchronization accuracy. Also, as long as electrical processing is not performed within the network, a separate wavelength is required for the downstream signal from the OLT, and as the number of ONUs increases, the load concentrates on the OLT that synchronizes with each of the multiple ONUs, and wavelength-by-wavelength RTT measurement is required for high-precision synchronization. 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 realizes high-precision synchronization not based on RTT measurement.

[0016] Therefore, the main problem of the present invention is to avoid collisions between data signals during multiplexing in an N-to-M optical connection optical TDM transmission network without measuring the RTT for each node.

Means for Solving the Problem

[0017] In order to solve the above problem, the optical TDM transmission device of the present invention has the following characteristics. The present invention is 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 receives a timing signal having different physical properties from the data signal, stores the reception time and reception period of the received timing signal as the reception timing of the timing signal, and is characterized in that it controls to superimpose the data signal transmitted from itself on a time slot grasped based on the stored reception timing.

Effect of the Invention

[0018] According to the present invention, it is possible to avoid collisions between data signals during multiplexing without measuring the RTT for each node in an N-to-M optical connection network.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Embodiments for Carrying Out the Invention

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0021] FIG. 1 is a configuration diagram 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 in a state where time slots between the nodes are synchronized. The TDM transmission system in FIG. 1 includes a T (Timing) transmitter 30 instead of an OLT that measures the RTT (two-way synchronization process) with each ONU on the transmission side in FIG. 18. The T transmitter 30 transmits a timing signal P15 to each node on the transmission side using one time slot on the same wavelength as the data signal. Each node on the transmission side receives the timing signal P15 and stores the reception time and reception period of the received timing signal P15 as its own reception timing. By each node grasping the reception timing of the timing signal, it is possible to accurately grasp the time slot for superimposing the data signal (one-way synchronization process).

[0022] The T transmitter 30 transmits the timing signal P15, and each node stores the received timing signal P15 as the reception timing. By a plurality of nodes receiving the timing signal P15 for each wavelength at which the data signal is transmitted, an inter-node time slot synchronization state in which the propagation delay time for each wavelength is indirectly corrected is achieved.

[0023] Here, in order to distinguish the timing signal P15 from the data signal P12 for each node, 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 the signal exemplified below. · A timing signal P15 whose optical power (intensity) is different from the data signal P12 · A timing signal P15 whose time slot width (TS width) is different from the data signal P12

[0024] Then, each node receives a timing signal P15 that is physically different from 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 to superimpose the data signal P12 transmitted from itself on the time slot grasped based on the stored reception timing. Also, even after the reception timing is stored, each node receives the timing signal P15 transmitted to each node, and corrects the stored reception timing based on the received timing signal P15.

[0025] As a result, each node can extract signals with different physical properties by regarding them as the timing signal P15. This means that each node can grasp the accidental deviation of the timing signal P15 at the physical layer and correct the deviation. Therefore, by causing each node to detect the timing signal P15 superimposed on the optical path for signal transmission and reception at the physical layer, even if the synchronization state of the time slots between nodes is interrupted for some reason, it is possible to re-establish a high-precision synchronization state only by receiving the timing signal P15 again. Also, 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.

[0026] FIG. 2 is a configuration diagram when the N-to-M optical connection 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 the transmission side, and three nodes are arranged on the right side of the drawing as the reception side. In FIG. 2, four nodes are arranged on the left side of the drawing as the transmission side, and five nodes are arranged on the right side of the drawing as the reception side. The T transmitter 30 transmits the timing signal T to the four nodes on the transmission 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 transmission side superimpose the data signal D on the timing signal T. The five nodes on the reception side receive the timing signal T and the data signal D.

[0027] FIG. 3 is an explanatory diagram of the T transmitter 30. The T transmitter 30 transmits the timing signal P15 to node A. Node A receives the timing signal P15 and transmits the data signal transmitted from 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 the timing signal P15. Node C extracts only the timing signal P15 from among the 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 the timing signal P15. As a result, the timing signal P15 and the data signals P12 transmitted from each of nodes A, B, and C are multiplexed as the signal P13.

[0028] FIG. 4 is an explanatory diagram of the time slots constituting the burst signal P13 in FIG. 3. Reference numeral 101 is a time slot of wavelength λ1 at the time when the T transmitter 30 first transmits the timing signal T. Each node receives the timing signal T. The timing signal T is periodically inserted according to the pattern for each signal shown by reference numeral 103, and the other time slots are empty slots. Reference numeral 102 is a time slot of wavelength λ1 at the time when a certain one node transmits (superimposes) a data signal as a burst signal (burst light) on the empty slot of reference numeral 101.

