Patent Application
20230275682
The present invention relates to a technology for conducting communication by performing time-division multiplexing on optical signals in an optical ring network that forms a communication system.
A conventional optical ring network system conducts communication by multiplexing optical signals having wavelengths allocated beforehand to a plurality of optical transmission devices connected to an optical ring network by an optical add-drop multiplexer (OADM) technology (see Non Patent Literature 1, for example).
On the other hand, there is a known optical burst ring network technology for transmitting optical signals by time-division multiplexing, instead of OADM. By this technology, one optical transmission among a plurality of optical transmission devices connected to an optical ring network operates as a master device, and the other optical transmission devices operate as slave devices. The master device transmits an allocation signal and a search signal, to control the data transmission timings of the slave devices including the subject device, and register a slave device newly connected to the optical ring network. In this manner, the plurality of optical transmission devices connected to the optical ring network can conduct communication by perform time-division multiplexing on optical signals by the optical burst ring network technology.
Non Patent Literature 1: Sakamaki et al., “Optical Switch Technology for Obtaining More Flexible Optical Nodes”, NTT Technology Journal, November 2013 (https://www.ntt.co.jp/journal/1311/files/jn201311016.pdf)
By the optical burst ring network technology, however, in a case where the master device cannot operate properly due to a failure or the like, the data transmission timing and the like are not controlled, and therefore, it is difficult to continue the system operation.
The present invention aims to provide a communication device, a communication method, a communication system, and a communication program that enable continuation of a system operation by causing a slave device to operate as a new master device in a case where the master device that controls a plurality of optical transmission devices connected to an optical ring network that conducts communication by performing time-division multiplexing on optical signals cannot operate properly.
A communication device according to the present invention includes: a communication unit that is connected to an optical ring network, conducts optical signal communication by time-division multiplexing, and receives a control signal for controlling an optical signal transmission timing from a master communication device; and a determination unit that determines the master communication device not to be operating properly and causes the subject communication device to operate as a new master communication device, in a case where the control signal is not received in a predetermined period.
The present invention also relates to a communication method that is used in a communication system in which a plurality of communication devices is connected by an optical ring network, one of the communication devices being a master communication device, the other ones of the communication devices being slave communication devices. The master communication device transmits a control signal for controlling the transmission timings to transmit optical signals to a plurality of the slave communication devices by time-division multiplexing. Each slave communication device transmits an optical signal to the optical ring network on the basis of the transmission timing of the control signal received from the master communication device, and, in a case where the control signal is not received in a predetermined period, determines the master communication device not to be operating properly, and causes the subject communication device to operate as a new master communication device.
The present invention also relates to a communication system in which a plurality of communication devices is connected by an optical ring network, one of the communication devices being a master communication device, the other ones of the communication devices being slave communication devices. The master communication device transmits a control signal for controlling the transmission timings to transmit optical signals to a plurality of the slave communication devices by time-division multiplexing. Each slave communication device transmits an optical signal to the optical ring network on the basis of the transmission timing of the control signal received from the master communication device, and, in a case where the control signal is not received in a predetermined period, determines the master communication device not to be operating properly, and causes the subject communication device to operate as a new master communication device.
Further, a communication program according to the present invention causes a computer or an integrated circuit to perform the processes that are performed by the determination unit of the communication device described above.
A communication device, a communication method, a communication system, and a communication program according to the present invention enable continuation of a system operation by causing a slave device to start operating as the new master device, in a case where the master device that controls a plurality of optical transmission devices connected to an optical ring network that conducts communication by performing time-division multiplexing on optical signals cannot operate properly.
The following is a description of an embodiment of a communication device, a communication method, a communication system, and a communication program according to the present invention, with reference to the drawings. Note that the embodiment described below concerns an optical ring network system (corresponding to the communication system) that includes a plurality of optical transmission devices (corresponding to the communication devices) connected via an optical ring network.
In the example illustrated in
In a case where an explanation common to the optical transmission device 101-A, the optical transmission device 101-B, the optical transmission device 101-C, and the optical transmission device 101-D is made herein, the alphabet at the end of each reference numeral is omitted, and each optical transmission device is referred to as the optical transmission device 101. In a case where a specific device among the plurality of optical transmission devices 101 is described, the specific device is referred to as the optical transmission device 101-A, for example, with an alphabet added at the end of reference numeral. The same applies to an external network (NW) 103-A, an external NW 103-B, an external NW 103-C, and an external NW 103-D.
