JP2017073752A - Pon system transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain high accuracy of time synchronization, regardless of asymmetry of transmission delay in a PON section, in a PON system where an uplink PTP packet is received by a master ONU, and time information is provided to the OLT side, and delivered to all other slave ONUs via the OLT.SOLUTION: A master ONU compares the time of the own device with the reference time of a PTP packet, and notifies the OLT of the time difference. The OLT adjusts the time of the own device by using the notified time difference, and synchronizes the times of the master ONU and slave ONU with the time of the own device by applying a synchronization system. The slave ONU generates a PTP packet based on the time information acquired from the OLT, and transmits the PTP packet thus generated to a subordinate PTP slave device. By using the time information indicated in the PTP packet acquired from the slave ONU, the PTP slave device adjusts the time of the own device or executes PTP basic sequence between the slave ONU and itself thus synchronizing the time.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a PON (Passive Optical Network) system 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 been reduced. 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.

  In the base station apparatus, time synchronization between the base station apparatuses is indispensable in order to realize a handover of the communication terminal and the like. 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.

  Therefore, a loopback method has been proposed in which GPS signals are acquired by one ONU under the control of the OLT, time information is provided from the ONU to the OLT side, and distributed to all other ONUs via the OLT. According to this, even if it is a case where a GPS antenna cannot be installed in a base station apparatus, it can respond flexibly. The time information included in the GPS signal may be configured to transmit the PON section on a packet basis such as IEEE 1588v2 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 assumption that the upper and lower transmission delays of the master device that provides the reference time and the slave device that depends on and synchronizes with the time provided by the master device are the same. . For this reason, when IEEE 1588v2 is applied to a PON system whose transmission delay is vertically asymmetric, time synchronization accuracy is degraded.

  Further, in the technique described in Patent Document 1, in consideration of the asymmetry of the uplink and downlink transmission delays, the PLT packet is identified by the OLT, and the delay is added to the downlink PTP packet, so that the uplink and downlink are delayed. Downlink transmission delay is symmetrized. However, in this method, since the OLT needs to have new functions such as a function for identifying a PTP packet and a function for adding a delay, it cannot be applied to an existing system.

  In addition, as a method that does not change the existing OLT side, in order to transmit a PTP packet, an uplink fixed time slot is allocated to the ONU, thereby making the delay constant, and between the PTP master device and the PTP slave device. In PTP packet transmission, it is conceivable to symmetrize the upstream and downstream transmission delays of PTP packet transmission by intentionally delaying the ONU transmission timing in the transmission direction with a small transmission delay.

  However, when allocating a fixed time slot to the ONU, if the PTP packet interval reaching the master ONU (ONU receiving the PTP packet from the PTP master device) from the PTP master device does not match the fixed time slot interval of the master ONU, Jitter occurs in the PTP packet, making time synchronization difficult. When intentionally adding a delay in the transmission direction with a small transmission delay in transmission between the PTP master device and the PTP slave device, RTT (Round Trip Time) 1 is set as ONT from the master ONU via the OLT. If the delay time when the PTP packet arrives is adjusted, the delay when the PTP packet arrives at the master ONU from the ONU via the OLT also changes as RTT2, which makes time synchronization difficult. .

  The present invention has been made in view of such circumstances. A PON that receives an upstream PTP packet at a master ONU, provides time information to the OLT side, and distributes it to all other ONUs via the OLT. It is an object of the present invention to provide a PON system and a transmission method that can maintain high accuracy of time synchronization regardless of asymmetry of transmission delay in the PON section.

  (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) that realizes optical fiber transmission of point-to-multipoint connection between an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units). A master ONU (Optical Network Unit) that acquires time information from a GPS (Global Positioning System) signal or receives a PTP packet generated based on the time information acquired from a GPS signal; At least one slave ONU other than the master ONU is connected to the master ONU and the slave ONU via an optical branching unit, and the upstream bandwidth is dynamically increased by time division multiplexing for the master ONU and the slave ONU. OLT (Optical Line Terminal) to be assigned, and applying a synchronous system (802.1AS, etc.) in the PON section The time information transmitted from the master ONU via the OLT is notified to the communication device under the master ONU or the slave ONU, or the time information acquired by the master ONU is transmitted to the master ONU. Is notified to the communication devices under the control.

  In this way, the synchronization system is applied in the PON section to perform time synchronization, and the time information transmitted from the master ONU via the OLT is notified to the communication device under the master ONU or the slave ONU, or Since the time information acquired by the master ONU is notified to the communication device under the master ONU, high accuracy of time synchronization can be maintained regardless of the asymmetry of the transmission delay in the PON section.

