JP6426459B2 - PON system, ONU, OLT and transmission method - Google Patents

Description

  The present invention relates to a PON (Passive Optical Network) system that realizes optical fiber transmission, an ONU (Optical Network Unit), 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 congestion is generated in the OLT when adopting a loopback 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, Fluctuation occurs in the transfer processing time of the time information transmitted from the ONU, and the time synchronization accuracy in each ONU is degraded.

  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. An object of the present invention is to provide a PON system, an ONU, an OLT, and a transmission method capable of maintaining the accuracy of time synchronization even when traffic is congested on the OLT side while realizing the scheme.

  (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 in which an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units) are connected via an optical splitter to realize optical fiber transmission. A clock generation unit for acquiring at least time information from a GPS signal receiving apparatus that receives a GPS (Global Positioning System) signal, and transmitting the acquired time information to the OLT; and the time information transmitted from the clock generation unit And RTT monitoring unit for monitoring the round-trip transmission delay time until returning from the OLT, wherein the RTT monitoring unit corrects when the round-trip transmission delay time under monitoring is larger than a predetermined threshold value. When information is transmitted to the OLT, and the OLT receives the correction information, the time information is corrected using the correction information, and after correction Time information, the multicast distributed to each ONU, each ONU based on the time information of the corrected received from the OLT, and wherein the establishing a mutual synchronization.

  As described above, the RTT monitoring unit transmits correction information to the OLT when the round-trip transmission delay time under monitoring is larger than a predetermined threshold, and the OLT receives the correction information when the correction information is received. The time information is corrected using the time information, and the time information after correction is distributed by multicast to each ONU, and each ONU establishes synchronization with each other based on the time information after correction received from the OLT. When the round trip transmission delay time fluctuates and becomes larger than the threshold due to a cause such as congestion, correction information is provided to the OLT and time information is corrected, so that accurate time information is multicasted to each ONU It is possible to This makes it possible to maintain the accuracy of time synchronization in each ONU.

  (2) In the PON system of the present invention, when the OLT does not receive the correction information, it multicasts the time information received from the clock generation unit to the ONUs, and the ONUs And establishing synchronization with each other based on time information received from the OLT.

  As described above, when the OLT does not receive the correction information, it multicasts the time information received from the clock generation unit to each ONU, and each ONU mutually transmits the time information based on the time information received from the OLT. Since synchronization is established, it is possible to apply a loopback method using GPS signals to the PON system.

  (3) The PON system according to the present invention is characterized in that the clock generation unit and the RTT monitoring unit are provided in any one ONU as a master ONU.

  As described above, since the clock generation unit and the RTT monitoring unit are provided in any one ONU as a master ONU, time information is acquired from the GPS signal by any one ONU among a plurality of ONUs, Loopback transfer via the OLT can be realized, and time information can be multicast distributed to each ONU. This makes it possible to maintain the accuracy of time synchronization between each ONU in the PON system.

  (4) Also, the ONU of the present invention is an ONU (Optical Network Unit) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission, and is a GPS signal that receives a GPS (Global Positioning System) signal. A clock generation unit that acquires at least time information from a receiving apparatus and transmits the acquired time information to the OLT, and time information transmitted from the clock generation unit to the time information transmitted from the clock generation unit And RTT monitoring unit for monitoring a round trip transmission delay time until returning from the OLT, and transmitting correction information to the OLT if the round trip transmission delay time under monitoring is larger than a predetermined threshold. It is characterized by

  In this manner, at least time information is acquired from the GPS signal receiving apparatus that receives the GPS signal, and the acquired time information is transmitted to the OLT, and the time information transmitted from the clock generation unit reciprocates until it returns from the OLT The transmission delay time is monitored, and correction data is sent to the OLT if the monitored round trip transmission delay time is larger than a predetermined threshold, the round trip transmission delay time is determined due to traffic congestion at the OLT. If it fluctuates and becomes larger than the threshold value, it becomes possible to provide correction information to the OLT. As a result, in the OLT, time information can be corrected to a correct one, and accurate time information can be distributed by multicast to each ONU. This makes it possible to maintain the accuracy of time synchronization in each ONU.

