JP6425568B2 - OLT, PON system and program - Google Patents

Description

  The present invention relates to a technology for realizing optical fiber transmission, and more particularly to an optical line terminal (OLT) and a passive optical network (PON) system and program.

  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, if a single ONU that is under the OLT acquires GPS signals, providing time information from the ONU to the OLT, and distributing it to all other ONUs via the OLT, the GPS Even when the antenna can not be installed, it can flexibly cope. The GPS signal may be configured to transmit a PON section using a packet such as IEEE 1588 v2 PTP (Precision Time Protocol) described in Non-Patent Document 1.

JP, 2014-165557, A

IEEE Std 1588-2008, "IEEE Standard for a Precision Clock Synchronization Protocol for Network Measurement and Control Systems," 2008.

  However, the technique described in Non-Patent Document 1 operates on the premise that the upper and lower transmission delays of the master device providing the reference time and the slave device slave-synchronized with the time of the master device are the same. Therefore, when IEEE 1588 v 2 is applied to a PON system in which the transmission delay is asymmetric in the vertical direction, there is a problem that the time synchronization accuracy is degraded.

  In Patent Document 1, in consideration of the asymmetry of uplink and downlink transmission delays, the OLT identifies PTP packets at the OLT and adds uplink delay to downlink PTP packets to make uplink and downlink transmission delays symmetrical. Technology is disclosed. However, this method can not be applied to existing systems because it is necessary to configure a special OLT having a function of identifying PTP packets and a function of adding delay.

  The present invention has been made in view of such circumstances, and a PON system in which a GPS signal is received on the ONU side, time information is provided to the OLT side, and is distributed to all other ONUs via the OLT. It is an object of the present invention to provide an OLT, a PON system and a program capable of maintaining the accuracy of time synchronization even when the upper and lower transmission delays of the PON section are asymmetric.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, 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 is transmitted from a master ONU (Optical Network Unit) having a GPS signal receiving apparatus. First RTT (Round-Trip Time) when the looped signal is transferred to the slave ONU other than the master ONU, and when the signal transmitted from the slave ONU is folded and transferred to the master ONU A control unit that calculates a difference between the second RTT and the second RTT, and a smaller one of the first RTT and the second RTT, and an ONU on the transmission side when the smaller RTT is measured. And a band allocation unit configured to set the RTT difference as a transmission waiting time.

  Thus, since the RTT difference is set as the transmission waiting time for the ONU on the transmitting side when the smaller one of the first RTT or the second RTT is specified and the smaller RTT is measured, And the downstream transmission delay can be made symmetrical. As a result, in the PON system, it is possible to maintain high time synchronization accuracy even in the case where uplink and downlink transmission delays between the master ONU and slave ONU are asymmetric in loopback control via the OLT. Become. Also, by performing dynamic band allocation on the OLT side, uplink and downlink transmission delays can be made symmetrical, so there is no need to repair the OLT on a large scale, and the existing PON system can be quickly implemented. It becomes possible to apply.

  (2) Further, the OLT according to the present invention is information indicating the distance between the slave ONU obtained by the initial registration of the slave ONU and the slave ONU, and an upstream delay time and a downstream delay of a signal transmitted in a fixed time slot. The information processing apparatus further comprises a table including information indicating time.

  Thus, since the table is provided, when the OLT calculates the RTT difference, it indicates the information indicating the distance between itself and the slave ONU, and indicates the upstream delay time and the downstream delay time of the signal transmitted in the fixed time slot. Information can be easily used.

  (3) Further, in the OLT of the present invention, the control unit calculates the first and second RTTs and the RTT difference based on information indicating upstream delay time and downstream delay time of the table. It is characterized by

  As described above, since the first and second RTTs and the RTT difference are calculated based on the information indicating the uplink delay time and the downlink delay time of the table, it is possible to make uplink and downlink transmission delays symmetrical. It becomes possible.

  (4) Further, in the OLT according to the present invention, the control unit is configured to set the first and the second on the basis of the information indicating the distance of the table, the wavelength of light used in upstream transmission and the wavelength of light used in downstream transmission. Calculating an RTT of 2, and the RTT difference.

