Optical communication system

Abstract

An optical communication system according to the present invention comprises: a first passive optical network system that has a first optical subscriber line device and a plurality of first optical subscriber line terminal devices; a second passive optical network system that has a second optical subscriber line device and a plurality of second optical subscriber line terminal devices; and a control device for controlling connection and disconnection between the first optical subscriber line device and the plurality of second optical subscriber line terminal devices, wherein the control device connects between the first optical subscriber line device and the plurality of second optical subscriber line terminal devices, the first optical subscriber line device stops communication between the plurality of first optical subscriber line terminal devices and the first optical subscriber line device before the first optical subscriber line device and the plurality of second optical subscriber line terminal devices are connected, and when the first optical subscriber line device acquires a plurality of uplink signals transmitted from the plurality of second optical subscriber line terminal devices after the first optical subscriber line device and the plurality of second optical subscriber line terminal devices are connected, it is determined that the plurality of second optical subscriber line terminal devices can be aggregated to the first optical subscriber line device.

Description

Optical Communication Systems

[0001] The present invention relates to optical communication systems.

[0002] An optical communication system may include a plurality of passive optical network (PON) systems. Patent Document 1 discloses 1+1 protection in an optical communication system including two passive optical network systems.

[0003] Patent No. 4821738

[0004] A passive optical network system has a plurality of optical network units (ONUs) under an optical subscriber unit (OSU). In an optical communication system, a plurality of optical network units are aggregated in a first optical subscriber unit, and a control device may put a second optical subscriber unit to sleep, depending on the status of the number of authentications of the optical subscriber unit, the traffic status, and the time period.

[0005] Here, depending on the line loss in the optical transmission path between the optical subscriber line device and the optical subscriber line terminal, as soon as multiple optical subscriber line terminals are aggregated into the first optical subscriber line device, the first optical subscriber line device may no longer be able to communicate with those multiple optical subscriber line terminals.

[0006] However, there is a problem in that it is not possible to determine whether it is possible to aggregate multiple optical subscriber line terminal devices under the second optical subscriber line device into the first optical subscriber line device before actually aggregating them into the first optical subscriber line device.

[0007] In view of the above circumstances, the present invention aims to provide an optical communication system that is capable of determining whether multiple optical subscriber line terminal devices under a second optical subscriber line device can be aggregated into a first optical subscriber line device before actually aggregating them into the first optical subscriber line device.

[0008] One aspect of the present invention is an optical communication system comprising: a first passive optical network system having a first optical subscriber line device and a plurality of first optical subscriber line terminals; a second passive optical network system having a second optical subscriber line device and a plurality of second optical subscriber line terminals; and a control device that uses an optical selection unit to control connection and disconnection between the first optical subscriber line device and the plurality of second optical subscriber line terminals, wherein the control device connects the first optical subscriber line device and the plurality of second optical subscriber line terminals using the optical selection unit, and and a line device stops communication between the plurality of first optical line terminal devices and the first optical line device before the first optical line device is connected to the plurality of second optical line terminal devices, and determines that the plurality of second optical line terminal devices can be aggregated into the first optical line device when the first optical line device acquires a plurality of upstream signals transmitted from the plurality of second optical line terminal devices after the first optical line device is connected to the plurality of second optical line terminal devices.

[0009] According to the present invention, it is possible to determine whether it is possible to aggregate multiple optical subscriber line terminal devices under a second optical subscriber line device into a first optical subscriber line device before actually aggregating them into the first optical subscriber line device.

[0010] It is a diagram showing a configuration example of an optical communication system in an embodiment. It is a flowchart showing an operation example of the optical communication system in an embodiment. It is a diagram showing a configuration example of an optical communication system in a modified example of an embodiment. It is a diagram showing a hardware configuration example of an optical line terminal in an embodiment and a modified example of an embodiment.

[0011] An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of an optical communication system 1a according to the embodiment. The optical communication system 1a is a system that communicates using optical signals. The optical communication system 1a includes multiple passive optical network (PON) systems. In the following description, the optical communication system 1a includes, as an example, two passive optical network systems. The passive optical network systems include optical transmission paths having optical fibers.

[0012] The optical communication system 1a includes an optical line terminal (OLT) 10, an optical selector 20a, a plurality of optical network units (ONUs) 30, a plurality of branching units 40, and a plurality of branching units 50. The optical communication system 1a includes the optical line terminal 10 as a central office-side communication device. The optical communication system 1a includes the optical line terminal 30 as a user terminal-side communication device.

