JP2012019264A - Communication system and communication device - Google Patents

Abstract

When a PON in which a communication distance between an OLT and an ONU is dispersed over a specific range is configured using a conventional optical receiver, the optical intensity required for communication between the OLT and a remote ONU is obtained. When a signal is received by a nearby ONU, the problem is that the light intensity is too high, leading to failure of the ONU receiver.
The optical intensity of a downstream signal is measured by an ONU, and a variable ATT is provided before the optical signal is input to the optical receiver to attenuate the optical intensity. As a result, the light intensity of the downstream signal that changes in accordance with the path distance from the OLT to each ONU can be adjusted so that it becomes an appropriate light intensity before being input to the optical receiver of the ONU. In addition, when the upstream signal is emitted from the ONU, the optical signal emitted from the optical transmitter is attenuated by the variable ATT with reference to the attenuation setting when the downstream optical signal is received, and the path distance reaching the OLT is set. Accordingly, the ONU is adjusted so as to obtain an appropriate light intensity.
[Selection] Figure 1

Description

  The present invention relates to a communication system and a communication device, and more particularly to a communication system and a communication device in which the communication device shares a part of an optical transmission line.

  The PON (Passive Optical Network) transmits optical signals between a subscriber accommodation device (hereinafter referred to as OLT; Optical Line Terminal) and a subscriber device (hereinafter referred to as ONU; Optical Network Unit). This is a system for transmitting and receiving by branching and multiplexing using a splitter. G-PON (Gigabit-PON) defined in ITU-T (International Telecommunication Union Telecommunication Standardization Sector) Recommendation G.984.3 (Non-Patent Document 1) is placed in a station using different wavelengths in upstream and downstream. The communication between the accommodation station (OLT) and the ONUs placed in each user is a system in which signals are communicated by a TDM (Time Division Multiplexing) system in which signal communication time is assigned to each ONU. Introduction of G-PON into the field started around 2006, and introduction into access networks is being promoted mainly in North America and the EU.

  As general household subscribers (communication network users) gain access to the Internet and collect information and communicate for social life, the development of the communication network, especially the provision of an access network that connects subscribers to the communication network Improvement of service has been demanded. That is, carriers that provide a communication network are required to make additional investments to increase the number of users accommodated in each station as the number of users on the access line increases. As a method for increasing the number of users, there can be considered a method of additionally introducing a PON itself used for an access network, that is, a method of adding an OLT, and a method of expanding the number of accommodated users for each PON system, that is, the number of accommodated ONUs. Here, the PON generally has a configuration in which the OLT performs all control of complicated systems such as bandwidth control and management of ONUs to be accommodated. OLT is therefore much more expensive than ONU. Also, the cost of laying a new optical fiber creates a great expense for the carrier. From the above, it is a desirable solution to increase the number of accommodated ONUs per OLT.

  Therefore, a method of extending the communication distance is considered as one specific measure. By extending the communication distance in the PON section, it becomes possible to consolidate ONUs accommodated in other OLTs into one same OLT. In addition, when the range of dispersion of ONUs that can be accommodated in one OLT increases, the degree of freedom with respect to the arrangement of ONUs increases. As a result, it is possible for the communication carrier to efficiently lay the fiber according to the region.

  Using the current device technology, a practical configuration in G-PON has a maximum communication section of 20 km and a maximum number of branches (number of ONUs that can be connected to the OLT) of 64. Factors that determine the upper limit of the communication distance include the setting value of the number of branches and the limit of the dynamic range that can be realized in the light receiving device of the OLT / ONU.

  In Patent Document 1, a variable optical attenuator is provided in a preceding stage of a video optical receiver connected to an optical termination unit (ONU), and the control apparatus controls the light of the variable optical attenuator so that the input of the video optical receiver has an appropriate power. A technique for controlling the amount of attenuation is disclosed.

JP 2007-053647 A

ITU-T Recommendation G.984.3 ITU-T Recommendation G.984.6

  As a method for extending the PON section, a method for increasing optical power by applying an optical amplifier to an optical laser for OLT downlink signal transmission and an optical amplifier (optical signal repeater) called a Reach Extender (RE) are provided in the PON section. Thus, there is a method for extending the communication distance (Non-Patent Document 2).

  By introducing the optical amplifier, the communication distance is extended as compared with the conventional PON, and the subscriber ONU existing in a remote place can be accommodated in the same OLT. As a result, the number of ONUs to be accommodated is increased and the accommodation efficiency is also improved. In addition, the communication distance between the OLT and the ONU is extended, and the distribution range between the ONU and the ONU is widened. As a result, it is possible to reduce the OLT that is forced to be placed by being limited by the distance. That is, it leads to reduction of the number of OLTs installed in the station building.

  However, on the other hand, due to the expansion of the ONU distribution, a phenomenon occurs in which the strength of the downstream signal transmitted from the OLT to the ONU differs greatly between the nearest ONU and the remote ONU with respect to the OLT. As a result, the allowable range of the light receiving sensitivity of the light receiving device may be exceeded, leading to the destruction of the light receiving device of the nearest ONU.

  When there is only one branching point by the splitter, the signal intensity received by the ONU is a loss of only the fiber distance difference, and the light intensity difference is not so large. However, in the case of a PON composed of a plurality of stages of splitters, the light intensity of the downstream signal received by the ONU varies greatly depending on the number of splitters that pass until the optical signal reaches each ONU.

