JPWO2012032566A1 - PON system and OLT - Google Patents

Abstract

In downstream transmission of a long-distance PON system that uses an optical amplifier to extend the transmission distance, signal degradation occurs due to chromatic dispersion of the optical fiber, so dispersion compensation is required. Also, the appropriate amount of dispersion compensation varies depending on the distance between OLT and ONU. The OLT has a dispersion compensation unit capable of switching the dispersion compensation amount. When downlink data is received from the upper network, the OLT refers to the dispersion compensation amount information of the transmission destination ONU and uses the buffers A and B to perform the same compensation. Downlink data is grouped and sent together for each amount. Further, an idle pattern is inserted at the timing of dispersion compensation amount switching by a switching signal from the timing control unit.

Description

  The present invention relates to a PON system, and more particularly to a dispersion compensation technique for PON system and OLT downlink transmission.

  The PON (Passive Optical Network) system is a high-speed / high-capacity optical access that shares optical fiber and subscriber accommodation equipment (OLT: Optical Line Terminal) among multiple optical subscriber termination equipment (ONU: Optical Network Unit). This system supports the current FTTH (Fiber To The Home) service as a technology that can control the cost per user. Downlink transmission from OLT to ONU adopts Time Division Multiplexing (TDM) method using continuous signal. The OLT allocates a LLID (Logical Link Identifier) for each ONU, and the ONU reads the LLID inserted in the data to determine the data addressed to itself. On the other hand, uplink transmission from ONU to OLT employs a time division multiple access (TDMA) system in order to prevent signal collision. Since the distance between ONU and OLT differs depending on the user, OLT receives different levels of burst signals. Due to the expansion of FTTH service needs and the advancement of transmission technology, the next-generation PON system is speeding up. 10G-EPON (Ethernet PON) (ETHERNET is a registered trademark) standardized in IEEE802.3av Task Force in 2009 is defined in Non-Patent Document 1 as a transmission speed of 10 Gbps, a maximum number of branches of 32, and a maximum transmission distance of 20 km. ing.

  While FTTH services have expanded rapidly due to the PON system, there are areas in depopulated areas where services are not provided due to constraints such as fiber installation costs. As a method for providing services to such a region, a long-distance PON system in which an optical amplifier is installed in a device or on a transmission line of the PON system to extend the transmission distance of the optical signal is considered. The long-distance PON system extends the transmission distance to 20 km or more of the 10G-EPON standard, so that the network can be made more efficient and efficient services can be provided for the above-depopulated areas. It becomes possible.

  However, signal degradation due to chromatic dispersion of optical fibers becomes a problem when extended by a long-distance PON system. This chromatic dispersion has a greater effect at higher transmission speeds, so it has not been a problem in conventional PON systems, but it is a major problem in high-speed next-generation PON systems. In a PON system with a transmission rate of 10 Gbps, when a single-mode fiber with a zero-dispersion wavelength of 1.3 μm is used as the transmission line and the signal wavelength is 1.55 μm, the chromatic dispersion value is approximately 20 ps / nm / km. At this time, a cumulative chromatic dispersion difference of 800 ps / nm occurs when the transmission distance difference between ONUs is 40 km, and 1600 ps / nm when 80 km. Therefore, in order to realize a high-speed long-distance PON system, dispersion compensation according to the transmission distance is required.

  In a PON system that accommodates multiple ONUs, if dispersion compensation is implemented with ONUs, the system cost increases significantly, so it is desirable to implement it on the OLT or transmission line. However, since the transmission distance between OLT and ONU varies depending on the ONU, the appropriate amount of dispersion compensation varies. For example, a dispersion compensation amount corresponding to an ONU with a long transmission distance cannot handle an ONU with a short transmission distance. Therefore, it is necessary to set an appropriate dispersion compensation amount for the transmission destination ONU.

  So far, several technologies have been devised as dispersion compensation technologies in PON systems. Patent Document 1 discloses a PON system that enables dispersion compensation of an upstream signal with a single dispersion compensator by setting the distance between the OLT and all ONUs to the same length during system design. Yes. Patent Document 2 proposes a method in which an OLT is provided with a variable dispersion compensation device for an upstream signal, and the dispersion compensation amount is switched for each burst signal from ONU RTT (Round Trip Time) information.

JP 2006-304170 A JP 2008-245179 A

IEEE Std P802.3av

  Regarding the technique of Patent Document 1, it is practically difficult to arrange all the distances between the OLT and the ONU to be the same length, and the accommodation efficiency is not improved. Patent Document 2 discloses a technique for switching the dispersion compensation amount with a guard time GT between upstream burst signals. However, since continuous transmission uses continuous signals, there is no GT, and dispersion compensation is switched in the middle of the data, resulting in bit errors. Furthermore, since encoding is performed in a state where data addressed to a plurality of ONUs are mixed and the same signal is transmitted to all ONUs, the dispersion compensation amount cannot be switched for each transmission destination ONU. Further, the dispersion compensation technique of the above-described known example is targeted for upstream transmission of the PON system. However, the 10G-EPON standard uses 1.3 μm wavelength for upstream transmission and 1.5 μm wavelength for downstream transmission, so dispersion compensation for downstream transmission is important.

  Therefore, an object of the present invention is a long-distance PON system that uses an optical amplifier to extend the transmission distance, and a PON system that performs appropriate dispersion compensation according to ONU for a downstream signal, and an OLT. Is to provide.

