Optical path multiplexing system and path multiplexing control method for optical network

Abstract

The present invention transmits signals of many optical paths to an upper node by time-division multiplexing optical signals of many lower nodes using a single wavelength. The present invention suppresses a decrease in a transmittable band for each time slot due to an increase in the number of time slots to be statically allocated to each node with an increase in the number of optical paths. A shared time slot (16) which a plurality of lower nodes can use for transmission is prepared. An upper node regularly transmits an optical path header signal (15) including allocation information of the shared time slot and the plurality of lower nodes. Each lower node grasps the shared time slot allocated thereto from the allocation information of the optical path header, and transmits a time-division multiplexed optical signal at the timing when the corresponding shared time slot is in an empty state. The lower node that performs transmission transmits a shared timed slot state signal indicating the state of the corresponding shared time slot in a guard time interval (17). The upper node can designate an ID of a priority node capable of preferentially using the corresponding time slot among the plurality of lower nodes allocated to each shared time slot. The lower nodes other than the priority node wait for transmission until the time slot comes into an empty state.

Description

Optical path multiplexing system and path multiplexing control method for optical network

[0001] The present invention relates to an optical path multiplexing system and a path multiplexing control method for an optical network, and in particular to a technique suitable for sharing one wavelength among a plurality of optical paths by multiplexing optical signals using time division multiplexing.

[0002] For example, in large-scale optical transmission networks managed by telecommunications carriers, it is necessary to interconnect multiple optical networks and realize low-latency communication connections among a huge number of subscribers. Therefore, it is necessary to aggregate a large number of subscriber lines belonging to a relatively slow lower-level network and connect them to a high-speed, high-capacity upper-level network.

[0003] Furthermore, as the number of connected subscriber lines increases, it becomes necessary to expand the number of optical paths, i.e., the number of transmission routes between the transmitting and receiving ends. One technology for increasing the number of optical paths is optical time division multiplexing (TDM), which multiplexes optical signals on the time axis. Optical time division multiplexing is superior in frequency utilization efficiency within a limited transmission band compared to wavelength division multiplexing technology.

[0004] Optical time division multiplexing technologies include the Passive Optical Network (PON) system, which has already been put into practical use, and the optical TDM system based on the PON system (see Non-Patent Document 1). Both the PON system and the optical TDM system multiplex TDM signals using optical couplers, but collisions between TDM signals are avoided by controlling the light emission timing of lower nodes based on RTT (Round Trip Time) measurements. The main difference between the two is whether or not the bandwidth of lower nodes is dynamically controlled.

[0005] Kota Nishiyama et al., "Proposal of a timing adjustment method to achieve high-precision synchronization in optical TDM transmission," IEICE Technical Report, vol. 122, no. 71, PN2022-6, pp. 7-11, June 2022.

[0006] In the PON system, a lower node begins transmission after receiving a gate signal from the upper node to notify it of its light emission timing. This poses a problem of long delays. On the other hand, the optical TDM system statically assigns a time slot (TS) to each lower node. This results in small delays, but the problem is that the bandwidth is limited in inverse proportion to the number of lower nodes, i.e., the number of optical paths. In other words, as the number of lower nodes increases, the total number of time slots increases, and the time width of the time slots available to each lower node becomes smaller. This reduces the amount of information that each lower node can transmit in one transmission process, resulting in lower transmission efficiency.

[0007] The present invention has been made in consideration of the above situation, and aims to provide an optical path multiplexing system and an optical network path multiplexing control method that enable each lower node to efficiently transmit optical signals even when the number of lower nodes increases when an optical TDM method is adopted.

[0008] (1) An optical path multiplexing system of the present invention comprises: an optical transmission line connected in a ring shape via optical fiber; a plurality of lower node devices connected to the optical transmission line; and an upper node device connected to the optical transmission line and managing the plurality of lower node devices, wherein the upper node device has: a header transmitting unit that repeatedly transmits an optical path header signal at a predetermined time interval; and a shared time slot allocating unit that forms one or more shared time slots in the section between two of the optical path header signals, and allocates each of the plurality of lower node devices to the section of each shared time slot, and writes information about the plurality of lower node devices allocated to each shared time slot into the optical path header signal, wherein each lower node device has an optical signal transmission control unit that identifies the shared time slot allocated to it by the received optical path header signal, and when it detects that the corresponding shared time slot is available, transmits its own optical signal at the timing of the shared time slot.

[0009] (2) A path multiplexing control method for an optical network of the present invention comprises the steps of: utilizing an optical network including an optical transmission line connected in a ring shape via optical fiber, a plurality of lower node devices connected to the optical transmission line, and an upper node device connected to the optical transmission line and managing the plurality of lower node devices; repeatedly transmitting an optical path header signal from the upper node device to the optical transmission line at a predetermined time interval; the upper node device forming one or more shared time slots in the section between two of the optical path header signals, and respectively assigning a plurality of the lower node devices to the section of each shared time slot, and writing information of the plurality of lower node devices assigned to each shared time slot into the optical path header signal; and each lower node device identifying the shared time slot assigned to itself from the received optical path header signal, and, when it is detected that the corresponding shared time slot is vacant, transmitting its own optical signal at the timing of the shared time slot.

