JP6529063B2 - PON system, OLT and transmission method - Google Patents

Description

  The present invention relates to a PON (Passive Optical Network) system that realizes optical fiber transmission, an OLT (Optical Line Terminal), and a transmission method.

  In recent years, as the speed of the radio access network provided by the mobile communication network is increased, the area (cell) covered by the base station apparatus becomes narrower, and as a result, the number of base station apparatuses to be installed to configure the mobile communication network. Is increasing. For this reason, as a network for accommodating a plurality of base station apparatuses, a passive optical network (PON: Passive Optical Network) system in which one optical transmission path is shared by a plurality of subscribers has been studied.

  In the PON system, one optical transmission line terminal (OLT: Optical Line Terminal) installed at a station of a telecommunications carrier is connected to a plurality of subscriber home terminals (ONUs: Optical Network Unit) via an optical splitter. It is done. The OLT realizes high bandwidth utilization efficiency by dynamically allocating an upstream band to a plurality of ONUs, for example, 64 ONUs by a time division multiplexing method.

  When a plurality of base station apparatuses are accommodated in the PON system, frequency and time synchronization between the base station apparatuses are essential. Conventionally, it has been common to install a GPS (Global Positioning System) antenna in each base station apparatus to receive reference time information. However, there have been cases in which the GPS antenna can not be installed due to restrictions such as the installation environment in the base station apparatus. Therefore, for example, Non-Patent Documents 1 and 2 disclose techniques for distributing frequency and time information from upper network devices to lower network devices and synchronizing the frequency and time of the entire network. In Non-Patent Document 3 and Patent Document 1, as shown in FIG. 6, a GPS antenna is installed in the OLT, and the frequency and time information received by the GPS antenna are distributed to each ONU via the optical access distribution network. Technology is disclosed.

JP, 2011-040870, A

IEEE Std 1588-2008, "IEEE Standard for a Precision Clock Synchronization Protocol for Network Measurement and Control Systems," 2008. K. Hann, "Synchronous Ethernet to Transport Frequency and Phase / Time," IEEE Communication Magazine, vol. 50, no. 8, pp. 152-160, August 2012. Takayoshi Tashiro et al., “A 10G-EPON System with Frequency and Time Synchronization for Mobile Backhaul Applications,” Theory of Communication (B), vol. J96-B, no. 3, pp. 321-329, March 2013.

  However, in the techniques described in Non-Patent Documents 1 and 2, upper and lower network devices must all be replaced with devices dedicated to frequency and time synchronization. For example, in order to provide time information from the OLT to each ONU via the IP network according to IEEE 1588, all devices on the IP network side must support IEEE 1588. For this reason, when there is at least one device that does not support IEEE 1588 on the IP network side, the clock signal can not be provided to each ONU.

  In the technology described in Non-Patent Document 3 and Patent Document 1, a coaxial cable for transmitting a GPS signal and a receiving device for receiving a GPS signal are installed in a station where an OLT is installed. Although it must be used, it is difficult to apply when the equipment installation space of the central office is limited.

  Furthermore, when adopting a loop back method in which the ONU acquires GPS signals, provides time information based on the GPS signals to the OLT, and distributes the time information from the OLT to each ONU, a failure of the ONU transmitting the GPS signals, etc. As a result, when time information based on GPS signals can not be transmitted to the OLT, the base stations under the system can not mutually synchronize time.

  The present invention has been made in view of such circumstances, and provides loopback of GPS signal time information acquired on the ONU side to the OLT, and distributes the time information to each ONU via the OLT. It is an object of the present invention to provide a PON system, an OLT and a transmission method capable of continuously performing time synchronization even when an ONU providing time information of GPS signals fails while realizing the system. Do.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the PON system of the present invention is a PON (Passive Optical Network) system that realizes optical fiber transmission, and acquires and acquires at least time information from a GPS signal receiving apparatus that receives a GPS (Global Positioning System) signal. First and second master ONUs that output the respective time information, and at least one slave ONU that acquires the time information output from the first or second master ONU and establishes synchronization; Through the connection device, it connects with the first and second master ONUs and at least one of the slave ONUs, acquires time information output from the first and second master ONUs, respectively, and the first master The first and second master ONUs and at least one of the slaves ON the time information acquired from the ONU If time information can not be acquired from the first master ONU while multicast distribution is performed, time information acquired from the second master ONU is determined by the distance from the first master ONU and the second information. Correction based on the round-trip propagation delay time due to the difference from the distance from the master ONU, and OLT that multicasts the corrected time information to the first and second master ONUs and at least one slave ONU. , And.