  (2) In the PON system of the present invention, the master ONU compares the time of its own device with the reference time of the PTP packet, notifies the OLT of the time difference, and the OLT notifies the notified time. Using the difference, the time of the own device is adjusted, and a synchronization system (802.1AS or the like) is applied to synchronize the time of the master ONU and the slave ONU with the time of the own device. The PTP packet generated based on the acquired time information, PPS (Pulse per Second) and ToD (Time of Day), or a GPS pseudo signal is transmitted to the subordinate PTP slave device, and the PTP slave device is transmitted from the slave ONU. Using the time information indicated in the acquired PTP packet, PPS and ToD, or GPS pseudo signal, adjust the time of its own device, Alternatively, time synchronization is performed by executing a PTP basic sequence with the slave ONU.

  In this way, the master ONU compares the time of its own device with the reference time of the PTP packet, notifies the OLT of the time difference, and the OLT uses the notified time difference of the own device. The time is adjusted, and the time of the master ONU and the slave ONU is synchronized with the time of its own device by applying a synchronization system (802.1AS or the like), and the slave ONU is generated based on the time information acquired from the OLT PTP packet, PPS (Pulse per Second) and ToD (Time of Day), or GPS pseudo signal is transmitted to the subordinate PTP slave device, and the PTP slave device acquires the PTP packet, PPS and ToD acquired from the slave ONU. Or the time information indicated in the GPS pseudo signal is used to adjust the time of the device itself, or with the slave ONU Since time synchronization is performed by executing the PTP basic sequence, a time is applied by applying a synchronization system that functions on the assumption that the vertical transmission delay is symmetric regardless of whether the transmission delay in the PON section is asymmetric. Synchronization can be performed.

  (3) In the PON system of the present invention, the slave ONU transmits a PTP packet to the PTP slave device when a delay in transmission between the own device and the PTP slave device or a subordinate base station device cannot be ignored. , PPS and ToD, or adding a delay time to the GPS pseudo signal.

  In this way, the slave ONU, when the transmission delay between the own device and the PTP slave device or the subordinate base station device cannot be ignored, is a PTP packet, PPS and ToD, or GPS pseudo signal transmitted to the PTP slave device. Since a delay time is added to the signal, it becomes possible to perform time synchronization in consideration of the delay.

  (4) Further, in the PON system of the present invention, the master ONU, when the transmission delay between the own device and the subordinate communication device cannot be ignored, the PTP packet, PPS and ToD transmitted to the subordinate communication device, or A delay time is added to the GPS pseudo signal.

  As described above, when the transmission delay between the own device and the subordinate communication device cannot be ignored, the master ONU adds a delay time to the PTP packet, PPS and ToD, or GPS pseudo signal transmitted to the subordinate communication device. Therefore, it is possible to perform time synchronization considering delay.

  (5) Further, in the PON system of the present invention, time synchronization is performed by applying a synchronization system (802.1AS or the like), and the slave ONU passes the time when the PTP packet arrives at the master ONU and the OLT. The difference information with the time when the PTP packet arrived at the local device is reflected in the time information of the PTP packet and the PTP packet is transmitted to the subordinate PTP slave device, or the difference information is transmitted together with the PTP packet to the subordinate PTP slave. When the PTP slave device acquires the PTP packet in which the difference information is reflected in the time information from the slave ONU, the PTP slave device uses the time information indicated in the acquired PTP packet. Adjust the time, or execute the PTP basic sequence with the slave ONU to perform time synchronization, Alternatively, when the difference information is acquired from the slave ONU together with the PTP packet, the time of the own apparatus is adjusted by reflecting the difference information in the time information indicated in the acquired PTP packet.

  In this way, time synchronization is performed by applying a synchronization system (such as 802.1AS), and the slave ONU receives the PTP packet at the master ONU and the PTP packet arrives at its own device via the OLT. The difference information with respect to the received time is reflected in the time information of the PTP packet, and the PTP packet is transmitted to the subordinate PTP slave device, or the difference information is transmitted together with the PTP packet to the subordinate PTP slave device, and the PTP slave When the device acquires a PTP packet in which the difference information is reflected in the time information from the slave ONU, the device adjusts the time of the device using the time information indicated in the acquired PTP packet, or the slave The PTP basic sequence is executed with the ONU to perform time synchronization, or the difference information is stored in the PTP packet. When the time is acquired from the slave ONU together with the data, the difference information is reflected in the time information indicated in the acquired PTP packet to adjust the time of the own device, so that the transmission delay in the PON section is asymmetric. Regardless of whether the time is synchronized, it is possible to apply a synchronization system that functions on the assumption that the vertical transmission delay is symmetrical.