  In order to achieve the above object, the present invention is a PON system in which an OLT and a plurality of ONUs are connected, and the OLT performs dispersion compensation with a plurality of different dispersion compensation amounts for transmission of downlink data, Provided is a PON system that controls the transmission order of downlink data according to the dispersion compensation amount corresponding to each ONU of the transmission destination.

  In order to achieve the above object, the present invention provides a PON system in which an OLT and a plurality of ONUs are connected, wherein the OLT includes a plurality of electric / optical converters having different wavelengths and an electric / optical converter. Multiple dispersion compensators with different dispersion compensation amounts connected to each other, and downlink data from OLT to ONU is transmitted by optical signals of multiple wavelengths given different dispersion compensation amounts by these dispersion compensators To provide a PON system.

Furthermore, in order to achieve the above object, in the present invention, an OLT connected to a plurality of ONUs through an optical fiber, a control unit for controlling transmission of downlink data,
A dispersion compensator capable of providing a plurality of different dispersion compensation amounts for transmission of downlink data, and the control unit uses the dispersion compensation unit to transmit downlink data according to the dispersion compensation amount corresponding to the ONU of the transmission destination. An OLT that controls the dispersion of data is provided.

  In order to achieve the above object, according to the present invention, an OLT connected to a plurality of ONUs via an optical fiber, a plurality of electric / optical converters having different wavelengths, and an electric / optical converter. A plurality of dispersion compensators with different dispersion compensation amounts connected to each of them, and a control unit that controls downlink data to be transmitted to the ONU by using optical signals of a plurality of wavelengths given different dispersion compensation amounts by the dispersion compensators. An OLT having a configuration comprising:

  That is, in a preferred embodiment of the present invention, in a long-distance PON system using an optical amplifier, the OLT includes a variable dispersion compensator capable of switching the dispersion compensation amount, and when downlink data is received from an upper network, Provided is a PON system that refers to the dispersion compensation amount information of the transmission destination ONU, groups downlink data for each same compensation amount, sends them together, and inserts an idle pattern at the dispersion compensation amount switching timing.

  In another preferred embodiment of the present invention, in a long-distance PON system using an optical amplifier, the OLT includes a plurality of dispersion compensators having different dispersion compensation amounts and optical / electrical conversions having different wavelengths for each dispersion compensator. A PON system is provided that is configured to transmit data at different optical wavelengths for each compensation amount by referring to the dispersion compensation amount information of the transmission destination ONU when downlink data is received from an upper network.

  According to the present invention, it is possible to suppress signal deterioration due to fiber dispersion in downstream transmission, which has a significant effect in a long-distance PON system, and to extend the transmission distance.

  In addition, by providing an appropriate dispersion compensation amount according to the transmission destination ONU, the user accommodation area of the long-distance PON system can be expanded.

It is a figure which shows the structural example of a long distance PON system. It is a block diagram of OLT in a 1st Example. It is a figure which shows the ONU information table based on a 1st Example. It is a figure which shows the operation | movement flowchart of the timing control part based on 1st Example. It is a figure which shows the data pattern of the downlink transmission signal based on 1st Example. It is a sequence diagram at the time of Discovery according to the first embodiment. It is a figure which shows the flowchart of the OLT operation | movement at the time of Discovery based on a 1st Example. It is a block diagram of OLT in a 2nd Example. It is a figure which shows the data pattern of the downlink transmission signal based on 2nd Example. It is a block diagram of OLT1 in a 3rd Example. It is a figure which shows one specific example of the pre-equalization transmitter based on 3rd Example. It is a block diagram of OLT and ONU in a 4th Example.

  First, FIG. 1 shows a configuration block diagram of a long-distance PON system to which each embodiment of the present invention is applied. As shown in FIG. 1, the entire system includes an OLT 1, a plurality of ONUs 2, an optical fiber 3 and an optical splitter 4 installed between them, and transmits upstream / downstream signals. An optical amplifier 5 is installed between the OLT 1 and the ONU 2. The optical amplifier 5 amplifies the optical signal intensity to compensate for the attenuation of the optical signal due to the extension of the transmission distance, thereby transmitting the up / down signal. In this specification, an uplink / downlink signal may be referred to as uplink / downlink data or an uplink / downlink frame depending on the form of the signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to various examples. Unless otherwise stated, the explanation is based on the extended system of the 10G-EPON standard PON system. In addition, the same code | symbol is provided to the common part in each figure.

  First, the configuration of the OLT 1 in the first embodiment will be described below with reference to FIG.

<OLT1 configuration explanation>
The OLT 1 in this embodiment includes a WDM (Wavelength Division Multiplexing) coupler 10 that controls the transmission direction of uplink / downlink signals and uplink / downlink data, a dispersion compensation unit 20 that can switch a dispersion compensation amount using a switching signal, An electrical / optical converter (E / O) 30 that converts an electrical signal into an optical signal and sends it to the ONU 2; and a serial / parallel conversion circuit (Serializer / Deserializer: Serdes) 40 that performs serial / parallel conversion of input / output signals; , MAC (Media Access Control) frame processing, PON system control protocol (MPCP: Multi-Point Control Protocol) and the like, and the NNI (Network-Network Interface) that connects the OLT and the upper network ) 60, an optical / electrical converter (O / E) 70 for converting the upstream optical signal from the ONU 2 into an electrical signal, and an LA (Limiting Amplifier) 80.