The external NWs 103 are connected to the respective optical transmission devices 101, and communication between these external NWs 103 can be performed via the optical ring network 102.
The external NWs 103 are NWs connected to the optical ring network system mentioned above, and have NW devices or the like connected thereto.
Here, the optical ring network system 100 according to the embodiment uses an optical burst ring network technology. By this technology, the plurality of optical transmission devices 101 performs time-division multiplexing (optical time division multiple access (TDMA)) on optical signals, to conduct communication in the optical ring network 102. Note that the optical ring network system 100 may be operated with one wavelength, or may be operated by wavelength multiplexing. In the case of wavelength multiplexing, optical signals are subjected to time-division multiplexing for each wavelength.
In
The optical transmission device 101 as the master device determines the optical signal transmission timings for the optical transmission devices 101 including the master device, and transmits an allocation signal for allocating the optical signal transmission timings to the optical transmission devices 101 as the slave devices. The optical transmission device 101 as the master device also transmits a search signal for detecting an optical transmission device 101 as a slave device newly connected to the optical ring network 102. Note that the allocation signal and the search signal correspond to the control signal transmitted from the master device to the slave devices.
Here, an allocation signal includes information for allocating an optical signal transmission timing. For example, an allocation signal includes information such as a device identifier for identifying the allocation-target optical transmission device 101, a transmission start time indicating the time to start transmitting the optical signal, and a transmission time (transmission duration) indicating the time during which the optical signal is to be transmitted. A search signal includes information such as a transmission start time indicating the time at which the newly connected optical transmission device 101 is to start transmitting a registration request signal for requesting registration to the master device, and a transmission time indicating the time during which the registration request signal is to be transmitted.
An optical transmission device 101 as a slave device transmits an optical signal at the transmission timing allocated by an allocation signal received from the master device. Further, in a case where an optical transmission device 101 as a slave device is newly connected to the optical ring network 102, the optical transmission device 101 transmits a registration request signal to the master device, on the basis of a search signal received from the master device. In this manner, the optical transmission device 101 as a slave device newly connected to the optical ring network 102 can be registered with the master device. After that, the registered optical transmission device 101 as a slave device can transmit an optical signal at the transmission timing allocated by an allocation signal received from the master device.
As described above, in the embodiment, the optical transmission device 101 functioning as the master device controls the timings at which all the optical transmission devices 101 including the master device transmit optical signals, registration of an unregistered optical transmission device 101 to be newly connected, and the like.
(Allocation Signals)
The optical transmission device (master) 101-A transmits an allocation signal (a control signal) for allocating a transmission timing to each optical transmission device (slave) 101 at time T1 (shown as [allocation Tx]). At time T2, the optical transmission device (slave) 101-B then receives the allocation signal (shown as [allocation Rx]). Likewise, the optical transmission devices (slaves) 101-C and 101-D receive the allocation signal at times T3 and T4, respectively. Note that the optical transmission device (master) 101-A also allocates a timing for transmitting a data signal to the master device. In the example in
The data signal transmitted from the optical transmission device (master) 101-A at time T5 is then received by the optical transmission devices (slaves) 101-B, 101-C, and 101-D at times T6, T7, and T8, respectively. Here, the above operation is represented by T5 [A Tx]->T6 [A Rx]->T7 [A Rx]->T8 [A Rx]. Likewise, the data signal transmitted from the optical transmission device (slave) 101-B at time T9 is received by the optical transmission devices (slaves) 101-C and 101-D and the optical transmission device (master) 101-A at times T10, T11, and T12, respectively. Likewise, the data signal transmitted from the optical transmission device (slave) 101-C at time T13 is received by the optical transmission device (slave) 101-D, the optical transmission device (master) 101-A, and the optical transmission device (slave) 101-B at times T14, T15, and T16, respectively. Likewise, the data signal transmitted from the optical transmission device (slave) 101-D at time T17 is received by the optical transmission device (master) 101-A and the optical transmission devices (slaves) 101-B and 101-C at times T18, T19, and T20, respectively.
As described above, since one of the optical transmission devices 101 connected to the optical ring network 102 operates as the master device, and the master device allocates optical signal transmission timings to all the optical transmission devices 101, communication by time-division multiplexing becomes possible.