  (6) Further, in the PON system of the present invention, the slave ONU adds a delay time to the PTP packet transmitted to the PTP slave device when the delay in transmission between the slave device and the PTP slave device cannot be ignored. It is characterized by.

  Thus, the slave ONU adds a delay time to the PTP packet transmitted to the PTP slave device when the transmission delay between the own device and the PTP slave device cannot be ignored. Can be done.

  (7) In the PON system of the present invention, the master ONU adds a delay time to the PTP packet to be transmitted to the subordinate communication apparatus when the transmission delay between the own apparatus and the subordinate communication apparatus cannot be ignored. It is characterized by.

  In this way, the master ONU adds a delay time to the PTP packet transmitted to the subordinate communication device when the transmission delay between the own device and the subordinate communication device cannot be ignored. Can be done.

  (8) Further, the transmission method of the present invention is a PON (Point to Multi Point) optical fiber transmission between an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units). A transmission method of a Passive Optical Network (CIS) system, in which a master ONU (Optical Network Unit) acquires time information from a GPS (Global Positioning System) signal or is generated based on time information acquired from a GPS signal The PTP packet is received, time synchronization is performed by applying a synchronization system (802.1AS, etc.) in the PON section, and the master ONU and a slave ONU other than the master ONU are connected to the slave ONU via the optical splitter. Transmission via the OLT (Optical Line Terminal) that dynamically allocates the upstream bandwidth to the master ONU and the slave ONU by time division multiplexing. The received time information is notified to the communication device under the master ONU or the slave ONU, or the time information acquired by the master ONU is notified to the communication device under the master ONU.

  As described above, the master ONU acquires time information from the GPS signal, or receives a PTP packet generated based on the time information acquired from the GPS signal, and applies a synchronization system (802.1AS or the like) in the PON section. Time synchronization is performed, and the master ONU and the slave ONU other than the master ONU are connected to the master ONU and the slave ONU via the optical branching unit. The time information transmitted via the OLT for allocating the bandwidth is notified to the communication device under the master ONU or the slave ONU, or the time information acquired by the master ONU is sent to the communication device under the master ONU. Notification, so that the transmission delay in the PON section is up or down regardless of whether the transmission delay is asymmetrical or not. It is possible to perform time synchronization by applying a synchronization system that functions on the assumption that the extension is symmetrical.

  According to the present invention, it is possible to perform time synchronization by applying a synchronization system that functions on the assumption that the vertical transmission delay is symmetric, regardless of whether the transmission delay in the PON section is asymmetric. Become.

It is a figure showing a schematic structure of a PON system concerning an embodiment of the present invention. It is a figure which shows the time synchronous sequence between the PTP master apparatus of IEEE1588v2, and a PTP slave apparatus. It is a figure which shows the mechanism of the time information transmission to the PTP slave apparatus which concerns on Example 1. FIG. It is a figure which shows the mechanism of the time information transmission to the PTP slave apparatus which concerns on Example 2. FIG.

  That is, the PON system of the present invention is a PON (Passive Optical Network) that realizes optical fiber transmission of point-to-multipoint connection between an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units). A master ONU (Optical Network Unit) that acquires time information from a GPS (Global Positioning System) signal or receives a PTP packet generated based on the time information acquired from a GPS signal; At least one slave ONU other than the master ONU is connected to the master ONU and the slave ONU via an optical branching unit, and the upstream bandwidth is dynamically increased by time division multiplexing for the master ONU and the slave ONU. OLT (Optical Line Terminal) to be assigned, and applying a synchronous system (802.1AS, etc.) in the PON section The time information transmitted from the master ONU via the OLT is notified to the communication device under the master ONU or the slave ONU, or the time information acquired by the master ONU is transmitted to the master ONU. Is notified to the communication devices under the control.

  Accordingly, the present inventors apply time synchronization by applying a synchronization system that functions on the assumption that the vertical transmission delay is symmetric regardless of whether the transmission delay in the PON section is asymmetric. Made possible. 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, in this PON system, a total of n ONUs 40-1 to 40-n (n is an arbitrary integer) are connected to an OLT 10 via an optical splitter (optical splitter) 30. Yes. A PTP master device 50 is connected to the ONU 40-1, and the PTP master device 50 has a GPS antenna 51. Also, PTP slave devices 52-1 to 52- (n-1) are connected to the ONUs 40-2 to 40-n, respectively. Base station apparatuses 60-1 to 60-n are connected to the PTP master apparatus 50 and the PTP slave apparatuses 52-1 to 52- (n-1), respectively.

