JP5411805B2 - Passive optical network system, transmission light control method, optical multiple termination device, and optical network termination device - Google Patents

Description

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

  In order to transmit and receive large-capacity image signals and data via a communication network, the speed and bandwidth of the communication network has been increased in the access network connecting subscribers to the communication network. Recommendation G. A passive optical network system (Passive Optical Network system: hereinafter referred to as PON) defined in 984.1-3 and the like is being introduced. The PON is an optical multiple terminator (hereinafter referred to as OLT) connected to a host communication network and an optical network terminator (Optical Network Unit) that accommodates a plurality of subscriber terminals (PCs and telephones). (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 development and introduction of PON begins with a system that handles low-speed signals such as 64 kbit / s, and BPON (Broadband PON) or Ethernet (registered trademark) variable-length packets that transmit and receive fixed-length ATM cells at a maximum of approximately 600 Mbit / s. Ethernet (registered trademark) PON (EPON) that transmits and receives at a maximum of about 1 Gbit / sec, and ITU-T recommendation G.2 that handles higher-speed signals of about 2.4 Gbit / sec. 984.1, G.A. 984.2 and G.A. Introduction of GPON (Gigabit PON) standardized in 984.3 is underway. 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, multiplexing methods such as TDM (Time Division Multiplexing) for time division multiplexing of a plurality of signals, WDM (Wavelength Division Multiplexing) for wavelength multiplexing, CDM (Code Division Multiplexing) for code multiplexing, and the like. Is being considered. The current PON uses TDM. For example, GPON uses different wavelengths for upstream (ONU to OLT) and downstream (OLT to ONU) signals, and communication between the OLT and each ONU is performed. The signal communication time is assigned to each ONU. Further, the conventional configuration for processing fixed-length signals has been configured to process burst-like variable-length signals (burst signals) that can easily handle various types of signals (sound, image, data, etc.). As for the future high-speed PON, as described above, various multiplexing methods have been studied, but studies in the direction of adopting TDM are becoming main.
In the above-described PON forms, ONUs are installed at subscriber homes scattered in various places, and the distance from the OLT to each ONU is different. That is, since the length (transmission distance) of the optical fiber including 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 is different. Even if signals are transmitted at the timing, optical signals output from the ONUs on the backbone optical fiber may collide and interfere with each other. For this reason, in each PON, for example, G.M. After measuring the distance between the OLT and the ONU using a technique called ranging as defined in Chapter 10 of 984.3, the ONUs of each ONU are prevented from colliding. The delay of the output signal is adjusted.

Further, when the OLT determines a band of a signal permitted to be transmitted to each ONU based on a transmission request from each ONU using a technique called dynamic bandwidth assignment (hereinafter referred to as DBA), Considering the delay amount measured by the ranging, 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 signal transmission / reception between the OLT and each ONU, for example, G. According to the provisions of section 83.3 of 984.2, for example, each ONU can receive an OLT signal so that the OLT can identify and process the signal from each ONU multiplexed on the backbone optical fiber. A burst time called a delimiter for identifying a received signal delimiter and a guard time for preventing interference consisting of a maximum of 12 bytes at the beginning of the signal from the receiver, a preamble used for determining a signal identification threshold of the receiver in the OLT and for clock extraction Bytes, PON control signals (sometimes called overhead or header), and the like are added to data (sometimes called payload). Since each data is variable-length burst data, a header called a GEM (G-PON Encapsulation Method) header for processing variable-length data is also added to the head of each data.
On the other hand, for signals addressed to each ONU from the OLT, for example, the head is identified at the head of the signal transmitted from the OLT to each ONU so that each ONU can identify and process the signal from the OLT. Frame synchronization pattern, PLOAM area for transmitting monitoring / maintenance / control information, and overhead (sometimes referred to as a header) called a grant indication area for instructing the signal transmission timing of each ONU. In this configuration, the data is added to the time-division multiplexed data. 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. 984.1 (P.1) ITU-T Recommendation G. 984.2 (P.9-P.27) ITU-T Recommendation G. 984.3 (P.64-P.84) ITU-T Recommendation G. 984.2 Amendment 1 (P.1 to P.3)

