JP2013102483A - Passive optical network system and operation method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a passive optical network system for reducing power consumption by controlling transmission speed of a downstream signal.SOLUTION: A passive optical network system has: a master station for simultaneously transmitting a frame signal time-division multiplexing signals addressed to a plurality of slave stations to the plurality of slave stations; and the slave stations, each of which processes a signal addressed to the slave station in the frame signal. The master station comprises: an optical transmission interface for transmitting a signal to the plurality of slave stations at first transmission speed or at second transmission speed higher than the first transmission speed; a packet buffer for accumulating a signal addressed to each of the plurality of slave stations; a control part which determines transmission timing and transmission speed of a signal to be transmitted to each of the slave stations on the basis of a signal amount accumulated in the buffer, transmits the signal at the transmission timing and the transmission speed, and notifies each slave station of the transmission timing and transmission speed. Each of the slave stations comprises: an optical reception interface for receiving a signal at the first or second transmission speed; and a control part for controlling the optical reception interface on the basis of the notified transmission timing and transmission speed.

Description

  The present invention relates to a passive optical network system, an optical multiple termination device, and an optical network termination device, and more particularly to a passive optical network system in which a plurality of subscriber connection devices share an optical transmission line.

  High-speed and broadband communication networks are also being promoted in access networks connecting subscribers, and passive optical network systems (Passive Optical Network systems) defined by Recommendation T984.3 of the International Telecommunications Union (hereinafter referred to as ITU-T). : Hereinafter referred to as PON). The PON is equivalent to an optical multiple terminator (hereinafter referred to as OLT) corresponding to a master station connected to a higher-level communication network and a slave station that accommodates a plurality of subscriber terminals (PCs and telephones). The optical network termination device (Optical Network Unit: hereinafter referred to as ONU) is connected by an optical passive network including a backbone optical fiber, an optical splitter, and a plurality of branch optical fibers. Specifically, signals from terminals (PCs, etc.) connected to each ONU are optically (time-division-multiplexed) from the branch optical fiber via the optical splitter via the optical fiber splitter (time division) and sent to the OLT. Communication is performed in a form in which signals from each ONU are processed and transmitted to a higher-level communication network, or transmitted to other ONUs connected to the OLT.

  The introduction of PON begins with a system that handles a low-speed signal of 64 kbit / sec, and is a BPON (Broadband PON) or Ethernet (registered trademark; the registered trademark is omitted below) that transmits and receives fixed-length ATM cells at about 600 Mbit / sec. Introduction of Ethernet PON (EPON) that transmits and receives variable-length packets at a maximum of about 1 Gbit / sec and GPON (Gigabit capable PON) that handles higher-speed signals of about 2.4 Gbit / sec are being promoted. Furthermore, in the future, it is required to realize a high-speed PON capable of handling signals of 10 Gbit / second to 40 Gbit / second. As means for realizing these high-speed PONs, use of TDM (Time Division Multiplexing) in which a plurality of signals similar to the current PON are time-division multiplexed is being studied. Note that the current PON using TDM uses different wavelengths for upstream (ONU to OLT) signals and downstream (OLT to ONU) signals, and communication between the OLT and each ONU is communicated to each ONU. It is the structure which allocates time. Specifically, it is a configuration in which a burst-like variable length signal (burst signal) that can easily handle various signals (sound, image, data, etc.) is assigned.

  In each of the above PONs, ONUs are installed in subscriber homes scattered in various places, and therefore the distance from the OLT to each ONU is different. That is, since the length (transmission distance) of the optical fiber composed of the backbone optical fiber and the branch optical fiber from the OLT to each ONU varies, the transmission delay (delay amount) between each ONU and the OLT varies, and each ONU has a different timing. Even if the signal is transmitted by the optical signal, the optical signals from the ONUs may collide and interfere with each other on the backbone optical fiber. For this reason, in each PON, for example, the distance measurement between the OLT and the ONU is performed using the ranging technique defined in the ITU-T recommendation G984.3 so that the signal output from each ONU does not collide after the distance measurement is performed. Adjust the output signal delay. In addition, the OLT determines a delay measured by ranging when a bandwidth of a signal permitted to be transmitted to each ONU is determined based on a transmission request from each ONU using a dynamic bandwidth assignment (hereinafter referred to as DBA) technique. In consideration of the amount, the transmission timing is designated to each ONU so that the optical signal from each ONU does not collide or interfere on the backbone optical fiber. That is, the PON is configured such that communication is performed in a state where the timing of signals transmitted and received between the OLT and each ONU is managed in the system.

  In the GPON, the transmission signal from each ONU is transmitted with a guard time for interference prevention consisting of a maximum of 12 bytes and an OLT so that signals from each ONU multiplexed on the backbone optical fiber can be identified and processed by the OLT. A burst overhead byte called a delimiter for identifying a preamble and a received signal delimiter used for determination of a signal identification threshold of an internal receiver and clock extraction, and a control signal (sometimes called overhead or header) of PON are data ( (It may be called a payload). Each data is variable-length burst data, and a header called a GEM (G-PON Encapsulation Method) header for processing the variable-length data is added to the head of each data.

  On the other hand, at the head of the signal transmitted from the OLT to each ONU, a frame synchronization pattern for identifying the head, and monitoring / maintenance / control information so that each ONU can identify and process the signal from the OLT A PLOAM area for transmitting a signal and an overhead (sometimes referred to as a header) called a grant instruction area for instructing signal transmission timing of each ONU are added to data time-division multiplexed to each ONU It is. Note that a GEM header for processing variable length data is added to the data addressed to each ONU to be multiplexed, similarly to the signal from the ONU. The OLT specifies the upstream transmission permission timing (transmission start (Start) and end (Stop)) of each ONU in units of bytes using the grant indication area. This transmission permission timing is called a grant. When each ONU transmits data addressed to the OLT at the permission timing, these are optically (time-division) multiplexed on the optical fiber and received by the OLT.

ITU-T Recommendation G. 984.3

  PON has been developed and introduced to process higher-speed signals, such as the transition from BPON to GPON. It is known that optical modules and LSIs that realize the PON signal transmission function consume a large amount of power as the transmission speed increases. For example, in order to achieve a higher transmission speed, the optical module secures a necessary band by flowing a larger amount of current as the transmission speed is higher. In addition, a digital signal processing LSI using CMOS technology consumes power approximately proportional to the square of the speed of the operation clock. That is, a larger amount of power consumption tends to be consumed as the transmission speed increases.