<Description of WDM coupler 10>
The WDM coupler 10 controls the transmission direction of upstream / downstream optical signals. Since 10G-EPON uses the 1.3μm band for upstream and the 1.5μm band for downstream, each signal can be separated by wavelength. An upstream signal input from the optical fiber 3 to the WDM coupler 10 is transmitted to the optical / electrical converter 70, and a downstream signal input from the dispersion compensation unit 20 to the WDM coupler 10 is transmitted to the optical fiber 3.

<Description of dispersion compensation unit 20>
The dispersion compensator 20 includes dispersion compensators 21 and 22 and a switch 23. The dispersion compensators 21 and 22 can be realized by a dispersion compensating fiber, for example. The dispersion compensators 21 and 22 have different dispersion compensation amounts A and B. As the binary dispersion compensation amount, a value is selected so that all ONUs accommodated in the applied long-distance PON system can receive with either or both compensation amounts. The switch 23 performs path control of the optical signal output from the electrical / optical converter 30 in the previous stage and inputs the path to the dispersion compensator 21 or 22. The path control of the switch 23 is performed by a switching signal 57 transmitted from the logic control unit 50 functioning as a control unit.

<Description of the electrical / optical converter 30>
The electrical / optical converter 30 converts the downstream electrical signal transmitted from the previous Serdes 40 into an optical signal and transmits the optical signal to the dispersion compensation unit 20. The electrical / optical converter 30 is composed of, for example, a laser diode, a modulator, or the like.

<Description of optical / electrical converter 70>
The optical / electrical converter 70 converts the upstream optical signal input from the WDM coupler 10 into an electrical signal and transmits it to the LA 80 at the subsequent stage. The optical / electrical converter 70 includes, for example, an APD (Avalanche Photo Diode), a TIA (Trans-Impedance Amplifier), or the like.

<Explanation of LA80>
The LA 80 limits and amplifies the electrical signal input from the front-stage optical / electrical converter 70 to an amplitude that enables bit determination, and transmits the amplified signal to the subsequent-stage Serdes 40.

<Description of Serdes 40>
The Serdes 40 performs serial / parallel conversion on the input signal. The downlink parallel signal input from the logic control unit 50 is converted into a serial signal and transmitted to the electrical / optical converter 30. The upstream serial signal input from LA 80 is clock-synchronized, and after bit determination, is converted into a parallel signal and transmitted to the logic control unit 50.

<Description of the logic control unit 50>
The logical control unit 50 is a control unit in which an uplink and downlink frame processing function that is uplink / downlink data, MPCP that is a control protocol of the PON system, and the like are mounted. In addition, in order to perform dispersion compensation, which is a feature of the present embodiment, a timing control unit 51, a frame storage unit 52, an ONU information holding unit 55, and a transmission selection unit 56, which are functional configuration blocks shown in FIG. To do.

  The frame storage unit 52 includes buffers 53 and 54 that store downstream frames. Specifically, the areas of the buffers 53 and 54 may be provided in the storage unit. The buffers 53 and 54 correspond to the dispersion compensators 21 and 22, that is, the dispersion compensation amounts A and B, respectively. The ONU information holding unit holds an information table regarding registered ONUs and appropriate dispersion compensation amounts for each. When receiving a downlink frame from the NNI 60, the transmission selection unit 56 refers to the transmission destination of the downlink frame and the information table of the ONU information holding unit 55, and stores it in the corresponding dispersion compensation amount buffer in the frame storage unit 52.

  The timing control unit 51 calculates the transmittable time of the downlink frame in each buffer from the buffer amounts of the buffers 53 and 54 in the frame storage unit 52 at regular intervals, and can transmit the frame stored for each buffer. The data is sent to the Serdes 40 for each buffer in time. The timing control unit 51 also controls the switch 23 with the switching signal 57 so that the dispersion compensation amount of the dispersion compensation unit 20 becomes a corresponding value when frames are transmitted from the buffers 53 and 54. Further, an idle pattern is inserted at the timing of controlling the switch 23 in order to prevent loss of user data. The insertion of the idle pattern can be realized by reading data corresponding to the idle pattern stored in a predetermined area of the storage unit.

  As a mounting method of the logic control unit 50, for example, a central processing unit (CPU) that is a processing unit that performs program processing, and a RAM that is a storage unit that functions as the frame storage unit 52 and the ONU information holding unit 55 Needless to say, it can be realized by CPU program processing using (Random Access Memory). Note that the processing function for the upstream frame in the logical control unit 50 is a normal processing function, and therefore illustration and description thereof are omitted here.

<Description of NNI60>
The NNI 60 is an interface for connecting the PON system and the upper network, and sends an upstream signal from the logic control unit 50 to the upper network. Further, the downstream signal from the upper network is output to the logic control unit 50.

<Description of operation of the first embodiment (normal transmission)>
Here, an example of operation during normal transmission in the first embodiment will be described. A dispersion compensation operation for downlink transmission, which is a characteristic operation of this embodiment, will be described.

  When the NNI 60 receives a downstream frame from the upper network, it is transmitted to the transmission selection unit 56 in the logic control unit 50. The transmission selection unit 56 refers to the transmission destination address of the downstream frame and the ONU information holding unit 55 and selects a buffer to be stored in the frame storage unit 52.