PON has been developed and introduced from one that processes low-speed signals to one that processes higher-speed signals, such as a transition from BPON to GPON. It is known that optical modules and LSIs, which are component parts that provide a PON signal transmission function, consume a large amount of power as the transmission speed increases. Further, the increase in power consumption of the master station due to the increase in subscribers has become a problem.
On the other hand, with regard to PON, the loss in the transmission line section from the master station to each subscriber differs for each subscriber depending on the branching by the optical splitter, fiber length, etc., but the laser transmission output is constant for both OLT and ONU. Each of the receivers performs gain control of the amplifier in accordance with the reception level. In addition, downstream light for subscribers with little loss on the transmission path corresponds to being output with transmission power more than necessary, and there is a case where power consumption is wasted.
In view of the above, the present invention provides a passive optical network system and a transmission light control method capable of reducing waste of power consumption as much as possible by reducing the optical output to a level at which no error occurs for each optical network termination device. An object of the present invention is to realize an optical multiple termination device and an optical network termination device.

  In order to solve the above-described problem, the passive optical network system of the present invention notifies the reception level of downstream light received by the ONU that is the slave station to the OLT that is the master station, and the difference from the optical output level of the passive optical network system in the OLT. Then, the transmission line loss is calculated, and the optical output is reduced to a level at which no error occurs during reception on the ONU side. Optimum energy efficiency can be obtained by performing this output level control for each downlink data addressed to each ONU.

According to the first solution of the present invention,
An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. In a passive optical network system connected by an optical fiber network including a plurality of branch optical fibers,
The OLT transmits a downstream signal to each ONU,
Each ONU receives the downstream signal , determines its reception level, notifies the OLT of the reception level ,
The OLT receives the reception level from each of the ONUs, specifies a reception level equal to or lower than a minimum value or a predetermined value that can be received by the ONU as a set level,
The OLT refers to the optical output level of the downstream signal, and the reception level at each ONU becomes the set level according to each transmission line loss or each optical fiber length between the OLT and each ONU. so as to transmit light power to each said ONU respectively set,
The ONU is
Determining whether or not there is a period of a level that cannot be received in the downstream signal from the OLT;
If there is no period that cannot be received, it is determined that the link is established,
When there is a period of a level that cannot be received, it is determined whether or not a control signal has been received. When the control signal is received within a predetermined period or time, it is determined that a link has been established, and within the predetermined period or the predetermined time If the control signal is not received within, it is determined that the link is broken
A passive optical network system is provided.

According to the second solution of the present invention,
An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. A transmission light control method in a passive optical network system connected by an optical fiber network including a plurality of branch line optical fibers,
The OLT transmits a downstream signal to each ONU,
Each of the ONUs receives the downstream signal , determines the reception level, notifies the reception level to the OLT,
The OLT receives a reception level from each of the ONUs, specifies a reception level equal to or lower than a minimum value or a predetermined value that can be received by the ONU as a set level,
The OLT refers to the optical output level of the downstream signal, and the reception level at each ONU becomes the set level according to each transmission line loss or each optical fiber length between the OLT and each ONU. so as to transmit light power to each said ONU respectively set,
The ONU is
Determining whether or not there is a period of a level that cannot be received in the downstream signal from the OLT;
If there is no period that cannot be received, it is determined that the link is established,
When there is a period of a level that cannot be received, it is determined whether or not a control signal is received, and when the control signal is received within a predetermined period or within a predetermined time, it is determined that a link is established, and within the predetermined period or the predetermined time. If the control signal is not received within, it is determined that the link is broken
A transmission light control method is provided.