  On the other hand, PON subscribers tend to seek faster PONs, but they do not always want fast transmission rates. In addition to not requiring a high transmission speed during non-communication time periods, data transmission in Internet access is required even during communication, and a high transmission speed is required during the period of downloading or uploading a large amount of image data or large-capacity files. However, a high transmission rate is not required while browsing or working with the contents. Further, in the TCP protocol used for data transmission, it is necessary to return a confirmation signal packet when a certain number of packets are received, and the data transmission side does not transmit subsequent data until the confirmation signal packet is received. In other words, even in the course of data transmission, the actual state of operation is that data traffic often has a transmission form with extremely high burstiness. However, optical modules and LSIs constituting an actual PON operate and consume power in a time zone in which data is not substantially transmitted, causing a significant waste of power. For this reason, there is a need for a PON system that can perform transmission at a low transmission rate when end-user traffic is small and can perform transmission at a high transmission rate when end-user traffic is large.

  In the upstream direction of the PON, since the signal output in burst form from each slave station is time-division multiplexed, the power consumption is reduced by changing the transmission rate of the signal transmitted from each slave station according to the traffic. I can do it. On the other hand, in the downlink direction of the PON, a frame in which signals destined for each slave station are multiplexed is continuously broadcast to all slave stations, and a signal that is not destined for the slave station is also received for a certain slave station. It becomes. That is, even when a signal addressed to another station is coming, components such as optical modules operate continuously and consume power. If power consumption can be reduced during this time period, the power consumption of the PON can be reduced. Will go further. In view of the above, the present invention reduces waste of power consumption as much as possible by switching the transmission speed based on the end user traffic in the downstream direction, particularly in a PON having a configuration in which signals having different transmission speeds can be mixed and operated. The purpose is to realize a possible PON.

  In order to solve the above problems, the passive optical network system of the present invention broadcasts to a plurality of slave stations by a frame signal obtained by time-division multiplexing signals addressed to a plurality of slave stations received from the host network by the master station, A passive optical network system in which each of a plurality of slave stations processes a signal addressed to itself from a received frame signal, and the master station has a first transmission speed or a second transmission speed higher than the first transmission speed. An optical transmission interface for transmitting signals to a plurality of slave stations, a packet buffer for storing signals received from the upper network corresponding to each of the plurality of slave stations that are the destinations of the signals, and a buffer stored in the buffer Determining the transmission timing and transmission speed of a signal to be transmitted to each of a plurality of slave stations based on the amount of signals, and transmitting signals from the optical transmission interface to each of the plurality of slave stations at the transmission timing and transmission speed; Determined transmission data And an optical reception interface for receiving a signal of the first transmission rate or the second transmission rate to each of the plurality of slave stations, And a control unit that controls the optical reception interface based on the transmission timing and transmission speed notified from the master station.

  Then, when the control unit of the master station determines the amount of the signal to be transmitted to any slave station based on the amount of the signal received from the upper network and transmitted to each of the plurality of slave stations, the amount of the signal to be transmitted is the first. If the transmission rate is less than the maximum transmission rate that can be transmitted at 1, the transmission rate of the master station signal is the first transmission rate, and the amount of signals to be transmitted exceeds the maximum transmission rate that can be transmitted at the first transmission rate. In this case, the signal transmission rate addressed to any slave station among the plurality of slave stations is determined as the second transmission rate.

  According to the present invention, a passive optical network system capable of reducing power consumption waste as much as possible based on end-user traffic in a PON having a configuration in which a plurality of signals having different downlink transmission rates can be mixed and operated in a time division manner is realized. can do.

It is a network block diagram which shows the structural example of the optical access network using PON. It is a frame block diagram which shows the structural example of the downstream signal from OLT to ONU. It is a block block diagram which shows the structural example of ONU. It is a block block diagram which shows the structural example of an optical reception interface. It is a block block diagram which shows the structural example of OLT. It is a block block diagram which shows the structural example of a downstream packet buffer. It is explanatory drawing explaining the structure and operation example of an OLT control part. It is an operation | movement flowchart which shows the operation example of an OLT control part. Similarly, it is an operation | movement flowchart which shows an operation example (the 2). Similarly, it is an operation | movement flowchart which shows an operation example (the 3). It is a memory block diagram which shows the structural example of each table with which OLT was equipped. It is a frame block diagram which shows another structural example of a downstream signal. Similarly, it is a frame block diagram which shows another structural example. Similarly, it is a frame block diagram which shows another structural example (the 2). Similarly, it is a frame block diagram which shows another structural example (the 3). It is an operation | movement flowchart which shows another operation example (the 1) of an OLT control part. Similarly, it is an operation | movement flowchart which shows an operation example (the 2). It is a memory block diagram which shows another structural example of an allocation byte length table. It is a memory block diagram which shows another structural example of a transmission timing table.

Hereinafter, the configuration and operation of the PON according to this embodiment will be described with reference to the drawings. The GPON specified in ITU-T recommendation G984.3, and the next generation GPON expected to be introduced in the future, This will be described in detail by taking the configuration and operation of a PON with a mixture of two as an example.
The following description assumes a PON configured to process variable-length data with TDM as in GPON. The transmission rate of downlink data from the OLT to each ONU is 10 Gbit / sec (9.953328 Gbit / sec). However, this is a mixed configuration of 10 Gbit / second) and 2.4 Gbit / second (2.48882 Gbit / second, but also referred to as 2.4 Gbit / second), and transmission of upstream data from the ONU to the OLT. An example will be described in which the speed is one type of 1.2 Gbit / sec (1.24416 Gbit / sec, but hereinafter also referred to as 1.2 Gbit / sec). These numerical values such as the transmission speed are examples, and other transmission speeds may be used, and the present embodiment is not limited to these numerical values. Further, there may be three or more downlink transmission rates, or a configuration in which a plurality of types of uplink transmission rates are mixed.