  FIG. 3 shows an example of an information table held by the ONU information holding unit 55. The ONU information holding unit 55 holds information regarding the MAC address, RTT (Round Trip Time), an appropriate dispersion compensation amount, and the assigned LLID acquired at the time of ONU registration (Discovery). A method for determining the dispersion compensation amount will be described later. For example, when the transmission destination MAC address of the frame received by the transmission selection unit 56 is MAC_1, ONU # 1 that is the corresponding LLID is inserted into the preamble of the MAC frame and transmitted with the dispersion compensation amount A. Store in the buffer 53.

  Next, a method for transmitting a downstream frame after being stored in the frame accumulation unit 52 will be described. An example of the operation of the timing controller 51 in this operation is shown in FIG. FIG. 5 shows a data pattern of the downlink transmission signal in this operation example.

  This operation example assumes that the frames 101 are grouped and transmitted in the order of the buffer 53 and the buffer 54 for each period. The timing control unit 51 calculates frame transmission possible times T_A and T_B of each buffer from the buffer amounts of the buffers 53 and 54 in the frame storage unit 52 at regular intervals. Assuming that the calculation cycle is T, the buffer amount of the buffer 53 is a, the buffer amount of the buffer 54 is b, and the insertion time of the idle pattern 110 required when switching the dispersion compensation amount is T_i, the transmission possible time T_A from the buffer 53 is ( T-T_i * 2) * a / (a + b), and similarly T_B becomes (T-T_i * 2) * b / (a + b) (S200).

  After calculating the transmittable time, the timing control unit 51 inserts the idle pattern 110 during T_i. Then, at the timing when the electrical / optical converter 30 sends the idle pattern 110, the switch signal 57 is transmitted, the switch 23 is controlled to switch to the path passing through the dispersion compensator 21, and the dispersion compensation amount is set to A. Set (S210). The time T_i for inserting the idle pattern 110 is set to a sufficiently stable time when the dispersion compensation amount is switched. After setting the dispersion compensation amount to A, the maximum number of frames that can be transmitted between T_A is transmitted from the buffer 53, and the remaining time is adjusted by padding. As the idle pattern 110, for example, a “101010101010 ---” pattern of about 2 μs can be used. This can be generated by storing the idle pattern 110 in a predetermined storage area and performing reading under the control of the timing control unit 51.

  The transmission signal is inserted with IFG (Inter Flame Gap) between each frame 101, scrambled by 64B / 66B encoding method, coded by FEC (Forward Error Correction), and CW (Code Word) Sent in 100 units. (S220). After transmission for T_A, the idle pattern 110 is inserted again for T_i, the control signal 57 is transmitted, and the dispersion compensation amount is switched to B (S230). After setting the dispersion compensation amount to B, the T_B frame 101 is transmitted from the buffer 54 (S240). By repeating the above operation, the downstream frame can be transmitted to the ONU 2 with an appropriate dispersion compensation amount. In addition, loss of user data is prevented by switching the dispersion compensation amount during transmission of the idle pattern 110. Furthermore, by grouping and transmitting downlink frames for each dispersion compensation amount, the insertion amount of the idle pattern 110 can be suppressed, and a decrease in transmission efficiency can be suppressed. The broadcast frame is duplicated by the transmission selection unit 56, stored in both the buffers 53 and 54, and transmitted with both dispersion compensation amounts.

  In the present embodiment, the dispersion compensators 21 and 22 are arranged in parallel. For example, it may be arranged in series so as to control the number of dispersion compensators to be transmitted. Further, although the transmission selection unit 56 and the frame storage unit 52 are arranged in the logical control unit 50 and the buffer is provided for each dispersion compensation amount, it does not depend on this if a function of grouping and transmitting each dispersion compensation amount can be realized. . There is no problem even if other calculation formulas are used for the calculation method of the transmittable times T_A and T_B.

  A mounting method in the case of broadcast frame processing will be briefly described. In the case of the configuration of the above-described embodiment, when the CPU reads a frame from the RAM serving as the storage unit, the destination address of the frame is referred to. When the frame is a broadcast address, the transmission time (T_A) of the dispersion compensation amount A Broadcast frame processing can be executed by transmitting the same frame twice within both transmission times of the dispersion compensation amount B transmission time (T_B).

<Description of Operation of Example 1 (Discovery)>
Next, a method for determining the dispersion compensation amount for each ONU at the time of ONU registration (Discovery) in the first embodiment will be described. FIG. 6 shows a sequence at the time of Discovery, and FIG. 7 shows a flowchart of the OLT operation at the time of Discovery. Note that this flowchart is executed by the CPU of the logical control unit 50 functioning as the above-described control unit based on an instruction from a higher-level device or its own determination.

  First, the OLT 1 sets the dispersion compensation amount to A and broadcasts the GATE 400 to all the ONUs 2 by the above-described processing (S300). Thereafter, the OLT 1 switches the dispersion compensation amount to B and broadcasts the GATE 410 to all the ONUs 2 (S310). Here, the GATEs 400 and 410 have a dispersion compensation amount field 430 that clearly indicates the dispersion compensation amount at the time of transmission. The GATEs 400 and 410 notify the transmission start time (Grant Start time), the transmission available time (Grant Length), and the like for the ONU 2 that has received them to return a registration request (Register_req). These times are common values for GATE 400 and 410. The unregistered ONU 2 that has received the GATEs 400 and 410 returns Register_req 420 to the OLT 1 after a random time from the given Grant Start, and makes a registration request.