[0013] Hereinafter, the direction from the optical line termination 10 to the optical line terminal 30 will be referred to as "downstream." Hereinafter, the direction from the optical line terminal 30 to the optical line terminal 10 will be referred to as "upstream."

[0014] The optical line termination 10 includes a control device 11 and two optical line units (OSUs) 12. The optical line termination 10 includes a port 13 (PON port) for each optical line unit 12.

[0015] The control device 11 (control panel) includes an identification information storage device 111, a determination control unit 112, and a switching control unit 113. The optical subscriber line device 12 includes a determination device 121, a communication unit 122, a transfer unit 123, a bandwidth control unit 124, and an interface 125. The determination device 121 includes an identification information storage unit 126, a maintenance control unit 127, an allocation control unit 128, a transmission control unit 129, and a determination unit 130.

[0016] The optical selector 20 a includes two branching units 21 , two branching units 22 , and two optical switching units 23 .

[0017] In the optical communication system 1a, 1+1 protection (redundancy and power saving) is possible in two passive optical network systems. That is, the optical selector 20a switches between two paths in the optical transmission line between the optical line termination 10 and the optical network unit 30. The optical network unit 30 transmits the same upstream signal (optical signal) to these two paths. The optical line termination 10 receives the upstream signal from the optical network unit 30 via the path connected to the optical line termination 10.

[0018] The optical communication system 1a determines whether it is possible to aggregate multiple optical network units 30 in two passive optical networks into one optical network unit 12 before actually aggregating the multiple optical network units 30 into one optical network unit 12. For example, during the period when the optical network unit 12-1 is determining whether all the optical network units 30 in the optical communication system 1a can be aggregated into the optical network unit 12-1, the optical network unit 30-2 may communicate with the optical network unit 12-2.

[0019] The optical network unit 30 may be aggregated in the optical subscriber line unit 12-1, or the optical subscriber line unit 30 may be aggregated in the optical subscriber line unit 12-2. In the following, as an example, a case where the optical network unit 30 is aggregated in the optical subscriber line unit 12-1 will be described. When the optical subscriber line unit 30 is aggregated in the optical subscriber line unit 12-2, in the following description, the branch number "-1" of the symbol will be read as "-2", and the branch number "-2" of the symbol will be read as "-1".

[0020] The identification information storage device 111 stores a logical link identifier (LLID) assigned to each optical line terminal 30-1 in association with the optical line device 12-1. The identification information storage device 111 stores a logical link identifier assigned to each optical line terminal 30-2 in association with the optical line device 12-2.

[0021] The determination control unit 112 instructs the optical subscriber line device 12-1 to start a process for determining whether aggregation is possible. The determination control unit 112 obtains a determination result indicating whether aggregation is possible from the determination unit 130-1. If the determination result indicates that aggregation is possible, the determination control unit 112 may aggregate all optical subscriber line devices 30 in the optical communication system 1a to the optical subscriber line device 12-1 depending on at least one of the status of the number of authentications of the optical subscriber line devices 30, the traffic status, and the time period. If the optical subscriber line device 12-2 fails, the determination control unit 112 may aggregate all optical subscriber line devices 30 in the optical communication system 1a to the optical subscriber line device 12-1. The determination control unit 112 may also put the optical subscriber line device 12-2 into sleep mode.

[0022] When the switching control unit 113 receives a link and authentication maintenance response from the optical network unit 30-1, it transmits a route switching instruction for the optical transmission path to the optical selection unit 20a. The maintenance response is a response indicating that the optical network unit will maintain the link and authentication based on the PON protocol for a certain period of time even if the optical network unit (ONU) cannot receive a downstream signal from the optical network unit (OSU). The PON protocol is not limited to a specific PON protocol, but may be, for example, the GPON (Gigabit Passive Optical Network) or XGS-PON (10-Gigabit Capable Symmetric Passive Optical Network) of the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), or the Multi-Point Control Protocol (MPCP) of the EPON (Ethernet (registered trademark) Passive Optical Network) or 10G-EPON (10-Gigabit Ethernet (registered trademark) Passive Optical Network) of the Institute of Electrical and Electronics Engineers (IEEE). In the following, the PON protocol is MPCP as an example.