(Search Signals)
At time T1, the optical transmission device (master) 101-A transmits a control signal (referred to as a search signal) for searching for an unregistered optical transmission device (slave) 101-B to be newly connected to the optical ring network 102 (shown as [search Tx]). At time T2, the optical transmission device (slave) 101-B then receives the search signal (shown as [search Rx]). At time T3, which is the transmission start time written in the search signal, the unregistered optical transmission device (slave) 101-B that has received the search signal transmits a control signal (referred to as a registration request signal) for requesting registration to the optical transmission device (master) 101-A. The optical transmission device (master) 101-A that has received the registration request signal at time T4 performs a registration process, and transmits a control signal (a registration notification signal) for issuing a registration notification, to notify the optical transmission device (slave) 101-B that the registration is completed (T5). Note that the optical transmission device (slave) 101-B that has received the registration notification signal at time T6 may transmit an acknowledgement signal indicating that the registration notification signal has been confirmed to the optical transmission device (master) 101-A at time T7, which is the transmission start time written in the registration notification signal. In this case, the optical transmission device (master) 101-A receives the acknowledgement signal at time T8.
In this manner, one of the optical transmission devices 101 connected to the optical ring network 102 operates as the master device, and the master device can transmit a search signal and register the optical transmission device 101 to be newly connected.
Here, in a case where the master device cannot operate properly due to a failure or the like in the optical ring network system 100 illustrated in
(Example Configuration of an Optical Transmission Device 101)
In this manner, the four optical transmission devices 101 described with reference to
In
The L1 unit 201 has a function of processing an OSI-reference-model first layer (a physical layer).
The L2 unit 202 has a function of processing an OSI-reference-model second layer (a data link layer). In the embodiment, the L2 unit 202 includes a signal sensing unit 211 described later. The signal sensing unit 211 senses an allocation signal or a search signal from an optical signal received from the optical ring network 102. The L2 unit 202 also has the functions of a master device and the functions of a slave device, and operates with the functions of either device, on the basis of a command from the master-slave selection unit 210 described later. In the case of a master device, the L2 unit 202 performs transmission timing control, and senses and registers an unregistered optical transmission device 101. In the case of a slave device, the L2 unit 202 controls the transmission timing of the optical signal to be transmitted from the B-Tx unit 204 in accordance with the transmission start time and the transmission time designated by the master device, and receives a search signal from the master device to perform registration.
The SW unit 203 is an electric packet switch such as a L2-SW connected to the external NW 103, and has a function of processing a packet transfer between the L2 unit 202 and the external NW 103 in accordance with preset rules.
The B-Tx unit 204 is a transmission unit that intermittently outputs an optical signal, and transmits a signal transferred from the L1 unit 201 as an optical signal to an optical fiber via an optical coupler in a burst manner.
The B-Rx unit 205 is a reception unit that intermittently receives an optical signal, receives an optical signal from an optical fiber in a burst manner via an optical coupler, and transfers the signal to the L1 unit 201. Here, the B-Tx unit 204 and the B-Rx unit 205 correspond to the communication unit.
The optical coupler 206 and the optical coupler 207 each have a function of branching the power of an input optical signal.
The signal information storage unit 208 is formed with a storage medium such as a semiconductor memory. In a case where the subject device to which the signal information storage unit 208 belongs is a slave device, the information written in an allocation signal or a search signal received from the master device is stored in a list format (referred to as a band information list) item by item in the signal information storage unit 208, and can be rearranged item by item by the determination unit 209 described later. For example, in a case where the items in the band information list of an allocation signal are “device identifier, transmission start time, and transmission time”, the list can be rearranged in descending order of transmission start times. Note that, as described above with reference to
The determination unit 209 receives a notification of the reception status of an allocation signal or a search signal from the signal sensing unit 211 of the L2 unit 202, and determines the state of the master device. For example, in a case where neither an allocation signal nor a search signal is received in a predetermined period, the determination unit 209 determines that the master device cannot operate properly due to a failure or the like. In a case where the determination unit 209 determines that the master device cannot operate properly due to a failure or the like, the determination unit 209 then determines whether the subject device is to operate as the master device. For example, the determination unit 209 determines whether the subject device should operate as the new master device, on the basis of the band information list of the allocation signal stored in the signal information storage unit 208. Note that the method for determining whether the subject device should operate as the new master device on the basis of the band information list will be described later. The determination unit 209 then instructs the master-slave selection unit 210 that the subject device is to operate as the master device or is to operate as a slave device. Here, the determination as to whether the subject device is to operate as the master device is performed simultaneously in all the optical transmission devices 101 operating as the slave devices connected to the optical ring network 102. Note that, in the embodiment, a process is performed so that a plurality of slave devices does not operate as master devices. This process will be described later with reference to a flowchart.