  (5) The OLT according to the present invention is an OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission, and receives time information provided from a GPS signal receiving apparatus Receiving unit, a transmitting unit for multicasting the time information to a subordinate ONU (Optical Network Unit), and the receiving unit are transmitted when the round-trip transmission delay time of the time information is larger than a predetermined threshold value. A control unit that corrects time information using the correction information when the correction information is received, and the transmission unit multicasts the corrected time information to each of the ONUs. .

  As described above, when the receiving unit receives the correction information to be transmitted when the round-trip transmission delay time of the time information is larger than the predetermined threshold, the time information is corrected using the correction information, and the corrected time information is corrected. Since time information is distributed by multicast to each ONU, even if the round trip transmission delay time fluctuates and becomes larger than the threshold due to traffic congestion at the OLT, etc., the time information is corrected using correction information It becomes possible to make corrections, and it becomes possible to multicast accurate time information to each ONU. This makes it possible to maintain the accuracy of time synchronization in each ONU.

  (6) Further, according to the transmission method of the present invention, an optical line terminal (OLT) and a plurality of optical network units (ONUs) are connected via an optical splitter to realize an optical fiber transmission (passive optical network) A transmission method of a system, wherein a clock generation unit acquires at least time information from a GPS signal receiving apparatus that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT, and RTT monitoring And monitoring the round-trip transmission delay time until the time information transmitted from the clock generation unit returns from the OLT, and the round-trip transmission delay time being monitored by the RTT monitoring unit is predetermined. Sending correction information to the OLT if the threshold is larger than the threshold value, and the correction information if the OLT receives the correction information. The time information is corrected using the following step, and the time information after correction is distributed by multicast to each of the ONUs, and each of the ONUs mutually establishes synchronization based on the time information after correction received from the OLT. And at least including the step of

  As described above, the RTT monitoring unit transmits correction information to the OLT when the round-trip transmission delay time under monitoring is larger than a predetermined threshold value, and the OLT receives the correction information when the correction information is received. The time information is corrected using the time information, and the time information after correction is distributed by multicast to each ONU, and each ONU establishes synchronization with each other based on the time information after correction received from the OLT. When the round trip transmission delay time fluctuates and becomes larger than the threshold due to a cause such as congestion, correction information is provided to the OLT and time information is corrected, so that accurate time information is multicasted to each ONU It is possible to This makes it possible to maintain the accuracy of time synchronization in each ONU.

  According to the present invention, when the round trip transmission delay time fluctuates due to traffic congestion at the OLT and becomes larger than the threshold, the correction information is provided to the OLT, and the time information is corrected. It is possible to multicast the appropriate time information to each ONU. This makes it possible to maintain the accuracy of time synchronization in each ONU.

FIG. 1 is a diagram showing a schematic configuration of a PON system according to an embodiment of the present invention. It is a block diagram which shows schematic structure of master ONU50-1. FIG. 2 is a block diagram showing a schematic configuration of an OLT 10; The schematic block diagram of slave ONU 50-2 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 traffic congestion or the like occurs, fluctuations occur in the transfer processing time of the time information transmitted from the ONU, and attention is paid to the fact that the time synchronization accuracy between the ONUs is degraded. In the case where the round trip transmission delay time fluctuates due to the congestion, the time difference is notified to the OLT, and by correcting the time information on the OLT side, it is found that the accuracy of time synchronization between the ONUs can be maintained. It came to do this invention.

  That is, the PON system of the present invention is a PON (Passive Optical Network) system in which an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units) are connected via an optical splitter to realize optical fiber transmission. A clock generation unit for acquiring at least time information from a GPS signal receiving apparatus that receives a GPS (Global Positioning System) signal, and transmitting the acquired time information to the OLT; and the time information transmitted from the clock generation unit And RTT monitoring unit for monitoring the round-trip transmission delay time until returning from the OLT, wherein the RTT monitoring unit corrects when the round-trip transmission delay time under monitoring is larger than a predetermined threshold value. When information is transmitted to the OLT, and the OLT receives the correction information, the time information is corrected using the correction information, and after correction Time information, the multicast distributed to each ONU, each ONU based on the time information of the corrected received from the OLT, and wherein the establishing a mutual synchronization.