  As described above, since the first RTT and the second RTT and the RTT difference are calculated based on the information indicating the distance of the table, the wavelength of light used for upstream transmission, and the wavelength of light used for downstream transmission, It becomes possible to eliminate the time difference caused by the different wavelengths of the downstream light and the downstream light, and to make the upstream and downstream transmission delays symmetrical.

  (5) Further, in the PON system 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 optical fiber transmission. The OLT is a first RTT (Round) when a OLT transmits a signal transmitted from a master ONU (Optical Network Unit) having a GPS signal reception apparatus to a slave ONU which is an ONU other than the master ONU. A control unit that calculates, as an RTT difference, a difference between (Trip Time) and a second RTT when the signal transmitted from the slave ONU is folded back to the master ONU, the first RTT or the second RTT Waits for transmission of the RTT difference to the ONU on the transmitting side when the smaller one of the RTTs is identified and the smaller RTT is measured. And a bandwidth allocation unit configured to set the time, and the ONU on the transmission side when measuring the smaller RTT performs signal transmission after the transmission waiting time set from the OLT has elapsed. It features.

  Thus, since the RTT difference is set as the transmission waiting time for the ONU on the transmitting side when the smaller one of the first RTT or the second RTT is specified and the smaller RTT is measured, And the downstream transmission delay can be made symmetrical. As a result, in the PON system, it is possible to maintain high time synchronization accuracy even in the case where uplink and downlink transmission delays between the master ONU and slave ONU are asymmetric in loopback control via the OLT. Become. Also, by performing dynamic band allocation on the OLT side, uplink and downlink transmission delays can be made symmetrical, so there is no need to repair the OLT on a large scale, and the existing PON system can be quickly implemented. It becomes possible to apply.

  (6) Further, the program of the present invention is a program of an OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission, and is a master ONU (Optical Optical ONU) having a GPS signal receiving device. The first RTT (Round-Trip Time) when the signal transmitted from the Network Unit is transferred back to the slave ONU other than the master ONU, and the signal transmitted from the slave ONU to the master ONU The process of calculating the difference between the second RTT and the second RTT when the aliasing transfer is performed, and the smaller one of the first RTT or the second RTT, and measuring the smaller RTT. The computer executes a series of processes of setting the RTT difference as the transmission waiting time for the transmitting ONU. It is characterized by

  Thus, since the RTT difference is set as the transmission waiting time for the ONU on the transmitting side when the smaller one of the first RTT or the second RTT is specified and the smaller RTT is measured, And the downstream transmission delay can be made symmetrical. As a result, in the PON system, it is possible to maintain high time synchronization accuracy even in the case where uplink and downlink transmission delays between the master ONU and slave ONU are asymmetric in loopback control via the OLT. Become. Also, by performing dynamic band allocation on the OLT side, uplink and downlink transmission delays can be made symmetrical, so there is no need to repair the OLT on a large scale, and the existing PON system can be quickly implemented. It becomes possible to apply.

  According to the present invention, it is possible to make uplink and downlink transmission delays symmetrical. As a result, in the PON system, it is possible to maintain high time synchronization accuracy even in the case where uplink and downlink transmission delays between the master ONU and slave ONU are asymmetric in loopback control via the OLT. Become. Also, by performing dynamic band allocation on the OLT side, uplink and downlink transmission delays can be made symmetrical, so there is no need to repair the OLT on a large scale, and the existing PON system can be quickly implemented. It becomes possible to apply.

It is a figure which shows schematic structure of a time delivery PON system. It is a figure which shows the time synchronization sequence between the master apparatus and slave apparatus in IEEE1588v2. It is a figure which shows the time synchronous sequence between the master apparatus and slave apparatus which used PON. FIG. 1 is a diagram showing a schematic configuration of a PON system according to a first embodiment. It is a figure which shows an example of the table which OLT10 has. It is a figure which shows the sequence of the time delivery PON system which concerns on 1st Embodiment.