FIG. 1 is a network configuration diagram showing a configuration example of an optical access network using the PON of the present invention.
The access network 1 includes, for example, a public communication network (PSTN) / Internet 20 (hereinafter may be referred to as an upper network) via a PON 10 and a subscriber terminal (Tel: 400, PC: 410, etc.) for communication. The PON 10 includes a plurality of ONUs (hereinafter referred to as slave stations) that accommodate an OLT (hereinafter also referred to as a master station) 200 connected to the upper network 20 and subscriber terminals (telephone (Tel) 400, PC 410, etc.). 300). The OLT 200 and each ONU 300 are connected by an optical passive network having a backbone optical fiber 110, an optical splitter 100, and a plurality of branch optical fibers 120, and communication between the host network 20 and the subscriber terminals 400 and 410, or the subscriber terminal 400 , 410 communicate with each other. The ONU 300 is an ONU that can be used in, for example, 10 GPON or GPON (for example, an ONU that can transmit both 10 Gbit / sec and 2.4 Gbit / sec in the downlink, and may be referred to as 2.4 G / 10 GONU hereinafter). It is. In the figure, five ONUs 300 are connected to the OLT 200. Note that the maximum number of ONUs that can be connected to the OLT 200 is 254 according to ITU-T recommendation G984.3.

  The downlink signal 130 from the OLT 200 to each ONU 300 is broadcast by time-division-multiplexing the signal addressed to each ONU 300. Each ONU 300 receives the signal by determining whether the arrived frame is its own transmission rate or a signal addressed to itself. The ONU 300 sends a received signal to the telephone 400 or the PC 410 based on the signal destination. Further, the upstream signal 140 from each ONU 300 to the OLT 200 includes an upstream signal 150-1 transmitted from the ONU 300-1, an upstream signal 150-2 transmitted from the ONU 310-2, and an upstream signal transmitted from the ONU 300-3. 150-3, an upstream multiplexed signal 150-4 transmitted from the ONU 300-4, and an optical multiplexed signal in which the signal 150-n transmitted from the ONU 300-n is optically time-division multiplexed via the optical splitter 100. 140 and transmitted to the OLT 200. Since the fiber lengths between the ONUs 300 and the OLTs 200 are different, the signal 140 has a form in which signals having different amplitudes are multiplexed. The downstream signal 130 is an optical signal having a wavelength band of 1.5 μm, for example, and the upstream signals 140 and 150 are optical signals having a wavelength band of 1.3 μm, for example. Both optical signals are transmitted through the same optical fibers 110 and 120. Multiplexed (WDM) and transmitted / received.

FIG. 2 is a frame configuration diagram illustrating a configuration example of a downlink signal.
The downstream signal 130 (hereinafter also referred to as a downstream frame or simply a frame) is a signal having a period of 125 μs as defined in ITU-T recommendation G984.3 and signals of 2.4 Gbit / second and 10 Gbit / second. The 2.4G / 10G mixed frame 20 that can be mixedly accommodated at an arbitrary ratio is repeatedly transmitted. Each frame 20 includes a frame synchronization pattern 21, a PLOAM (Physical Layer Operation, Admission and Maintenance) 22, a grant instruction 23, and a frame payload 24. The frame synchronization pattern 21 is a fixed pattern for each ONU 300 to identify the head of a frame having a period of 125 μsec. The PLOAM 22 stores information used by the OLT 200 for managing the physical layer of each ONU 300. The grant instruction 23, which will be described in detail later, instructs the ONU 300 about signal transmission timing and transmission speed. In this frame, areas up to the frame synchronization pattern 21, the PLOAM 22, and the grant instruction 23 are transmitted at a speed of 2.4 Gbit / sec. On the other hand, a user signal from the OLT 200 to each ONU 300 is stored in the frame payload 24, and a 2.4 Gbit / second signal and a 10 Gbit / second signal are mixedly accommodated for each ONU 300.

  The grant instruction 23 further includes an ascending grant instruction 30 and a descending grant instruction 31. The uplink grant instruction 30 indicates the uplink signal transmission timing (grant) of each ONU 300. More specifically, the uplink grant instruction 30 indicates a grant for each TCONT that is a user signal control unit within each ONU 300. On the other hand, the downlink grant instruction 31 is introduced in the present invention separately from the provisions of ITU-T recommendation G984.3, and the data stored in the frame payload 24 transmitted from the OLT to the ONU is transmitted for each destination ONU number. The start time, transmission end time, and transmission speed are reported.

  This figure shows an example of the configuration of the frame 20 corresponding to the network configuration of FIG. 1, and the ONU-ID # 1 signal 40a for controlling the ONU 300-1 and the ONU- for controlling the ONU-2. An ID # 2 signal 40b and an ONU-ID # 3 signal 40c for controlling the ONU-3 are shown. Each ONU signal 40 is composed of an ONU-ID 41 for identifying the ONU, a Start 42 indicating the signal transmission start timing, an End 43 indicating the transmission end timing, and a transmission rate designation area 44. The transmission rate designation area 44 indicates whether to use a 2.4 Gbit / second signal or a 10 Gbit / second signal for the downstream signal. Start 42 and End 43 indicate the transmission start timing and the transmission end timing for the above two speed signals, but in units of time at the signal speed of 1.2 Gbit / sec, which is the slowest transmission speed through uplink and downlink. The time unit of the 2.4 Gbit / second signal is 2 bytes, and the time unit of the 10 Gbit / second signal is 8 bytes. This is because, if defined in this way, a plurality of signals having different speeds can be operated with one notation. The OLT 200 periodically transmits a grant instruction 23 to each ONU 300 to instruct how much downlink data is transferred to each ONU. The Start 42 and End 43 are information indicating at what timing data reception should be started and ended in each cycle in which the OLT 200 transmits a grant instruction. Within this designated section, the ONU 300 receives the downlink signal at the transmission rate designated in the transmission rate designation area 44. Instead of End 43, the data length of the data to be transmitted may be specified, and it may be instructed to receive data for the specified data length from the timing of Start 42.