  The time information received by the GPS antenna 51 is distributed to the other ONUs 40-2 to 40-n via the PTP master device 50, the ONU 40-1, and the OLT 10. The time information may be distributed to the ONU 40-1 via the OLT 10.

FIG. 2 is a diagram showing a time synchronization sequence between the IEEE 1588v2 PTP master device and the PTP slave device. Sends a "Sync (t _1)" to the slave ONU master the ONU at the time _{t 1,} and arrived in time _{t 2} to the slave ONU. Assume that the slave ONU transmits “Delay_Req” to the master ONU at time t ₃ , and this arrives at the master ONU at time t ₄ . Further, it is assumed that the master ONU transmits “Delay_Resp (t ₄ )” at time t ₄ . In this case, the slave ONU can calculate the time difference from the master ONU from the following equation and correct the time of the own device.
(Delay) = {(t ₂ −t ₁ ) + (t ₄ −t ₃ )} / 2

  In the first embodiment, a method of using a synchronization function (802.1AS or the like) in the PON section, transmitting no PTP packet, and not using a basic sequence of PTP will be described. Note that the time difference may be transmitted to the OLT side using a PTP packet. FIG. 3 is a diagram illustrating a mechanism of time information transmission to the PTP slave apparatus according to the first embodiment.

  (1) First, time synchronization is performed with high accuracy between the OLT and all ONUs using IEEE802.1AS or the like.

  (2) Next, the master ONU compares its own time with the reference time of the PTP packet (or 1PPS + ToD), and notifies the OLT of the time difference. The GM (PTP Grand Master) is connected to the master ONU, and the PTP slave device is connected to one of the slaves ONU1 to N. A PTP slave device may be connected under the master ONU. Then, when the delay in each section cannot be ignored, the time difference information considering the delay is notified.

  (3) The OLT adjusts its own time based on the time difference information from the master ONU.

  (4) The slave ONU (or master ONU) generates a PTP packet based on its own time locked to the OLT and transmits it to the PTP slave device. When the delay between the slave ONU and the PTP slave device cannot be ignored, the delay is also reflected in the generated PTP packet. That is, the delay time is added to the time of the own device.

  (5) The PTP slave device adjusts its own time to the time information described in the received PTP packet. Alternatively, the slave ONU is regarded as a PTP master, and time synchronization is performed using the PTP basic sequence.

  This makes it possible to perform time synchronization by applying a synchronization system that functions on the assumption that the vertical transmission delay is symmetric regardless of whether the transmission delay in the PON section is asymmetric.

  In the second embodiment, a method of using a synchronization function (802.1AS or the like) of a PON section, transmitting a PTP packet, and not using a basic sequence of PTP will be described. FIG. 4 is a diagram illustrating a mechanism of time information transmission to the PTP slave apparatus according to the second embodiment.

  (1) Time synchronization is performed with high accuracy between the OLT and all ONUs using IEEE802.1AS or the like.

(2) The ONU reflects the difference information t ₂ −t ₁ between the time t ₁ when the PTP packet arrives at the master ONU and the time t _{2 when} it arrives at the slave ONU via the OLT in the time information of the PTP packet To do. The difference information t ₂ −t ₁ may be transmitted in another control packet or the like. The GM is connected to the master ONU, and the PTP slave device is connected to one of the slaves ONU1 to N. When the distance delay in each section cannot be ignored, correction (delay correction) is performed in consideration of the delay amount.

(2 ′) The slave ONU uses the PTP slave to obtain the difference information t ₂ −t ₁ between the time t ₁ when the PTP packet arrives at the master ONU and the time t _{2 when} it arrives at the slave ONU via the OLT, together with the PTP packet. Transmit to the device. Here, as described above, the GM is connected to the master ONU, and the PTP slave device is connected to one of the slaves ONU1 to N. When the distance delay in each section cannot be ignored, the delay amount is also determined. Make corrections (delay correction) in consideration.

  (3) The PTP slave device adjusts its own time to the time information described in the received PTP packet. Alternatively, the slave ONU is considered as a PTP master and is synchronized by the PTP sequence.

  (3 ′) Further, the PTP slave device may reflect the time difference information of the above (2 ′) to the time information described in the received PTP packet to adjust its own time.