  As described above, since the first master ONU and the second master ONU are provided, even if the first master ONU can not provide time information based on the GPS signal due to a failure or the like, the GPS from the second master ONU It is possible to provide time information based on a signal. As a result, it becomes possible to continue time synchronization between subordinate base station apparatuses and to improve the reliability of the system. When time information can not be acquired from the first master ONU, the time information acquired from the second master ONU is the difference between the distance from the first master ONU and the distance from the second master ONU. It corrects based on the resulting round-trip propagation delay time, and multicasts the corrected time information to the first and second master ONUs and at least one slave ONU. Thereby, even if time information from the first master ONU can not be received, time synchronization between subordinate base station apparatuses is performed as if the time information is continuously provided from the first master ONU. It is possible to

  (2) In the PON system of the present invention, the OLT discards time information acquired from the second master ONU in a state in which time information is acquired from the first master ONU. I assume.

  As described above, in the state where the OLT acquires time information from the first master ONU, the time information acquired from the second master ONU is discarded, so that the processing load is not increased. On the other hand, when time information can not be acquired from the first master ONU, it is instantaneously acquired from the second master ONU that has been received until then, and the corrected time information is multicast-distributed continuously. It becomes possible to achieve time synchronization between subordinate base station apparatuses.

  (3) Further, the OLT of the present invention is an OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission, and the subordinate OLT that is connected via an optical splitter is A reception unit for receiving time information based on a GPS (Global Positioning System) signal from each of the first and second master ONUs; and time information received from the first master ONU as the first and second master ONUs. And, while multicasting to at least one subordinate slave ONU connected via an optical splitter, when time information can not be acquired from the first master ONU, the time acquired from the second master ONU Information is based on the round trip propagation delay time due to the difference between the distance from the first master ONU and the distance from the second master ONU Correct, the time information corrected, characterized in that it comprises a transmitter which multicast distribution to the first and second master ONU and at least one of said slave ONU.

  As described above, since the first master ONU and the second master ONU are provided, even if the first master ONU can not provide time information based on the GPS signal due to a failure or the like, the GPS from the second master ONU It becomes possible to acquire time information based on a signal. As a result, it becomes possible to continue time synchronization between subordinate base station apparatuses and to improve the reliability of the system. When time information can not be acquired from the first master ONU, the time information acquired from the second master ONU is the difference between the distance from the first master ONU and the distance from the second master ONU. It corrects based on the resulting round-trip propagation delay time, and multicasts the corrected time information to the first and second master ONUs and at least one slave ONU. Thereby, even if time information from the first master ONU can not be received, time synchronization between subordinate base station apparatuses is performed as if the time information is continuously provided from the first master ONU. It is possible to

  (4) Further, in the OLT according to the present invention, the receiving unit discards the time information acquired from the second master ONU in a state where the time information is received from the first master ONU. I assume.

  As described above, in a state in which time information is acquired from the first master ONU, the reception unit discards the time information acquired from the second master ONU, so that the processing load is not increased. On the other hand, when time information can not be acquired from the first master ONU, it is instantaneously acquired from the second master ONU that has been received until then, and the corrected time information is multicast-distributed continuously. It becomes possible to achieve time synchronization between subordinate base station apparatuses.