  The start position, end position, and transmission speed of the ONU # 1-addressed signal payload 32 stored in the payload 23 are notified by the combination of the Start 42, End 43, and the transmission speed designation area 44. In the ONU 300 to be described later, the time interval and transmission rate of the signal to be received by the own station are detected using this downlink grant instruction, and the signal of the designated transmission rate is controlled by controlling the internal optical reception interface. Receive. Hereinafter, the same applies to the signal payload 33 addressed to ONU # 2 and the signal payload 34 addressed to ONU # 3. In this figure, the signal payload 32 addressed to ONU # 1 is 2.4 Gbit / sec, and the signal payload 33 addressed to ONU # 2 The signal payload 34 addressed to ONU # 3 is 10 Gbit / sec.

  In the above description, the total number of bytes that can be transmitted in 125 μs of the frame period is 311040 bytes, assuming a transmission rate of 2.4 Gbit / sec. If the frame synchronization pattern 21 is assigned 4 bytes, the PLOAM 22 is assigned 16 bytes, the grant instruction 23 is assigned 16 bytes × 256 bytes corresponding to the number of ONUs 32, and the frame payload 24 has a transmission rate of 2.4 Gbit / second, The transmission capacity is 311040 bytes−532 bytes = 310508 bytes. Further, if all the signals of 10 Gbit / second are accommodated in the frame payload 24, a signal of 310508 bytes × 4 = 1242032 bytes can be accommodated.

FIG. 3 is a block diagram showing a configuration example of the ONU used in the PON of the present invention.
The ONU 300 includes a WDM filter 501, a reception unit 540, a transmission unit 541, a control unit 511, and a user interface (IF) 508. The reception unit 540 includes an optical reception interface 502, a PON frame separation unit 505, a frame distribution unit 506, and a packet buffer 507. The transmission unit 541 includes a packet buffer 509, a transmission control unit 510, a PON frame generation unit 504, an optical transmission interface 503, and a queue length monitoring unit 530. The operation clock of the transmission unit 541 is supplied by the uplink 1.2G clock generation unit 542. The operation clock of the reception unit 540 is supplied by selecting the output of either the downlink 10G clock generation unit 543 or the downlink 2.4G clock generation unit 544 by the selector 545. This selector control is determined by a transmission rate instruction (44 in FIG. 2) from the OLT 200 read by the control unit 511.

  The optical signal received from the branch optical fiber 120 is wavelength-separated by the WDM filter 501 and then converted into an electric signal by the optical reception interface 502, and becomes a digital bit string through a process described later with reference to FIG. The optical reception interface 502 can process an optical reception signal at two transmission rates of 10 Gbit / sec and 2.4 Gbit / sec, and the control unit 511 transmits a transmission rate (44 in FIG. 2) indicated by the OLT 200 to the optical interface 502. ) To perform selection control to receive a signal. Subsequently, the PON frame separation unit 505 performs signal separation described with reference to FIG. Specifically, the signals in the PLOAM area 22 and the grant indication area 23 are sent to the control unit 511, and the signals in the frame payload area 24 are addressed to themselves by the transmission range indication (41, 42 and 43 in FIG. 2) from the OLT 200. The part determined to be sent to the frame sorting unit 506. The user signal output from the frame distribution unit 506 is temporarily stored in the packet buffer 507-1 and the packet buffer 507-2, and then output through the user IF 508-1 and the user IF 508-2, respectively.

  The signals input from the user IF 508-1 and the user IF 508-2 are temporarily stored in the packet buffer 509-1 and the packet buffer 509-2, respectively, and then read under the control of the transmission control unit 510. And is assembled into a packet by the PON frame generation unit 504. The queue length monitoring unit 530 monitors the usage amount of the packet buffer 509. The buffer usage information is stored in the upstream signal and transmitted to the OLT, and the OLT 200 controls the grant amount to be issued by performing DBA based on this information. The signal assembled by the PON frame generation unit 504 is converted into an optical signal by the optical transmission interface 503 and transmitted to the branch optical fiber 120 through the WDM filter 501. The transmission control unit 510 performs control to transmit a signal toward the OLT based on the grant value extracted from the control unit 511.

  Each functional block of the ONU 300 described above is realized by a CPU or firmware stored in a memory, or by an electrical component such as an electrical / optical conversion circuit, a memory, or an amplifier. Further, these functions may be realized by dedicated hardware (LSI or the like) specialized for each processing. Further, the configuration of the ONU 300 is not limited to the above description, and various functions may be mounted as necessary.

FIG. 4 is a block configuration diagram showing a detailed configuration example of the optical reception interface 502.
The APD 402 connected to the high voltage variable bias source 401 is reverse-biased with a high voltage, and a received optical signal is amplified by the avalanche effect and converted into a current. By this amplification action, even when a high-speed signal exceeding 1 Gbit / sec is inputted as a weak optical signal of about −30 dBm, data can be correctly identified. The converted current is converted into a voltage by a transimpedance amplifier (TIA) including resistors 403 and 404 and an amplifier 406. Subsequently, the signal amplified by the variable gain amplifier 407 is converted into a digital bit string by the flip-flop 410. Here, the clock input to the flip-flop 410 is generated by the optimum phase selection circuit 409 that selects the clock closest to the optimum discrimination point of the signal from the output of the multiphase clock generation circuit 408. In the above configuration, the high voltage variable bias source 401 outputs a bias voltage corresponding to the transmission speed under the control of the control unit 511, and appropriately amplifies the received signal. The switch 405 selects the resistors 403 and 404 according to the transmission speed under the control of the control unit 511, and determines the band and the transimpedance gain. The variable gain amplifier 407 is set with a gain corresponding to the transmission rate under the control of the control unit 511. The multi-phase clock generation circuit 408 outputs a multi-phase clock having a frequency corresponding to the transmission speed under the control of the control unit 511, and the optimum phase selection circuit 409 sets the optimum discrimination point according to the transmission speed under the control of the control unit 511. Select the nearest clock.

FIG. 5 is a block diagram showing a configuration example of the OLT used in the PON of the present invention.
The OLT 200 includes a network IF unit 607, a control unit 700, a transmission unit 710, a reception unit 711, and a WDM 606. The transmission unit 710 includes a downlink data buffer 701, a downlink signal processing unit 702, and an optical transmission interface 703. The reception unit 711 includes an optical reception interface 704, an upstream signal processing unit 705, and an upstream data buffer 706. The operation clock of the reception unit 711 is supplied from the uplink 1.2G clock generation unit 712. The operation clock of the transmission unit 710 is supplied by selecting one of the outputs of the downlink 10G clock generation unit 713 and the downlink 2.4G clock generation unit 714 by the selector 715. This selector control is performed by the downstream band control unit 708. A specific transmission rate determination method will be described in detail later with reference to the drawings.