  In this embodiment, Register_req 420 includes a required compensation amount field 440. In the required compensation amount field 440, the dispersion compensation amount field of the GATEs 400 and 410 correctly received by the ONU 2 is referred to and the compensation amount is written. When both GATE 400 and 410 are received correctly, one of the values is adopted and written. The OLT allocates a certain time as a Discovery Window to the time for receiving Register_req 420 (S320). If Register_req 420 is not received during the Discovery Window, it is determined that there is no ONU 2 to be registered (S321). When Register_req 420 is received, the request compensation amount field 440 is referred to (S330). Then, the compensation amount described in the requested compensation amount field 440 is registered in the ONU information holding unit together with the information such as the MAC address and RTT of the ONU 2 (S340, S341).

  In this embodiment, the dispersion compensation amount for each ONU is determined based on the required compensation amount field in the Register_req frame. However, the dispersion compensation amount may be determined by other information, for example, RTT.

  The OLT 1 in the second embodiment will be described below with reference to FIG.

<OLT1 configuration explanation>
The OLT 1 in this embodiment is similar to the first embodiment in that the WDM coupler 10, the dispersion compensation unit 20, the electrical / optical converter 30, the Serdes 40, the logic control unit 50, the NNI 60, and the optical / electrical conversion. The unit 70 and the LA 80 are included. The difference from the first embodiment is the configuration of the dispersion compensator 20 and the frame storage unit 52 in the logic control unit 50. Needless to say, the logic control unit 50 in the present embodiment also uses the above-described memories such as the CPU and the RAM for the implementation.

<Description of dispersion compensation unit 20>
The dispersion compensator 20 according to the present embodiment includes dispersion compensators 21, 22, and 24 and a switch 23. The dispersion compensators 21, 22, and 24 include different dispersion compensation amounts A, B, and C. As the binary dispersion compensation amount, a value is selected so that all ONUs 2 accommodated in the applied long-distance PON system can receive with one or a plurality of compensation amounts. The switch 23 controls the path of the optical signal output from the preceding electrical / optical converter 30 and inputs the path to the dispersion compensator 21, 22, or 24. The path control of the switch 23 is performed by a switching signal 57 transmitted from the timing control unit 51 in the logic control unit 50.

<Description of Frame Storage Unit 52>
The frame storage unit 52 of this embodiment includes buffers 53, 54, and 58 that store downstream frames. Buffers 53, 54, and 58 correspond to dispersion compensators 21, 22, and 24, that is, dispersion compensation amounts A, B, and C, respectively.

<Description of operation of the second embodiment>
Here, an operation example of downlink transmission in the second embodiment will be described. When the NNI 60 receives a downstream frame from the upper network, it is transmitted to the transmission selection unit 56 in the logic control unit 50. The transmission selection unit 56 refers to the transmission destination address of the downstream frame and the ONU information holding unit 55 and selects a buffer to be stored in the frame storage unit 52. Next, a method for transmitting a downstream frame after being stored in the frame accumulation unit 52 will be described.

  FIG. 9 shows a data pattern of a downlink transmission signal in this operation example. In this operation example, it is assumed that the frames 101 are grouped and transmitted in the order of the buffer 53, the buffer 54, and the buffer 58 every period T. The timing control unit 51 calculates frame transmission possible times T_A, T_B, and T_C of each buffer from the buffer amounts of the buffers 53, 54, and 58 in the frame storage unit 52 for each period T. If the calculation cycle is T, the buffer amount of the buffer 53 is a, the buffer amount of the buffer 54 is b, the buffer amount of the buffer 58 is c, and the insertion time of the idle pattern 110 required when switching the dispersion compensation amount is T_i, the buffer 53 Transmission time T_A from (T-T_i * 3) * a / (a + b + c), similarly T_B is (T-T_i * 3) * b / (a + b + c), and T_C is ( T−T_i * 3) * c / (a + b + c). After calculating the transmittable time, the timing control unit 51 inserts the idle pattern 110 during T_i.

  Then, at the timing when the electrical / optical converter 30 sends the idle pattern 110, the switch signal 57 is transmitted, the switch 23 is controlled to switch to the path passing through the dispersion compensator 21, and the dispersion compensation amount is set to A. Set. After setting the dispersion compensation amount to A, the maximum number of frames that can be transmitted between T_A is transmitted from the buffer 53, and the remaining time is adjusted by padding. After transmission for T_A, the idle pattern 110 is inserted again for T_i, a control signal 57 is transmitted, and the dispersion compensation amount is switched to B. After setting the dispersion compensation amount to B, the T_B frame 101 is transmitted from the buffer 54. Further, the idle pattern 110 is inserted between T_i, the control signal 57 is transmitted, and the dispersion compensation amount is switched to C. After setting the dispersion compensation amount to C, the T_C frame 101 is transmitted from the buffer 58. By repeating the above operation, an appropriate compensation amount can be selected from the three types of dispersion compensation amounts for each transmission destination ONU. Further, discovery in the present embodiment is executed in the same manner as in the first embodiment by transmitting GATE with three types of dispersion compensation amounts.

  In this embodiment, three types of dispersion compensators are arranged. However, by adding a dispersion compensator and performing the same operation, it is possible to set various types of dispersion compensation amounts.

  Next, OLT 1 in the third embodiment will be described below with reference to FIGS.

<OLT1 configuration explanation>
The OLT 1 in this embodiment includes a WDM coupler 10, a pre-equalization transmitter 90, a Serdes 40, a logic control unit 50, an NNI 60, an optical / electric conversion unit 70, and an LA 80. The OLT 1 of this embodiment replaces the dispersion compensation unit 20 and the electrical / optical converter 30 in the first and second embodiments, and a pre-equalization transmitter that itself functions as the dispersion compensation unit and the electrical / optical converter. 90.