According to the third solution of the present invention,
An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. An optical multiple termination device in a passive optical network system connected by an optical fiber network including a plurality of branch line optical fibers,
A frame separation unit that extracts a reception level of a downstream signal in each ONU;
A reception level processing unit that calculates a transmission line loss or an optical fiber length from the difference between the reception level of each ONU extracted by the frame separation unit and the optical output level transmitted by the own OLT;
When transmitting the downlink signal , the transmission optical power is controlled so as to reduce the optical output from the transmission line loss or optical fiber length calculated by the reception level processing unit to a level at which no error occurs in reception on the ONU side. When transmitting a control signal, a transmission power control unit that controls transmission optical power so as to perform optical output at an optical output level equal to or higher than a maximum value that can be transmitted by the own OLT or a predetermined value ;
With
Send a downstream signal to each ONU,
The frame separation unit receives the reception level of the downlink signal from each ONU,
The reception level processing unit identifies a reception level equal to or lower than a minimum value or a predetermined value that can be received by the ONU as a set level,
The transmission power control unit refers to the optical output level of the downlink signal, and the reception level at each ONU is determined according to each transmission line loss or each optical fiber length between the own OLT and each ONU. Set the transmission optical power to each ONU so as to reach the setting level.
An optical multiple termination apparatus is provided.

According to the fourth solution of the present invention,
An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. An optical network termination device in a passive optical network system connected by an optical fiber network including a plurality of branch optical fibers,
Determining the reception level, and a control unit which extracts the transmission permission timings, based on the received presence or absence of the control signal extracted by the reception level and the frame termination, to control the link establishment or link break judgment,
A frame generation unit for transmitting by adding the reception level to an uplink signal at a transmission permission timing extracted by the control unit;
With
The control unit receives a downstream signal from the OLT , determines its reception level ,
The frame generation unit notifies the reception level to the OLT,
The controller is
Determining whether or not there is a period of a level that cannot be received in the downstream signal from the OLT;
If there is no period that cannot be received, it is determined that the link is established,
If there is a period of not received level, the control whether the received determines the signal, when receiving the control signal within a predetermined period or within a predetermined time period determines that the link establishment, within a predetermined period or within a predetermined time period If the control signal is not received during
An optical network terminating device is provided.

  According to the present invention, a passive optical network system and a transmission capable of reducing waste of power consumption as much as possible in the output power of the OLT in a PON configured to optimize the output power of downstream light due to a difference in transmission path loss in each ONU and transmission An optical control method, an optical multiple termination device, and an optical network termination device can be realized.

It is a network block diagram which shows the structural example of the optical access network using PON. It is an ONU block diagram in this Embodiment. It is an OLT block diagram in this Embodiment. It is a flowchart which optimizes the transmission output power of OLT from the reception level of ONU. It is a network block diagram which shows the structural example of the optical access network after the optimization of the transmission output power of OLT. It is a sequence diagram which shows the operation example of PON. It is a block diagram of ONU which added the control part of PON link maintenance. It is a flowchart of PON link judgment by grant information reception.

1. Transmission output power optimization

FIG. 1 shows the configuration of an optical access network to which the present embodiment is applied.
The access network 1 is connected to a public communication network (in this example, a PSTN / Internet 20 (hereinafter also referred to as an upper network)) via the PON 10 to transmit and receive data. The PON 10 includes a plurality of ONUs 200 that accommodate an optical splitter 100, a trunk optical fiber 110, a branch optical fiber 120, an OLT 300, and subscriber terminals (telephone (TEL) 40, PC 41, etc.). The OLT 300 and each ONU 200 are connected by an optical passive network having a trunk 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 40 and 41, or the subscriber terminal 40 , 41 communicate with each other. A plurality of (n, for example, 32, etc.) ONUs 200 can be connected to the OLT 300 via one main optical fiber 110, the optical splitter 100, and the branch optical fiber 120. FIG. 1 shows five ONUs 200 (n = 5) as an example, and the fiber lengths from the OLT 300 are different. In the illustrated example, the ONU 200-1 has a fiber length from the OLT 300 of 1 km, the ONU 200-2 has a fiber length from the OLT 300 of 10 km, the ONU 200-3 has a fiber length of 20 km from the OLT 300, and the ONU 200-4 has a fiber length from the OLT 300. The length is 10 km, and the ONU 200-n has a fiber length from the OLT 300 of 15 km. In the figure, the parenthesis (XX Km) under each ONU 200 indicates the fiber length between the OLT and the ONU.

