JP2016119578A - PON system, ONU, OLT and transmission method - Google Patents

Abstract

The present invention provides a loopback method in which time information of GPS signals acquired on the ONU side is provided to the OLT and the time information is distributed to each ONU via the OLT, and traffic is congested on the OLT side Even so, the accuracy of time synchronization is maintained. A clock generation unit that acquires time information of a GPS signal and transmits the acquired time information to the OLT, and a round-trip transmission delay until the time information transmitted from the clock generation unit returns from the OLT. An RTT monitoring unit 57 that monitors time, and when the round-trip transmission delay time being monitored is larger than a predetermined threshold, the RTT monitoring unit 57 transmits correction information to the OLT, and the OLT When the information is received, the time information is corrected using the correction information, the corrected time information is multicast-distributed to each ONU, and each ONU is based on the corrected time information received from the OLT. To establish synchronization [selection figure] Fig. 2

Description

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

  In recent years, the area (cell) covered by a base station apparatus has become narrower as the speed of a radio access network provided by a mobile communication network has decreased, and as a result, the number of base station apparatuses to be installed to configure the mobile communication network Has increased. For this reason, a passive optical network (PON) system in which a single optical transmission line is shared by a plurality of subscribers has been studied as a network for accommodating a plurality of base station apparatuses.

  In the PON system, one optical transmission line terminal (OLT: Optical Line Terminal) installed at a telecommunications carrier's station connects to multiple subscriber-side terminals (ONU: Optical Network Unit) via an optical splitter. Has been. The OLT achieves high band utilization efficiency by dynamically allocating an upstream band to a plurality of ONUs, for example, 64 ONUs, by a time division multiplexing method.

  When accommodating a plurality of base station devices in the PON system, frequency and time synchronization between the base station devices is essential. Conventionally, a GPS (Global Positioning System) antenna is generally installed in each base station apparatus in order to receive reference time information. However, there are cases where the GPS antenna cannot be installed due to restrictions such as the installation environment in the base station apparatus. For this reason, for example, Non-Patent Documents 1 and 2 disclose techniques for distributing frequency and time information from an upper network device to a lower network device 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 frequency and time information received by the GPS antenna is distributed to each ONU via the optical access distribution network. The technology to do 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., “10G-EPON system with frequency / time synchronization function for mobile backhaul applications,” IEICE Tech. (B), vol.J96-B, no.3, pp.321-329, March 2013.

  However, in the techniques described in Non-Patent Documents 1 and 2, all the upper and lower network devices must be replaced with devices dedicated to frequency and time synchronization. For example, in order to provide time information from the OLT via the IP network to each ONU by IEEE 1588, all devices on the IP network side must support IEEE 1588. For this reason, if there is at least one device on the IP network side that does not support IEEE 1588, a clock signal cannot 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 the GPS signal are installed in a station where an OLT is installed. However, it is difficult to apply when the equipment installation space is limited.

  Furthermore, when a loopback method is adopted in which a GPS signal is acquired on the ONU side, time information based on the GPS signal is provided to the OLT, and time information is distributed from the OLT to each ONU, traffic congestion occurs in the OLT. A fluctuation occurs in the transfer processing time of the time information transmitted from the ONU, and the time synchronization accuracy in each ONU deteriorates.

  The present invention has been made in view of such circumstances, and provides a loopback in which time information of a GPS signal acquired on the ONU side is provided to the OLT and the time information is distributed 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 the traffic is congested on the OLT side while realizing the system.

  (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 branching device to realize optical fiber transmission. A clock generating unit that acquires at least time information from a GPS signal receiving device that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT, and time information transmitted from the clock generating unit includes: An RTT monitoring unit that monitors a round trip transmission delay time until returning from the OLT, and the RTT monitoring unit corrects when the round trip transmission delay time being monitored is larger than a predetermined threshold value. When information is transmitted to the OLT and the OLT receives the correction information, the OLT corrects time information using the correction information, and 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 the correction information to the OLT when the round-trip transmission delay time being monitored is larger than the predetermined threshold, and the OLT receives the correction information when the correction information is received. The time information is corrected, and the corrected time information is multicast-distributed to each ONU, and each ONU establishes synchronization with each other based on the corrected time information received from the OLT. If the round-trip transmission delay time fluctuates due to congestion, etc., and exceeds the threshold, correction information is provided to the OLT and the time information is corrected, so accurate time information is distributed to each ONU by multicast. It becomes possible to do. 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, the OLT multicasts the time information received from the clock generation unit to each ONU, and each ONU The synchronization is established based on the time information received from the OLT.