[0010] According to the optical path multiplexing system and path multiplexing control method for an optical network of the present invention, even if the number of lower nodes increases significantly when an optical TDM system is adopted, each lower node can efficiently transmit optical signals. In other words, according to the present invention, since multiple lower node devices can share the same shared time slot, there is no need to reduce the time width of each shared time slot even if the number of lower node devices connected to the optical network increases and the number of optical paths increases. Therefore, the amount of information in the optical signal transmitted by each lower node device using its own shared time slot can be increased. Furthermore, since each lower node device transmits an optical signal when its assigned shared time slot is available, collisions between multiple optical signals transmitted by multiple lower node devices can be avoided. Furthermore, each lower node device can start transmission without waiting for bandwidth allocation from the upper node device, thereby suppressing increases in delay.

[0011] 1 is a block diagram showing an example of the configuration of an optical path multiplexing system in an embodiment of the present invention. FIG. 2 is a time chart showing an outline of the configuration of an optical signal sent to a ring-shaped optical transmission path in the present invention. FIG. 3 is a schematic diagram showing an example of the configuration of an optical path header. FIG. 4 is a time chart showing an example of an input side optical signal of one lower node device, an optical signal output by the lower node device, and an optical signal appearing on a downstream optical transmission path of the lower node device. FIG. 5 is a flowchart showing an example of the operation of an upper node device. FIG. 6 is a flowchart showing an example of the operation of a lower node device. FIG. 7 is a time chart showing an example of optical signals appearing at each part of the optical transmission path of the optical path multiplexing system shown in FIG. 1. FIG. 8 is a block diagram showing main functions of an upper node device and a lower node device.

[0012] Embodiments of the present invention will be described below with reference to the accompanying drawings. <Configuration of Optical Path Multiplexing System> An example configuration of an optical path multiplexing system in an embodiment of the present invention is shown in FIG. 1. The optical path multiplexing system shown in FIG. 1 comprises one upper node device 10 and four lower node devices 20-1, 20-2, 20-3, and 20-4 connected to an optical transmission path 30 connected in a ring shape via optical fiber. The number of lower node devices 20 connected to the ring-shaped optical transmission path 30 can be increased or decreased as needed. The ring-shaped optical transmission path 30 is composed of optical fiber cables and optical amplifiers.

[0013] The upper node device 10 is equipped with a high-speed optical communication interface 11 that supports relatively high-speed optical communication processing. The high-speed optical communication interface 11 is equipped with a transmitter 12 and a receiver 13. Each of the lower node devices 20-1 to 20-4 is equipped with a low-speed optical communication interface 21. The low-speed optical communication interface 21 is equipped with a receiver 22 and a transmitter 23. The upper node device 10 is connected to an optical transmission path 30, and manages the multiple lower node devices 20-1, 20-2, 20-3, and 20-4.

[0014] As shown in FIG. 1, the ring-shaped optical transmission path 30 forms a ring-shaped route that runs from the node output terminal 30a of the upper node device 10, through the node input terminal 30b and node output terminal 30c of the lower node device 20-1, the node input terminal 30d and node output terminal 30e of the lower node device 20-2, the node input terminal 30f and node output terminal 30g of the lower node device 20-3, and the node input terminal 30h and node output terminal 30i of the lower node device 20-4, to the node input terminal 30j of the upper node device 10.

[0015] Furthermore, two optical couplers 24 and 25 are connected to the ring-shaped optical transmission path 30 between the node input terminal 30b and the node output terminal 30c of the lower node device 20-1. The optical coupler 24 in the lower node device 20-1 branches a portion of the optical signal 41 input to the node input terminal 30b and inputs the branched portion to the receiver 22 in the lower node device 20-1. The optical coupler 25 in the lower node device 20-1 generates a time-division multiplexed optical signal 42 by superimposing the optical signal sent out by the transmitter 23 in the lower node device 20-1 on the optical signal passing through the ring-shaped optical transmission path 30.

[0016] Similarly, two optical couplers 24 and 25 are connected to the ring-shaped optical transmission path 30 between the node input terminal 30d and the node output terminal 30e of the lower node device 20-2. The optical coupler 24 in the lower node device 20-2 branches a portion of the optical signal 42 input to the node input terminal 30d and inputs the branched portion to the receiving unit 22 in the lower node device 20-2. The optical coupler 25 in the lower node device 20-2 generates a time-division multiplexed optical signal 43 by superimposing the optical signal sent out by the transmitting unit 23 in the lower node device 20-2 on the optical signal passing through the ring-shaped optical transmission path 30.