Hereinafter, the levels of transmission signals and reception signals in the OLT 300 and the ONUs 200-1 to n in the technology related to the present invention and the present embodiment will be described. Downlink transmission signals 130-1 to 130-n addressed to the respective ONUs 200 are time-division multiplexed and transmitted in the downlink signal 130 transmitted from the OLT 300 to the ONU 200. The downlink reception signals 140-1 to 140-n received by the respective ONUs 200-1 to 200-n have different reception levels depending on the fiber length (or transmission path loss) between the OLT 300 and each of the ONUs 200-1 to 200-n. For example, the downlink transmission signal 130-1 addressed to the ONU 200-1 becomes the downlink reception signal 140-1 at the ONU-1, and the downlink transmission signal 130-2 addressed to the ONU 200-2 is the downlink reception signal 140 at the ONU-2. -2. Here, since the reception level differs depending on the fiber length for each ONU 200, the downlink transmission signals 130-1 and 130-2 transmitted as broadcast signals with the same transmission power as illustrated in FIG. The reception levels are different as in 1-2. That is, according to the fiber length (or transmission path loss), the downlink reception signal 140-1 is at a level higher than the downlink reception signal 140-2. Further, it is determined in the ONU 200 whether or not the signal is addressed to itself, and is sent to the telephone 40 or the PC 41 based on the destination of the signal. In the direction from ONU 200 to OLT 300, upstream transmission signal 160-1 transmitted from ONU 200-1, upstream transmission signal 160-2 transmitted from ONU 200-2, upstream transmission signal 160-3 transmitted from ONU 200-3, ONU 200 -4 and the upstream transmission signal 160-n transmitted from the ONU 200-n are time-division multiplexed after passing through the optical splitter 100 to become an optically multiplexed upstream signal 150. The OLT 300 is reached. Since the fiber length (or transmission path loss) between each ONU 200 and the OLT 300 is different, the uplink signal 150 is multiplexed with the uplink reception signals 150-1 to 150-n having different amplitudes. For example, the upstream transmission signals 160-1 and 160-2 have the same transmission power, but the upstream reception signal 150-1 has a level higher than that of the upstream reception signal 150-2 according to the fiber length (or transmission path loss).
The downlink signal 130, the downlink transmission signals 130-1 to n, and the downlink reception signals 140-1 to n are, for example, an optical signal having a wavelength band of 1.5 μm, an uplink signal 150, and uplink reception signals 150-1 to n, For example, optical signals having a wavelength band of 1.3 μm are used as the transmission signals 160-1 to 160-n, and both optical signals are wavelength-division multiplexed (WDM) on the same optical fibers 110 and 120 and transmitted / received.

FIG. 2 shows a configuration example of the ONU 200 to which the present embodiment is applied.
The ONU 200 includes a WDM filter 201, a receiving unit 240, a transmitting unit 241, and a user interface unit 207. The reception unit 240 includes an O / E conversion unit 202, an AGC 203, a clock extraction unit 204, a PON frame separation unit 205, a packet buffer 206, a grant termination unit 213, and a reception level control unit 214. The transmission unit 241 includes a packet buffer 208, a transmission control unit 209, a PON frame generation unit 210, a driver 211, and an E / O conversion unit 212.
The optical signal received from the branch fiber 120 is wavelength-separated by the WDM filter 201, converted to an electric signal by the O / E converter 202, and controlled so that the amplitude value becomes constant by the AGC 203. Then, the clock extraction unit 204 performs retiming, the PON frame separation unit 205 separates the overhead of the PON section, temporarily stores it in the packet buffer 206, and then outputs it via the user IF 207. The signal input from the user IF 207 is temporarily stored in the packet buffer 208 and then read out under the control of the transmission control unit 209. The PON frame generation unit 210 adds the overhead of the PON section. Assembled. The assembled signal is converted into current by the driver 211, converted to an optical signal by the E / O conversion unit 212, and transmitted to the branch fiber 120 through the WDM filter 201. Further, the transmission control unit 209 reads data from the packet buffer 208 in accordance with the transmission permission timing extracted from the grant termination unit 213. Further, the reception level control unit 214 determines the reception level based on the voltage value at the AGC 203, and the PON frame generation unit 210 adds the reception level of the downstream reception signal at the ONU to the data, and the upstream transmission signal is directed to the OLT 300. Thus, the OLT 300 is notified of the reception level by transmitting at the extracted transmission permission timing.