  As described above, when the OLT does not receive the correction information, the OLT distributes the time information received from the clock generation unit to each ONU by multicast, and the ONUs mutually communicate with each other based on the time information received from the OLT. Since synchronization is established, it becomes possible to apply a loopback method using a GPS signal to the PON system.

  (3) Further, the PON system of 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.

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

  (4) 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 receives a GPS (Global Positioning System) signal. A clock generation unit that acquires at least time information from a receiving device, transmits the acquired time information to the OLT, and time information transmitted from the clock generation unit includes time information transmitted from the clock generation unit, An RTT monitoring unit that monitors a round-trip transmission delay time until returning from the OLT and transmits correction information to the OLT when the round-trip transmission delay time being monitored is larger than a predetermined threshold. It is characterized by.

  As described above, at least time information is acquired from the GPS signal receiving device that receives the GPS signal, the acquired time information is transmitted to the OLT, and the time information transmitted from the clock generator returns to and from the OLT. When the transmission delay time is monitored and the round-trip transmission delay time being monitored is larger than a predetermined threshold, correction information is transmitted to the OLT. Therefore, due to traffic congestion in the OLT, the round-trip transmission delay time When it fluctuates and becomes larger than the threshold value, the correction information can be provided to the OLT. Thereby, in the OLT, time information can be corrected to be correct, and accurate time information can be multicast-distributed to each ONU. This makes it possible to maintain the accuracy of time synchronization in each ONU.

  (5) 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 receives time information provided from a GPS signal receiver. Is transmitted when the round-trip transmission delay time of the time information is larger than a predetermined threshold value, the transmission unit that multicasts the time information to an ONU (Optical Network Unit) under control thereof, and the reception unit. A control unit that corrects time information using the correction information when the correction information is received, and the transmission unit multicast-distributes the corrected time information to each ONU. .

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

  (6) Also, the transmission method of the present invention is a PON (Passive Optical Network) in which an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units) are connected via an optical branching device to realize optical fiber transmission. A system transmission method, wherein a clock generation unit acquires at least time information from a GPS signal receiving device that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT; and RTT monitoring A step of monitoring a round trip transmission delay time until the time information transmitted from the clock generator returns from the OLT; and a round trip transmission delay time that the RTT monitoring unit is monitoring is predetermined. The correction information is transmitted to the OLT, and the correction information is received when the OLT receives the correction information. Is used to correct the time information and multicast the corrected time information to each ONU, and each ONU establishes synchronization based on the corrected time information received from the OLT. And at least including the step of:

  As described above, when the round-trip transmission delay time being monitored is larger than the predetermined threshold, the RTT monitoring unit transmits the correction information to the OLT, and when the OLT receives the correction information, the correction information is displayed. The time information is corrected, and the corrected time information is multicast-distributed to each ONU, and each ONU establishes synchronization with each other based on the corrected time information received from the OLT. If the round-trip transmission delay time fluctuates due to congestion, etc., and exceeds the threshold, correction information is provided to the OLT and the time information is corrected, so accurate time information is distributed to each ONU by multicast. It becomes possible to do. This makes it possible to maintain the accuracy of time synchronization in each ONU.