  That is, in order to expand the ONU distribution, a wider dynamic range is required for the ONU optical receiving device than for the conventional ONU optical receiving device for PON. However, it is technically difficult to greatly expand the dynamic range of the optical receiving device in a short period of time. Moreover, generally it leads to high cost. Therefore, mounting an optical receiving device with a wide dynamic range in all ONUs is considered to be less feasible from the viewpoint of development / introduction costs. Furthermore, from the viewpoint of reducing the PON introduction cost, it is generally required that all ONUs have the same performance.

  The present invention provides means for extending the dispersion range of ONUs using ONUs having the same performance while providing an extension of the communication distance between the OLT and the ONU without interposing the optical amplification repeater. In addition, the present invention provides a mechanism for preventing failure of an optical receiver due to excess received light intensity, etc., with ONUs having the same performance without changing the functions provided in the conventional PON.

  In order to solve the above problems, the optical communication system of the present invention has the following configuration. In the embodiments, specific numerical values will be used to clearly show the effects, but this does not indicate the necessity of giving restrictions to these numerical values in carrying out the present invention. The essence of the present invention is not affected by these numerical examples.

  The light emission intensity of the downstream signal from the OLT to the ONU is the minimum light receiving condition of the ONU (even if the total loss including the maximum loss due to the multi-stage splitter and the maximum distance loss due to the fiber length (64 branches × 2, 60 km)) is considered. Light intensity, S / N ratio, etc.). The OLT optical module always emits light with this transmitted light intensity when transmitting a downstream signal. Similarly, regarding the light emission intensity of the upstream signal from the ONU to the OLT, the minimum light receiving sensitivity of the OLT can be satisfied even when the maximum loss of the splitter loss and the optical fiber transmission loss is taken into consideration. The ONU includes an optical module that can realize such transmission light intensity. Further, similarly to the OLT, a light emitting device in which the light emission intensity of the upstream signal can always sufficiently satisfy the above condition is used.

  The light emission intensity of the downstream signal from the OLT to the ONU emits light with the maximum intensity that matches the farthest ONU. For this reason, the ONU at the nearest end exceeds the allowable range of the light receiving sensitivity, leading to destruction of the light receiving device. In order to prevent this, a variable ATT (Attenuator) such as a VOA (Variable Optical Attenuator) is mounted on the ONU before the O / E conversion unit (Optical / Electrical conversion unit) for the main signal, and has an optical intensity attenuation function. Regarding the setting of VOA (variable ATT), since it is necessary to measure the received light intensity more accurately, the downlink signal is split into a main signal and a measurement using a Tap-PD (Tap-Photo Diode). . As a result, the downstream VOA set value according to the received light intensity is determined and attenuated before entering the main signal O / E converter to prevent destruction of the light receiving device.

  The light emission intensity of the upstream signal from the ONU to the OLT may also exceed the permissible range of the light reception sensitivity of the OLT when light is emitted at the maximum intensity from the nearest ONU. In order to prevent this, the VOA is mounted after the ONU E / O conversion (Electrical / Optical conversion unit) to attenuate the emission intensity of the upstream signal.

  After the setting of the downlink received light intensity is completed, the uplink VOA is set based on the setting information so that the received light intensity is equivalent when the opposite OLT receives the uplink signal. That is, for the upstream signal, the communication light intensity is adjusted in the ONU.

  The above-described problem includes a branch fiber connected to a plurality of subscriber devices, a splitter connected to the branch fiber, a trunk fiber connecting the splitter and the subscriber accommodation device, and the subscriber accommodation device. In the communication system, the subscriber accommodation device includes a first optical amplifier that amplifies the downstream optical signal, and the subscriber device is amplified by the first optical amplifier and attenuated by the trunk fiber, the splitter, and the branch fiber. This can be solved by a communication system including a first variable optical attenuator that attenuates or passes an optical signal.

  An O / E conversion processing unit connected to the optical fiber and receiving a downstream optical signal from the optical fiber, and a first variable optical attenuator provided between the O / E conversion processing unit and the optical fiber A light intensity measuring unit that measures the intensity of the downstream optical signal, and a control that controls the amount of attenuation given to the downstream optical signal by the first variable optical attenuator based on the downstream optical signal intensity measured by the optical intensity measuring unit This can be solved by a communication device composed of a unit.

  With the optical communication system (PON) of the present invention, the communication distance between the OLT and the ONU is extended, and the dispersion distance between the ONU and the ONU can be extended.

It is a block diagram of the network structure explaining the extended PON system. It is a block diagram explaining the structure of OLT. It is a block diagram explaining the structure of ONU. It is a block diagram of the light measurement part / control part of ONU. It is a flowchart explaining the starting process of ONU. It is a flowchart explaining the normal operation process after ONU starting. It is a flowchart explaining the process of a control circuit. It is a figure explaining a light intensity measurement result. It is a flowchart explaining the process of an attenuation amount determination part. It is a figure explaining an attenuation determination table. It is a flowchart explaining the process at the time of LINK Down generation | occurrence | production. It is a light intensity figure explaining the downstream received light intensity of each ONU. It is a light intensity figure explaining the upstream transmission light intensity | strength of each ONU.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings using examples. The same reference numerals are assigned to substantially the same parts, and the description will not be repeated. Further, in the following embodiment, a description will be given based on the configuration and operation of the GPON defined in ITU-T recommendation G984.3 (Non-patent Document 1). However, the configuration and operation of the PON is not limited to the GPON.