  (5) Further, the transmission method of the present invention is a transmission method of a PON (Passive Optical Network) system that realizes optical fiber transmission, wherein the first master ONU and the second master ONU are GPS (Global Positioning System). ) Obtaining at least time information from the GPS signal receiving apparatus that receives the signal, and outputting the acquired time information, and the time when at least one slave ONU is output from the first or second master ONU Acquiring information to establish synchronization; and an OLT connected to the first and second master ONUs and at least one of the slave ONUs via an optical splitter, the first and second masters. The time information output from the ONU is acquired respectively, and the time information acquired from the first master ONU is Multicast distribution to the master ONU and at least one slave ONU, and when the OLT can not acquire time information from the first master ONU, the time information acquired from the second master ONU is Correcting based on a round trip propagation delay time due to a difference between a distance from the first master ONU and a distance from the second master ONU, and correcting the time information after correction as the first and second time information; Multicasting to a master ONU as well as at least one said slave ONU.

  As described above, since the first master ONU and the second master ONU are provided, even if the first master ONU can not provide time information based on the GPS signal due to a failure or the like, the GPS from the second master ONU It is possible to provide time information based on a signal. As a result, it becomes possible to continue time synchronization between subordinate base station apparatuses and to improve the reliability of the system. When time information can not be acquired from the first master ONU, the time information acquired from the second master ONU is the difference between the distance from the first master ONU and the distance from the second master ONU. It corrects based on the resulting round-trip propagation delay time, and multicasts the corrected time information to the first and second master ONUs and at least one slave ONU. Thereby, even if time information from the first master ONU can not be received, time synchronization between subordinate base station apparatuses is performed as if the time information is continuously provided from the first master ONU. It is possible to

  (6) In the transmission method according to the present invention, the step of discarding the time information acquired from the second master ONU is further performed in a state where the OLT acquires time information from the first master ONU. It is characterized by including.

  As described above, in the state where the OLT acquires time information from the first master ONU, the time information acquired from the second master ONU is discarded, so that the processing load is not increased. On the other hand, when time information can not be acquired from the first master ONU, it is instantaneously acquired from the second master ONU that has been received until then, and the corrected time information is multicast-distributed continuously. It becomes possible to achieve time synchronization between subordinate base station apparatuses.

  According to the present invention, even if the first master ONU can not provide time information based on the GPS signal due to a failure or the like, the second master ONU can provide time information based on the GPS signal. As a result, it becomes possible to continue time synchronization between subordinate base station apparatuses and to improve the reliability of the system.

FIG. 1 is a diagram showing a schematic configuration of a PON system according to an embodiment of the present invention. FIG. 5 is a block diagram showing a schematic configuration of a primary and secondary master ONU. FIG. 2 is a block diagram showing a schematic configuration of an OLT 10; The schematic block diagram of slave ONU 50-3 is shown. It is a flowchart which shows operation | movement of the PON system which concerns on this embodiment. It is a figure which shows schematic structure of the conventional PON system.

  The present inventors provide the OLT with time information of GPS signals acquired on the ONU side, and distribute the time information to each ONU via the OLT. If the master ONU providing time information fails, time synchronization can not be achieved, and attention is paid to the fact that the reliability of the system is impaired, and a plurality of master ONUs providing time information of GPS signals are provided. When the master ONU can not provide time information due to a failure or the like, it has been found that the reliability of the system can be maintained by using the time information provided from another master ONU, and the present invention has been achieved.

  That is, the PON system of the present invention is a PON (Passive Optical Network) system that realizes optical fiber transmission, and acquires and acquires at least time information from a GPS signal receiving apparatus that receives a GPS (Global Positioning System) signal. First and second master ONUs that output the respective time information, and at least one slave ONU that acquires the time information output from the first or second master ONU and establishes synchronization; Through the connection device, it connects with the first and second master ONUs and at least one of the slave ONUs, acquires time information output from the first and second master ONUs, respectively, and the first master The first and second master ONUs and at least one of the slaves ON the time information acquired from the ONU If time information can not be acquired from the first master ONU while multicast distribution is performed, time information acquired from the second master ONU is determined by the distance from the first master ONU and the second information. Correction based on the round-trip propagation delay time due to the difference from the distance from the master ONU, and OLT that multicasts the corrected time information to the first and second master ONUs and at least one slave ONU. , And.