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

It is a figure showing a schematic structure of a PON system concerning an embodiment of the present invention. It is a block diagram which shows schematic structure of master ONU50-1. It is a block diagram which shows schematic structure of OLT10. The schematic block diagram of slave ONU50-2 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 time information of GPS signals acquired on the ONU side to the OLT, and when the loop information method of distributing the time information to each ONU via the OLT is to be realized, the OLT side Paying attention to the fact that when traffic congestion occurs, the transfer processing time of the time information transmitted from the ONU fluctuates, and the time synchronization accuracy between the ONUs deteriorates. Traffic generated on the OLT side When the round-trip transmission delay time fluctuates due to congestion, the time difference is notified to the OLT, and the time information is corrected on the OLT side, thereby finding that the accuracy of time synchronization between the ONUs can be maintained. It came to make 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 branching device to realize optical fiber transmission. A clock generating unit that acquires at least time information from a GPS signal receiving device that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT, and time information transmitted from the clock generating unit includes: An RTT monitoring unit that monitors a round trip transmission delay time until returning from the OLT, and the RTT monitoring unit corrects when the round trip transmission delay time being monitored is larger than a predetermined threshold value. When information is transmitted to the OLT and the OLT receives the correction information, the OLT corrects time information using the correction information, and 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 due to traffic congestion or the like in the OLT. By correcting the above, accurate time information can be multicasted to each ONU. And it became possible to maintain the precision of the time synchronization in each ONU. Embodiments of the present invention will be specifically described below 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, a total of n ONUs 50-1 to 50 -n (n is an arbitrary integer) are connected via an optical splitter 30 under the OLT 10. A GPS antenna 51 is connected to one of them (ONU 50-1 in FIG. 1), and time information received by the GPS antenna is distributed to other ONUs 50-2 to 50-n via the OLT 10. Base stations 100-1 to 100-n are connected to 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 a “master ONU”, and the other ONUs 50-2 to 50-n are referred to as “slave ONUs”.

  FIG. 2 is a block diagram showing a schematic configuration of the master ONU 50-1. The master ONU 50-1 includes 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 master clock generation unit 56 and an RTT monitoring unit 57. The GPS signal received by the GPS antenna 51 is converted into time information (for example, IEEE1588 PTP packet) 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 with the OLT 10 and multiplexes time information and a data signal on the time axis in accordance with the time slot. The TRX 52 transmits time information and a data signal to the OLT 10.

  The master ONU 50-1 receives the time information transmitted by itself by the TRX 52 via the OLT 10. The CPU 54 selects only the time information from the downstream signal and transfers it to the master clock generation unit 56. The clock generation unit 56 constantly monitors the round trip time (RTT) until the time information transmitted by the RTT monitoring unit 57 is received. When the RTT fluctuates greatly due to traffic congestion or the like processed on the OLT 10 side, and the RTT fluctuation continues for a preset threshold time or more, a 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 illustrating 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 concentrator 18 aggregates 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 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 SW (switch) 16.

  Downlink signals received by the upper network are distributed to the OLT line cards 10-1 to 10-m in the concentrator 18, and the SW 16 distributes the downlink signals to the TRXs 12-1 to p to be transferred via the CPU 14. Here, the flow of the time information signal will be described by taking TRX 12-1 as an example. The upstream signal received by the TRX 12-1 enters the SW 16 via the CPU 14. In SW16, only the time information from the master ONU 50-1 in the upstream signal is selectively returned to the CPU 14 side. Thereafter, the time information is multicast-distributed to all ONUs under the control via TRX 12-1.

  Here, in order to accurately synchronize the time with all the ONUs, even if the traffic processed by the SW 16 is congested and the fluctuation of the RTT monitored by the master ONU 50-1 becomes large, the RTT fluctuation is correctly grasped. Then, the time difference corresponding to the RTT variation must be corrected appropriately. Therefore, in the PON system according to the present embodiment, when the ONT 50-1 continuously detects the RTT fluctuation, the time difference corresponding to the RTT fluctuation is notified to the OLT 10 side, 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 is notified of the time stamp of the time information returned from the SW 16 from the ONU 50-1. The correction is performed using the difference, and the corrected time information is multicast distributed to all the subordinate ONUs 50-1 to 50-n. As a result, even when traffic processed on the OLT 10 side is congested, time synchronization with all ONUs can be performed with high accuracy while appropriately correcting the time difference.

  In order to suppress timing fluctuation due to upstream transmission of time information, it is preferable to control the time information from the ONU 50-1 to the OLT 10 so as to be transmitted at a fixed time slot and at a constant cycle. Further, on the OLT 10 side, it is preferable to control the time information so as to give a certain processing delay with priority. Further, when RTT fluctuation is continuously detected on the master ONU 50-1 side, the transmission rate of the time information transmitted by the master ONU 50-1 may be lowered in order 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 50-n have the same configuration, in this embodiment, the slave ONU 50-2 will be described as an example. The slave ONU 50-2 includes a TRX 52, a CPU 54, and a UNI 58. A slave clock generator 60 is also provided. Since the slave ONUs 50-2 to n connected to the OLT 10 have different optical fiber connection distances, the CPU 54 holds the RTT obtained when the logical link with the OLT 10 is established, and the time received from the OLT 10 at half the value of the RTT 10 Correct the time stamp of the information. The corrected time information is supplied to the slave clock generator 60, converted to a GPS signal by the slave clock generator 60, and supplied to the subordinate base stations.