[0023] The switching control unit 113 acquires the determination result from the determining unit 130-1. When the switching control unit 113 acquires the determination result from the determining unit 130-1, the switching control unit 113 transmits a path switchback instruction to the optical selecting unit 20a.

[0024] The communication unit 122-1 communicates with each optical network unit 30 via port 13-1. The timestamps of the multiple upstream signals (MPCP frames) transmitted from the optical network unit 30-2 are synchronized with the time of the communication unit 122-2. Therefore, the communication unit 122-1 ignores the timestamps of the multiple upstream signals transmitted from the optical network unit 30-2 and acquires these multiple upstream signals.

[0025] The transfer unit 123-1 transfers to the determination device 121-1 the upstream signals transmitted from each optical network unit 30. As a result, the logical link identifiers of each optical network unit 30-2 are stored in the identification information storage unit 126 in advance.

[0026] The bandwidth control unit 124-1 controls the bandwidth of upstream signals based on the control by the allocation control unit 128-1. For example, when the allocation control unit 128-1 stops allocating upstream signals transmitted from the optical network unit 30-1, the bandwidth control unit 124-1 stops transmitting gate frames to the optical network unit 30-1. For example, when the allocation control unit 128-1 resumes allocating upstream signals transmitted from the optical network unit 30-1, the bandwidth control unit 124-1 resumes transmitting gate frames to the optical network unit 30-1.

[0027] The interface 125-1 is a service node interface, and transmits, for example, a signal transferred from the transfer unit 123-1 to an external node (not shown).

[0028] The identification information storage unit 126-1 stores the logical link identifiers assigned to each optical network unit 30-1. The identification information storage unit 126-1 pre-stores the logical link identifiers assigned to each optical network unit 30-2.

[0029] The maintenance control unit 127-1 transmits a link and authentication maintenance instruction to the optical network unit 30-1. The maintenance instruction is an instruction to the optical network unit to maintain the MPCP link and authentication between the optical network unit and the optical network unit for a certain period of time even if the optical network unit (ONU) cannot acquire (receive) a downstream signal from the optical network unit (OSU) (Reference 1: Japanese Patent No. 5767183, Reference 2: Japanese Patent No. 5932627). The allocation control unit 128-1 acquires a maintenance response to the maintenance instruction from the optical network unit 30-1.

[0030] When the transmission control unit 129-1 resumes transmission of the downstream signal, the maintenance control unit 127-1 transmits a release instruction to the optical network unit 30-1. The release instruction is an instruction to the optical network unit to release the maintenance of the MPCP link and authentication between the optical network unit and the optical network unit.

[0031] The allocation control unit 128-1 of the optical subscriber line device 12-1 pre-allocates logical link identifiers to the plurality of optical network units 30-1 that are different from the logical link identifiers assigned to the plurality of optical network units 30-2. Here, the logical link identifiers assigned to the plurality of optical network units 30-1 and the logical link identifiers assigned to the plurality of optical network units 30-2 are different from each other and do not overlap.

[0032] When the allocation control unit 128-1 receives a maintenance response from the optical network unit 30-1, it transmits the maintenance response to the control device 11. When the allocation control unit 128-1 receives a maintenance response from the optical network unit 30-1, it stops the allocation of upstream signals transmitted from the optical network unit 30-1. In other words, the allocation control unit 128-1 stops the transmission of gate frames from the bandwidth control unit 124-1 to the optical network unit 30-1.

[0033] The allocation control unit 128-1 resumes allocation of the upstream signal transmitted from the optical network unit 30-1 when the determination unit 130-1 transmits a determination result indicating whether aggregation is possible or not to the control device 11. That is, the allocation control unit 128-1 resumes transmission of gate frames from the bandwidth control unit 124-1 to the optical network unit 30-1.

[0034] The transmission control unit 129-1 stops transmitting downlink signals when the allocation control unit 128-1 stops allocating uplink signals, and resumes transmitting downlink signals when the allocation control unit 128-1 resumes allocating uplink signals.

[0035] The determining unit 130-1 acquires an upstream signal from each optical network unit 30-2 via the branching unit 50-2, the branching unit 40-2, the optical selecting unit 20a, the port 13-1, and the communication unit 122-1.

[0036] The determination unit 130-1 determines whether or not upstream signals have been acquired from all optical network terminals 30-2. The determination unit 130-1 compares the MPCP link information or authentication information of all optical network terminals 30-2 under the optical network terminal 12-2 with the MPCP link information or authentication information of each upstream signal acquired from the multiple optical network terminals 30-2. The determination unit 130-1 transmits a determination result indicating whether aggregation is possible to the control device 11.