<Description of pre-equalization transmitter 90>
The pre-equalization transmitter 90 has a function of controlling a modulator driving signal, performing dispersion compensation, and transmitting an optical signal. The dispersion compensation amount can be switched by changing the parameter of the drive signal of the modulator by the switching signal 57. For example, it can be realized by using a laser, a Mach-Zehnder type modulator, and a FIR (Finite Impulse ResPONse) filter.

  FIG. 11 shows a specific example of the pre-equalization transmitter 90 in the present embodiment. In FIG. 11, 91 is a laser diode, 92 is a Mach-Zehnder modulator, 93 is a DA converter, and 94 is an FIR filter. The pre-equalization transmitter 90 inputs a transmission signal to an FIR filter 94 that is a digital filter, converts a digital signal output from the FIR filter 94 into an analog signal by a DA converter 93, and uses the analog signal to convert the digital signal into a Mach-Zehnder. The modulator 92 modulates the continuous light from the laser diode 91 to transmit an optical signal with dispersion compensation. The dispersion compensation amount is changed and controlled by changing the parameter of the FIR filter 94 by the switching signal 57.

<Description of operation of the third embodiment>
Here, the dispersion compensation operation for downlink transmission in the third embodiment will be described. It is assumed that the pre-equalization transmitter 90 of the present embodiment can transmit by giving two types of dispersion compensation amounts A and B. In FIG. 10, when the NNI 60 receives a downstream frame from the upper network, it is transmitted to the transmission selection unit 56 in the logical control unit 50. The transmission selection unit 56 refers to the transmission destination address of the downstream frame and the ONU information holding unit 55, selects a buffer to be stored in the frame storage unit 52, and stores the frame. This operation example assumes that the frames 101 are grouped and transmitted in the order of the buffer 53 and the buffer 54 every period T.

  The timing control unit 51 calculates the frame transmittable times T_A and T_B of each buffer as in the operation example of the first embodiment. After calculating the transmittable time, the timing control unit 51 inserts the idle pattern 110 during T_i. Then, the Serdes 40 transmits the switching signal 57 at the timing when the idle pattern 110 is transmitted, and controls the drive signal parameter of the pre-equalization transmitter 90, thereby setting the dispersion compensation amount to A. After setting the dispersion compensation amount to A, the maximum number of frames that can be transmitted between T_A is transmitted from the buffer 53, and the remaining time is adjusted by padding. After transmission for T_A, the idle pattern 110 is inserted again for T_i, a control signal 57 is transmitted, and the dispersion compensation amount is switched to B. After setting the dispersion compensation amount to B, the inter-T_B frame 101 is similarly transmitted from the buffer 54. By repeating the above operation, it is possible to transmit a downstream frame with an appropriate dispersion compensation amount to each ONU 2.

  The OLT 1 and ONU 2 in the fourth embodiment will be described below with reference to FIG.

<OLT1 configuration explanation>
The OLT 1 in this embodiment includes a WDM coupler 10, dispersion compensators 21 and 22, electrical / optical converters 31 and 32, Serdes 41 and 42, a logic control unit 50, an NNI 60, and an optical / electrical conversion unit 70. And LA80. Each of the electrical / optical converters 31 and 32 includes an optical transmitter having a different wavelength. The optical signal sent from the electrical / optical converter 31 is sent from the WDM coupler 10 after being given a dispersion compensation amount A by the dispersion compensator 21. Similarly, the optical signal sent from the electrical / optical converter 32 is sent from the WDM coupler 10 after being given a dispersion compensation amount B. The dispersion compensation amounts A and B are values that can be received by all ONUs 2 in the long-distance PON system to which this embodiment is applied with either one or both of the compensation amounts. In addition to the MPCP and the frame processing function, the logic control unit 50 includes an ONU information holding unit 55 and a transmission selection unit 56 in order to execute the dispersion compensation operation of this embodiment. The ONU information holding unit 55 holds the MAC address, LLID, RTT, and dispersion compensation amount for each ONU 2 as in the ONU information table in the first embodiment shown in FIG. When receiving a downstream frame from the NNI 60, the transmission selection unit 56 has a function of referring to the ONU information holding unit, selecting one of the Serdes 41 and 42, and transmitting it. The configuration for receiving the uplink signal is not changed from the first embodiment.

<ONU2 configuration explanation>
The ONU 2 in this embodiment includes WDM couplers 500 to 502 that transmit the wavelength of either the electrical / optical converter 31 or 32 of the OLT 1. As for the wavelength to be transmitted, the wavelength for which an appropriate dispersion compensation amount is given is selected in consideration of the distance from the OLT 1 when the ONU 2 is installed.

<Description of Operation of Example 4>
Here, the dispersion compensation operation for downlink transmission in the fourth embodiment will be described with reference to FIGS. It is assumed that a downstream frame is input from the upper network to the NNI 60 and transmitted to the transmission selection unit 56 in the logic control unit 50. Then, the transmission selection unit 56 refers to the transmission destination address of the downstream frame and the ONU information holding unit 55 and selects either the Serdes 41 or 42 for transmission. For example, when the transmission destination is MAC_1, since the appropriate dispersion compensation amount is A, the downlink frame is transmitted to the Serdes 41.