  With this configuration, even if the first master ONU can not provide time information based on the GPS signal due to a failure or the like, the second master ONU provides the time information based on the GPS signal. It is possible to continue the time synchronization between the subordinate base station apparatuses and improve the reliability of the system. Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a PON system according to an embodiment of the present invention. As shown in FIG. 1, under the OLT 10, a total of n (n is an arbitrary integer) ONUs 50-1 to n are connected via an optical splitter (optical splitter) 30. The GPS antennas 51-1 and 51-2 are respectively connected to two of them (in FIG. 1, the ONUs 50-1 and 50-2), and the time information received by the GPS antenna is transmitted to the other via the OLT 10. It is distributed to ONUs 50-3 to n. This time information may be distributed to the ONUs 50-1 and 50-2 via the OLT.

  Base stations 100-1 to 100-n are connected under the control of the ONUs 50-1 to 50-n. In the present embodiment, the ONU 50-1 to which the GPS antenna 51-1 is connected is referred to as "primary master ONU (first master ONU)", and the GPS antenna 51-2 is connected. The ONU 50-2 that is present is called a "secondary master ONU (second master ONU)". Also, the other ONUs 50-3 to n are referred to as “slave ONU”. Although the master ONU will be described as two primary and secondary in this embodiment, the present invention is not limited to two master ONUs.

  FIG. 2 is a block diagram showing a schematic configuration of the primary master ONU 50-1. In addition, since the secondary master ONU 50-2 also adopts the same configuration as the primary master ONU 50-1, the primary master ONU 50-1 will be described as an example here. The primary master ONU 50-1 is composed of a TRX 52 that performs optical transmission and reception, a CPU 54, and a UNI 58 that is a user network interface. In addition, the master master ONU 50-1 is provided with a master clock generation unit 56.

  The GPS signal received by the GPS antenna 51-1 is converted into time information (for example, an IEEE 1588 PTP packet or the like) by the clock generation unit 56 of the master. The upstream data signal is supplied to the CPU 54 via the UNI 58. The CPU 54 schedules an uplink signal to a transmittable time slot with the OLT 10, and multiplexes the time information and the data signal on the time axis in accordance with the time slot. The TRX 52 transmits time information and data signals to the OLT 10.

  FIG. 3 is a block diagram showing a schematic configuration of the OLT 10. The OLT 10 includes m (m is an arbitrary integer) OLT line cards 10-1 to 10-m. The line concentrator 18 collects the upstream signals of the OLT line cards 10-1 to 10-m and transfers them to the upper network, and distributes the downstream signals received from the upper network to the OLT line cards 10-1 to 10-m. Since the OLT line cards 10-1 to 10-m have the same configuration, in the present embodiment, the OLT line card 10-1 will be described as an example. The OLT line card 10-1 includes p TRXs 12-1 to 12 -p, a CPU 14, and a switch (SW) 16.

  The downstream signal received by the upper network is distributed to the OLT line cards 10-1 to 10-m in the line concentrator 18, and the SW 16 distributes the downstream signal to the TRX 12-1 to p to be transferred via the CPU 14. The flow of the time information signal will be described here using the TRX 12-1 as an example. The TRX 12-1 receives time information from the primary master ONU 50-1 and the secondary master ONU 50-2. When establishing a logical link with each master ONU, the OLT 10 recognizes one as a primary master ONU and one as a secondary master ONU. In the present embodiment, the primary is a master ONU 50-1 and the secondary is a master ONU 50-2.

  The upstream signal received by the TRX 12-1 is incident on the SW 16 via the CPU 14. In the SW 16, only the time information from the primary master ONU 50-1 in the upstream signal is selectively returned to the CPU 14 side. After that, time information is distributed by multicast to all ONUs under its control via the TRX 12-1.