[0017] Furthermore, two optical couplers 24 and 25 are connected to the ring-shaped optical transmission path 30 between the node input terminal 30f and the node output terminal 30g of the lower node device 20-3. The optical coupler 24 in the lower node device 20-3 branches a portion of the optical signal 43 input to the node input terminal 30f and inputs the branched portion to the receiver 22 in the lower node device 20-3. The optical coupler 25 in the lower node device 20-3 generates a time-division multiplexed optical signal 44 by superimposing the optical signal sent by the transmitter 23 in the lower node device 20-3 on the optical signal passing through the ring-shaped optical transmission path 30.

[0018] Furthermore, two optical couplers 24 and 25 are connected to the ring-shaped optical transmission path 30 between the node input terminal 30h and the node output terminal 30i of the lower node device 20-4. The optical coupler 24 in the lower node device 20-4 branches a portion of the optical signal 44 input to the node input terminal 30h and inputs the branched portion to the receiving unit 22 in the lower node device 20-4. The optical coupler 25 in the lower node device 20-4 generates a time-division multiplexed optical signal 45 by superimposing the optical signal sent by the transmitting unit 23 in the lower node device 20-4 on the optical signal passing through the ring-shaped optical transmission path 30.

[0019] <Overview of the Configuration of the Transmitted Optical Signal> Figure 2 shows an overview of the configuration of the optical signal transmitted to the ring-shaped optical transmission line 30 in the present invention. In the present invention, an optical signal with the configuration shown in Figure 2 is used as a time-division multiplexed optical signal. This optical signal includes an optical path header signal 15 that appears repeatedly at predetermined time periods T0 and multiple shared time slots 16. The example shown in Figure 2 shows a case where n shared time slots 16-1, 16-2, ..., 16-n exist between two adjacent optical path header signals 15. In the drawing, the shared time slots are referred to as S-TS (Shared Time Slot).

[0020] Each shared time slot 16 is a time slot that can be used by multiple lower node devices 20 to transmit optical signals, that is, can be shared by multiple nodes. For example, the first and second lower node devices 20-1 and 20-2 can be assigned to the same first shared time slot 16-1, and the third and fourth lower node devices 20-3 and 20-4 can be assigned to the same second shared time slot 16-2. However, special transmission control, as described below, is required to prevent the transmission outputs of multiple nodes from colliding at the timing of the same shared time slot 16.

[0021] By adopting time slots that can be shared by multiple nodes, i.e., shared time slots 16, it is possible to prevent an increase in the total number of time slots even when the number of optical paths increases. Therefore, it is possible to ensure a sufficient time width for each time slot, and to efficiently transmit time-division multiplexed optical signals. The time width (length) of each shared time slot 16 is constant.

[0022] <Structure of Optical Path Header> Fig. 3 shows an example of the structure of the optical path header signal 15. In the example of Fig. 3, one optical path header signal 15 includes a preamble 15a, shared time slot allocation information 15b, and priority designation information 15c.

[0023] The shared time slot allocation information 15b is information that indicates the allocation status between each shared time slot 16 and the multiple nodes that can use it. This shared time slot allocation information 15b is determined and sent by the upper node device 10 side.

[0024] The priority designation information 15c includes ID information indicating a specific node that has been given the right to use each shared time slot 16 preferentially among the multiple nodes assigned to that shared time slot 16. In the example of Fig. 3, the IDs of the nodes that have the right to use the first, second, ..., mth shared time slots 16 (S-TS1, S-TS2, ..., S-TSm) are written in order as the priority designation information 15c. The priority designation information 15c is determined and sent by the upper node device 10.

[0025] <Specific Example of Optical Signals> FIG. 4 shows an example of an input optical signal 40-1 of one lower node device, an optical signal 40-2 output by the lower node device, and an optical signal 40-3 appearing on the downstream optical transmission path of the lower node device.

[0026] The input-side optical signal 40-1 shown in Fig. 4 includes an optical path header signal 15 that appears periodically, as in the example of Fig. 2. Furthermore, a plurality of shared time slots 16 are allocated to the input-side optical signal 40-1. Furthermore, in the example of Fig. 4, a guard time interval 17 is arranged between each optical path header signal 15 and the first shared time slot (S-TS1) 16. The guard time interval 17 is used for signals that indicate the state of each of the plurality of shared time slots 16.

[0027] In the example of Figure 4, it is assumed that a specific lower node device 20 transmits a valid optical signal 16A at the timing of the second shared time slot 16-2, and does not transmit an optical signal 16B in other shared time slots 16.

[0028] Therefore, optical signal 16A appears in shared time slot 16-2 in optical signal 40-2. Furthermore, lower node device 20 transmitting this optical signal 16A transmits shared time slot status signal 17a indicating that shared time slot 16-2 is currently in use at the timing of the corresponding slot in guard time interval 17.