  With reference to FIG. 1, the PON system of a present Example is demonstrated. In FIG. 1, the PON system 40 includes an OLT 10, a plurality of ONUs 20, optical fibers 70 and 75 that connect the OLT 10 and the ONU 20, and splitters 30 and 31. The OLT 10 transmits / receives information to / from a higher-order communication network via the access network 90. The OLT 10 is a device that transmits and receives information signals by further transferring information to the ONU. The PSTN / Internet 90 often uses a packet communication network including an IP router and an Ethernet (Ethernet (registered trademark)) switch. However, it may be a communication network other than PSTN or the Internet.

  The subscriber accommodation device OLT 10 includes a PON control unit 1000 and an optical amplifier 100. The optical amplifier 100 is used to extend the PON section distance to 60 km.

  The PON can connect 32 to 64 ONUs 20 via the optical splitter 30, the trunk fiber 70, and the branch fibers 75A to 75D.

  In a conventional PON using GPON as a representative example, there is a restriction on the communication distance distribution range of the subscriber unit ONU included in each PON system. That is, the distance difference between the ONU 20 installed closest to the OLT 10 and the ONU 20 installed farthest has been within 20 km.

  On the other hand, the maximum distance difference between the OLT and the ONU in the PON system of the present embodiment is 60 km. However, the ONU is divided into a dispersion range of 80A with a distance difference of 0 to 20 km, 80B with 20 to 40 km, and 80C with 40 to 60 km. This is classified according to the light emission intensity range and the light receiving sensitivity range of the optical devices mounted on the OLT and the ONU.

  In the present embodiment, as a first feature, the distance difference between the OLT 10 constituting the PON 40 and each ONU, that is, the PON section distance 80 is connected within 60 km. That is, the ONU can be freely arranged in the range of 0 to 60 km. The ONU in the section 80A is referred to as ONU 20-1A to ONU 20-3A, the ONU in the section 80B is referred to as ONU 20-1B to ONU 20-2B, and the ONU in the section 80C is referred to as ONU 20-1C to ONU 20-3C. Further, below the splitter 30, second splitters 31A, 31B, and 31C are arranged. The second splitters 31A, 31B, and 31C branch the optical signal again. The nearest end ONU installed at a position closest to the OLT 10 is the ONU 20-1A. The farthest end ONU installed at the farthest position is the ONU 20-2C. Here, all ONU groups (short-distance ONU group 20A, medium-distance ONU group 20B, long-distance ONU group 20C) that are dispersedly arranged in a range exceeding 20 km, which is the prescription of the existing PON, are accommodated for one OLT 10. .

  The ONU 20 is installed at a user's home or company site. The ONU 20 is connected to a subscriber network 50-1B that is a LAN or a corresponding network. The subscriber network 50-1B is connected to an IP telephone, a telephone terminal that provides an existing telephone service, or an information terminal such as a PC / mobile terminal.

  The flow of frames between the OLT and the ONU 20-1B will be described below. The wavelength of the optical signal used in the PON is different from the upstream λup and downstream λdown. A downstream signal transmitted from the OLT 10 to the ONU 20-1B is amplified by the intensity control unit 100 configured by an optical amplifier or the like, branched by the splitter 30 and the splitter 31A, and reaches the ONU 20-1B configuring the optical access network. To do. A downlink signal from the OLT 10 is transmitted using a frame used for communication in the PON section 80 (hereinafter referred to as a downlink basic frame). This downlink basic frame accommodates a frame called a GEM (G-PON Encapsulation Method) frame (not shown). The GEM frame is composed of a header and a payload, and an identifier (hereinafter also referred to as a Port-ID) for identifying the ONU 20 that is the destination of each GEM frame is inserted in each header. Each ONU 20 extracts the header of the GEM frame, and performs processing of the frame when the destination Port-ID of the frame indicates itself. If each ONU 20 is a frame addressed to another ONU, the ONU 20 discards the frame.

  For upstream communication from each ONU 20 to the OLT 10, all ONUs 20 use optical signals having the same wavelength λup. The uplink signal uses a variable-length frame composed of a header and a payload for each ONU as in the downlink signal. Each upstream frame includes a GEM frame. The OLT 10 manages transmission timing so that uplink signals including individual GEM frames do not collide / interfer. Based on the transmission timing managed by the OLT 10, the ONU 20 transmits an upstream signal. Each upstream signal is time-division multiplexed on the collecting optical fibers 75A to 75D and the trunk optical fiber 70, and reaches the OLT 10.

  Specifically, (1) adjust the signal delay amount after measuring the distance from the OLT 10 to each ONU in the ranging process, and (2) let each ONU report the amount of data waiting to be transmitted under the instruction of the OLT 10 (3) DBA (Dynamic Bandwidth Assignment; function for dynamically allocating communication band (time slot) for upstream signal to ONU. Also called dynamic bandwidth allocation) function, upstream signal of each ONU based on declaration Instructs the transmission timing and the amount of uplink communication data that can be transmitted. (4) When each ONU transmits uplink communication data at a timing instructed by the OLT 10, these signals are time-division multiplexed on the concentrating optical fiber and reach the OLT 10. (5) Since the OLT 10 knows the timing instructed to each ONU, the signal of each ONU is identified from the multiplexed signal and the received frame is processed.

  A system operation for performing the above uplink communication will be described. First, when the PON 40 is started up, the OLT 10 individually measures a round trip delay (RTD: Round Trip Delay) to the ONU 20 in the ranging process when each ONU is started up. The OLT 10 determines an equivalent delay (EqD) value based on the measurement result. EqD is stored in the ranging management DB of the OLT 10. For this ranging, a ranging method defined in ITU-T recommendation G.984.3 (Non-patent Document 1) may be used. Note that EqD is set so that the response times from the individual ONUs 20 to the OLT 10 are the same in the system, similar to the EqD of the existing PON.

