WO2010064554A1

WO2010064554A1 - Optical network band control apparatus and optical network band control method

Info

Publication number: WO2010064554A1
Application number: PCT/JP2009/069771
Authority: WO
Inventors: 成五高橋; 章雄田島
Original assignee: 日本電気株式会社
Priority date: 2008-12-02
Filing date: 2009-11-24
Publication date: 2010-06-10

Abstract

Provided are an optical network band control apparatus and an optical network band control method wherein the sensitivity of receiving an upstream signal light will not be degraded. A band control apparatus comprises: a light emission control unit that causes a light source located at a first node to perform a light emission for a predetermined time period until a time t0 and provides a first optical signal generated by the light source through a transmission path to a second node; an influence factor determining unit that, when a part of the first optical signal is reflected, as a return light, on the transmission path toward the first node, determines, as an influence factor, a parameter based on the status of the return light; a first relationship calculating unit that calculates, as a first relationship, the relationship between a time having elapsed since the time t0 and the influence factor; and a control unit that decides, based on the first relationship, a time slot to be used for communication between the first and second nodes. The first node is so configured as to receive, during the decided time slot, an upstream signal light generated by the fact that a downstream signal light generated by the light source is reflected and modulated at the second node.

Description

Optical network bandwidth control apparatus and optical network bandwidth control method

The present invention relates to an optical network, and more particularly to an optical network bandwidth control device and an optical network bandwidth control method.

An optical network using Passive optical network (PON) is known. In the PON, by using a splitter, a plurality of remote node transmission / reception devices (ONUs) can be accommodated in one center node transmission / reception device (OLT). However, the S / N ratio of signal light used for communication deteriorates due to loss depending on the fiber transmission path length, splitter branching loss, and the like. Therefore, the number of ONUs that can be accommodated in one PON is limited. As an example, the upper limit of the number of ONUs that can be accommodated in one PON is 32 in GEPON (IEEE802.3ah) and 62 in GPON (FSAN / ITU-T).

In order to increase the number of ONUs that can be accommodated, it is conceivable to adopt a TDM / WDM hybrid PON system that combines wavelength division multiplexing (WDM) technology and time division (TDM) technology (for example, Non-Patent Document 1, Non-patent document 2).

FIG. 1 is a schematic diagram showing an example of an optical network employing a TDM / WDM hybrid PON system. This optical network includes an OLT 101, a wavelength division multiplexing filter 102, a plurality of branch splitters (103-1 to 103-i), and a plurality of ONUs 104. In this optical network, the downstream signal light generated from the OLT 101 is separated by the wavelength demultiplexing filter 102 into light of multiple wavelengths (λ1 to λn). Each downstream signal light after separation is further time-divided into a plurality of downstream signal lights by the branching splitter 103. Each time-divided downstream signal light is supplied to each ONU 104. On the other hand, each ONU 104 generates upstream signal light having the same wavelength as that of each received downstream signal light, and transmits it to the OLT side.

The wavelength demultiplexing filter 102 can demultiplex an optical signal with a significantly lower loss than the branching loss of the branching splitter 103. Therefore, if the TDM / WDM hybrid PON system is adopted, in principle, the number of ONUs that can be accommodated can be expanded in proportion to the number of multiplexed wavelengths. However, when the wavelength division multiplexing filter 102 is used, each ONU 104 must be provided with a light source capable of emitting light having a wavelength assigned to the ONU 104. In effect, each ONU 104 must be equipped with a light source that can selectively emit each of a plurality of wavelengths. Providing such a light source in the ONU 104 is disadvantageous in terms of cost required for the light source. Further, in order to selectively emit light of a specific wavelength, complicated control must be performed in each ONU 104.

On the other hand, in Patent Document 1 (Japanese Patent Laid-Open No. 9-219680), different wavelengths are assigned to each slave station, the slave station and the center station are connected by a wavelength division division multiple access system, and a modulation element is provided in the slave station. Are listed. Patent Document 1 describes that the use of a modulation element in a slave station eliminates the need for precise wavelength control on the slave station side, thereby realizing a low-cost system.

In addition, as related techniques that the present inventors have known, Patent Document 2 (Japanese Patent Laid-Open No. 8-65252), Patent Document 3 (Japanese Patent Laid-Open No. 8-51412), Patent Document 4 (Japanese Patent Laid-Open No. 9-214440), Patent Document 5 (Patent No. 3431515), Non-Patent Document 3 (Han Wu Hu and Hanan Anis, Degradation of Bi-Directional Single Fiber Transmission in WDM-PON DUE to HO LUE, TWO LOVE. 15, 2008) and Non-Patent Document 4 (Tanaka et al., Development of high-speed quantum cryptography communication system (2)-QKD in burst mode, 200 Year of Electronics, Information and Communication Engineers General Conference, B-10-60) there is.