The master-slave selection unit 210 exclusively controls whether the optical transmission device 101 is to function as the master device or a slave device, on the basis of an instruction from the determination unit 209. In a case where the optical transmission device 101 is to function as the master device, the master-slave selection unit 210 activates the timing control master unit 212 and the network registration master unit 213 of the L2 unit 202. In a case where the optical transmission device 101 is to function as a slave device, on the other hand, the master-slave selection unit 210 activates the timing control slave unit 312 and the network registration slave unit 313 of the L2 unit 202.
The signal sensing unit 211 senses an allocation signal or a search signal from an optical signal received from the optical ring network 102. The signal sensing unit 211 then stores information regarding the sensed allocation signal or search signal into the signal information storage unit 208, and notifies the determination unit 209 of the reception status. Here, the information regarding the allocation signal or search signal includes information such as the device identifier, the transmission start time, and the transmission time. Further, a reception status is information such as the presence/absence of reception of an allocation signal or a search signal, and a reception time, for example.
The timing control master unit 212 operates in a case where the master-slave selection unit 210 causes the subject device to function as the master device. The timing control master unit 212 has a function of determining transmission timings for all the optical transmission devices 101 connected to the optical ring network 102 including the subject device, and gives the subject device (or a slave device) an instruction regarding the time to transmit an optical signal and the duration of transmission. Note that, for the subject device, the timing control master unit 212 controls the transmission timing of the optical signal to be transmitted from the B-Tx unit 204. Instructions regarding the transmission timings for the optical transmission devices 101 other than the subject device are issued through communication performed by the L1 unit 201, the L2 unit 202, the B-Tx unit 204, and the B-Rx unit 205.
The network registration master unit 213 operates in a case where the master-slave selection unit 210 causes the subject device to function as the master device. The network registration master unit 213 executes an initial connection sequence with an unregistered optical transmission device 101, to sense connection of the unregistered optical transmission device 101 to the optical ring network 102 and register the unregistered optical transmission device 101 in the optical ring network system 100. Specifically, the network registration master unit 213 transmits a search signal to search for an unregistered optical transmission device 101 to be newly connected. When receiving a registration request signal from the unregistered optical transmission device 101 in response to the search signal, the network registration master unit 213 then performs a registration process as a connection device to the optical ring network 102, and transmits a registration notification signal to the unregistered optical transmission device 101.
The timing control slave unit 312 operates in a case where the master-slave selection unit 210 causes the subject device to function as a slave device. The timing control slave unit 312 controls the transmission timing of the optical signal to be transmitted from the B-Tx unit 204, in accordance with the transmission start time and the transmission time designated by the master device.
The network registration slave unit 313 operates in a case where the master-slave selection unit 210 causes the subject device to function as a slave device. As described above with reference to
As described above, each optical transmission device 101 according to the embodiment can operate as a master device or a slave device. In a case where the subject device is a slave device, a check is made to determine whether the master device is operating properly, on the basis of the reception status of an allocation signal or a search signal transmitted from the master device. In a case where it is determined that the master device cannot operate properly due to a failure or the like, the subject device or another slave device operates as the master device. Thus, the optical ring network system 100 can have redundancy, and the system operation can be continued.
(Band Information List)
Next, the band information list is described. For example, in a case where the items in the band information list obtained through an allocation signal is “device identifier, transmission start time, and transmission time”, the band information list shown below is stored into the signal information storage unit 208. Here, each item in the band information list can be rearranged by the determination unit 209. Also, s (s being integers) indicates the order in the list. Note that an allocation signal contains information such as the “device identifiers, transmission start times, and transmission times” of all the allocation target devices, and thus, each slave device can be notified of information about the other slave devices.
(Example of the Band Information List)
The band information list is rearranged in descending order of transmission start times. For example, the list is rearranged in the order of TA<TB<TC. In the list with s=0 and the earliest transmission start time, the device identifier is AAA, the transmission start time is TA, and the transmission time is 10. In the list with s=1, the device identifier is BBB, the transmission start time is TB, and the transmission time is 5. In the list with s=2, the device identifier is CCC, the transmission start time is TC, and the transmission time is 10. Note that the transmission start times and the transmission times are indicated on the order of nanoseconds, for example. The determination unit 209 determines whether the subject device is to operate as the new master device, in accordance with the list rearranged in this manner. For example, by determining beforehand that the slave device having the device identifier with the earliest transmission start time is to operate as the new master device, the determination unit 209 can select one new master device from a plurality of slave devices.