  The ranging management DB of the OLT 10 holds EqD information and the RTD of the PON section 80. This is to allow the upstream signal from the ONU 20 to be correctly received when the OLT 10 receives the upstream signal from the corresponding ONU 20 after allocating the bandwidth to each ONU 20.

  The configuration of the OLT will be described with reference to FIG. In FIG. 2, the OLT 10 includes n interfaces (IF) 1100, a downstream frame processing unit 1210, an E / O 1310, a WDM 1500, an O / E 1320, an upstream frame processing unit 1410, and a PON control unit 1000. Composed. The downlink frame processing unit 1210 holds a downlink route information database (DB) 1211. The uplink frame processing unit 1410 holds an uplink route information database 1411. The E / 01310 is configured to include the optical amplifier 100. The PON control unit 1000 includes an ONU management unit 1060. The ONU management unit 1060 holds the ranging / DBA information DB.

  The access network 90 inputs the downlink signal to IFs 1100-1 to 1100-n called SNI (Service Network Interface). As the access network 90, a packet network is often used. The IF 1100 uses a 10/100 Mbit / s or 1 Gbit / s Ethernet interface. However, it is not limited to this configuration. A received signal (hereinafter, the signal may be referred to as data or a packet) is transferred to the downlink frame processing unit 1210. The downlink frame processing unit 1210 analyzes packet header information. Specifically, the downlink frame processing unit 1210 determines a destination ONU 20 to which the received packet is to be transferred, based on flow identification information including destination information, transmission source information, and path information included in the packet header. Along with the determination of the destination information, the downlink frame processing unit 1210 converts or adds the header information of the received packet as necessary. The downlink frame processing unit 1210 includes a downlink route information DB 1211 for determining processing including the destination determination, header information conversion and addition. The downlink frame processing unit 1210 performs the above processing by referring to the DB 1211 using one or more parameters included as header information of the received packet as a trigger.

  The downlink frame processing unit 1210 further includes a frame generation function that changes the received packet to a frame format for PON section 80 transmission according to the header processing content determined in the downlink frame processing unit 1210. A specific process when an Ethernet reception packet is transmitted to the PON section 80 of GPON is as follows. (1) Extract header information of the Ethernet packet. (2) Search the downlink path information DB 1211 in the downlink frame processing unit 1210 using the header information as a trigger. Thereby, VLAN tag processing (conversion, deletion, transparency, addition, etc.) for the received packet and its transfer destination are determined. (3) Further, a GEM header including the Port-ID set in the corresponding transfer destination ONU by the frame generation function is generated. (4) The GEM header is attached to the received packet, and the Ethernet packet is encapsulated as a GEM frame.

  The E / O processing unit 1310 reads out the GEM frame encapsulating the Ethernet packet from the downstream frame processing unit 1210. The E / O processing unit 1310 converts the read electrical signal of the GEM frame into an optical signal. The E / O processing unit 1310 transmits the signal to the ONU 20 via the wavelength demultiplexer (WDM) 1500 and the concentrating optical fiber 70. At this time, the strong amplifier 100 provided in the E / O processing unit 1310 amplifies the optical signal and transmits it at the maximum light intensity. The optical amplifier 100 has a transmission light intensity that can satisfy the minimum light reception of the ONU even when the maximum loss due to the splitters connected in multiple stages and the maximum distance loss due to the fiber length (64 branches × 2 stages, 60 km) are added.

  The PON control unit 1000 provided in the OLT 10 is a part that performs overall control of the PON 40 including control of setting and management of each ONU 20 as well as bi-directional signal transmission control. The information held in the ranging / DBA information DB 1061 of the PON control unit 1000 includes an EqD set value for each ONU 20. This is information corresponding to the transmission distance (delay time) from the OLT 10 to each ONU 20, and is stored in the ranging / DBA information DB 1061 and used for DBA processing during PON operation. The data amount (bandwidth) and transmission timing (position information and time / timing on the frame) of the downlink signal sent to each ONU 20 are calculated and stored in the ranging / DBA information DB 1061.

  With respect to the upstream reception signal from each ONU 20, the O / E processing unit 1320 converts the optical signal into an electrical signal through the concentrated optical fiber 70 and the wavelength demultiplexer (WDM) 1500. The upstream frame processing unit 1410 disassembles the GEM frame and separates the header information and the payload. The separated payload includes an Ethernet frame. The upstream frame processing unit 1410 extracts these frames. The upstream frame processing unit 1410 converts the packet into an Ethernet frame (packetized) based on the header information of the Ethernet frame and transfers the packet to the access network 90.

  The configuration of the ONU will be described with reference to FIG. In FIG. 3, the ONU 20 includes a WDM 2500, a VOA 2330, an O / E 230, a downstream frame processing unit 2210, a plurality of IFs 2100, an upstream frame processing unit 2410, an E / O 2320, a VOA 2340, and a PON control unit 2000. The optical measurement unit / control unit 300 is configured. The downlink frame processing unit 2210 holds a downlink route information DB 2211. The uplink frame processing unit 2410 holds an uplink route information DB 2411. The E / O 2320 includes the optical amplifier 100. The PON control unit 200 includes an uplink transmission control unit 2070 and an ONU control unit 2060. The uplink transmission control unit 2070 holds a DBA information DB 2071 and an EdQ information DB 2072.