[0029] The optical signal 40-3 shown in Fig. 4 is the result of superimposing the input-side optical signal 40-1 and the optical signal 40-2 by the optical coupler 25. Therefore, in the optical signal 40-3 in Fig. 4, one shared time slot status signal 17a transmitted by the lower node device 20 appears during the guard time interval 17 following the optical path header signal 15. Furthermore, an optical signal 16A transmitted by one lower node device 20 appears at the timing of the second shared time slot 16-2 of the optical signal 40-3.

[0030] <Operation of Upper Node Device> An example of operation of the upper node device 10 in the embodiment of the present invention is shown in Fig. 5. The operation of the upper node device 10 shown in Fig. 5 will be described below.

[0031] In order to make it possible to identify each of the lower node devices 20 connected to the ring-shaped optical transmission line 30, the upper node device 10 assigns ID information to each of the lower node devices 20 in advance in step S11.

[0032] In step S12, the upper node device 10 determines a combination of multiple lower node devices 20 to be assigned to each shared time slot 16. For example, the upper node device 10 simultaneously assigns two lower node devices 20-1 and 20-2 to the first shared time slot 16-1, and simultaneously assigns two lower node devices 20-3 and 20-4 to the second shared time slot 16-2.

[0033] In step S13, the upper node device 10 determines a lower node that will have priority for each shared time slot 16. For example, if two lower node devices 20-1 and 20-2 are simultaneously assigned to the first shared time slot 16-1, control can be performed so that only one of the two lower node devices 20-1 and 20-2 can use the first shared time slot 16-1 with priority. Information about the lower node that will have priority for this purpose is determined in step S13.

[0034] In step S14, the upper node device 10 determines the contents of the shared time slot allocation information 15b and priority designation information 15c to be written in the optical path header signal 15. In step S15, the upper node device 10 transmits the optical path header signal 15 from the transmitter 12 to the ring-shaped optical transmission path 30 via the node output terminal 30a at a predetermined timing. The optical path header signal 15 transmitted here includes the shared time slot allocation information 15b and priority designation information 15c determined in step S14, in addition to the preamble 15a. The operation of step S15 is repeatedly executed at a predetermined time period T0.

[0035] In step S16, the upper node device 10 captures the optical signals transmitted from each lower node device 20 at the timing of each shared time slot 16. The upper node device 10 also distinguishes the optical signals captured for each shared time slot 16 in step S16 by optical path and transmits them to an upper-level optical transmission path in step S17. By transmitting the optical signals directly without converting them from optical signals to electrical signals, it is possible to prevent an increase in delay due to processing. In the upper-level optical transmission path, for example, wavelength division multiplexing technology can be applied, using a different optical wavelength for each upper node device 10, making it possible to distinguish information from each path and transmit it over a single optical transmission path.

[0036] <Operation of Lower Node Device> An example of the operation of the lower node device 20 in the embodiment of the present invention is shown in Fig. 6. The operation of the lower node device 20 shown in Fig. 6 will be described below.

[0037] In step S21, each lower node device 20 monitors the optical signal input from the ring-shaped optical transmission path 30 via the optical coupler 24, and receives the optical path header signal 15 included in this optical signal. By synchronizing with the preamble 15a of the received optical path header signal 15, each lower node device 20 can grasp the appropriate timing of each shared time slot 16, etc.

[0038] In step S22, each lower node device 20 recognizes the shared time slot allocation information 15b and the priority designation information 15c indicating the priority node contained in the optical path header signal 15 received in step S21.

[0039] Based on the shared time slot allocation information 15b recognized in step S22 and the priority designation information 15c representing the priority node, each lower node device 20 grasps the information of the shared time slot 16 assigned to its own node in step S23 and the ID information of the priority node in that shared time slot 16.

[0040] Each lower node device 20 performs transmission control as follows in steps S24 to S28 for a specific shared time slot 16x assigned to itself among the n shared time slots 16-1 to 16-n between two optical path header signals 15.

[0041] In step S24, the lower node device 20 determines from the priority designation information 15c whether the specific shared time slot 16x has a self-node priority. If the specific shared time slot 16x satisfies the self-node priority condition, the process proceeds from step S24 to S27; if this condition is not met, the process proceeds from step S24 to S25.

[0042] In step S25, each lower node device 20 identifies the presence or absence of the shared time slot status signal 17a associated with the relevant shared time slot 16x by monitoring the optical signal in the guard time interval 17.

[0043] In step S26, each lower node device 20 determines whether a specific shared time slot 16x is free or not based on the result of determining whether or not the shared time slot status signal 17a is present. If the shared time slot 16x is free, the process proceeds from step S26 to S27, and if the shared time slot 16x is not free, the process proceeds from step S26 to S28.