  At this time, the downstream frame is scrambled by 64B / 66B, added with an error correction code by FEC, and transferred to Serdes 41 or 42. Thereafter, the electrical / optical converter 31 or 42 converts the electrical signal into an optical signal and sends it to the dispersion compensator 21 or 22. The dispersion compensators 21 and 22 perform dispersion compensation of dispersion compensation amounts A and B on the input optical signal, and are transmitted from the OLT 1 via the WDM coupler 10. Then, the ONU 2 selects and receives a wavelength for which appropriate dispersion compensation has been performed by the WDMs 500 to 502.

  At the time of Discovery, the OLT 1 sends GATE by both the electrical / optical converters 31 and 32. At this time, the dispersion compensation amount field 430 indicates the dispersion compensation amount. Since the ONU 2 includes a WDM coupler that transmits one of the wavelengths of the electrical / optical converter 31 or 32 in advance, it receives one of the GATEs of the dispersion compensation amount A or B. The ONU 2 indicates the dispersion compensation amount of the GATE received in the request compensation amount field 440 in Register_req, and returns it to the OLT 1. The OLT 1 registers the ONU request compensation amount in the ONU information holding unit according to the received Register_req.

  In this embodiment, the ONU information holding unit 55 and the transmission selection unit 56 are provided in the logical control unit 50. However, there is no problem if all downlink frames are duplicated and transmitted to both the Serdes 41 and 42. Further, in the present embodiment, the case where the two types of dispersion compensations A and B are performed is shown. However, if only the types of dispersion compensation amounts for implementing the dispersion compensator, the electrical / optical converter, and Serdes are provided. Obviously, more dispersion compensation can be given. Furthermore, although the method of determining the dispersion compensation amount for each ONU based on the required compensation amount field in the Register_req frame at the time of Discovery has been shown, the dispersion compensation amount may be determined by other information, for example, RTT.

  It should be noted that each of the above-described embodiments is a preferred embodiment of the present invention, and it is needless to say that each embodiment can be modified without departing from the scope of the present invention.

  Further, in the present specification, various related inventions are disclosed in addition to the inventions representatively described in the claims. An example of the invention of the PON system is as follows.

  That is, a PON system in which an OLT and a plurality of ONUs are connected, and the OLT includes a pre-equalization transmitter having a modulator for performing dispersion compensation with a plurality of different dispersion compensation amounts for downlink data transmission. And a control unit for sending downlink data by giving a plurality of different dispersion compensation amounts according to the dispersion compensation amount corresponding to each ONU of the transmission destination by changing the control parameter of the drive signal of the modulator. A PON system characterized by the above is disclosed.

  Furthermore, in the PON system in which an OLT and a plurality of ONUs are connected, the OLT performs dispersion compensation with a plurality of different dispersion compensation amounts for transmission of downlink data, and the dispersion compensation amount corresponding to each ONU of the transmission destination Accordingly, the control unit controls the transmission order of the downlink data according to the information, and the control unit holds the dispersion compensation amount information for each ONU, and transmits the downlink data by referring to the dispersion compensation amount information. Disclosed is a PON system that determines a dispersion compensation amount to be given at the time, groups downlink data according to the determined dispersion compensation amount, and collectively transmits downlink data of the same group at regular intervals.

  Furthermore, the OLT control unit in this PON system calculates the transmittable time from the accumulated amount of downlink signals of the same group when the downlink signals of the same group are sent together at regular intervals. Disclosed is a PON system characterized by being transmitted.

  Furthermore, in the PON system in which an OLT and a plurality of ONUs are connected, the OLT performs dispersion compensation by using a plurality of different dispersion compensation amounts for downlink data transmission, and dispersion compensation corresponding to each ONU at the transmission destination. And a control unit that controls a transmission order of downlink data according to the amount, and the control unit inserts an idle pattern into the downlink data at a timing when a plurality of different dispersion compensation amounts are changed. Disclose the system.

  The present invention is useful as a dispersion compensation technique for downlink transmission in a PON system.

1 ... OLT
2 ... ONU
DESCRIPTION OF SYMBOLS 3 ... Optical fiber 4 ... Optical splitter 5 ... Optical amplifier 10, 11, 12, 13 ... WDM coupler 20 ... Dispersion compensator 21, 22, 24 ... Dispersion compensator 23 ... Switch 30, 31, 32 ... Electric / optical converter 40, 41, 42 ... Serdes
DESCRIPTION OF SYMBOLS 50 ... Logic control part 51 ... Timing control part 52 ... Frame storage part 53, 54, 58 ... Buffer 55 ... ONU information holding part 56 ... Transmission selection part 57 ... Switching signal 60 ... NNI
70 ... Optical / electrical converter 80 ... LA
90 ... Pre-equalization transmitter 100 ... FEC CW
101 ... Frame 102 ... IFG
110 ... Idle pattern 400,410 ... GATE
420 ... Register_req
430: Dispersion compensation field 440 ... Required compensation amount field.