  In the transmission of the PTP packet that reaches the slave ONU from the master ONU via the OLT, it is possible to reflect the time information once in the PTP by the OLT and to perform it again by the slave ONU.

  This makes it possible to perform time synchronization by applying a synchronization system that functions on the assumption that the vertical transmission delay is symmetric regardless of whether the transmission delay in the PON section is asymmetric.

10 OLT
30 Optical splitter
40-1 Master ONU
40-2 to 40-n Slave ONU
50 PTP master device 51 GPS antenna 52-1 to 52- (n-1) PTP slave device 60-1 to 60-n Base station

Claims (8)

A PON (Passive Optical Network) system that realizes optical fiber transmission of point-to-multipoint connection between an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units),
A master ONU (Optical Network Unit) that acquires time information from a GPS (Global Positioning System) signal or receives a PTP packet generated based on time information acquired from a GPS signal;
At least one slave ONU other than the master ONU;
An OLT (Optical Line Terminal) that connects to the master ONU and the slave ONU via an optical branching unit and dynamically allocates an upstream band to the master ONU and the slave ONU by time division multiplexing. ,
Apply the synchronization system in the PON section to synchronize the time,
Time information transmitted from the master ONU via the OLT is notified to the communication device under the master ONU or the slave ONU, or the time information acquired by the master ONU is communicated under the master ONU. A PON system that notifies a device. The master ONU compares its own time with the reference time of the PTP packet, notifies the OLT of the time difference,
The OLT adjusts the time of its own device using the notified time difference, applies a synchronization system to synchronize the time of the master ONU and the slave ONU with the time of its own device,
The slave ONU transmits a PTP packet, PPS (Pulse per Second) and ToD (Time of Day) generated based on time information acquired from the OLT, or a GPS pseudo signal to a subordinate PTP slave device,
The PTP slave device adjusts the time of its own device using the time information indicated in the PTP packet, PPS and ToD, or GPS pseudo signal acquired from the slave ONU, or communicates with the slave ONU. 2. The PON system according to claim 1, wherein time synchronization is performed by executing a basic sequence.   If the delay of transmission between the slave ONU and the PTP slave device or the subordinate base station device cannot be ignored, the slave ONU delays the PTP packet, PPS and ToD, or GPS pseudo signal transmitted to the PTP slave device. The PON system according to claim 2, wherein:   The master ONU adds a delay time to the PTP packet, PPS and ToD, or GPS pseudo signal transmitted to the subordinate communication device when the delay in transmission between the own device and the subordinate communication device cannot be ignored. The PON system according to claim 2. Apply a synchronization system to synchronize time,
The slave ONU reflects the difference information between the time when the PTP packet arrives at the master ONU and the time when the PTP packet arrives at its own device via the OLT in the time information of the PTP packet to reflect the PTP packet Is transmitted to the subordinate PTP slave device, or the difference information is transmitted together with the PTP packet to the subordinate PTP slave device,
When the PTP slave device acquires the PTP packet in which the difference information is reflected in the time information from the slave ONU, the PTP slave device adjusts the time of the own device using the time information indicated in the acquired PTP packet, Alternatively, a time synchronization is performed by executing a PTP basic sequence with the slave ONU, or when the difference information is acquired from the slave ONU together with the PTP packet, the time information indicated in the acquired PTP packet includes the time information The PON system according to claim 1, wherein the time of the own apparatus is adjusted by reflecting the difference information.   6. The PON system according to claim 5, wherein the slave ONU adds a delay time to a PTP packet transmitted to the PTP slave device when a delay in transmission between the slave device and the PTP slave device cannot be ignored.   6. The PON system according to claim 5, wherein the master ONU adds a delay time to the PTP packet to be transmitted to the subordinate communication apparatus when the transmission delay between the self apparatus and the subordinate communication apparatus cannot be ignored. A transmission method of a PON (Passive Optical Network) system that realizes optical fiber transmission of point-to-multipoint connection between an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Units),
In a master ONU (Optical Network Unit), time information is acquired from a GPS (Global Positioning System) signal, or a PTP packet generated based on time information acquired from a GPS signal is received,
Apply the synchronization system in the PON section to synchronize the time,
An OLT (Optical Line) that is connected to a slave ONU that is an ONU other than the master ONU and the master ONU via an optical branching unit and dynamically allocates an upstream band to the master ONU and the slave ONU by time division multiplexing. The time information transmitted via the terminal) is notified to the communication device under the master ONU or the slave ONU, or the time information acquired by the master ONU is notified to the communication device under the master ONU. A transmission method characterized by the above.

Images