FIG. 3 shows a configuration example of the OLT 300 to which the present embodiment is applied.
The OLT 300 is roughly provided with a network IF 301, a control unit 330, a transmission unit 340, a reception unit 341, and a WDM filter 306. The transmission unit 340 includes a packet buffer 302, a PON frame generation unit 303, a driver 304, and an E / O conversion unit 305. The reception unit includes an O / E conversion unit 307, a fixed gain amplification unit 308, a clock extraction unit 309, a PON frame separation unit 310, and a packet buffer 311. The control unit 330 includes an ONU reception level processing unit 312 and a transmission power control unit 313.
The network IF 301 receives a signal from the PSTN / Internet 20. This signal is temporarily stored in the packet buffer 302, and then sent to the PON frame generation unit 303 to add an overhead of the PON section to generate an electric transmission signal, which is converted into a current by the driver 304, and the E / O The signal is converted into an optical signal by the conversion unit 305 and transmitted to the trunk optical fiber 110 through the WDM filter 306. The optical signal received from the trunk optical fiber 110 is wavelength-separated by the WDM filter 306, converted into an electrical signal by the O / E converter 307, amplified by the fixed gain amplifier 308, and clock extractor At 309, retiming is performed, and the overhead is separated by the PON frame separation unit 310 and temporarily stored in the packet buffer 311, and then a signal is output from the network IF 301 to the network side.

  Further, the downstream optical reception level value in the ONU extracted by the PON frame decomposition unit 310 is sent to the ONU reception level processing unit 312, and the transmission line loss is calculated from the difference from the optical output level of the OLT 300 itself. The value is sent to the transmission power control unit 313. The transmission power control unit 313 controls the transmission optical power by sending a signal to the driver 304 so as to reduce the optical output from the value calculated by the ONU reception level processing unit 312 to a level at which no error occurs in reception on the ONU 200 side. . A specific example of reducing the optical output to a level at which no error occurs in reception on the ONU 200 side is as follows. In the access network configuration of FIG. 1, the fiber length is the longest (or the transmission line loss is the largest). When the reception level at the ONU 200-3 connected to the fiber is the minimum light reception level, the transmission optical power of the OLT 300 is set so that the reception levels of the ONUs 200-1 to n are the same as the reception level of the ONU 200-3. Lower. In the specific example, the control method for setting the minimum light reception level in the ONUs 200-1 to 200-n has been described. However, the control amount of the transmission optical power of the OLT 300 may take other values.

FIG. 4 shows a flowchart for transmitting the reception level of the ONU 200 to the OLT 300 and setting the optimum optical transmission output power to each of the ONUs 200-1 to 200-n.
First, the OLT 300 transmits a downstream signal 130 (401), and each ONU 200-1 to n receives the signal (402). Each ONU 200-1 to n determines the reception level of the voltage value in the AGC 203 by the reception level control unit 214 and notifies the OLT 300 of the reception level (403). The OLT 300 receives the reception level from each ONU 200-1 to n (404), and the ONU reception level processing unit 312 calculates the transmission line loss for each ONU 200-1 to n from the difference from the optical output level of the OLT 300 itself. The calculation is performed (405), and the transmission power control unit 313 sets the output power so as to reduce the optical output to a level at which no error occurs in the reception on each of the ONUs 200-1 to 200-n (406). For example, the OLT 300 extracts the downlink reception signal level received from each of the ONUs 200-1 to 200-n, and selects the ONU that is the minimum light reception level from the extracted downlink reception signal levels. The OLT 300 then sets the downstream transmission signal level (output power) of each ONU 200-1 to n so that the downstream reception signal level of each ONU 200-1 to n is the same level as the downstream reception signal level of the ONU having the minimum light reception level. Control.