  In the time synchronization system such as IEEE 1588 v 2, the present inventors operate on the premise that the upper and lower transmission delays between the master and the slave are the same, and therefore, IEEE 1588 v 2 is applied to the PON system in which the transmission delays are asymmetric. In this case, noting that the time synchronization accuracy is degraded, the difference between the upstream and downstream transmission delays between the master ONU and slave ONU is calculated, and for the transmitting ONU whose transmission delay is smaller, It has been found that uplink and downlink transmission delays can be made symmetrical by performing dynamic bandwidth allocation (DBA: Dynamic Bandwidth Allocation) in which a difference is set as transmission waiting time, and the present invention has been achieved.

  That is, 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 is transmitted from a master ONU (Optical Network Unit) having a GPS signal receiving apparatus. First RTT (Round-Trip Time) when the looped signal is transferred to the slave ONU other than the master ONU, and when the signal transmitted from the slave ONU is folded and transferred to the master ONU A control unit that calculates a difference between the second RTT and the second RTT, and a smaller one of the first RTT and the second RTT, and an ONU on the transmission side when the smaller RTT is measured. And a band allocation unit configured to set the RTT difference as a transmission waiting time.

  By this means, in the PON system, in the loopback control via the OLT, even if the upstream and downstream transmission delays between the master ONU and slave ONU are asymmetrical, high time synchronization accuracy can be achieved. It was possible to maintain. In addition, there is no need to remodel the OLT to a large scale, and it is possible to apply it to the existing PON system quickly. Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

  First, a general description of the PON system is given. FIG. 1 is a diagram showing a schematic configuration of a time delivery PON system. Under the OLT 10, a total of n (n is an arbitrary integer) ONUs 40-1 to 40-n are connected via the optical splitter 30. The master device 50 for acquiring the reference time is connected to one of them (the ONU 40-1 in FIG. 1).

  Slave devices 52-1 to (n-1) slave-synchronized to the master device 50 are connected to the other ONUs (ONUs 40-2 to n in FIG. 1), and the master device 50 and slave devices 52-1 to (n) are connected. Base stations 60-1 to 60-n are connected under the control of -1). The master device 50 includes a GPS antenna 51, and distributes time information received by the GPS antenna 51 to other ONUs 40-2 to n through the OLT 10. In the present embodiment, the ONU 40-1 to which the master device 50 is connected is referred to as a master ONU, and the other ONUs 40-2 to n are referred to as slave ONUs.

FIG. 2 is a diagram showing a time synchronization sequence between a master device and a slave device in IEEE 1588 v2. The master device, the Sync message sent to the slave device at time _{t 1,} the slave device receives the Sync message at time _{t 2.} The Sync message, the time t ₁ the master device transmits is written. Next, slave device, and transmits a "delay_request message" at time t ₃ to the master device, the master device receives the "delay_request message" at time t _4. Then, the master device, the "Delay_Response message" and transmitted to the slave device notifies the time t ₄ when the master device receives the "delay_request message" from the slave device.

By the above procedure, the slave device is to grasp the time _t 1 ~t _4, to measure the following equation (1) the master device and the slave device and between the transmission delay time (delay).

delay = {(t ₂ −t ₂ ) + (t ₄ −t ₃ )} / 2 (1)
The slave device corrects the delay obtained by the above equation to the time of the slave device and synchronizes the time with the master device. Here, it is assumed that the transmission delay (t ₂ −t ₁ ) from the master device to the slave device and the transmission delay (t ₄ −t ₃ ) from the slave device to the master device are the same.

  FIG. 3 is a diagram showing a time synchronization sequence between a master device and a slave device using PON. The master ONU 40-1 transmits the PTP packet to the OLT 10, and the PTP packet is looped back and transferred by the OLT 10 to reach the slave ONU 40-2. The transmission delay until the PTP packet reaches the slave ONU 40-2 from the master ONU 40-1 is RTT_1.

  On the other hand, the slave ONU 40-2 transmits a PTP packet toward the OLT 10, and the PTP packet is looped back and transferred by the OLT 10 and reaches the master ONU 40-1. The transmission delay until the PTP packet reaches from the slave ONU 40-2 to the master ONU 40-1 is RTT_2. RTT_1 and RTT_2 do not have the same value due to the shift of the upstream transmission start time instructed by the OLT 10, the buffering delay for each ONU, the optical fiber connection distance difference, and the like.