Claims (19)

A passive optical network (PON) system in which an optical transmission line termination unit (OLT) and a plurality of optical line termination units (ONU) are connected,
The OLT performs dispersion compensation with a plurality of different dispersion compensation amounts for downlink data transmission, and controls the transmission order of the downlink data according to a dispersion compensation amount corresponding to each ONU of a transmission destination.
PON system characterized by that. The PON system according to claim 1,
The OLT is
An electrical / optical converter that receives the downlink data and outputs an optical signal; and a plurality of dispersion compensators having the plurality of different dispersion compensation amounts;
A controller that controls input of the optical signal to the dispersion compensator;
The control unit controls the plurality of different dispersion compensation amounts for the optical signal.
PON system characterized by that. The PON system according to claim 1,
The OLT is
At the time of Discovery, a GATE message including a dispersion compensation amount field indicating the dispersion compensation amount is transmitted to the ONU with all different dispersion compensation amounts that can be given.
The ONU is
Returning the Register_req message indicating the dispersion compensation amount indicated in the dispersion compensation amount field of the GATE message correctly received in the required compensation amount field to the OLT,
The OLT is
The dispersion compensation amount indicated in the required compensation amount field of the received Register_req message is held as the dispersion compensation amount corresponding to the ONU that has returned the Register_req message.
PON system characterized by that. A PON system in which OLT and multiple ONUs are connected,
The OLT is
Multiple electrical / optical converters with different wavelengths;
A plurality of dispersion compensators connected to each of the electrical / optical converters and having different dispersion compensation amounts;
Transmitting downlink data from the OLT to the ONU by optical signals of a plurality of wavelengths given different dispersion compensation amounts by the dispersion compensator,
PON system characterized by that. The PON system according to claim 4,
The OLT is
The dispersion compensation amount information corresponding to each of the ONUs is held, and the dispersion compensation amount given when transmitting the downlink data is determined by referring to the dispersion compensation amount information, and the determined dispersion compensation amount Selecting said electrical / optical converter for delivery by:
PON system characterized by that. The PON system according to claim 4,
The OLT is
Sending the downlink data to all the electrical / optical converters provided in the OLT, and transmitting the downlink data by optical signals of a plurality of wavelengths given the different dispersion compensation amounts,
PON system characterized by that. The PON system according to claim 4,
The ONU is
Provided with a WDM (Wavelength Division Multiplexing) coupler that transmits only the wavelength of an optical signal given a dispersion compensation amount corresponding to the ONU,
PON system characterized by that. OLT connected to multiple ONUs via optical fiber,
A control unit that controls transmission of downlink data;
A dispersion compensation unit capable of giving a plurality of different dispersion compensation amounts to the transmission of the downlink data,
The control unit controls the dispersion compensation unit to perform dispersion compensation of the downlink data according to a dispersion compensation amount corresponding to the ONU of a transmission destination.
OLT characterized by that. The OLT according to claim 8, wherein
The dispersion compensator controls input to the dispersion compensator of a plurality of dispersion compensators having the plurality of different dispersion compensation amounts and an optical signal transmitted from the electrical / optical converter to which the downlink data is input. And a switch to
The controller is
Controlling the switch to give one of the plurality of different dispersion compensation amounts to the optical signal;
OLT characterized by that. The OLT according to claim 8, wherein
The dispersion compensation unit includes a pre-equalization transmitter having a modulator,
The controller is
By controlling the control parameter of the drive signal of the modulator, control to give the plurality of different dispersion compensation amounts,
OLT characterized by that. The OLT according to claim 8, wherein
A storage unit for holding dispersion compensation amount information corresponding to each ONU;
The control unit determines a dispersion compensation amount to be given when transmitting the downlink data by referring to the dispersion compensation amount information, groups the downlink data according to the determined dispersion compensation amount, Control to send the downlink data of the same group together every time,
OLT characterized by that. The OLT according to claim 11, wherein
The controller is
Calculating the transmittable time from the buffer amount of the predetermined period of the grouped downlink data, and controlling the downlink data to be transmitted in the transmittable time for each group,
OLT characterized by that. The OLT according to claim 8, wherein
The controller is
The dispersion compensation unit controls to insert an idle pattern at a timing when the dispersion compensation amount is changed.
OLT characterized by that. The OLT according to claim 8, wherein
The controller is
At the time of Discovery, control is performed to transmit a GATE message including a dispersion compensation amount field indicating the dispersion compensation amount to all of the dispersion compensation amounts that can be given to the ONU.
OLT characterized by that. The OLT according to claim 14, wherein
Receiving from the ONU a Register_req message indicating the dispersion compensation amount in the dispersion compensation amount field of the GATE message that could be received by the ONU;
OLT characterized by that. The OLT according to claim 15, wherein
A storage unit,
The dispersion compensation amount indicated in the required compensation amount field of Register_req is held in the storage unit as a dispersion compensation amount corresponding to the ONU that has returned Register_req.
OLT characterized by that. An OLT connected to multiple ONUs via optical fiber,
Multiple electrical / optical converters with different wavelengths;
A plurality of dispersion compensators connected to each of the electrical / optical converters and having different dispersion compensation amounts;
A control unit that controls transmission of downlink data to the ONU by optical signals of a plurality of wavelengths given different dispersion compensation amounts by the dispersion compensator;
OLT characterized by that. The OLT according to claim 17, wherein
A storage unit for holding dispersion compensation amount information corresponding to each ONU;
The controller is
The dispersion compensation amount given when transmitting the downlink data is determined by referring to the information on the dispersion compensation amount in the storage unit, and the electrical / optical converter to be transmitted is selected based on the determined dispersion compensation amount. To control,
OLT characterized by that. The OLT according to claim 17, wherein
The controller is
Sending the downlink data to all the electrical / optical converters, and controlling the downlink data to be transmitted by optical signals of a plurality of wavelengths given the different dispersion compensation amounts.
OLT characterized by that.

Images