  The upstream signal from the terminal accommodated by the ONU 20 to the PON (ONU) is input from the user network to IFs 2100-1 to 2100-n called UNI (User Network Interface). The subscriber network (user network) 50-1B is often a LAN or packet network. In many cases, the IF 2100 uses an Ethernet interface of 10/100 Mbit / s or 1 Gbit / s. However, it is not limited to this configuration.

  The PON control unit 2000 includes an uplink transmission control unit 2070 and an ONU control unit 2060. The ONU control unit 2060 is a functional block used for parameter setting and communication state management when starting the ONU 20 in accordance with an instruction from the OLT 10. The ONU control unit 2060 determines whether it is necessary to analyze a received frame, manage apparatus maintenance management information, and communicate (reply) to the OLT 10. That is, the ONU control unit 2060 processes the downstream signal and upstream signal in the ONU 20.

  Regarding the downstream signal reception of the ONU 20, the optical measurement unit / control unit 3000 measures the optical reception intensity. The VOA 2330 is a variable ATT. VOA 2330 provides attenuation to the received signal. The O / E processing unit 2310 converts the received optical signal having the attenuated light intensity into an electrical signal.

  Regarding the upstream signal transmission of the ONU 20, the optical amplifier 100 provided in the E / O processing unit 2320 transmits at the maximum light intensity. This is the same reason as the optical amplifier 100 of the OLT 10. The optical amplification is set to a transmission light intensity that can satisfy the minimum light reception of the OLT even if the distance loss due to the fiber length and the maximum loss (60 km, 64 branches × 2) due to the multi-stage connected splitter are added. If this ONU is the ONU 20-1A arranged at the near end with respect to the OLT 10, the upstream transmission light to the OLT 10 exceeds the allowable range of the light receiving sensitivity of the optical receiver of the OLT 10. Therefore, the optical measurement unit / control unit 3000 sets a value fed back from the downstream optical reception intensity in the VOA 2340 and attenuates the upstream optical signal intensity. The internal configuration of the light measurement unit / control unit 3000 and the VOA 2330 setting procedure will be described next with reference to FIG.

  Details of the ONU light measurement unit / control unit 3000 will be described with reference to FIG. In FIG. 4, an optical measurement unit / control unit 3000 includes a Monitor PD 3020, an AMP (Amplifier) 3030, a BPF (Band Pass Filter) 3040, an I / V conversion range amplifier 3050, and an ADC (Analog to Digital Converter) 3090. And an internal clock source 3070, a clock distributor 3080, a control circuit 3100, a memory 3110, an attenuation determination unit 3120, a downlink VOA control unit 3130, and an uplink VOA control unit 3140. The memory 3110 holds the light intensity measurement result 3111. The attenuation amount determination unit 3120 holds an attenuation amount determination table 3121.

  The optical measurement unit / control unit 3000 measures the intensity of the downstream optical signal from the OLT 10 and controls the downstream received light adjustment VOA 2330. Further, based on the intensity of the downstream optical signal, the upstream transmission light adjustment VOA 2340 is adjusted and controlled.

  Specific operation will be described below. A downstream signal transmitted from the OLT 10 to the ONU 20 is branched by the optical fiber 70 and the splitters 30 and 31A to 31C for branching, and reaches the ONU 20 via branch fibers 75A to 75D and 71A to 71D. For the downstream optical signal after passing through the WDM filter 2500, a Tap-PD (Tap-Photo Diode) 3010 branches into a main signal and a measurement. The branched downstream optical signal reaches the Monitor PD 3020 and the downstream received light adjustment VOA 2330. Here, the light intensity ratio after branching with Tap-PD is set to 10: 1. The Monitor PD 3020 converts the received light into electricity. The AMP 3030 amplifies the electric signal. Further, the BPF 3040 removes a noise component of the amplified electric signal. The I / V conversion range amplifier 3050 converts a current value into a voltage value. The clock distributor 3080 distributes the internal clock from the internal clock source 3070 to the ADC 3090 and the control circuit 3100. The ADC 3090 starts sampling based on the input clock speed and digitizes the voltage value. The control circuit 3100 takes in the digital value and writes it in the memory 3110. Considering the intensity variation immediately after startup, the control circuit 3100 takes a value for a certain period of time and calculates an average value. The control circuit 3100 sends the calculated average value to the attenuation amount determination unit 3130. The attenuation amount determination unit 3130 passes the set value from the average value to the downlink VOA control unit 3130 and the uplink VOA control unit 3140 based on the determination table 3121.

  By the above operation, an optical signal whose light intensity is adjusted so as not to exceed the allowable range of the light receiving sensitivity of the optical receiver is input to the O / E processing unit 2310. Further, in order to prevent a high-intensity optical signal from being input to the ONU 20 immediately after activation, the attenuation amount by the downlink received light adjustment VOA 2330 is maximized when the power is turned off, and the apparatus is activated from the cutoff state. Similarly, the amount of attenuation by the upstream transmission light adjustment VOA 2340 is maximized, and the system is started from the cutoff state. This is to prevent the transmission optical signal from the ONU 20 to the OLT 10 from exceeding the allowable range of the light receiving sensitivity of the optical receiver of the OLT 10 and to prevent erroneous light emission.