[0029] FIG. 5 is a configuration diagram of the T transmitter 30. The T transmitter 30 includes a clock unit 31, a counter management unit 32, a control unit 33, and a timing signal transmission unit 34. The clock unit 31 supplies a clock to the counter management unit 32. The counter management unit 32 counts, as a counter value, the time from when it transmits a timing signal to when it transmits the next timing signal, based on the clock from the clock unit 31. The control unit 33 controls the timing signal transmission unit 34 to transmit a timing signal based on the counter value notified from the counter management unit 32. The timing signal transmission unit 34 transmits a timing signal in accordance with the control of the control unit 33.

[0030] Hereinafter, with reference to FIGS. 6 to 9, as an example of physical properties different from those of the data signal, the processing of timing signals with different light powers will be described. The outline of the processing of timing signals with different powers is as follows in (Processing 1A) to (Processing 3A). (Processing 1A) As a preparation period, the T transmitter 30 transmits a timing signal with a power different from that of the data signal to each node, so that each node stores the power threshold value of the timing signal. (Processing 2A) As an operation period, the T transmitter 30 transmits the same timing signal as in the preparation period to each node. Each node can distinguish whether the received signal is a data signal or a timing signal, using the stored power threshold value as a clue. The reception timing of the received timing signal is used as a reference (which TS to superimpose on) for the data signal to be transmitted hereafter. (Processing 3A) As an operation period, each node corrects the reference (reception timing) of the data signal in (Processing 2A) based on the received timing signal.

[0031] FIG. 6 is a time-series time slot diagram showing a method for extracting a timing signal. FIG. 7 is an enlarged time slot diagram of a part of FIG. 6. The coloring pattern of each signal is the same as that of reference numeral 103 in FIG. 4. The T transmitter 30 transmits a timing signal whose light power is greater than that of the data signal (longer upward in the drawing) at a predetermined timing T0. Each node compares the power of each signal received on the same wavelength with a predetermined power threshold, regards a signal exceeding the predetermined power threshold as a new timing signal, and regards a signal below the predetermined power threshold as a data signal. Then, each node sets a reference (reception timing) for superimposing the data signal based on the new timing signal.

[0032] Therefore, during the preparation period before transmitting and receiving the data signal, it is desirable for each node to receive only the timing signal from the T transmitter 30 and set the power (such as the average value) of the received timing signal as the predetermined power threshold. Alternatively, each node may directly receive an input from an administrator or the like with the predetermined power threshold as setting data. This threshold setting process during the preparation period can also be applied to the setting of thresholds for other physical properties such as the threshold of the TS width in addition to the threshold of the optical power. Also, during the operation period of transmitting and receiving the data signal, when each node receives a new timing signal exceeding the predetermined power threshold, it may correct the reference for superimposing the data signal.

[0033] FIG. 8 is a configuration diagram of the node 50. This node 50 is, for example, three transmission-side nodes arranged on the left side of FIG. 1 and four transmission-side nodes arranged on the left side of FIG. 2. The node 50 includes a burst optical reception 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 transmission unit 58. The burst optical reception unit 51 receives 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, notifies the control unit 54 of a signal exceeding the predetermined power threshold as a timing signal, and notifies the control unit 54 of a signal below the predetermined power threshold as a data signal.

[0034] Upon receiving the timing signal during the preparation period, the control unit 54 sets a predetermined power threshold calculated from the timing signal in the voltage detection circuit unit 53. Then, the control unit 54 notifies the reception timing obtained from the timing signal notified during the operation period to the TS control unit 55 and the counter management unit 56. Further, the control unit 54 may receive a new timing signal and correct the reception timing memorized until the previous time. Based on the reception timing notified from the control unit 54, the TS control unit 55 controls the time slot for superimposing the signal transmitted by its own device so as not to collide with other signals. The counter management unit 56 notifies the counter value to the control unit 54 and the TS control unit 55. As described with reference to FIG. 5, the counter value indicates the time from transmitting a timing signal to transmitting the next timing signal. The clock unit 57 supplies a clock to the counter management unit 56. The burst optical transmission unit 58 superimposes an arbitrary signal on the TS designated by the TS control unit 55 and transmits a data signal.

[0035] FIG. 9 is a sequence diagram showing the operation of the node 50 in FIG. 8. During the preparation period, the burst optical reception unit 51 receives 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 the voltage value serving as a threshold and notifies the voltage detection circuit unit 53 (S142).