FIG. 5 shows a configuration example of the optical access network 1 in which the output power of the OLT 300 is optimized.
The difference from the configuration example of the optical access network 1 in FIG. 1 is that the transmission optical power of the OLT 300 is optimized for each ONU 200-1 to n, so that the transmission signal amplitude is different for each ONU 200-1 to n. By being transmitted as the downlink transmission signal 530 including the transmission signals 530-1 to 530-n, the downlink reception signal 540-addressed to each ONU 200-1 to n at a level where no error occurs at each ONU 200-1 to n. The reception levels 1 to n are almost equal. For example, the downlink transmission signal 530-1 addressed to the ONU 200-1 becomes the downlink reception signal 540-1 at the ONU-1, and the downlink transmission signal 530-2 addressed to the ONU 200-2 is the downlink reception signal 540 at the ONU-2. -2. Here, since the reception level differs depending on the fiber length (or transmission path loss) for each ONU 200, the downlink transmission signals 530-1 and 530-2 transmitted by the broadcast signal after adjusting the transmission power are received at the time of reception. The reception levels are almost equal as in signals 540-1 and 540-2. In addition, in this example, since the transmission power (output power) of the OLT is set according to the reception level of the ONU 200-3 having the longest fiber length (or the largest transmission line loss), it is small compared with FIG. Although it is the reception level, the optical output is reduced to a level at which no error occurs in reception by all ONUs 200-1 to 200-n. Accordingly, it is possible to realize a passive optical network system capable of reducing waste of power consumption as much as possible in the transmission output power by optimizing the transmission power of the OLT 300.

2. Maintaining PON link establishment

However, the downstream signal 530 from the OLT 300 optimized for the shortest distance ONU 200-1 in the configuration example is a fiber having a longer fiber length than the ONU 200-1 (or a transmission line loss larger than the fiber to which the ONU 200-2 is connected). There is a possibility that the level may not be received by the ONU 200-2, ONU 200-3, ONU 200-4, and ONU 200-n. The downstream signal from the OLT 300 optimized for the ONU 200-2 is at a level that can be received by the ONU 200-1 and the ONU 200-4, but the fiber length is longer than the ONU 200-2 (or the fiber to which the ONU 200-2 is connected). There is a possibility that the ONU 200-3 and ONU 200-n (connected with a fiber having a large transmission line loss) cannot receive. The downlink signal from the OLT 300 optimized for the longest distance ONU 200-3 in the configuration example may be at a level that can be received by the ONU 200-1, ONU 200-2, ONU 200-4, and ONU 200-n. The downstream signal from the OLT 300 optimized for the ONU 200-4 is at a level that can be received by the ONU 200-1 and the ONU 200-2, but is longer than the fiber length of the ONU 200-4 (or the fiber to which the ONU 200-2 is connected). There is a possibility that the ONU 200-3 and ONU 200-n (connected with a fiber having a large transmission line loss) cannot receive. Downstream signals from the OLT 300 optimized for the ONU 200-n can be received by the ONU 200-1, the ONU 200-2, and the ONU 200-4, but have a longer fiber length than the ONU 200-n (or the ONU 200-2 is connected). There is a possibility that the ONU 200-3 (connected by a fiber having a transmission path loss larger than that of the transmission fiber) cannot receive.
For this reason, in the conventional technique, the ONU 200 may be in a PON link disconnection state during a period in which the ONU 200 cannot be received. Therefore, a method for always maintaining the PON link establishment is required. Hereinafter, an embodiment of a method for maintaining PON link establishment will be described.

FIG. 6 shows a sequence diagram of an example of PON operation. This shows the relationship between the DBA operation and cycle and the grant operation and cycle based on the result of each DBA.
For example, the OLT 300 transmits a transmission permission message 600 including a grant instruction to each ONU 200-1 to 200-3 at every grant period of 125 μs. This transmission permission message 600 also includes information (Request report) for requesting a report of the amount of transmission waiting data accumulated in the transmission queue of each ONU. Each of the ONUs 200-1 to 200-3 transmits data accumulated in the transmission queue in the time slot specified by the grant instruction Start and End, and uses the queue length included in the upstream message 601 to indicate the amount of data waiting for transmission using the OLT 300. To report to. Furthermore, each ONU 200-1 to 3 includes the ONU reception level notification already described with reference to FIG.
Here, since the OLT 300 transmits the transmission permission message 600 at a certain grant period 602 to 605, the ONU 200 has a period of a level that cannot be received by using the method for determining the establishment of the PON link depending on whether or not the transmission permission message 600 is received. The PON link establishment can be maintained.