  The ONU activation process will be described with reference to FIG. In FIG. 5, this flow is started when the ONU 20 is powered on. First, the ONU 20 sets the maximum for the downstream VOA and the upstream VOA, and puts it in the blocked state (S11). The ONU 20 activates the control circuit (S12). The ONU 20 issues a received light intensity measurement start command (S13). The ONU 20 issues a VOA setting table search start command (S14). The ONU 20 receives the downstream optical signal attenuated by the downstream VOA passage at the O / E unit (S16). The ONU 20 confirms whether it is synchronized with the downstream signal and whether it is in the Psync state (synchronization established state) (S17). When synchronization is established (YES), the ONU 20 determines whether a PLOAM (Physical Layer Operations, Administrations and Maintenance) Message has been received (S18). When the determination is YES, the ONU 20 receives a serial number request (S19).

  The ONU 20 transmits a Serial Number Response (S21). The ONU 20 converts the Serial Number Response into an optical signal (S22). The ONU 20 transmits the optical signal attenuated by the upstream VOA (S23). As described above, the ONU 20 transitions to the ONU normal operation state.

  With reference to FIG. 6, the normal operation process after the ONU is activated will be described. In FIG. 6, the control circuit 3100 of the ONU 20 periodically issues a received light intensity measurement start command (S31). The control circuit 3100 of the ONU 20 issues a VOA setting table search start command (S32), and returns to step 31.

  That is, the control circuit 3100 dynamically sets the downstream VOA and the upstream VOA. This is a mechanism in which the ONU always follows the transmission light of the OLT. The tracking function for the change in the optical transmission intensity of the OLT is a guard function for preventing a device failure or the like caused by receiving an optical signal of excessive energy during an abnormal situation such as a flashing light of the OLT. is important. Another purpose of the function is to cope with changes in fiber laying conditions due to construction, etc., and changes in physical environment such as fiber due to weather and the like.

  The received light intensity measurement start command issuance process will be described with reference to FIG. In FIG. 7, the control circuit 3100 reduces the attenuation amount of the downstream VOA by a predetermined amount, acquires the voltage value of the I / V conversion range amplifier 3050 from the ADC 3090 in synchronization with the internal clock, and takes in the digitized value (S131). . Since the downstream signal from the OLT is attenuated 10: 1 by Tap-PD, the light intensity input to the Monitor PD 3020 is different from the actual light intensity at the ONU receiving end. The control circuit 3100 performs correction so as to approximate the measured value (S132). The control circuit 3100 determines whether the corrected value is within the measurement range (S133). If it is out of range (NO), the control circuit 3100 returns to step 131. Step 133 If it is within the measurement range (YES), the control circuit 3100 checks the remaining memory capacity and determines the write number (S136). The control circuit 3100 writes the sampling number and the correction value in the memory 3110. The control circuit 3100 confirms issuance of a received light intensity measurement start command (S137). When YES, the control circuit 3100 returns to step 131. When NO at step 137, control circuit 3100 returns.

  With reference to FIG. 8, the light intensity measurement result 3111 in the memory 3110, which is the result obtained by issuing the received light intensity measurement command, will be described. In FIG. 8, the light intensity measurement result 3111 includes a physical address address 401 of memory, a sequence number 402, and a light intensity 403. Since the physical address area 401 of the internal memory is limited, there are address values from 0 to N. The control circuit 3100 determines whether or not the table is written by checking the remaining memory capacity (step 134) of FIG. When the memory is free, the control circuit 3100 writes the light intensity result measured simultaneously with the sampling number. When there is no free space in the memory, that is, when writing has been completed up to address N, the control circuit 3100 writes the sampling number and light intensity from the top address 0 by overwriting. FIG. 8 shows a state in which after writing to the N-th address memory, writing is started after returning to the beginning, and the latest information is held at the first memory address. The operation of the attenuation determination unit using the measurement values of this table will be described with reference to FIG.

  With reference to FIG. 9, the process of the attenuation determination unit 3120 of the light measurement unit / control unit 3000 will be described. When a VOA setting table search start command is issued from the control circuit 3100, the attenuation determination unit 3120 reads X measurement results from the oldest sampling number from the light intensity measurement result table 3111 in FIG. 8 (S141). The attenuation determination unit 3120 calculates an average value from the read X values (S142). Next, the attenuation determination unit 3120 searches for the closest value from the average value by searching the attenuation determination table (S143). The attenuation amount determination table will be described later. If there is no value closest to the search value in the attenuation determination table (NO), the attenuation determination unit 3120 returns to step 141. When the search is hit (step 143: YES), the attenuation determination unit 3120 acquires the downlink and uplink VOA set values (S144). The attenuation amount determination unit 3120 starts VOA setting, sends setting values to the downlink VOA control unit 3130 and the uplink VOA control unit 3140, and adjusts the downlink reception light adjustment VOA 2330 and the uplink reception light adjustment VOA 2340 (S146). . The attenuation determination unit 3120 confirms the issue of the search start command (S147). If YES, the attenuation determination unit 3120 returns to step 141. When NO in step 147, the attenuation determination unit 3120 returns.

  The attenuation determination table will be described with reference to FIG. In FIG. 10, the attenuation determination table includes an average value 411 of downstream received light intensity from the OLT to the ONU, a downstream VOA set value 412, and an upstream VOA set value 413. That is, it shows a list of downstream VOA values and upstream VOA values that should be set in correspondence with the average value of the downstream signal received intensity of a certain ONU. In FIG. 10, the minimum value P (AVG.X) is the light intensity received by the ONU at the farthest end. The light receiving intensity of the ONU is the minimum value obtained by subtracting the loss due to the 64-branch coupler and the loss due to the 60 km fiber length from the transmission light intensity of the OLT. At this time, if the downstream VOA value to be set is large, the minimum light receiving condition (sensitivity / light intensity) of the ONU O / E processing unit 2310 cannot be satisfied. Therefore, the minimum value of the VOA value to be set is correct. Similarly, when the value of the upstream VOA set value is large, the minimum light receiving condition (sensitivity / light intensity) of the OLT O / E processing unit 1320 cannot be satisfied. is there.