[0037] Here, if the determination unit 130-1 can acquire multiple upstream signals transmitted from all optical line terminals 30-2, the determination unit 130-1 determines that all optical line terminals 30 in the optical communication system 1a can be aggregated to the optical line terminal 12-1. If the determination unit 130-1 cannot acquire an upstream signal transmitted from any optical line terminal 30-2, the determination unit 130-1 determines that the optical line terminals 30 in the optical communication system 1a cannot be aggregated to the optical line terminal 12-1.

[0038] The branching unit 21 (optical splitter) is a two-branching unit. The branching unit 21-1 is connected to the port 13-1 and the optical switching unit 23-1. The branching unit 22 (optical splitter) is a two-branching unit. The branching unit 22-1 is connected to the branching unit 40-1 and the optical switching unit 23-2.

[0039] The optical switching unit 23 (optical switch) connects the optical subscriber line device 12 and the optical subscriber line terminal 30 by switching the path in the optical transmission line. For example, the optical switching unit 23-1 connects the optical subscriber line device 12-1 and all the optical subscriber line terminals 30-2 by switching the path in the optical selection unit 20a. The optical switching unit 23-1 releases the connection between the optical subscriber line device 12-1 and all the optical subscriber line terminals 30-2 by switching back the path in the optical selection unit 20a.

[0040] The optical network unit 30-1 is an ONU under the control of the optical network unit 12-1. If the optical network unit 30-2 is not accommodated in the optical network unit 30-1, it is an ONU under the control of the optical network unit 12-2.

[0041] The branching unit 40 is a four-branching unit. A plurality of (for example, four) optical network units 30-1 may be connected to the branching unit 40-1. A plurality of (for example, four) optical network units 30-1 may be connected to the branching unit 40-2.

[0042] The branching unit 50 is an eight-branching unit. A plurality of (e.g., eight) optical network units 30-2 may be connected to the branching unit 50-1. A plurality of (e.g., eight) optical network units 30-2 may be connected to the branching unit 50-2.

[0043] Next, an example of operation of the optical communication system 1a will be described. Fig. 2 is a flowchart showing an example of operation of the optical communication system 1a in the embodiment. In Fig. 2, during the period indicated by the dashed line for the optical subscriber line device 12-1, the optical subscriber line device 12-1 is capable of communication (normal communication) with the optical subscriber line terminal 30-1. Furthermore, during the period indicated by the dashed line for the optical subscriber line device 12-2, the optical subscriber line device 12-2 is capable of communication (normal communication) with the optical subscriber line terminal 30-2.

[0044] The determination control unit 112 instructs the optical subscriber line unit 12-1 to start the process of determining whether aggregation is possible (step S101). The maintenance control unit 127-1 transmits a maintenance instruction to the optical subscriber line terminal 30-1 (step S102).

[0045] The optical network unit 30-1 receives a maintenance instruction from the optical network unit 12-1 (step S103). The optical network unit 30-1 transmits a maintenance response to the optical network unit 12-1 (step S104). The optical network unit 30-1 maintains the MPCP link and authentication for a certain period of time (step S105).

[0046] The maintenance control unit 127-1 acquires a maintenance response from the optical network unit 30-1. The allocation control unit 128-1 transmits the maintenance response to the control device 11 (step S106). The allocation control unit 128-1 stops the allocation of upstream signals transmitted from the optical network unit 30-1 (step S107). The transmission control unit 129-1 stops the transmission of downstream signals (step S107).

[0047] The switching control unit 113 transmits a route switching instruction to the optical selecting unit 20a (step S106). The optical switching unit 23-1 switches the route in the optical transmission line to connect the optical subscriber line device 12-1 to all of the optical subscriber line terminals 30-2 (step S110).

[0048] Each optical network unit 30-2 may transmit an upstream signal. The optical network unit 12-2 acquires the upstream signal from each optical network unit 30-2 (step S111). Since the optical network unit 12-1 is connected to all of the optical network units 30-2, the determination unit 130-1 acquires the upstream signal from each optical network unit 30-2 via the branching unit 50-2, the branching unit 40-2, the optical selection unit 20a, the port 13-1, and the communication unit 122-1 (step S112).