[0044] In step S27, each lower node device 20 transmits its own time division multiplexed (TDM) signal at the timing of the corresponding shared time slot 16x. Furthermore, the lower node device 20 transmitting the time division multiplexed signal transmits a shared time slot status signal 17a associated with the corresponding shared time slot 16x at a specific position in the guard time interval 17. In other words, the lower node device 20 transmits, together with the time division multiplexed signal, a shared time slot status signal 17a for indicating to other nodes that the lower node device 20 is currently using this shared time slot 16x. In other words, the upper node device 10 forms a guard time interval 17 between the optical path header signal 15 and the first shared time slot 16.

[0045] In step S28, each lower node device 20 waits until a specific shared time slot 16x becomes available before transmitting a time division multiplexed signal from its own node. Note that the waiting time is assumed to be, for example, an integral multiple of a predetermined time period T0, but this length can be changed as necessary.

[0046] Even if the condition "own node has priority" is met in step S24, step S27 may be executed after confirming that the shared time slot 16 assigned to the own node is free by checking the absence of the shared time slot status signal 17a, as in step S26. This makes it possible to reliably avoid collisions of optical signals from multiple nodes using the same shared time slot 16. Furthermore, if the condition "own node has priority" is not met in step S24, the own node may wait for a certain period of time, and then the process may proceed to step S25.

[0047] Note that, when the lower node device 20 confirms in step S26 that there is no shared time slot status signal 17a for the assigned shared time slot 16 and then transmits its own node's time division multiplexed signal in step S27, it transmits its own node's shared time slot status signal 17a after the timing of the shared time slot status signal 17a for that period. Therefore, in reality, the lower node device 20 transmits its own node's shared time slot status signal 17a and time division multiplexed signal at a timing one period after it recognizes that the shared time slot 16 is vacant.

[0048] <Example of Optical Signals Appearing at Each Part of the Optical Transmission Path> Figure 7 shows examples of optical signals 41 to 45 appearing at each part of the optical transmission path of the optical path multiplexing system shown in Figure 1. The example of Figure 7 assumes that only two shared time slots 16-1 and 16-2 exist within a predetermined time period T0. Furthermore, the optical signals 41 to 44 in Figure 7 correspond to the inputs to the lower node devices 20-1 to 20-4 in the configuration of Figure 1, respectively, and the optical signal 45 in Figure 7 corresponds to the output of the lower node device 20-4 in the configuration of Figure 1.

[0049] The upper node device 10 also assigns "1," "2," "3," and "4" as ID information to the lower node devices 20-1, 20-2, 20-3, and 20-4, respectively. The upper node device 10 also assigns the two lower node devices 20-1 and 20-3 to the first shared time slot 16-1, and assigns the two lower node devices 20-2 and 20-4 to the second shared time slot 16-2.

[0050] In the shared time slot allocation information 15b of the optical path header signal 15 transmitted by the upper node device 10, two IDs "1, 3" are written as the IDs of the lower nodes that can use the first shared time slot 16-1. Also, two IDs "2, 4" are written as the IDs of the lower nodes that can use the second shared time slot 16-2. Each of the lower node devices 20-1 to 20-4 can ascertain the shared time slot 16 that has been allocated to it from the shared time slot allocation information 15b in the optical path header signal 15.

[0051] In this example, the upper node device 10 assigns the lower node device 20-4 as a priority node to the second shared time slot 16-2. The ID "4" of the lower node device 20-4 is written in the priority designation information 15c as the priority node for the shared time slot 16-2.

[0052] 7, an optical path header signal 15 transmitted by the upper node device 10 appears periodically at regular intervals. This optical path header signal 15 contains a preamble 15a, shared time slot allocation information 15b, and priority designation information 15c. However, in this optical signal 41, no signal appears in the guard time section 17 or in the sections of the shared time slots 16-1 and 16-2.

[0053] The first lower node device 20-1 determines from the optical path header signal 15 in the input optical signal 41 that the first shared time slot 16-1 is available for use. Furthermore, because the shared time slot status signal 17a does not appear in the guard time interval 17 in the optical signal 41, the lower node device 20-1 recognizes that the shared time slot 16-1 is free. Therefore, the lower node device 20-1 transmits its own time division multiplexed signal at the timing of the first shared time slot 16-1. At almost the same time, the lower node device 20-1 transmits the shared time slot status signal 17a indicating that the first shared time slot 16-1 is in use.

[0054] An optical signal 42 is obtained as a result of the optical signal 41 input to the lower node device 20-1 being superimposed by the optical coupler 25 on the time division multiplexed signal transmitted by the lower node device 20-1 and the shared time slot status signal 17a. Therefore, the optical signal 42 contains the time division multiplexed signal transmitted by the lower node device 20-1 and the shared time slot status signal 17a.

[0055] The second lower node device 20-2 recognizes from the optical path header signal 15 in the input optical signal 42 that the second shared time slot 16-2 has been assigned to itself. However, because another node's ID "4" is designated as the priority node for the second shared time slot 16-2, the lower node device 20-2 enters a standby state and does not transmit a time division multiplexed signal. Note that because the shared time slot status signal 17b does not appear in the guard time interval 17 in the optical signal 42, the lower node device 20-2 can recognize that the shared time slot 16-2 is free.