(Process of Switching to the Master Device)
In step S101, the optical transmission device 101 operating as a slave device starts performing a process of determining whether the master device is operating properly.
In step S102, the determination unit 209 resets a counter i and a counter s to 0.
In step S103, the determination unit 209 makes the process to stand by for a preset time t. Here, the time t has a greater value than the time intervals at which the master device transmits allocation signals or search signals.
In step S104, the determination unit 209 checks whether an allocation signal or a search signal has been received from the master device through the signal sensing unit 211. If an allocation signal or a search signal has been received (Y), the process returns to step S102, and the same process is repeated. If neither of the signals has been received (N), the process moves on to the process in step S105. Note that the signal sensing unit 211 stores the received allocation signal or information regarding a search signal into the signal information storage unit 208, and creates the band information list.
In step S105, the determination unit 209 increments the counter i by one, and moves on to the process in step S106.
In step S106, the determination unit 209 determines whether the counter i has reached a preset threshold k (k being an integer). If i=k (Y), the process moves on to the process in step S107. If i<k (N), the process returns to the process in step S103, and the same process is repeated. In the process in this step, a check is made to determine whether an allocation signal or a search signal is to be received in a predetermined period (a period of t×k in the example in
In step S107, the determination unit 209 refers to the band information list stored in the signal information storage unit 208, performs rearrangement under a predetermined condition, and determines whether the subject device satisfies the condition. For example, the band information list is rearranged in descending order of transmission start times, and a check is made to determine whether the sth device identifier is the identifier of the subject device. If the sth device identifier is the identifier of the subject device (Y), the process moves on to step S111. If the sth device identifier is not the identifier of the subject device (N), the process moves on to step S108. In the example of the band information list described above, the sth=0th device identifier with the earliest transmission start time is AAA. Therefore, if the identifier of the subject device is AAA, the process moves on to step S111, and the subject device starts operating as the master device.
In step S108, the determination unit 209 makes the process to stand by for a preset time t1. Here, time t1 has a greater value than the time required for another slave device to start operating as the master device.
In step S109, the determination unit 209 checks whether an allocation signal or a search signal has been received from the new master device through the signal sensing unit 211. If an allocation signal or a search signal has been received (Y), the process returns to step S102, and the same process is repeated. If neither of the signals has been received (N), the process moves on to the process in step S110.
In step S110, the determination unit 209 increments the counter s by one, and returns to the process in step S107. As the processes from step S107 to step S110 are repeated, one of the slave devices connected to the optical ring network system 100 can be selected, and the selected slave device can reliably start operating as the new master device.
In step S111, since the subject device is selected as the new master device, the determination unit 209 instructs the master-slave selection unit 210 that the subject device is to start operating as the master device.
In step S112, the optical transmission device 101 that has been operating as a slave device starts operating as the master device, and ends the process illustrated in
As described above, in a case where the subject device is a slave device, the optical transmission device 101 according to the embodiment determines whether the master device is operating properly, on the basis of the reception status of an allocation signal or a search signal transmitted from the master device. In a case where the master device is determined not to be able to operate properly due to a failure or the like, one of the optical transmission devices 101 operating as slave devices starts operating as the master device. Thus, it is possible to make the optical ring network system 100 redundant, and the system operation is continued even when a failure occurs in the master device.
The optical ring network system 800 of the comparative example in
Here, in
Here, in the comparative example, the optical transmission device (master) 801-A is set as the master device in advance, and the optical transmission device (slave) 801-B is set as the slave device in advance. On the other hand, the optical transmission device 101 according to the embodiment in
In
Like the timing control master unit 212 of the embodiment illustrated in
Like the network registration master unit 213 of the embodiment illustrated in
As described above, the optical transmission device (master) 801-A of the comparative example is designed beforehand to function as the master device.
Meanwhile, the optical transmission device (slave) 801-B set as a slave device in
Like the timing control slave unit 312 of the embodiment illustrated in
Like the network registration slave unit 313 of the embodiment illustrated in
As described above, each optical transmission device 801 of the comparative example is set as the master device or a slave device in advance. For example, in the case illustrated in
On the other hand, each optical transmission device 101 according to the embodiment described above with reference to
As described so far, with a communication device, a communication method, a communication system, and a communication program according to the present invention, a slave device starts operating as the new master device in a case where the master device that controls a plurality of optical transmission devices connected to an optical ring network that conducts communication by performing time-division multiplexing on optical signals cannot operate properly. Thus, the system operation can be continued.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/027563 | 7/15/2020 | WO |