  With this configuration, the present inventors provide correction information to the OLT even when the round trip transmission delay time fluctuates and becomes larger than the threshold value due to traffic congestion in the OLT, etc. It is possible to multicast accurate time information to each ONU by correcting. Then, it is possible to maintain the accuracy of time synchronization in each ONU. 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 50-n are connected via the optical splitter 30. The GPS antenna 51 is connected to one of them (the ONU 50-1 in FIG. 1), and the time information received by the GPS antenna is distributed to the other ONUs 50-2 to n through the OLT 10. 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 is connected is referred to as "master ONU", and the other ONUs 50-2 to n are referred to as "slave ONU".

  FIG. 2 is a block diagram showing a schematic configuration of the master ONU 50-1. The 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. The master ONU 50-1 is provided with a clock generation unit 56 and an RTT monitoring unit 57 of the master. The GPS signal received by the GPS antenna 51 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 a time slot capable of transmitting an uplink signal to and from the OLT 10, and multiplexes time information and 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.

  The master ONU 50-1 receives the time information transmitted by itself at the TRX 52 via the OLT 10. The CPU 54 selects only the time information from the downlink signal and transfers it to the clock generation unit 56 of the master. The clock generation unit 56 constantly monitors round trip delay time (RTT: Round Trip Time) until the RTT monitoring unit 57 receives the time information transmitted by itself. When the RTT largely fluctuates due to congestion of traffic processed on the OLT 10 side and the RTT fluctuation continues more than a preset threshold time, the time difference corresponding to the RTT fluctuation is notified to the OLT 10. Here, when the traffic fluctuation occurs in a very short time, the time difference is not notified to the OLT 10, and the time correction on the OLT 10 side is not performed.

  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, a time correction unit 15, 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 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 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, in order to perform time synchronization with all ONUs accurately, congestion occurs in the traffic to be processed by the SW 16 and RTT fluctuation is correctly grasped even when the fluctuation of RTT monitored by the master ONU 50-1 becomes large. And the time difference corresponding to the RTT fluctuation must be properly corrected. Therefore, in the PON system according to the present embodiment, when the RTT fluctuation is continuously detected by the ONU 50-1, the time difference corresponding to the RTT fluctuation is notified to the OLT 10, and the time difference is corrected on the OLT side. Take

  More specifically, when the OLT line card 10-1 receives the time difference from the master ONU 50-1, the time correction unit 15 of the CPU 14 notifies the time stamp of the time information to be turned back from the SW 16 from the ONU 50-1. It corrects with difference and distributes the corrected time information to all ONUs 50-1 to 50-n under the control by multicast. As a result, even when traffic to be processed on the OLT 10 side is congested, time synchronization can be performed with high accuracy with all ONUs while correcting the time difference appropriately.

  In addition, in order to suppress the timing fluctuation | variation by the uplink transmission of time information, it is preferable to control so that the time information from ONU50-1 to OLT10 may transmit with a fixed time slot and a fixed period. Furthermore, on the OLT 10 side, it is preferable to control time information preferentially so as to have a predetermined processing delay. When RTT fluctuation is continuously detected on the side of the master ONU 50-1, the transmission rate of the time information transmitted by the master ONU 50-1 may be lowered to avoid further traffic congestion.

  FIG. 4 shows a schematic block diagram of the slave ONU 50-2. Since the slave ONUs 50-2 to n have the same configuration, in the present embodiment, the slave ONU 50-2 will be described as an example. The slave ONU 50-2 includes the TRX 52, the CPU 54, and the UNI 58. Also, a slave clock generator 60 is provided. The slave ONUs 50-2 to 50-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 n, and starts upper and lower signal transmission including time information (step S1). Next, in the master ONU 50-1, the RTT of the time information for looping back in the OLT 10 is measured (step S2), and it is determined whether or not the RTT fluctuation occurs (step S3). When RTT fluctuation does not occur in step S3, the process transitions to step S2, while when RTT fluctuation occurs, it is determined whether the RTT fluctuation exceeds a predetermined threshold (step S4). ). If the RTT fluctuation does not exceed the predetermined threshold in step S4, the process transitions to step S2, while if the RTT fluctuation exceeds the predetermined threshold, the master ONU is used as correction information. The time difference is notified to the OLT (step S5). Next, the OLT corrects the time stamp of the time information with the time difference received from the master ONU 50-1 (step S6), transfers the corrected time information to all subordinate ONUs, and returns to step 2.