First Embodiment
FIG. 4 is a diagram showing a schematic configuration of the PON system according to the first embodiment. The OLT 10 includes m (m is an arbitrary integer) optical transceivers (TRX) 12-1 to m, a CPU 14, a table 16, and a switch (SW) 18. The CPU 14 includes a band allocation unit 15 that schedules uplink transmission start times and transmission periods of the ONUs 40-1 to 40-n. The GPS signal received by the GPS antenna 51 is converted into time information (for example, a PTP packet of IEEE 1588 v2) in the master device 50, and the ONU 40-1 converts the time information into an upstream optical signal and directs it to the OLT 10. Send.

  The OLT 10 supplies the time information received by the TRX 12-1 to the CPU 14, and the CPU 14 supplies the time information to the SW 18. The SW 18 identifies only the time information, and loops back and transfers the time information from the OLT 10 to the ONUs 40-1 to 40-n. Uplink data signals and the like other than time information are transferred to the upper network without being looped back by the SW 18.

In the PON system, since the uplink and downlink transmission delays are asymmetric, it is necessary to make them symmetrical. That is, in order to make RTT_1 and RTT_2 symmetrical, the bandwidth allocation unit 15 of the OLT 10 instructs each ONU to always transmit an upstream PTP packet in a fixed time slot. Also, the difference between RTT_1 and RTT_2 is calculated, and the smaller RTT is identified. Then, the above difference (RTT difference) is set as the transmission waiting time to the ONU on the transmission side when the smaller RTT is measured, and the uplink transmission start time is instructed.

  FIG. 5 is a diagram showing an example of a table that the OLT 10 has. When the OLT 10 initially registers the ONUs 40-1 to 40-n, the connection distance (D_1 to n) with each ONU, the upstream delay (Tup_1 to n) and the downstream delay (Tdn_1 to Tdn) of PTP packets transmitted in fixed time slots. n) hold information.

  FIG. 6 is a diagram showing a sequence of the time delivery PON system according to the first embodiment. The OLT 10 calculates the transmission delay RTT_1 from the master device to the slave device and the transmission delay RTT_2 from the slave device to the master device based on the information recorded in the table shown in FIG. For example, as shown in FIG. 6, taking the master ONU 40-1 and slave ONU 40-2 as an example, RTT_1 is calculated by Tup_1 + Tdn_1, RTT_2 is calculated by Tup_2 + Tdn_2, and the difference between RTT_1 and RTT_2 (ΔRTT) is obtained.

  Specify the smaller one of RTT_1 and RTT_2, and measure the RTT on the smaller one. Start the transmission of the upstream PTP packet to the ONU on the transmission side (master ONU 40-1 in the example of FIG. 6), ΔRTT Dynamic bandwidth allocation is performed so as to be delayed by the latency time of. Thus, RTT_1 and RTT_2 can be apparently made the same value by intentionally delaying the transmission start time.

  As described above, the OLT 10 can make the uplink and downlink transmission delays symmetrical by instructing the ONU having a small RTT including the waiting time and the uplink transmission start time.

  Although the buffering delay in the SW 18 of the OLT 10 may also cause a time lag, in this embodiment, the buffering delay of the SW 18 is assumed to be negligible. For example, the SW 18 may control the PTP packet so as to always have a constant buffering delay amount, or may always control transfer of the PTP packet with re-priority regardless of the processing conditions of other data signals. Fluctuation of buffering delay can be suppressed.

Second Embodiment
In the PON system, generally, the wavelength of light used for upstream transmission and the wavelength of light used for downstream transmission are different. From this, in the second embodiment, uplink and downlink transmission delays are made symmetrical by taking into consideration the time difference caused by the difference between the uplink and downlink wavelengths.

  Assuming that the refractive index in the optical fiber of the upstream wavelength in the PON system is n_up and the refractive index of the downstream wavelength is n_dn, the upstream velocity (C_up) and the downstream velocity (C_dn) in the optical fiber are respectively C_up = C / n_up, It is expressed by C_dn = C / n_dn. Where C is the speed of light in vacuum.

  If RTT_1 and RTT_2 are calculated with reference to the distance information from the table shown in FIG. 5, equations (2) and (3) are obtained, respectively.