[0036] During the operation period, the burst optical reception unit 51 receives 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 the time response (timing signal) of a voltage value exceeding the threshold (S132). The control unit 54 notifies the counter management unit 56 of the reception timing of the timing signal (S143). The clock unit 57 supplies a clock (S161). The counter management unit 56 starts the counter (S151).

[0037] The control unit 54 notifies the TS control unit 55 of the reference (reception timing) of the time slot (S144). The counter management unit 56 notifies the TS control unit 55 of a counter value indicating the time from receiving a timing signal to receiving the next timing signal (S152). The TS control unit 55 determines a TS (time slot) for superimposing a Data (data) signal (S171). The burst optical transmission unit 58 superimposes an arbitrary signal on the TS specified by the TS control unit 55 and transmits a data signal (S181).

[0038] As described above, with reference to FIGS. 6 to 9, as an example of physical properties different from those of the data signal, the processing of a timing signal with different light powers has been described. Hereinafter, with reference to FIGS. 10 to 13, as an example of physical properties different from those of the data signal, the processing of a timing signal with different TS widths will be described. The outline of the processing of a timing signal with different TS widths is as follows in (Processing 1B) to (Processing 3B). (Processing 1B) As a preparation period, the T transmitter 30 transmits a timing signal with a TS width different from that of the data signal to each node, causing each node to store the TS width of the timing signal. (Processing 2B) As an operation period, the T transmitter 30 transmits the same timing signal as in the preparation period to each node. Each node can distinguish whether the received signal is a data signal or a timing signal based on the stored TS width. The reception timing of the received timing signal is used as a reference (which TS to superimpose on) for the data signal to be transmitted hereafter. (Process 3B) As the operation period, each node corrects the reference (reception timing) of the data signal in (Process 2B) based on the received timing signal.

[0039] Figure 10 is a time - slot diagram in time series showing the method of extracting the timing signal. Figure 11 is an enlarged time - slot diagram of a part of Figure 10. The coloring pattern of each signal is the same as reference numeral 103 in Figure 4. The T transmitter 30 transmits a timing signal whose TS width is narrower than the data signal (shorter in the left - right time - axis direction in the illustration) at a predetermined timing T0. Also, each node superimposes the data signal with a certain guard time (GT). Each node compares the TS width of each signal received on the same wavelength with a predetermined TS width threshold value, regards a signal below the predetermined TS width threshold value as a new timing signal, and regards a signal equal to or above the predetermined TS width threshold value as a data signal. Then, each node sets a reference for superimposing the data signal based on the new timing signal.

[0040] Figure 12 is a configuration diagram of node 50B. When comparing this node 50B with node 50 in Figure 8, the voltage detection circuit section 53 is replaced by the TS width detection circuit section 53B. The TS width detection circuit section 53B monitors the TS width of the converted voltage value, notifies the control section 54 of a signal below the predetermined TS width (pulse width) threshold value as a timing signal, and notifies the control section 54 of a signal equal to or above the predetermined TS width threshold value as a data signal. The control section 54 receives the timing signal in the preparation period and sets a predetermined TS width threshold value calculated from the timing signal in the TS width detection circuit section 53B. The processing contents of the other processing sections are as described in Figure 8.

[0041] Figure 13 is a sequence diagram showing the operation of node 50B in Figure 12. In the preparation period, the burst optical reception section 51 receives 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 measurement result to the control unit 54 (S231). The control unit 54 grasps the TS width value of the timing signal (S241). The control unit 54 determines the TS width serving as a trigger and notifies the TS width detection circuit unit 53B (S242).

[0042] During the operation period, the burst optical receiver 51 receives 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) with a TS width equal to or less than the specified TS width and notifies the timing signal to the control unit 54 (S232). The control unit 54 grasps the reception time (reception timing) of the timing signal and notifies the reception time to the counter management unit 56 (S243). The clock unit 57 supplies a clock to the counter management unit 56 (S262). The counter management unit 56 starts the counter (S251).

[0043] The control unit 54 notifies the reception timing to the TS control unit 55 (S244). The counter management unit 56 notifies the counter value indicating the time from receiving the timing signal to receiving the next timing signal to the TS control unit 55 (S252). The TS control unit 55 determines the TS (time slot) for superimposing the Data signal (S271). The burst optical transmitter 58 superimposes an arbitrary signal on the TS specified by the TS control unit 55 and transmits a data signal (S281).