FIG. 7 shows a configuration example of the ONU 200 to which a PON link control unit is added.
A difference from the configuration example of FIG. 2 is that the control unit 220 is provided inside the ONU 200. The control unit 220 also includes the functions of the reception level control unit 214 and the grant termination unit 213 in FIG. Other constituent blocks and operations are the same as those described in FIG. In addition to reception level determination / control and grant termination (extraction of transmission permission timing, etc.) by the control unit 220, the PON link is controlled, and the voltage level at the AGC 203 is obtained by reception level determination / control. Based on whether or not the grant processing information is extracted at the end of the PON frame, the PON link determination is controlled. When transmitting the grant signal and / or the transmission permission message, the OLT transmits the signal with the maximum output optical power or an output optical power larger than a predetermined value. A specific example of PON link determination will be described with reference to FIG.

FIG. 8 shows a sequence diagram of an embodiment of PON link control.
First, it is determined whether there is a period of a level that cannot be received in the downstream signal from the OLT (801). Here, if there is no period of a level that cannot be received, the PON link is established (802). If there is a period in which the signal cannot be received, it is subsequently determined whether a grant signal is received (803). When the grant signal is received, the PON link is established (802). When the grant signal is not received, the transmission permission message is transmitted at a constant grant period, and therefore the presence / absence of reception of the next grant signal is confirmed (804). If the grant signal is received here, the PON link is established (802). If no grant signal is received, it is determined again whether or not a grant signal is received (805). If the grant signal is received here, the PON link is established (802). If no grant signal is received, the PON link is disconnected (806). In the embodiment, the sequence for determining the PON link based on the presence / absence of three grant signals has been described. However, the number of confirmations of whether or not a grant signal is received may be other than this.
As described above, when the ONU 200 adjusts the transmission optical output power on the OLT 300 side, the ONU 200 has a period that is less than the level at which no error occurs on the ONU 200 side due to the size of the transmission path loss, and thus the other ONUs 200 cannot receive. Period may occur. In such a case, it is conventionally determined that the PON link is broken. However, in the present invention and the present embodiment, even in such a case, the transmission message from the OLT is used to maintain the PON link establishment. This can be determined by the presence or absence of a grant signal.

10 PON
40, 41 Terminal 100 Splitter 110, 120 Optical fiber 130, 140, 530, 540 Down signal 150, 160 Up signal 200 ONU
240 ONU receiver 241 ONU transmitter 300 OLT
330 OLT control unit 340 OLT transmission unit 341 OLT reception unit

Claims (10)