[0049] The determination unit 130-1 compares the MPCP link information or authentication information of all optical network terminals 30-2 under the optical network terminal 12-2 with the MPCP link information or authentication information of each upstream signal acquired from the plurality of optical network terminals 30-2. The determination unit 130-1 determines whether or not upstream signals (for example, MPCP report frames) have been acquired from all optical network terminals 30-2.

[0050] For example, if the determination unit 130-1 can acquire a plurality of upstream signals transmitted from all the optical line terminals 30-2, the determination unit 130-1 determines that all the optical line terminals 30 in the optical communication system 1a can be aggregated to the optical line terminal 12-1 (step S113). The determination unit 130-1 transmits a determination result indicating whether aggregation is possible or not to the control device 11 (step S114).

[0051] The determination control unit 112 and the switching control unit 113 obtain the determination result from the determination unit 130-1 (step S115). The switching control unit 113 sends a path switchback instruction to the optical selecting unit 20a (step S116). The optical switching unit 23-1 switches back the path in the optical transmission line, thereby releasing the connections between the optical subscriber line device 12-1 and all of the optical subscriber line terminals 30-2 (step S117).

[0052] Each optical network unit 30-2 may transmit an upstream signal. The optical network unit 12-2 acquires the upstream signal from each optical network unit 30-2. Note that, since there is no connection between the optical network unit 12-1 and each optical network unit 30-2, the determination unit 130-1 does not acquire the upstream signal transmitted from the optical network unit 30-2 (step S118).

[0053] The allocation control unit 128-1 resumes allocation of the upstream signal transmitted from the optical network unit 30-1 (step S119). The transmission control unit 129-1 resumes transmission of the downstream signal (step S120). The maintenance control unit 127-1 transmits a release instruction to the optical network unit 30-1 (step S121).

[0054] The optical network unit 30-1 acquires a release instruction from the optical network unit 12-1 (step S122). The optical network unit 30-1 transmits a release response to the optical network unit 12-1. The release response is a response indicating that the optical network unit will release the MPCP link and maintenance of authentication between the optical network unit and the optical network unit (step S123). The allocation control unit 128-1 acquires the release response from the optical network unit 30-1 (step S124).

[0055] As described above, the first passive optical network system includes the optical subscriber line device 12-1 (first optical subscriber line device) and a plurality of optical subscriber line terminals 30-1 (a plurality of first optical subscriber line terminals). The second passive optical network system includes the optical subscriber line device 12-2 (second optical subscriber line device) and a plurality of optical subscriber line terminals 30-2 (a plurality of second optical subscriber line terminals).

[0056] The control device 11 controls connection and disconnection between the optical subscriber line device 12-1 and the plurality of optical subscriber line terminals 30-2 using the optical selection unit 20a. For example, the control device 11 connects between the optical subscriber line device 12-1 and the plurality of optical subscriber line terminals 30-2 using the optical switching unit 23-1 of the optical selection unit 20a.

[0057] Before the optical subscriber line device 12-1 and the plurality of optical network units 30-2 are connected, the optical subscriber line device 12-1 stops communication between the plurality of optical network units 30-1 and the optical subscriber line device 12-1.

[0058] After the optical subscriber line device 12-1 and the plurality of optical network units 30-2 are connected, if the optical subscriber line device 12-1 receives a plurality of upstream signals transmitted from the plurality of optical network units 30-2, the optical subscriber line device 12-1 determines that the plurality of optical network units 30-2 can be aggregated to the optical subscriber line device 12-1. For example, the optical subscriber line device 12-1 determines that all of the optical subscriber line units 30-2 subordinate to the optical subscriber line device 12-2 can be aggregated to the optical subscriber line device 12-1.

[0059] This makes it possible to determine whether or not it is possible to aggregate a plurality of optical network units under the second optical network unit into the first optical network unit before actually aggregating them into the first optical network unit. Also, it is possible to avoid a situation in which communication becomes impossible when optical network units are actually aggregated into the optical network unit, thereby improving communication quality.

[0060] (Modification) In the modification of the embodiment, the main difference from the above embodiment is that the optical selecting unit includes an optical switching unit that is common to the optical subscriber line devices 12-1 and 12-2. In the modification of the embodiment, the differences from the above embodiment will be mainly described.

[0061] 3 is a diagram showing an example of the configuration of an optical communication system 1b according to a modification of the embodiment. The optical selecting unit 20b includes two branching units 21, two branching units 22, and an optical switching unit 24. The optical switching unit 24 includes the optical switching units 23-1 and 23-2 in the above embodiment.