上式（２）及び（３）を用いると、ΔＲＴＴは式（４）で表される。

When the above equations (2) and (3) are used, ΔRTT is expressed by equation (4).

屈折率ｎ＿ｕｐおよびｎ＿ｄｎは、ＰＯＮシステムの使用波長が与えられれば、一意に決定されるので、必要なパラメータは距離情報Ｄ＿１及びＤ＿２のみとなる。以上により、上りの波長と下りの波長との相違により生じる時刻差分も考慮して、上りと下りの伝送遅延を対称化することが可能となる。

Since the refractive indices n_up and n_dn are uniquely determined given the used wavelength of the PON system, the necessary parameters are only the distance information D_1 and D_2. As described above, it is possible to make uplink and downlink transmission delays symmetrical, taking into consideration the time difference caused by the difference between the uplink wavelength and the downlink wavelength.

  As described above, according to the present embodiment, in the loopback control via the OLT, high time synchronization is achieved even when the uplink and downlink transmission delays between the master device and the slave device are asymmetric. It is possible to maintain the accuracy.

10-station optical termination unit (OLT)
12-1 to m Optical transceiver (TRX)
14 CPU
15 band allocation unit 16 table 18 switch (SW)
30 optical splitter (optical splitter)
40-1 to n Subscriber side optical termination unit (ONU)
50 master device 51 GPS antenna 52-1 to (n-1) slave device 60-1 to n base station

Claims (6)

An OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A signal transmitted from a master ONU (Optical Network Unit) (40-1) having a GPS signal receiver is returned to a slave ONU (40-2... 40-n) which is an ONU other than the master ONU (40-1). The first RTT (Round-Trip Time) when transferred and the second when the signal transmitted from the slave ONU (40-2... 40-n ) is folded back and transferred to the master ONU (40-1) A control unit that calculates the difference between RTT and RTT as RTT difference;
A band allocation unit for specifying the smaller one of the first RTT or the second RTT and setting the RTT difference as a transmission waiting time for the ONU on the transmission side when the smaller RTT is measured; An OLT characterized by comprising. The slave ONU (40-2 ... 40-n) information and indicating the distance between the the own device acquired at the time of initial registration slave ONU (40-2 ... 40-n) , the signal transmitted at a fixed time slot The OLT according to claim 1, further comprising a table including information indicating an upstream delay time and a downstream delay time. The said control part calculates said 1st and 2nd RTT and the said RTT difference based on the information which shows the upstream delay time of the said table, and the downstream delay time, It is characterized by the above-mentioned. OLT. The control unit calculates the first and second RTTs and the RTT difference based on the information indicating the distance of the table, the wavelength of light used for upstream transmission, and the wavelength of light used for downstream transmission. The OLT according to claim 2, characterized in that: 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,
The OLT (10) is
A signal transmitted from a master ONU (Optical Network Unit) (40-1) having a GPS signal receiver is returned to a slave ONU (40-2... 40-n) which is an ONU other than the master ONU (40-1). The first RTT (Round-Trip Time) when transferred and the second when the signal transmitted from the slave ONU (40-2... 40-n ) is folded back and transferred to the master ONU (40-1) A control unit that calculates the difference between RTT and RTT as RTT difference;
A band allocation unit for specifying the smaller one of the first RTT or the second RTT and setting the RTT difference as a transmission waiting time for the ONU on the transmission side when the smaller RTT is measured; , And
A PON system characterized in that the ONU on the transmitting side when measuring the smaller RTT transmits a signal after a transmission waiting time set from the OLT has elapsed. It is a program of OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A signal transmitted from a master ONU (Optical Network Unit) (40-1) having a GPS signal receiver is returned to a slave ONU (40-2... 40-n) which is an ONU other than the master ONU (40-1). The first RTT (Round-Trip Time) when transferred and the second when the signal transmitted from the slave ONU (40-2... 40-n ) is folded back and transferred to the master ONU (40-1) Calculating the difference between RTT and RTT as RTT difference;
A process of specifying the smaller one of the first RTT or the second RTT, and setting the RTT difference as a transmission waiting time for the ONU on the transmission side when the smaller RTT is measured. A program that causes a computer to execute a series of processes.

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