  P (AVG.Z) indicates the intensity of light received by the nearest ONU. OLT and ONU are connected at a ratio of 1: 1 in the state where there is no branching by the coupler, and they are connected with an extremely short fiber length. This is the case. At this time, the maximum value of the downstream VOA value to be set is set so as not to exceed the maximum intensity that can be received by the O / E processing unit 2310 of the ONU. Similarly, the maximum value of the upstream VOA setting value is set so that the value of the upstream VOA setting value does not exceed the maximum light intensity that the OLT O / E processing unit 1320 can receive.

  The distance 414 from the OLT is not a direct value that the attenuation determination table has. Here, the distance relationship with the average received light intensity from the OLT to the ONU is described so that it is easy to imagine. The magnitude relationship described in the column is a value indicating the average received light intensity. The magnitude relationship is shown in which the light intensity received by the farthest end ONU is X minimum and the light intensity Z received by the nearest end ONU is maximum.

  The processing of the ONU 20 when LINK Down occurs will be described with reference to FIG. In FIG. 11, LINK DOWN occurs during ONU normal operation (S41). The ONU 20 sets the downstream VOA 2330 / upstream VOA 2340 to the maximum setting (S42). This is a guard for preventing a device failure or the like of the O / E processing unit 2310 of the ONU 20 from suddenly changing the reception strength of the downstream signal to the ONU due to fiber addition, coupler branch connection work, or the like. It is a function. This is a case where relocation work or the like that suddenly places the ONU arranged at the far end near the OLT is performed. The ONU 20 sets the downstream VOA 2330 / upstream VOA 2340 to the maximum setting to block the input to the O / E processing unit 2310. Similarly, it is also a guard function for preventing a device failure or the like of the OLT O / E processing unit 1320 from occurring by blocking the upstream side. Again, the ONU 20 sets the downstream VOA 2330 and the upstream VOA 2340 appropriately by issuing a received light intensity measurement start command (S43) and issuing a VOA setting table search start command (S44), and returns to the normal sequence (S46). Normal operation. Step 46 is step 16 to step 23 in FIG. Specific processing has already been described with reference to FIGS. 7, 9, and 5, and detailed description thereof will be omitted.

  The downstream received light intensity of the ONU will be described with reference to FIG. In FIG. 12, the horizontal axis represents the distance from the OLT to each ONU. Here, a near-end ONU 20-1A, an intermediate ONU 20-2B, and a far-end ONU 20-2C are arranged. The dispersion range of each ONU is within 0 to 60 km. The vertical axis in FIG. 12 represents the light intensity of the received downlink signal of the ONU 20. The functional block diagram in FIG. 12 is an excerpt of the downstream optical reception block of the ONU in FIG. The light measurement unit / control unit 3000 described above measures the received light intensity by the Monitor PD 3020, and an appropriate set value is set in the downstream VOA 2330 and attenuated light is input to the O / E processing unit 2310.

  The PDO (Power Downstream OLT) on the vertical axis represents the light intensity of the downstream optical signal emitted from the OLT, and is the strongest light intensity. PDA, PDB, and PDC are reception strengths of the Monitor PD 3020 received by each ONU 20. Actually, since it branches to 10: 1 across the Tap-PD, the corrected measured value is more correct. Here, the actual measurement value corrected at the receiving end of the ONU 20 is graphed. The difference A between the PDO and PDA, the difference B between the PDO and PDB, and the difference C between the PDO and PDC are the sum of the fiber loss due to the distance from the OLT and the loss due to the branching of the coupler or the like. Differences A, B, and C are attenuation amounts of the optical signal.

  When the near-end ONU 20-1A receives the downstream signal from the OLT 10 as it is, the near-end ONU 20-1A exceeds the receivable intensity of the light receiving element included in the ONU 20-1A. Therefore, the light measurement unit / control unit 3000 sets an appropriate set value in the downstream VOA 2330. The amount of attenuation due to ATT when the setting to the downstream VOA 2330 is reflected is AA. The light intensity input to the O / E processing unit 2310 is the light intensity after passing through the VOA.

  On the other hand, the far-end ONU 20-2C cannot satisfy the minimum light receiving condition (sensitivity / light intensity) if attenuation due to ATT is included. For this reason, the VOA does not attenuate the received optical signal. It becomes the same value as 1213 after passing.

  The light intensity of each ONU 20 after passing through the VOA is all the same. This is a result of adjusting the dynamic range of the O / E processing unit 2310 of each ONU 20 to be small. The input light to the O / E processing unit can be adjusted by setting the VOA 2330. For this reason, there is no need to use an expensive PD with a wide dynamic range, and replacement with a cheaper product is possible.

  With reference to FIG. 13, the upstream transmission light intensity of the ONU and the reception intensity of the OLT will be described. In FIG. 13, the horizontal axis represents the distance from each ONU 20 to the OLT 10. Here, the near-end ONU 20-1A, the intermediate ONU 20-1B, and the far-end ONU 20-2C are arranged. The dispersion range of each ONU 20 is 0 to 60 km or less. The vertical axis represents the light intensity of the downstream signal from the ONU.