  The downlink data buffer 701 temporarily stores data received from the higher level network 20 via the network IF unit 607. The downstream signal processing unit 702 performs processing necessary for relaying the optical signal from the upper network 20 to the ONU 300. The downlink frame described in FIG. 2 is assembled in this block, and the downlink grant (31 in FIG. 2) output from the downlink bandwidth control unit 708 by a method described later is stored in the downlink frame. The optical transmission interface 703 converts the electrical signal into an optical signal and transmits the optical signal (downstream signal) to the ONU via the optical signal IF unit 606. The optical reception interface 704 converts the optical signal received from the ONU 300 via the optical signal IF unit 606 into an electrical signal. The upstream signal processing unit 705 performs processing necessary for relaying a signal from the ONU 300 to the upper network 20. The upstream data buffer 706 temporarily stores data to be transmitted to the higher level network 20 via the network IF unit 607. The control unit 700 is connected to each functional block described above and executes various processes necessary for communication (monitoring / control, etc.) with a plurality of ONUs 300. It also has a function of relaying signals between the upper network 20 and the ONU 300.

  The upstream bandwidth control unit 707 performs dynamic bandwidth allocation processing that determines how much communication bandwidth is allocated to each of the ONUs 300 (TCONT) accommodated by the OLT 200 within the cycle for each predetermined DBA cycle. The downlink bandwidth control unit 708 determines how many signals are transferred to each of the ONUs 300 accommodated by the OLT 200 within a predetermined period. The control unit 700 communicates with a control board (for example, a maintenance terminal configured by a PC) provided for the PON, and sets control parameters (for example, ONU subscription conditions, contract traffic, etc.) necessary for control in the control unit in advance. The monitoring information (for example, the failure occurrence status and the transmission permission data amount to each ONU) is received based on the request of the maintenance person. Each functional block of the OLT 200 described above is realized by firmware stored in a CPU or a memory, or realized by electric components such as an electric / optical conversion circuit, a memory, and an amplifier. Further, these functions may be realized by dedicated hardware (LSI or the like) specialized for each processing.

FIG. 6 is a block diagram illustrating a configuration example of the downlink packet buffer 701 provided in the OLT.
The downlink packet buffer 701 includes a distribution unit 721, a multiplexing unit 722, a queue length monitor unit 723, a buffer read control unit 724, and a packet buffer 725. Data received from the host network 20 via the network IF unit 607 is sorted by destination ONU with reference to, for example, VLAN labels and the like, and temporarily stored in a packet buffer 725 provided for each ONU. The queue length monitor unit 723 monitors the queue length of each packet buffer 725 and notifies the downlink bandwidth control unit 708 of the queue length. In response to an instruction from the downlink bandwidth control unit 708, the buffer read control unit 724 reads out the designated amount of data from the designated packet buffer 725 and transmits it to the subsequent stage via the multiplexing unit 722.

FIG. 7 is an explanatory diagram illustrating a configuration and an operation example of the downlink bandwidth control unit 708 provided in the OLT. FIG. 8, FIG. 9, and FIG. 10 are operation flowcharts each showing an operation example of the control unit of the OLT. FIG. 11 is a memory configuration diagram illustrating a configuration example of each table generated by the control unit. The allocation byte length table 733 stores the bandwidth (number of bytes) allocated to each ONU, and the signal transmission timing for each ONU. It is a memory block diagram which shows the structural example of the transmission timing table 734 which memorize | stores a use transmission rate.
Hereinafter, the operation and configuration of the PON according to the present invention, specifically, the bandwidth allocation to each ONU and the transmission rate determination operation and configuration performed by the OLT will be described in detail with reference to these drawings.
(1) The byte length determination unit 731 receives the queue length, which is the amount of data stored in the packet buffer 725 for each ONU 300 within the downstream bandwidth control period (0.125 msec in this embodiment), from the queue length monitor unit 723. Receive (FIG. 8: 801).
In the byte length determination unit 731, the policer band, which is the maximum band parameter that can be permitted to the ONU, is set by the maintenance person from the control board (see FIG. 5). Based on the policer band value thus determined, the number of bytes (downlink communication band) to be transmitted to each ONU 300 is determined, and an allocation byte length table 733 in which the ONU-ID that is the identifier of each ONU is associated with the byte length to be transmitted is stored. It is created and stored in the storage unit 732 (FIG. 7: (1), FIG. 8: 802).
The allocation byte length table 733 is configured to store an ONU-ID 901 that is an ONU identifier and a byte length 902 that is transmitted to the ONU, as shown in FIG.
(2) The transmission timing determination unit 735 performs the following calculation to transmit how many bytes are transmitted at 10 Gbit / sec and how many bytes are transmitted at 2.4 Gbit / sec in the payload of the downstream frame (24 in FIG. 2). To decide.
As described above, if all 2.4 Gbit / sec signals are accommodated in the frame payload 24 of the 2.4G / 10G mixed frame 20, a 310508 byte signal can be accommodated. Let X be the sum of the byte lengths assigned to each packet buffer 725 in (1) above, and Y be 310508 bytes when all the frame payload 24 accommodates 2.4 Gbit / sec signals. Here, of the total byte length allocated in (1), assuming that the number of bytes transmitted at 2.4 Gbit / sec is A and the number of bytes transmitted at 10 Gbit / sec is B, the frame payload 24 is filled with X bytes. In the exhausted situation, the following equation holds.