[0062] The optical switching unit 24 connects the optical subscriber line device 12-1 and all of the optical network terminals 30-2 by switching the path in the optical selection unit 20b. For example, the optical switching unit 24 connects the optical subscriber line device 12-2 and all of the optical network terminals 30-1 by switching the path in the optical selection unit 20b. The optical switching unit 24 releases the connections between the optical subscriber line device 12-1 and all of the optical network terminals 30-2 by switching back the path in the optical selection unit 20a.

[0063] As described above, the optical selection unit 20b may include the optical switching unit 23 common to the optical subscriber line devices 12-1 and 12-2. This makes it possible to determine whether or not multiple optical subscriber line terminal devices under the second optical subscriber line device can be aggregated into the first optical subscriber line device before actually aggregating them into the first optical subscriber line device.

[0064] (Hardware Configuration) The determination device 121 (OSU control unit) provided in the optical subscriber line device 12 and the control device 11 (OLT control panel) provided in the optical subscriber line terminal 10 can also be realized by a computer and a program. The program may be recorded on a recording medium or provided via a network.

[0065] FIG. 4 illustrates an example of a hardware configuration of the optical line termination 10 according to an embodiment and a modified example of the embodiment. The optical line termination 10 is realized as software by a processor 101, such as a CPU (Central Processing Unit), executing a program stored in a storage device 103 having a non-volatile recording medium (non-transitory recording medium) and a memory 102. The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), and a CD-ROM (Compact Disc Read Only Memory), and non-transitory recording media such as a hard disk or a solid-state drive (SSD) built into a computer system. The communication unit 104 executes predetermined communication processing.

[0066] The optical line termination device 10 may be realized using hardware (accelerator) including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0067] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0068] The present invention is applicable to optical communication systems.

[0069] 1a, 1b...optical communication system, 10...optical line termination device, 11...control device, 12...optical line device, 13...port, 20a, 20b...optical selection unit, 21...branching unit, 22...branching unit, 23...optical switching unit, 24...optical switching unit, 30...optical line terminal, 40...branching unit, 50...branching unit, 101...processor, 102...memory, 103...storage device, 104...communication unit, 111...identification information storage device, 112...determination control unit, 113...switching control unit, 121...determination device, 122...communication unit, 123...transfer unit, 124...bandwidth control unit, 125...interface, 126...identification information storage unit, 127...maintenance control unit, 128...allocation control unit, 129...transmission control unit, 130...determination unit

Claims

1. An optical communications system comprising: a first passive optical network system having a first optical subscriber line device and a plurality of first optical subscriber line terminals; a second passive optical network system having a second optical subscriber line device and a plurality of second optical subscriber line terminals; and a control device that uses an optical selection unit to control connection and disconnection between the first optical subscriber line device and the plurality of second optical subscriber line terminals, wherein the control device connects between the first optical subscriber line device and the plurality of second optical subscriber line terminals using the optical selection unit; an optical communication system in which the first optical subscriber line device stops communication between the plurality of first optical subscriber line terminal devices and the first optical subscriber line device before the first optical subscriber line device and the plurality of second optical subscriber line terminal devices are connected, and when the first optical subscriber line device acquires a plurality of upstream signals transmitted from the plurality of second optical subscriber line terminal devices after the first optical subscriber line device and the plurality of second optical subscriber line terminal devices are connected, the first optical subscriber line device determines that the plurality of second optical subscriber line terminal devices can be aggregated to the first optical subscriber line device.

2. The optical communications system of claim 1, wherein the plurality of first optical subscriber line terminal devices maintain link and authentication between the first optical subscriber line device and the plurality of first optical subscriber line terminal devices for a certain period of time even if communication between the plurality of first optical subscriber line terminal devices and the first optical subscriber line device is stopped and a downstream signal cannot be obtained from the first optical subscriber line device.

3. The optical communications system of claim 1, wherein the first optical subscriber line device assigns logical link identifiers to the plurality of first optical subscriber line terminal devices that are different from logical link identifiers assigned to the plurality of second optical subscriber line terminal devices.

4. The optical communications system according to claim 1, wherein the first optical subscriber line device acquires the upstream signals while ignoring timestamps of the upstream signals transmitted from the second optical subscriber line terminal devices.

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