  The functional block diagram in the figure is an excerpt of a part of the transmission block of the ONU 20. The E / O processing unit 2320 emits an upstream signal to the OLT 10. The VOA 2340 is set to an appropriate setting value by the light measurement unit / control unit 3000 described above. The VOA 2340 passes or attenuates the upstream signal.

  The PUC (Power Upstream ONU-C) on the vertical axis is the light intensity immediately after exiting the E / O processing unit 2320 of the ONU 20. Since it is before passing through the VOA 2340, it emits light at the maximum intensity. Each ONU 20 has the same light intensity as that of the component variation. PUC, PUB, and PUA are light intensities after passing through VOA 2340. Further, the difference A between PUA and PUO, the difference B between PUB and PUO, and the difference C between PUC and PUO are attenuation amounts obtained by adding the distance loss and the loss due to the branch of the coupler or the like to the fiber length from the ONU 20 to the OLT 10. . The differences A, B, and C in FIG. 13 are theoretically equivalent to the differences A, B, and C in FIG.

  In the case of the near-end ONU 20-1A, if the OLT 10 receives the upstream signal 1212 immediately after the E / O processing unit 2320 from the ONU 20-1A as it is, there is a possibility that the maximum value of the received light intensity of the PD of the OLT 10 is exceeded. Therefore, an appropriate setting value is set in the upstream VOA 2340 by the light measurement unit / control unit 3000. The amount of attenuation due to passing through the VOA is AAA. Actually, the intensity of the upstream optical signal to the OLT 10 is after passing through the VOA.

  On the other hand, the far-end ONU 20-2C cannot satisfy the minimum light receiving condition (sensitivity / light intensity) of the OLT if there is attenuation due to ATT. For this reason, the light intensity immediately after passing through the E / O processing unit 2320 of the ONU 20-2C and the light intensity after passing through the VOA have the same value. That is, the VOA 2340 does not give attenuation.

  As a result, the light intensity of the upstream signal from each ONU 20 reaching the OLT 10 is all the same. This is a result of adjustment to reduce the dynamic range of the OLT O / E processing unit. The upstream emission signal from the ONU 20 can be adjusted by setting the upstream VOA 2340 of the ONU 20. For this reason, there is no need to use an expensive PD with a wide dynamic range for the OLT 10, and replacement with a cheaper product is possible.

  10 ... OLT, 20 ... ONU, 30 ... splitter, 40 ... PON system, 50 ..., 70 ... trunk optical fiber, 75 ... branch optical fiber, 80 ... PON section, 90 ... PSTN / Internet, 100 ... optical amplifier, 230 ... O / E, 300 ... light measurement unit / control unit, 1000 ... PON control unit, 1100 ... interface (IF), 1210 ... downstream frame processing unit, 1310 ... E / O, 1320 ... O / E, 1410 ... upstream frame processing , 1500 ... WDM, 2000 ... PON control part, 2100 ... interface (IF), 2210 ... downstream frame processing part, 2320 ... E / O, 2330 ... VOA (downstream), 2340 ... VOA (upstream), 2410 ... upstream frame Processing unit, 2500 ... WDM, 3000 ... Light measurement unit / control unit, 3020 ... Monitor PD, 3030 ... AMP (Amplifier), 3040 ... BPF (Band Pass Filter), 3050 ... I / V conversion range amplifier, 3090 ... ADC (Analog to Digital Converter), 3070 ... Internal clock source, 3080 ... Clock distributor, 3100 ... Control Circuit, 3110... Memory, 3120... Attenuation amount determination unit, 3130... Downward VOA control unit, 3140.

Claims (6)

In a communication system comprising a branch fiber connected to a plurality of subscriber devices, a splitter connected to the branch fibers, a trunk fiber connecting the splitter and the subscriber accommodation device, and the subscriber accommodation device,
The subscriber accommodation device includes a first optical amplifier that amplifies a downstream optical signal,
The subscriber unit includes a first variable optical attenuator for attenuating or passing an optical signal amplified by the first optical amplifier and attenuated by the trunk fiber, the splitter, and the branch fiber. A featured communication system. The communication system according to claim 1,
The communication system, wherein the first optical amplifier amplifies the downstream optical signal so as to satisfy a light receiving condition of a farthest end subscriber device included in the plurality of subscriber devices. The communication system according to claim 1,
The subscriber unit further includes a second optical amplifier that amplifies the upstream optical signal, and a second variable optical attenuator that attenuates or passes the optical signal amplified by the first optical amplifier. A featured communication system.   An O / E conversion processing unit connected to the optical fiber and receiving a downstream optical signal from the optical fiber; a first variable optical attenuator provided between the O / E conversion processing unit and the optical fiber; A light intensity measuring unit for measuring the intensity of the downstream optical signal, and controlling the amount of attenuation given to the downstream optical signal by the first variable optical attenuator based on the downstream optical signal intensity measured by the optical intensity measuring unit. A communication device comprising a control unit. The communication device according to claim 4,
Further, an E / O conversion processing unit that sends an upstream optical signal to the optical fiber, an optical amplifier that amplifies the output light of the E / O conversion processing unit, and an optical signal amplified by the optical amplifier is attenuated or passed. A communication apparatus comprising: a second variable optical attenuator. The communication device according to claim 5,
The communication unit is characterized in that the second variable optical attenuator controls the amount of attenuation given to the amplified optical signal based on the downstream optical signal intensity measured by the optical intensity measurement unit.

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