A + B = X (Formula 1) A + B / 4 = Y (Formula 2)
Solving these simultaneous equations,
A = (4Y−X) / 3 (Formula 3) B = X−A (Formula 4)
Is obtained as a solution. Therefore, first, the byte length A to be transmitted at 2.4 Gbit / sec is calculated by (Equation 3) (however, rounded up to a multiple of 8; FIG. 8: 803), and then the byte length B to be transmitted at 10 Gbit / sec (Equation 3). Calculate according to 4) (however, rounded up to a multiple of 2; Fig. 8: 804) As described with reference to FIG. 2, the round-up process designates the time unit by the number of bytes at the signal speed of 1.2 Gbit / second, which is the slowest transmission speed through uplink and downlink, and the time unit of the 2.4 Gbit / second signal is This is because the time unit of the 2-byte unit and the 10 Gbit / second signal is configured in units of 8 bytes. When A + B / 4 after rounding exceeds Y, the fraction of B is rounded down (FIG. 8: 805). However, when X <Y, the above equation does not hold, and everything can be transmitted at 2.4 Gbit / sec.
(3) The transmission timing determination unit 735 reads the contents of the allocation byte length table 733 (FIG. 7: (2)), allocates a time slot corresponding to the byte length 902 to be transmitted to each ONU within the frame period, and -A transmission timing table 734 in which the ID and the byte length range assigned in each frame period are associated is created and stored in the storage unit 732 (FIG. 7: (3), FIG. 8: 806).
(4) Based on the transmission timing table 734, the downlink grant value is passed to the downlink signal processing unit 702 and transmitted (FIG. 8: 807).

FIG. 9 is an operation flowchart showing an operation for determining the number of bytes to be transmitted to each ONU executed in the process 802.
The number of bytes transmitted to the ONU is determined as follows. First, the determination is started from ONU-ID = 1 (901),
L = (Policer setting cycle of the ONU) × (Band control cycle = 0.125 msec) (Formula 5)
Thus, the policer allowable byte length L is obtained (902). Here, the queue length addressed to the operation target ONU is compared with the value of the policer allowable byte length L (903). If the queue length is large, the byte length assigned to the ONU is set to the value of L (904). If the queue length is small, the byte length allocated to the ONU is set as the queue length (905). This operation is repeated until the last ONU-ID is reached (906, 907).

FIG. 10 is an operation flowchart showing the operation for determining the transmission timing executed in the process 806.
(E1) First, the rows of the allocated byte length table 733 are rearranged in ascending order of byte length (1001). This process is performed in order to assign a transmission rate as low as possible to the ONU 300 having a small transmission data amount. After the rearrangement, the allocated byte length of the first ONU-ID is read from the allocated byte length table 733 (1002). Here, the transmission rate is set to 2.4 Gbit / sec (1003), and 1 is assigned to Start (1004).
(E2) End is calculated from Start-1 + byte length / 2, and the Start value is written in the row of the calculation target ONU-ID (1005). The calculated End value is compared with the value of A / 2 (A is the number of bytes transmitted at 2.4 Gbit / second described in FIG. 8) (1006). If the End value is small, the End value is calculated as the ONU-ID to be calculated. And the next ONU-ID is referenced, and End + 1 is substituted for Start (1007), and the calculation is repeated.
(E3) If the End value is large, the transmission rate is set to 10 Gbit / sec (1008), the value of A / 2 is written as End in the row of the calculation target ONU-ID, and then the byte length / 2−a in Start. / 2—Substitutes the previous Start value and writes the new Start value to a new row with the same ONU-ID (848).
(E4) End is calculated from Start-1 + byte length / 8, and the End value is written in the row of the calculation target ONU-ID (1009).
(E5) Repeat until calculation of all ONU-IDs is completed (1010 to 1012).

  As described above, the power consumption of an ONU with a small transmission band can be reduced by performing data transmission at a transmission rate as low as possible for an ONU with a small amount of data to be transmitted. An example of a result of writing the transmission timing and the like determined by executing this calculation in the transmission timing table 734 is shown in FIG.

FIG. 12 is a frame configuration diagram showing another configuration example of the downlink signal.
The difference from the frame configuration described above is that a dummy payload 34 transmitted at 2.4 Gbit / sec is provided at the end of the frame payload 24. This is because when the circuit as described in FIG. 4 is used for the optical reception transmission interface of the ONU 300, when the transmission speed changes from 10 Gbit / second to 2.4 Gbit / second, the number follows to synchronize with the change. This is because a time from 100 nsec to several μsec may be required. A frame synchronization pattern 20 following a certain frame is a periodic signal that all ONUs 300 must receive. By inserting the dummy payload 34, it is possible to secure time for the optical reception transmission interface of each ONU 300 to synchronize, and the synchronization pattern 20 can be received reliably. As a specific value of the dummy payload 34, a configuration using an “10” alternating pattern that is convenient for both signal amplitude adjustment and clock synchronization is optimal, but it is not necessary to limit to this value. Further, the length of the dummy payload 34 may be set in advance according to the characteristics of the optical receiving circuit to be used.

  FIG. 13 is also a frame configuration diagram showing another configuration example of the downlink signal. In this configuration, the dummy payload 35 is also inserted when the transmission rate of the payload addressed to the adjacent ONU in the frame payload 24 changes. In this figure, a dummy payload 35 is also inserted between the signal payload 32 addressed to ONU # 1 having a transmission rate of 2.4 Gbit / sec and the signal payload 33 addressed to ONU # 2 having a transmission rate of 10 Gbit / sec. When the frame having the configuration shown in FIG. 5 is used, the ONU # 2 monitors the start value of the ONU-ID # 2 in the downstream grant area 31 and waits for the timing when a 10 Gbit / second signal is received. Operate to synchronize. Also, the end value of ONU-ID # 1 and the start value of ONU-ID # 2 in the downstream grant area 31 are monitored, and the resynchronization of the reception optical interface is started immediately after the end value of ONU-ID # 1. A configuration may be adopted in which the synchronization of the optical reception interface is established over the time of 35, and there is an advantage that it is easy to apply a conventionally used device for continuous optical transmission.

  FIG. 14 is also a frame configuration diagram showing another configuration example of the downlink signal. In this configuration, the dummy payload 35 is inserted at the turn of all ONU-addressed payloads. When this frame is used, the amount of data that can be transmitted (allocated) is reduced by a plurality of dummy payloads 35. However, each ONU 300 stops the optical reception interface immediately before receiving a signal addressed to itself, and performs dummy processing. The configuration can be such that the reception optical interface can be synchronized using the payload 35. This may reduce power consumption.