  As described above, according to the present embodiment, the RTT monitoring unit 57 sends the time difference as correction information to the OLT 10 when the round-trip transmission delay time (RTT) being monitored is larger than the predetermined threshold. When the OLT 10 receives the time difference, it corrects the time information using the time difference, multicasts the corrected time information to each ONU 50-1 to n, and each ONU 50-1 to n Since the synchronization is mutually established based on the corrected time information received from the OLT 10, when the round trip transmission delay time fluctuates and becomes larger than the threshold value due to traffic congestion in the OLT 10, Since the time difference is provided to the OLT 10 and the time information is corrected, it becomes possible to multicast the accurate time information to each of the ONUs 50-1 to n. This makes it possible to maintain the accuracy of time synchronization in each of the ONUs 50-1 to n.

10 OLT
10-1 to 10-m OLT line card 12-1 to 12-p TRX (optical transceiver)
14 CPU
15 Time correction unit 16 SW (switch)
18 concentrator 30 optical splitter (optical splitter)
50-1 master ONU
50-2 to 50-n slave ONU
51 GPS antenna 52 TRX (optical transceiver)
54 CPU
56 Clock Generator (Master)
57 RTT monitoring unit 58 UNI (user network interface)
60 Clock Generators 100-1 to 100-n Base Station

Claims (6)

An Optical Line Terminal (OLT) and a plurality of ONUs (Optical Network Units) are connected via an optical splitter to provide a PON (Passive Optical Network) system that realizes optical fiber transmission,
A clock generation unit that acquires at least time information from a GPS signal receiving apparatus that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT;
Wherein the time information is transmitted from the clock generator to the OLT, and a RTT monitoring unit for comparison with the threshold time set in advance the round trip transmission delay time to come back to the clock generator from the OLT,
The RTT monitoring unit, when round trip transmission delay time being monitored is greater than the threshold time, transmits the correction information to the OLT,
When the OLT receives the correction information, it corrects time information using the correction information, and multicasts the corrected time information to each ONU.
The PON system, wherein the respective ONUs mutually establish synchronization based on time information after correction received from the OLT. When the OLT does not receive the correction information, the OLT distributes by multicast the time information received from the clock generation unit to each ONU.
The PON system according to claim 1, wherein the ONUs mutually establish synchronization based on time information received from the OLT.   The PON system according to claim 1 or 2, wherein the clock generation unit and the RTT monitoring unit are provided in any one ONU as a master ONU. An ONU (Optical Network Unit) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A clock generation unit that acquires at least time information from a GPS signal receiving apparatus that receives GPS (Global Positioning System) signals, and transmits the acquired time information to an OLT (Optical Line Terminal);
Wherein the time information, the sent from the clock generation unit to the OLT, the comparison with the threshold time set in advance the round trip transmission delay time until returning to the clock generator from the OLT, round-trip transmission delay time is the threshold And an RTT monitoring unit that transmits correction information to the OLT if the time is greater than the time. An OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A receiving unit that receives time information provided by the GPS signal receiving apparatus via a clock generation unit ;
A transmitter configured to multicast the time information to a subordinate ONU (Optical Network Unit);
When the time information is transmitted from the clock generation unit to the own apparatus, and the round-trip transmission delay time from the own apparatus to the return to the clock generation unit is larger than a preset threshold time , the RTT monitoring unit And a control unit that corrects time information using the correction information when the reception unit receives the correction information.
The OLT transmits the corrected time information by multicast to each of the ONUs. An optical line terminal (OLT) and a plurality of ONUs (Optical Network Units) are connected via an optical splitter to provide a transmission method of a PON (Passive Optical Network) system that realizes optical fiber transmission.
The clock generation unit acquires at least time information from a GPS signal receiving apparatus that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT;
The RTT monitoring unit monitors a round-trip transmission delay time until the time information transmitted from the clock generation unit returns from the OLT;
The RTT monitoring unit compares the round-trip transmission delay time until the time information is transmitted from the clock generation unit to the OLT and returns from the OLT to the clock generation unit with a preset threshold time , If the transmission delay time is greater than the threshold time, and transmitting the correction information to the OLT,
When the OLT receives the correction information, the OLT corrects time information using the correction information, and multicasts the corrected time information to the ONUs.
And D. each ONU establishing synchronization with each other based on the time information after correction received from the OLT.

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