[0056] As described above, since the lower node device 20-2 waits for transmission, the content of the optical signal 42 input to the lower node device 20-2 and the content of the optical signal 43 output from the lower node device 20-2 are the same and do not change.

[0057] The third lower node device 20-3 understands from the optical path header signal 15 in the input optical signal 43 that the first shared time slot 16-1 has been assigned to itself. However, because the shared time slot status signal 17a appears in the guard time interval 17, the lower node device 20-3 recognizes that the first shared time slot 16-1 is already in use. Therefore, the lower node device 20-3 enters a standby state and does not transmit a time division multiplexed signal.

[0058] As described above, since the lower node device 20-3 waits for transmission, the content of the optical signal 43 input to the lower node device 20-3 and the content of the optical signal 44 output from the lower node device 20-3 are the same and do not change.

[0059] The fourth lower node device 20-4 recognizes that the second shared time slot 16-2 has been assigned to itself from the optical path header signal 15 in the input optical signal 44. Furthermore, it recognizes that its own node ID "4" has been designated as the priority node for the second shared time slot 16-2.

[0060] Therefore, the lower node device 20-4 transmits its own time division multiplexed signal at the timing of the second shared time slot 16-2. At almost the same time, the lower node device 20-4 transmits a shared time slot status signal 17b indicating that the second shared time slot 16-2 is in use.

[0061] An optical signal 45 is obtained as a result of the optical signal 44 input to the lower node device 20-4 being superimposed by the optical coupler 25 on the time division multiplexed signal transmitted by the lower node device 20-4 and the shared time slot status signal 17b. Therefore, the optical signal 45 contains the time division multiplexed signal transmitted by the lower node device 20-4 and the shared time slot status signal 17b.

[0062] <Major Functions of Upper Node Device and Lower Node Device> Major functions of the upper node device 10 and the lower node device 20 are shown in Fig. 8. In the embodiment of the present invention, as shown in Fig. 8, the upper node device 10 includes a high-speed optical communication interface (IF) 11, a header transmission unit 10a, and a shared time slot allocation unit 10b.

[0063] The header transmitter 10a in the upper node device 10 generates an optical path header signal 15. The optical path header signal 15 generated by the header transmitter 10a is transmitted at a predetermined period from the high-speed optical communication interface 11 to the ring-shaped optical transmission path 30. The header transmitter 10a repeatedly transmits the optical path header signal 15 at predetermined time intervals.

[0064] The shared time slot allocation unit 10b in the upper node device 10 forms one or more shared time slots 16 in the section between two optical path header signals 15. The shared time slot allocation unit 10b allocates ID information of multiple lower node devices 20 to each shared time slot 16. The shared time slot allocation unit 10b also generates shared time slot allocation information 15b, information indicating the relationship between each shared time slot 16 and the multiple assigned lower node devices 20. Furthermore, if there is a lower node device 20 that can preferentially use each shared time slot 16, the shared time slot allocation unit 10b generates ID information of the corresponding lower node device 20 as priority designation information 15c. The shared time slot allocation information 15b and priority designation information 15c generated by the shared time slot allocation unit 10b are written into the optical path header signal 15 generated by the header transmission unit 10a.

[0065] The shared time slot allocation unit 10b allocates a plurality of lower node devices 20-1 to 20-4 to the sections of each shared time slot 16, and writes information about the plurality of lower node devices 20-1 to 20-4 allocated to each shared time slot into the optical path header signal 15.

[0066] The high-speed optical communication interface 11 takes in the time division multiplexed signals transmitted by the respective lower node devices 20 from the respective shared time slots 16 of the optical signal input from the ring-shaped optical transmission line 30 and sends them to the upper optical network 51 .

[0067] 8, each lower node device 20 includes a low-speed optical communication interface 21 and an optical signal transmission control unit 20a. The optical signal transmission control unit 20a receives an optical signal branched by an optical coupler 24 from the ring-shaped optical transmission line 30 at the low-speed optical communication interface 21, and grasps the timing of each shared time slot 16 in the optical signal in synchronization with a preamble 15a of an optical path header signal 15. Furthermore, the optical signal transmission control unit 20a grasps the specific shared time slot 16 assigned to its own node based on shared time slot allocation information 15b and priority designation information 15c of the optical path header signal 15, and identifies whether its own node is the node that can use the shared time slot 16 with priority.

[0068] The optical signal transmission control unit 20a controls transmission based on the optical path header signal 15 when transmitting transmission data input from a terminal device 52 such as a subscriber as a time-division multiplexed optical signal from the low-speed optical communication interface 21 to the ring-shaped optical transmission path 30. Specifically, when the shared time slot 16 assigned to the node is empty, the optical signal transmission control unit 20a transmits the time-division multiplexed optical signal at the timing of the shared time slot. At the same time, the optical signal transmission control unit 20a transmits a shared time slot status signal 17a indicating that the time slot is in use at a predetermined timing in the guard time interval 17. Furthermore, when the ID of the priority node of the shared time slot 16 assigned to the node is different from the node itself, the optical signal transmission control unit 20a waits for transmission from the node itself for, for example, a certain period of time.