FIG. 15 is also a frame configuration diagram showing another configuration example of the downlink signal. In this configuration, there are two types, a frame transmitted at 2.4 Gbit / sec and a frame transmitted at 10 Gbit / sec. Then, the transmission frequency is optimized by adjusting the transmission frequency of each frame.
A bandwidth allocation method when using this frame will be described below. FIG. 16 is an operation flowchart showing another example of operation of the OLT control unit, and shows an example of downlink signal allocation operation to each ONU 300 when the frame shown in FIG. 15 is used for downlink signals.

  In this operation example, one band control period (0.5 msec) is configured by four frame periods (125 μs each), and therefore one band control period when the transmission rate is 2.4 Gbit / sec. The number of bytes that can be transmitted is 310508 bytes × 4 cycles = 1242032 bytes when the numerical example described above is used. That is, if the total queue length, which is the amount of data waiting to be transmitted from all ONUs, is within 1242032 bytes, all allocated data can be transmitted at a transmission rate of 2.4 Gbit / sec. If the total queue length is larger than 1242032 bytes, it is necessary to increase the transmission rate to 10 Gbit / sec because it is impossible to transmit all the requested data at the transmission rate of 2.4 Gbit / sec.

  Here, of the four frame periods constituting one band control period, three are transmitted at a transmission rate of 2.4 Gbit / sec and the other one is transmitted at a transmission rate of 10 Gbit / sec. The number of possible bytes can be increased to 310508 × 3 periods + 1242032 × 1 period = 15552540 bytes. Similarly, when two of the four frame periods are transmitted at a transmission rate of 2.4 Gbit / sec and the remaining two are transmitted at a transmission rate of 10 Gbit / sec, the number of bytes that can be transmitted in the bandwidth control cycle is 310508 × It can be increased up to 2 periods + 1242032 × 2 periods = 3105080 bytes. Further, when one of the four frame periods is transmitted at a transmission rate of 2.4 Gbit / sec and the remaining three are transmitted at a transmission rate of 10 Gbit / sec, the number of bytes that can be transmitted in the bandwidth control cycle is 310508 × 1 Period + 1242032 × 3 period = 4033664 bytes can be raised. Finally, when all four frame periods are transmitted at a transmission rate of 10 Gbit / sec, the number of bytes that can be transmitted in the bandwidth control period can be increased to 1242032 × 4 periods = 4968128 bytes.

Therefore, the transmission timing determination unit 735 determines the transmission rate as follows based on the total of the allocated byte lengths obtained from the allocated byte length table 733 ′, and each frame period (hereinafter, referred to as the transmission timing table 734 ′). The value of the transmission rate is input in (sometimes referred to as Grant period).
(A) It is determined whether or not the sum of the allocated byte lengths ≦ 1242032 (FIG. 16: 1103), and in the case of Yes, the total grant period is determined at a speed of 2.4 Gbit / sec (FIG. 16: 1104).
(B) It is determined whether or not 1242032 <total of allocated byte lengths ≦ 1552540 (FIG. 16: 1105). If Yes, the first to third grant periods are set to a speed of 2.4 Gbit / second, and the fourth grant period is set. The speed is determined to be 10 Gbit / sec (FIG. 17: 1106).
(C) It is determined whether or not 1552540 <the total of allocated byte lengths ≦ 31050580 (FIG. 16: 1107). In the case of Yes, the first and second grant periods are set to a speed of 2.4 Gbit / sec, the third and fourth The grant period is determined at a speed of 10 Gbit / sec (FIG. 17: 1108).
(D) 3105080 <total sum of allocated byte lengths ≦ 4033664 is determined (FIG. 17: 1109). If yes, the first grant period is set to 2.4 Gbit / sec, and the second to fourth grant periods are set. The speed is determined to be 10 Gbit / sec (FIG. 17: 1110). In the case of No, the total grant period is determined to be a speed of 10 Gbit / sec (FIG. 17: 1111).
(E) When the transmission rate of each grant period is determined, the data transmission permission unit 735 refers to the byte length stored in the allocation byte length table 733 ′ (details will be described later in FIG. 18: 902), and for each ONU Then, the time slot for transmitting data within the grant period is determined, and the value of the transmission timing table 734 is generated (FIG. 16: 806 ′ (detailed operation example will be described later)). At this time, in the grant period using the transmission rate of 2.4 Gbit / sec, the grant period using the transmission rate of 10 Gbit / sec so that the number of allocated bytes in the allocation byte length table is divided by 2. In, the number of allocated bytes in the allocated byte length table is divided by 8.

FIG. 17 is also an operation flowchart showing another operation example of the OLT control unit, and shows an operation example for determining the data transmission timing to each ONU 300 executed in the process 806 ′ of FIG. Reference numeral 8 denotes an embodiment showing details of the processing 1112.
(E1) First, the rows of the allocated byte length table 733 ′ are rearranged in ascending order of byte length (1301), and the byte length of the first ONU-ID is read from the byte length table 733 ′ (1302).
(E2) The calculation is started from the row of the transmission timing table 734 ′ of the first grant period (1303), and it is determined whether or not the speed is 2.4 Gbit / sec in the grant period (1304). If there is, the byte length is divided by 2 in the subsequent calculation (1305), and if it is No, the transmission speed is 10 Gbit / sec. Therefore, the byte length is divided by 8 in the subsequent calculation and the same time as 1.2 Gbit / sec. The calculation is continued by converting into a byte value as a width (1306). When dividing, round up the fractional part. Subsequently, 0 is substituted for Start, and the value is written in the row of the calculation target ONU-ID (1307).
(E3) It is determined whether Start-1 + byte length ≦ 155253 (1308). If Yes, Start-1 + byte length is substituted for End, and End is written in the row of the operation target ONU-ID. The target ONU-ID is incremented by +1, and End + 12 + 1 is substituted for Start, and Start is written in the row of the new computation target ONU-ID (1309).
(E4) If the determination (1308) is No, 19439 is substituted for End, End is written in the row of the ONU-ID to be calculated, Start-1 + byte length-155253 is substituted for byte length ← (1310), By going back to the processing 1304, the process proceeds to the table calculation of the next grant period.
(E5) After recursively repeating the above process, it is determined whether all ONU-ID operations have been completed (1311). If Yes, the first ONU-ID is set for the operation in the next DBA cycle. The value is shifted by one and stored, and this process ends. If the determination (1311) is No, the processing returns to processing 1308.