  FIG. 5 is a flowchart showing the operation of the PON system according to this embodiment. First, the OLT 10 establishes logical links with the ONUs 50-1 to 50-n, and starts transmission of upper and lower signals including time information (step S1). Next, the master ONU 50-1 measures the RTT of the time information related to the return in the OLT 10 (step S2), and determines whether or not the RTT fluctuation has occurred (step S3). In step S3, when the RTT fluctuation does not occur, the process proceeds to step S2. On the other hand, when the RTT fluctuation occurs, it is determined whether or not the RTT fluctuation exceeds a predetermined threshold (step S4). ). In step S4, if the RTT fluctuation does not exceed the predetermined threshold value, the process proceeds to step S2. On the other hand, if the RTT fluctuation exceeds the predetermined threshold value, the master ONU is used as correction information. The time difference is notified from OLT to OLT (step S5). Next, in the OLT, the time stamp of the time information is corrected with the time difference received from the master ONU 50-1 (step S6), the corrected time information is transferred to all the ONUs under its control, and the process returns to step 2.

  As described above, according to the present embodiment, the RTT monitoring unit 57 sets the time difference as correction information to the OLT 10 when the round-trip transmission delay time (RTT) being monitored is larger than a predetermined threshold. When the time difference is received, the OLT 10 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 Are mutually synchronized based on the corrected time information received from the OLT 10, so that the round-trip transmission delay time fluctuates due to traffic congestion in the OLT 10 and becomes larger than the threshold. Since the time difference is provided to the OLT 10 and the time information is corrected, accurate time information can be multicast-distributed to each ONU 50-1 to n. Thereby, it is 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)

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 generating unit that acquires at least time information from a GPS signal receiving device that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT;
An RTT monitoring unit that monitors a round-trip transmission delay time until the time information transmitted from the clock generation unit returns from the OLT;
When the round-trip transmission delay time being monitored is larger than a predetermined threshold, the RTT monitoring unit transmits correction information to the OLT,
When the OLT receives the correction information, the OLT corrects time information using the correction information, multicasts the corrected time information to each ONU,
Each of the ONUs establishes synchronization with each other based on the corrected time information received from the OLT. If the OLT does not receive the correction information, the OLT multicasts the time information received from the clock generator to each ONU,
2. The PON system according to claim 1, wherein each of the ONUs establishes synchronization with each other based on time information received from the OLT.   The PON system according to claim 1, 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 generating unit that acquires at least time information from a GPS signal receiving device that receives a GPS (Global Positioning System) signal, and transmits the acquired time information to the OLT;
The time information transmitted from the clock generation unit monitors the round trip transmission delay time until it returns from the OLT. If the round trip transmission delay time being monitored is larger than a predetermined threshold, the correction information is displayed. An ONU comprising: an RTT monitoring unit that transmits to the OLT. An OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A receiver for receiving time information provided from the GPS signal receiver;
A transmission unit that multicasts the time information to a subordinate ONU (Optical Network Unit);
A control unit that corrects the time information using the correction information when the reception unit receives the correction information transmitted when the round-trip transmission delay time of the time information is larger than a predetermined threshold. ,
The OLT characterized in that the transmission unit multicast-distributes the corrected time information to each ONU. A transmission method of 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 and realizes optical fiber transmission,
A clock generation unit acquiring at least time information from a GPS signal receiving device that receives a GPS (Global Positioning System) signal, and transmitting the acquired time information to the OLT;
An RTT monitoring unit monitoring a round trip transmission delay time until the time information transmitted from the clock generation unit returns from the OLT;
The RTT monitoring unit, when the round-trip transmission delay time being monitored is larger than a predetermined threshold, sending correction information to the OLT;
When the OLT receives the correction information, the time information is corrected using the correction information, and the corrected time information is multicast distributed to the ONUs;
The ONU includes at least a step of establishing synchronization with each other based on the corrected time information received from the OLT.

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