An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. In a passive optical network system connected by an optical fiber network including a plurality of branch optical fibers,
The OLT transmits a downstream signal to each ONU,
Each ONU receives the downstream signal , determines its reception level, notifies the OLT of the reception level ,
The OLT receives the reception level from each of the ONUs, specifies a reception level equal to or lower than a minimum value or a predetermined value that can be received by the ONU as a set level,
The OLT refers to the optical output level of the downstream signal, and the reception level at each ONU becomes the set level according to each transmission line loss or each optical fiber length between the OLT and each ONU. so as to transmit light power to each said ONU respectively set,
The ONU is
Determining whether or not there is a period of a level that cannot be received in the downstream signal from the OLT;
If there is no period that cannot be received, it is determined that the link is established,
When there is a period of a level that cannot be received, it is determined whether or not a control signal is received, and when the control signal is received within a predetermined period or within a predetermined time, it is determined that a link is established, and within the predetermined period or the predetermined time. If the control signal is not received within, it is determined that the link is broken
A passive optical network system characterized by that.
The OLT specifies a reception level received from each ONU as a setting level at which no error occurs in reception on the ONU side,
2. The transmission path loss or optical fiber length between the OLT and each ONU is calculated by comparing the set level with the optical output level of the downstream signal. Passive optical network system.
The OLT transmits, as the downlink signal, a transmission permission message including the control signal at predetermined intervals toward each ONU,
3. Each of the ONUs transmits data in a time slot indicated by the control signal and reports the reception level to the OLT by including the notification of the reception level in an uplink signal. Passive optical network system.
The OLT when sending including transmit authorization message to said control signal, wherein, wherein the OLT is configured to output a maximum value or a predetermined value or more of the transmitted light power that can be transmitted Item 4. The passive optical network system according to any one of Items 1 to 3.
The passive optical network system according to claim 1 , wherein the control signal is a grant signal .
An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. A transmission light control method in a passive optical network system connected by an optical fiber network including a plurality of branch line optical fibers,
The OLT transmits a downstream signal to each ONU,
Each of the ONUs receives the downstream signal , determines the reception level, notifies the reception level to the OLT,
The OLT receives a reception level from each of the ONUs, specifies a reception level equal to or lower than a minimum value or a predetermined value that can be received by the ONU as a set level,
The OLT refers to the optical output level of the downstream signal, and the reception level at each ONU becomes the set level according to each transmission line loss or each optical fiber length between the OLT and each ONU. so as to transmit light power to each said ONU respectively set,
The ONU is
Determining whether or not there is a period of a level that cannot be received in the downstream signal from the OLT;
If there is no period that cannot be received, it is determined that the link is established,
When there is a period of a level that cannot be received, it is determined whether or not a control signal has been received. When the control signal is received within a predetermined period or time, it is determined that a link has been established, and within the predetermined period or the predetermined time If the control signal is not received within, it is determined that the link is broken
And a transmission light control method.
The OLT, the control signal when transmitting the including transmit permission message, to claim 6, wherein the OLT is output at the maximum value or a predetermined value or more of the transmitted light power that can be transmitted The transmission light control method described.
The transmission light control method according to claim 6 or 7, wherein the control signal is a grant signal .
An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. An optical multiple termination device in a passive optical network system connected by an optical fiber network including a plurality of branch line optical fibers,
A frame separation unit that extracts a reception level of a downstream signal in each ONU;
A reception level processing unit that calculates a transmission line loss or an optical fiber length from the difference between the reception level of each ONU extracted by the frame separation unit and the optical output level transmitted by the own OLT;
When transmitting the downlink signal , the transmission optical power is controlled so as to reduce the optical output from the transmission line loss or optical fiber length calculated by the reception level processing unit to a level at which no error occurs in reception on the ONU side. When transmitting a control signal, a transmission power control unit that controls transmission optical power so as to perform optical output at an optical output level equal to or higher than a maximum value that can be transmitted by the own OLT or a predetermined value ;
With
Send a downstream signal to each ONU,
The frame separation unit receives the reception level of the downlink signal from each ONU,
The reception level processing unit identifies a reception level equal to or lower than a minimum value or a predetermined value that can be received by the ONU as a set level,
The transmission power control unit refers to the optical output level of the downlink signal, and the reception level at each ONU is determined according to each transmission line loss or each optical fiber length between the own OLT and each ONU. Set the transmission optical power to each ONU so as to reach the setting level.
An optical multiple termination device.
An optical multiplex terminator (hereinafter referred to as OLT) connected to a communication network and a plurality of optical network terminators (hereinafter referred to as ONUs) that accommodate one or a plurality of terminals include one backbone optical fiber and an optical splitter. An optical network termination device in a passive optical network system connected by an optical fiber network including a plurality of branch optical fibers,
Determining the reception level, and a control unit which extracts the transmission permission timings, based on the received presence or absence of the control signal extracted by the reception level and the frame termination, to control the link establishment or link break judgment,
A frame generation unit for transmitting by adding the reception level to an uplink signal at a transmission permission timing extracted by the control unit;
With
The control unit receives a downstream signal from the OLT , determines its reception level ,
The frame generation unit notifies the reception level to the OLT,
The controller is
Determining whether or not there is a period of a level that cannot be received in the downstream signal from the OLT;
If there is no period that cannot be received, it is determined that the link is established,
If there is a period of not received level, the control whether the received determines the signal, when receiving the control signal within a predetermined period or within a predetermined time period determines that the link establishment, within a predetermined period or within a predetermined time period If the control signal is not received during
An optical network termination device.

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