FIG. 18 is a memory configuration diagram showing a configuration example of the allocated byte length table 733 ′ generated by the control according to the operation flowcharts of FIGS. FIG. 19 is a memory configuration diagram showing a configuration example of the transmission timing table 734 ′.
FIGS. 18 and 19 show an example in which the allocation byte length to each ONU is changed in five ways (a) to (e) based on the queue length from each ONU. Specifically, the queue length of the downstream packet buffer 725 corresponding to each ONU increases corresponding to (a) to (e), and the number of bytes transmitted to each ONU and the total number of allocated bytes in the bandwidth allocation cycle. As an example, the situation is increasing.
In the above operation example, an example is described in which one band control period is configured by four frame periods and the transmission rate is switched for each frame period. However, one band control period is configured by more frame periods. By switching the transmission rate more finely, it is possible to select the combination of transmission rates that is closest to the total number of bytes allocated to all ONUs and to minimize the overall power consumption by reducing the transmission rate as much as possible. .

10 ... PON, 100 ... splitter, 110, 120 ... optical fiber,
130 ... Downstream signal, 140, 150 ... Upstream signal,
200 ... OLT, 300 ... ONU, 400, 410 ... terminal,
700 ... control unit, 708 ... downlink bandwidth control unit,
731 ... Byte length determination unit, 735 ... Transmission timing determination unit,
733 ... allocated byte length table, 734 ... transmission timing table.

Claims (9)

A master station and a plurality of slave stations are connected by an optical fiber network composed of an optical splitter and a plurality of optical fibers, and the master station is a frame signal obtained by time-division-multiplexing signals addressed to the slave stations received from an upper network. A passive optical network system that broadcasts to the plurality of slave stations via the optical fiber network, and each of the plurality of slave stations receives the frame signal and processes a signal addressed to itself. ,
The master station is
An optical transmission interface for transmitting signals to the plurality of slave stations at a first transmission rate or a second transmission rate higher than the first transmission rate;
A packet buffer for storing a signal received from the upper network corresponding to each of the plurality of slave stations that are destinations of the signal;
Based on the amount of signal stored in the packet buffer, the transmission timing and transmission speed of a signal to be transmitted to each of the plurality of slave stations are determined, and the plurality of slave transmission terminals are transmitted from the optical transmission interface at the transmission timing and transmission speed. A control unit that transmits a signal to each of the stations and notifies the determined transmission timing and transmission speed to each of the plurality of slave stations,
Each of the plurality of slave stations is
An optical reception interface for receiving a signal of the first transmission rate or the second transmission rate;
A passive optical network system comprising: a control unit that controls the optical reception interface based on the transmission timing and transmission speed notified from the master station. The control unit of the master station determines the amount of signal to be transmitted to each of the plurality of slave stations based on the amount of signal accumulated in the packet buffer.
When the determined amount of the signal is less than the maximum transmission amount that can be transmitted at the first transmission rate, the transmission rate of the signal to the plurality of slave stations is set as the first transmission rate, and the determined signal When the amount exceeds the maximum transmission amount that can be transmitted at the first transmission rate, the transmission rate of the signal to the arbitrary slave station among the plurality of slave stations is determined as the second transmission rate. The passive optical network system according to claim 1. The control unit of the master station, a bandwidth control unit that determines the amount of signals to be transmitted to each of the plurality of slave stations based on the amount of signals accumulated in the packet buffer,
3. The transmission timing controller according to claim 1, further comprising: a transmission timing control unit that determines a transmission timing and a transmission speed of a master station that transmits the signal based on the determined amount of the signal. Passive optical network system.   The transmission rate information determined by the master station is inserted in the control signal area of the frame signal transmitted from the master station to the plurality of slave stations together with the transmission timing information determined by the master station, 4. The passive optical network system according to claim 1, wherein each of the plurality of slave stations is notified at a first transmission rate.   When determining the transmission timing for time-division multiplexing the signals addressed to the plurality of slave stations, the control unit of the master station also inserts a dummy signal consisting of a plurality of bytes after the signal addressed to the last slave station in time-division multiplexing. The passive optical network system according to claim 1, wherein:   When determining the transmission timing for time-division multiplexing the signals addressed to the plurality of slave stations, the control unit of the master station changes the transmission rate of the signal addressed to the slave station multiplexed next to the signal addressed to any slave station 6. The passive optical network system according to claim 5, wherein a dummy signal consisting of a plurality of bytes is inserted before the signal addressed to the next slave station.   The control unit of the master station inserts a dummy signal consisting of a plurality of bytes between signals destined for each slave station when determining a transmission timing for time-division multiplexing the signals destined for the slave stations. The passive optical network system according to claim 6. A master station and a plurality of slave stations are connected by an optical fiber network composed of an optical splitter and a plurality of optical fibers, and the master station is a frame signal obtained by time-division-multiplexing signals addressed to the slave stations received from an upper network. Broadcast to the plurality of slave stations via the optical fiber network, and each of the plurality of slave stations receives the frame signal and processes a signal addressed to the own station. An operation method,
Based on the amount of signals transmitted to each of the plurality of slave stations, the master station transmits a transmission timing of a signal transmitted from the master station to each of the plurality of slave stations, and a first transmission rate or the first Any one of the second transmission speeds higher than the first transmission speed is determined for each predetermined period, and the signal transmission at the determined transmission timing and the transmission speed and the notification of the determined transmission timing and the transmission speed are transmitted to the plurality of transmission speeds. To each of the child stations,
Each of the plurality of slave stations receives the signal of the first transmission speed or the second transmission speed based on the transmission timing and transmission speed notified from the master station. System operation method.   In determining the transmission rate, when the amount of the signal to be transmitted is less than the maximum transmission amount that can be transmitted at the first transmission rate, the transmission rate of the signal to the plurality of slave stations is set to the first transmission rate. When the amount of the signal to be transmitted exceeds the maximum transmission amount that can be transmitted at the first transmission rate, the transmission rate of the signal addressed to any slave station among the plurality of slave stations is set to the second transmission rate. 9. The method of operating a passive optical network system according to claim 8, wherein the transmission speed is determined.

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