[0069] The high-speed optical communication interface 11 in the upper node device 10 has the ability to handle high-speed signal processing compared to the low-speed optical communication interface 21 in the lower node device 20. Therefore, according to this embodiment, the high-speed optical communication interface 11 is capable of signal processing with high time precision. This embodiment can maintain, for example, the timing of the optical path header signal 15 sent to the ring-shaped optical transmission line 30 and the timing of capturing the time division multiplexed signal from each shared time slot 16 in a state with high time precision that satisfies the required specifications of the upper network.

[0070] <Features of the Present Invention> The following [1] to [4] are characteristic features of the optical path multiplexing system and the path multiplexing control method for an optical network of the present invention. [1] An optical transmission path (30) connected in a ring shape via optical fibers, a plurality of lower node devices (20-1 to 20-4) connected to the optical transmission path (30), and an upper node device (10) connected to the optical transmission path (30) and managing the plurality of lower node devices (20-1 to 20-4), wherein the upper node device (10) has: a header transmission unit (10a) that repeatedly transmits an optical path header signal (15) at a predetermined time interval; and a shared time slot allocation unit (10b) that forms one or more shared time slots (16) in a section between two of the optical path header signals (15), and allocates the plurality of lower node devices (20-1 to 20-4) to the section of each shared time slot (16), and writes information (shared time slot allocation information 15b) of the plurality of lower node devices (20-1 to 20-4) allocated to each shared time slot (16) into the optical path header signal (15), an optical signal transmission control unit (20a) for each of the lower node devices (20-1 to 20-4) identifying the shared time slot (16) assigned to itself by the received optical path header signal (15), and transmitting its own optical signal at the timing of the shared time slot (16) when it detects that the corresponding shared time slot (16) is free (steps S26, S27);

[0071] According to the optical path multiplexing system having the configuration described above in [1], optical signals transmitted by multiple lower node devices are time-division multiplexed and transmitted to an upper node device, allowing multiple optical paths to share a single wavelength. Furthermore, because multiple lower node devices use shared time slots available for transmission, an increase in the number of time slots associated with an increase in the number of optical paths can be suppressed. Therefore, the time width of each shared time slot can be increased, ensuring sufficient bandwidth for transmitting information for each optical path. Furthermore, each lower node device can identify its assigned shared time slot from the received optical path header signal, thereby suppressing an increase in delay before starting transmission. Furthermore, each lower node device starts transmission when its assigned shared time slot is available, preventing collisions between optical signals transmitted by multiple nodes within the same shared time slot.

[0072] [2] The optical path multiplexing system described in [1] above, wherein the upper node device (10) forms a guard time interval (guard time interval 17) between the optical path header signal (15) and the first shared time slot (16), and each of the lower node devices (20-1 to 20-4) identifies the presence or absence of a status signal transmitted from another lower node device (20-1 to 20-4) during the guard time interval, and when it detects that the shared time slot (16) assigned to itself is vacant, it transmits its own optical signal at the timing of the shared time slot (16).

[0073] According to the optical path multiplexing system having the configuration described in [2] above, by utilizing the guard time interval, a lower node device that transmits a time division multiplexed signal using each shared time slot can transmit a status signal indicating that the time slot is in use. Furthermore, the lower node device can check whether each shared time slot is free or not before starting transmission.

[0074] [3] The optical path multiplexing system described in [1] above, wherein the optical path header signal (15) is allowed to include, in addition to a preamble indicating the beginning of a header, priority designation information (15c) indicating the priority of the plurality of lower node devices (20-1 to 20-4) in each of the shared time slots, and the upper node device (10) writes the priority designation information (15c) into the optical path header signal (15) according to the status of the plurality of lower node devices (20-1 to 20-4) connected thereto (steps S13, S14), and each of the lower node devices (20-1 to 20-4) waits to transmit its own optical signal if another lower node device (20-1 to 20-4) with a higher priority than itself is assigned to the shared time slot (16) according to the priority designation information (15c) of the received optical path header signal (15) (step S28).

[0075] According to the optical path multiplexing system of the above configuration [3], it is possible to control so that only some of the multiple lower node devices assigned to the same shared time slot have priority in using that time slot. Therefore, for example, if the traffic input to only some of the lower node devices suddenly increases, by giving priority to the node with the increased traffic, it becomes possible to efficiently send the increased traffic to the upper node device.