  Here, if any failure occurs in the primary master ONU 50-1, the time synchronization means with all ONUs will be lost. Therefore, in the present embodiment, when the OLT 10 detects a failure of the primary master ONU 50-1, the time information to be looped and transferred by the SW 16 is switched to the secondary master ONU 50-2 side. Then, the difference between the optical fiber connection distance between the primary master ONU 50-1 and the OLT 10 and the optical fiber connection distance between the secondary master ONU 50-2 and the OLT 10 is an RTT (Round Trip Time) difference Correct with

  More specifically, when it is determined that a failure occurs in the primary master ONU 50-1 and the OLT line card 10-1 can not receive time information from the primary master ONU 50-1, the time information returned by the SW 16 is converted to the primary The master ONU 50-1 is switched to the secondary master ONU 50-2. Furthermore, the RTT difference between the primary master ONU 50-1 and the secondary master ONU 50-2 is calculated based on the RTT information acquired at the logical link establishment time of all ONUs, and the time difference of the time information corresponds to the RTT difference. Correct the stamp. As a result, even if a failure occurs in the primary master ONU 50-1, quick backup is possible in the secondary master ONU 50-2, and time synchronization with all ONUs can be continued.

  In addition, in order to suppress timing fluctuation due to uplink transmission of time information, it is preferable to control time information from the ONUs 50-1 and 50-2 to the OLT 10 to be transmitted in a fixed time slot and in a fixed cycle. Furthermore, on the OLT 10 side, it is preferable to control time information preferentially so as to have a predetermined processing delay.

  FIG. 4 shows a schematic block diagram of the slave ONU 50-3. Since the slave ONUs 50-3 to n have the same configuration, in the present embodiment, the slave ONU 50-3 will be described as an example. The slave ONU 50-3 includes the TRX 52, the CPU 54, and the UNI 58. Also, a slave clock generator 60 is provided. The slave ONUs 50-3 to n connected to the OLT 10 have different optical fiber connection distances, so the CPU 54 holds the RTT obtained when establishing the logical link with the OLT 10, and receives time from the OLT 10 at half the value of the RTT. Correct the information timestamp. The corrected time information is supplied to the slave clock generator 60, converted into a GPS signal by the slave clock generator 60, and supplied to the subordinate base station.

  FIG. 5 is a flowchart showing the operation of the PON system according to the present embodiment. First, the OLT 10 establishes a logical link with the ONUs 50-1 to 50-n (step S1), registers one of the two master ONUs as a primary master ONU, and transmits upper and lower signals including time information Is started (step S2). As described above, the primary master ONU is 50-1 and the secondary master ONU is 50-2.

  Next, the OLT 10 sets the SW 16 so as to loop back and transfer only the time information from the primary master ONU 50-1 (step S3). The OLT 10 determines whether or not there is a failure in the primary master ONU 50-1 (step S4). If the time information can be received normally, the process proceeds to step S3 on the assumption that there is no failure.

  On the other hand, if it is determined in step S4 that the time information from the primary master ONU 50-1 can not be received and it is determined that a failure has occurred in the primary master ONU 50-1, then only the time information from the secondary master ONU 50-2 is stored in the SW 16 It switches so as to transfer data back (step S5). Then, in the OLT 10, the time stamp of the time information acquired from the secondary master ONU 50-2 is corrected by the time difference corresponding to the RTT difference between the two master ONUs (step S6), and the corrected time information The multicast is distributed to the ONU, and the process proceeds to step S3.