[0044] FIG. 14 is a hardware configuration diagram of the optical TDM transmission device (node 50 in FIG. 8 and 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, an HDD 904, a communication I / F 905, an input / output I / F 906, and a media I / F 907. Similarly, the T transmitter 30 in FIG. 5 is also configured as a computer 900. 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 and to a recording medium 917. Further, the CPU 901 controls each unit by executing a program (also called an application or an app for short) read into the RAM 902. And this program can be distributed via a communication line or recorded on a recording medium 917 such as a CD-ROM and distributed.

[0045] [Effect] In the optical TDM transmission system in which a plurality of nodes 50 transmit data signals in a state where time slots between the nodes are synchronized, each node 50 receives a timing signal having a physical property different from that of the data signal, stores the reception time and reception period of the received timing signal as the reception timing of the timing signal, and is characterized in that it controls to superimpose the data signal transmitted from itself on the time slot grasped based on the stored reception timing.

[0046] Thereby, each node 50 can discriminate whether it is a data signal or a timing signal by measuring the physical property of the received signal. Therefore, each node on the transmission side stores the period and reception time of the received timing signal as the reception timing in itself, and synchronizes with other nodes (1-way synchronization processing). Therefore, in an N-to-M optical connection network, it is possible to avoid collisions between signals at the time of multiplexing without measuring the RTT for individual nodes.

[0047] The present invention is characterized in that each node 50 receives a timing signal whose optical power is different from that of the data signal as a timing signal having a physical property different from that of the data signal.

[0048] Thereby, each node 50 can quickly determine whether it is a timing signal by measuring the power of the physical layer without referring to the signal content of the timing signal.

[0049] The present invention is characterized in that each node 50 receives a timing signal whose time slot width is different from that of the data signal as a timing signal having a physical property different from that of the data signal.

[0050] Thereby, each node 50 can quickly determine whether it is a timing signal by measuring the time slot width of the physical layer without referring to the signal content of the timing signal.

[0051] The present invention is characterized in that each node 50 receives a timing signal transmitted to each node 50 even after the reception timing is stored, and corrects the stored reception timing based on the received timing signal.

[0052] Thereby, even for an accidental deviation of the timing signal, a highly accurate time slot synchronization state between nodes can be maintained by autonomous extraction of the timing signal.

Explanation of Signs

[0053] 30 Transmitter 31 Clock Unit 32 Counter Management Unit 33 Control Unit 34 Timing Signal Transmission Unit 50, 50B Nodes (Optical TDM Transmission Device) 51 Burst Optical Receiver 52 TIA 53 Voltage Detection Circuit Unit 53B TS Width Detection Circuit Unit 54 Control Unit 55 TS Control Unit 56 Counter Management Unit 57 Clock Unit 58 Burst Optical Transmission Unit

Claims

1. In an optical TDM transmission system in which a plurality of optical TDM transmission devices transmit data signals while synchronizing time slots between nodes, each of the optical TDM transmission devices, receives a timing signal having a physical property different from that of the data signal, stores the reception time and reception period of the received timing signal as the reception timing of the timing signal, and is characterized by controlling to superimpose the data signal transmitted from itself on a time slot grasped based on the stored reception timing. Optical TDM transmission device.

2. Each of the optical TDM transmission devices is characterized by receiving, as the timing signal having a physical property different from that of the data signal, a timing signal whose optical power is different from that of the data signal. The optical TDM transmission device according to claim 1.

3. Each of the optical TDM transmission devices is characterized by receiving, as the timing signal having a physical property different from that of the data signal, a timing signal whose time slot width is different from that of the data signal. The optical TDM transmission device according to claim 1.

4. Each of the optical TDM transmission devices is characterized by receiving the timing signal transmitted to each of the optical TDM transmission devices even after the reception timing is stored, and correcting the stored reception timing based on the received timing signal. The optical TDM transmission device according to claim 1.

5. In a synchronization method executed by an optical TDM transmission system in which a plurality of optical TDM transmission devices transmit data signals while synchronizing time slots between nodes, each of the optical TDM transmission devices, receives a timing signal having a physical property different from that of the data signal, stores the reception time and reception period of the received timing signal as the reception timing of the timing signal, and is characterized by controlling to superimpose the data signal transmitted from itself on a time slot grasped based on the stored reception timing. Synchronization method.

6. A synchronization program for causing a computer to function as the optical TDM transmission device according to any one of claims 1 to 4.

Images