[0076] [4] A step of utilizing an optical network including an optical transmission path (30) connected in a ring shape via optical fiber, a plurality of lower node devices (20-1 to 20-4) connected to the optical transmission path, and an upper node device (10) connected to the optical transmission path and managing the plurality of lower node devices (20-1 to 20-4); and a step (S15) of repeatedly transmitting an optical path header signal (15) from the upper node device (10) to the optical transmission path (30) at predetermined time intervals. a step (S14) in which the upper node device (10) forms one or more shared time slots (16) in the section between two of the optical path header signals (15), and assigns a plurality of the lower node devices (20-1 to 20-4) to the section of each shared time slot (16) (step S12), and writes information (shared time slot assignment information 15b) of the plurality of lower node devices (20-1 to 20-4) assigned to each shared time slot (16) into the optical path header signal (15); and a step (S26, S27) in which each of the lower node devices (20-1 to 20-4) identifies the shared time slot (16) assigned to itself by the received optical path header signal (15) (steps S21 to S23), and when it detects that the corresponding shared time slot (16) is vacant, transmits its own optical signal at the timing of the shared time slot (16).

[0077] According to the path multiplexing control method for an optical network described in [4] above, optical signals transmitted by multiple lower node devices are time-division multiplexed and sent to an upper node device, allowing multiple optical paths to share a single wavelength. Furthermore, because multiple lower node devices use shared time slots available for transmission, an increase in the number of time slots associated with an increase in the number of optical paths can be suppressed. Therefore, the time width of each shared time slot can be increased, ensuring sufficient bandwidth for transmitting information for each optical path. Furthermore, each lower node device can identify its assigned shared time slot from the received optical path header signal, thereby suppressing an increase in delay before starting transmission. Furthermore, each lower node device starts transmission when its assigned shared time slot is available, preventing collisions between optical signals transmitted by multiple nodes within the same shared time slot.

[0078] 10 Upper node device 10a Header transmission unit 10b Shared time slot allocation unit 11 High-speed optical communication interface 12 Transmission unit 13 Reception unit 15 Optical path header signal 15a Preamble 15b Shared time slot allocation information 15c Priority designation information 16, 16-1, 16-2, 16-n Shared time slot 17 Guard time interval 17a, 17b Shared time slot status signal 20, 20-1, 20-2, 20-3, 20-4 Lower node device 20a Optical signal transmission control unit 21 Low-speed optical communication interface 22 Reception unit 23 Transmission unit 24, 25 Optical coupler 30 Optical transmission path 30a, 30c, 30e, 30g, 30i Node output terminal 30b, 30d, 30f, 30h, 30j Node input terminal 41, 42, 43, 44, 45 Optical signal 51 Upper optical network 52 Terminal device

Claims

1. An optical path multiplexing system comprising: an optical transmission line connected in a ring shape via optical fiber; a plurality of lower node devices connected to the optical transmission line; and an upper node device connected to the optical transmission line and managing the plurality of lower node devices, wherein the upper node device has: a header transmitter unit that repeatedly transmits an optical path header signal at a predetermined time interval; and a shared time slot allocation unit that forms one or more shared time slots in the section between two of the optical path header signals and allocates each of the plurality of lower node devices to the section of each shared time slot, and writes information about the plurality of lower node devices allocated to each shared time slot into the optical path header signal, wherein each lower node device identifies the shared time slot allocated to it from the received optical path header signal, and, when it detects that the corresponding shared time slot is available, has an optical signal transmission controller that transmits its own optical signal at the timing of the shared time slot.

2. The optical path multiplexing system of claim 1, wherein the upper node device forms a guard time interval between the optical path header signal and the first shared time slot, and each lower node device identifies the presence or absence of a status signal transmitted from another lower node device during the guard time interval, and when it detects that the shared time slot assigned to itself is vacant, it transmits its own optical signal at the timing of the shared time slot.

3. The optical path multiplexing system of claim 1, wherein the optical path header signal is allowed to include, in addition to a preamble indicating the beginning of the header, priority designation information indicating the priority of multiple lower node devices in each shared time slot, the upper node device writes the priority designation information into the optical path header signal depending on the status of the multiple lower node devices connected, and each lower node device waits to transmit its own optical signal if another lower node device with a higher priority than itself is assigned to the shared time slot in accordance with the priority designation information of the received optical path header signal.

4. A path multiplexing control method for an optical network, comprising the steps of: utilizing an optical network including an optical transmission path connected in a ring shape via optical fiber, a plurality of lower node devices connected to the optical transmission path, and an upper node device connected to the optical transmission path and managing the plurality of lower node devices; repeatedly transmitting an optical path header signal from the upper node device to the optical transmission path at a predetermined time interval; the upper node device forming one or more shared time slots in the section between two of the optical path header signals, and respectively assigning a plurality of the lower node devices to the section of each shared time slot, and writing information about the plurality of lower node devices assigned to each shared time slot into the optical path header signal; and each lower node device identifying the shared time slot assigned to it from the received optical path header signal, and when it detects that the corresponding shared time slot is vacant, transmitting its own optical signal at the timing of the shared time slot.

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