  As described above, according to the present embodiment, since primary master ONU 50-1 and secondary master ONU 50-2 are provided, it is not possible to provide time information based on a GPS signal due to failure or the like of primary master ONU 50-1. Also, the secondary master ONU 50-2 can provide time information based on the GPS signal. As a result, it becomes possible to continue time synchronization between subordinate base station apparatuses and to improve the reliability of the system. Also, when time information can not be acquired from the primary master ONU 50-1, the time information time stamp acquired from the secondary master ONU 50-2 is determined by the optical fiber connection distance from the primary master ONU 50-1 and the distance from the secondary master ONU 50-2. It corrects based on the RTT difference resulting from the difference with the optical fiber connection distance, and multicasts the time information after correction to all subordinate ONUs. As a result, even if time information from the primary master ONU 50-1 can not be received, time synchronization between subordinate base station apparatuses is performed as if the time information is continuously provided from the primary master ONU 50-1. It is possible to

10 OLT
10-1 to 10-m OLT line card 12-1 to 12-p TRX (optical transceiver)
14 CPU
16 SW (switch)
18 concentrator 30 optical splitter (optical splitter)
50-1 Primary Master ONU
50-2 Secondary Master ONU
50-3 to 50-n slave ONU
51-1, 51-2 GPS antenna 52 TRX (optical transceiver)
54 CPU
56 Clock Generator (Master)
58 UNI (User Network Interface)
60 Clock Generator (Slave)
100-1 to 100-n base station

Claims (6)

A PON (Passive Optical Network) system in which a plurality of ONUs are connected via an optical splitter under an OLT to realize optical fiber transmission,
First and second master ONUs that acquire at least time information from a GPS signal receiving apparatus that receives GPS (Global Positioning System) signals and output the acquired time information to the OLT, respectively;
The time information output from the first master ONU and looped back at the OLT, or the time information output from the second master ONU corrected at the OLT, and at least one slave ONU establishing synchronization ,
The optical splitter connects to the first and second master ONUs and at least one of the slave ONUs via the optical splitter, and acquires time information output from the first and second master ONUs, respectively, If time information acquired from one master ONU is distributed by multicast to the first and second master ONUs and at least one slave ONU, but time information can not be acquired from the first master ONU, The time information acquired from the second master ONU is corrected based on the RTT difference caused by the difference between the distance from the first master ONU and the distance from the second master ONU, and the corrected time is obtained. An OLT for multicasting information to the first and second master ONUs and at least one slave ONU; PON system comprising: a.   The PON system according to claim 1, wherein the OLT discards time information acquired from the second master ONU in a state in which time information is acquired from the first master ONU. An OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A receiving unit for receiving time information based on a GPS (Global Positioning System) signal from the subordinate first and second master ONUs connected via the optical branching device;
The time information received from the first master ONU is distributed by multicast to at least one subordinate slave ONU connected via the first and second master ONUs and an optical splitter, while the first master When time information can not be acquired from the ONU, the time information acquired from the second master ONU is caused by the difference between the distance from the first master ONU and the distance from the second master ONU An OLT comprising: a transmitter that performs correction based on RTT differences and multicasts the corrected time information to the first and second master ONUs and at least one slave ONU.   The OLT according to claim 3, wherein the receiving unit discards time information acquired from the second master ONU in a state in which time information is received from the first master ONU. A transmission method of a PON (Passive Optical Network) system in which a plurality of ONUs are connected via an optical splitter under an OLT to realize optical fiber transmission,
A step of the first master ONU and the second master ONU acquiring at least time information from a GPS signal receiving apparatus that receives GPS (Global Positioning System) signals, and outputting the acquired time information to the OLT, respectively;
At least one slave ONU obtains time information output from the first master ONU and looped back at the OLT, or acquired from the second master ONU and corrected at the OLT, and establishes synchronization. Step of
Through the optical splitter, OLT connecting the first and second master ONU and at least one of said slave ONU is the time information output from said first and second master ONU obtains respectively, Multicast distributing time information acquired from the first master ONU to the first and second master ONUs and at least one slave ONU;
When the OLT can not acquire time information from the first master ONU, the time information acquired from the second master ONU, the distance from the first master ONU, and the second master ONU Multicasting the corrected time information to the first and second master ONUs and the at least one slave ONU based on the RTT difference caused by the difference between the first and second master ONUs. Transmission method characterized by   6. The transmission according to claim 5, further comprising: discarding time information acquired from the second master ONU in a state where the OLT acquires time information from the first master ONU. Method.

Images