JP-A-9-219680 JP-A-8-65252 JP-A-8-51412 JP-A-9-214440 Japanese Patent No. 3431515

As described in Patent Document 1, if a modulation element is provided in the ONU 104, the upstream signal light from the ONU 104 to the OLT 101 can be generated by reflecting the downstream signal light transmitted from the OLT 101. Therefore, it is not necessary to provide a light source on the ONU 104 side. However, the downstream signal light and the upstream signal light have the same wavelength. Therefore, the coherency between the downstream signal light and the upstream signal is increased. A part of the downstream signal light transmitted from the OLT 101 may be reflected on the transmission path between the OLT 101 and the ONU 104 and may enter the OLT 101 as reflected return light. The main origin of the reflected return light is, for example, a local reflection point such as Rayleigh scattering or a splice point in the entire transmission line. This return light is likely to interfere with the upstream signal light. As a result, coherent beat noise occurs in the upstream signal light received by the OLT 101, and the reception sensitivity of the upstream signal light deteriorates.

Accordingly, an object of the present invention is to provide an optical network bandwidth control apparatus and an optical network bandwidth control method that do not deteriorate the reception sensitivity of upstream signal light.

The bandwidth control apparatus for an optical network according to the present invention causes a light source provided at a first node to emit light during a predetermined period until time t0, and a second optical signal generated by the light source is transmitted through a transmission line to a second time. When a part of the first optical signal supplied to the node is reflected as a return light to the first node side in the transmission path, a parameter based on the state of the return light is used as an influence level. An influence measuring unit for measuring, a first relationship calculating unit for obtaining a relationship between an elapsed time from the time t0 and the degree of influence as a first relationship, and based on the first relationship, the first node and the first And a control unit for determining a time slot used for communication with the two nodes.

The center device of the optical network according to the present invention transmits an optical signal to the second node based on the bandwidth control device of the optical network and the time slot determined by the bandwidth control device of the optical network. A light source and a receiver for receiving an optical signal returned from the second node in a time slot determined by a bandwidth control device of the optical network.

An optical network system according to the present invention includes the optical network center apparatus and a user apparatus connected to the optical network center apparatus as the second node.

In the bandwidth control method for an optical network according to the present invention, a light source provided at a first node is caused to emit light during a predetermined period until time t0, and a first optical signal generated by the light source is transmitted via a transmission line. Supplying to two nodes, and when the first optical signal is reflected and modulated by the second node and received by the first node as a second optical signal, a signal included in the second optical signal Measuring an error rate; obtaining a relationship between an elapsed time from the time t0 and the error rate as a first relationship; and comparing the first relationship with a predetermined error rate threshold. Calculating the elapsed time such that the error rate is equal to or less than the error rate threshold as the first elapsed time t1, and communication between the first node and the second node based on the first elapsed time t1 And a step of determining the time slots used.

The optical network bandwidth control program according to the present invention is a program for realizing the above-described optical network bandwidth control method by a computer.

According to the present invention, there are provided an optical network bandwidth control device and an optical network bandwidth control method that do not deteriorate the reception sensitivity of uplink signals.

FIG. 1 is a configuration diagram showing an optical network. FIG. 2 is a configuration diagram illustrating the optical network system according to the first embodiment. FIG. 3A is a timing diagram showing time until the downstream optical signal reaches the OLT as the upstream optical signal. FIG. 3B is a graph showing the relationship between the output and the bit error rate. FIG. 3C is a graph showing the relationship between the output and the bit error rate. FIG. 4 is a configuration diagram illustrating the OLT according to the first embodiment. FIG. 5 is a flowchart illustrating the bandwidth control method according to the first embodiment. FIG. 6A is an explanatory diagram showing an initial time slot. FIG. 6B is an explanatory diagram showing the maximum time slot length. FIG. 7 is a timing chart showing time slots and light emission periods in the first embodiment. FIG. 8 is a functional block diagram showing the bandwidth control device. FIG. 9 is a timing chart showing the relationship between the light emission period and the time slot. FIG. 10 is a configuration diagram illustrating an OLT according to the second embodiment. FIG. 11 is a flowchart illustrating the bandwidth control method according to the second embodiment. FIG. 12 is a timing chart showing the relationship between time slots and light emission periods in the second embodiment.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic configuration diagram showing the optical network system 40 according to the present embodiment. The optical network system 40 includes a center device (OLT) 2 (first node), a transmission path (ODN) 3, and a plurality of ONUs 4 (second nodes). Each of the OLT 2 and the plurality of ONUs 4 is connected via the transmission path 3.

The transmission path 3 includes a wavelength multiplexing / demultiplexing filter 20 and a plurality of branch splitters 30, and these are connected by an optical fiber. The wavelength multiplexing / demultiplexing filter 20 is connected to the OLT 2. The plurality of branching splitters 30 are connected to the wavelength multiplexing / demultiplexing filter 20. A plurality of ONUs 4 are connected to one branching splitter 30.

The OLT 2 is configured to generate downstream signal light and to receive upstream signal light from each ONU 4. The OLT 2 can selectively emit each of a plurality of wavelengths.

Each ONU 4 is provided with a reflection modulator 17 and a signal source 18. The modulation signal source 18 generates a modulation signal s 42 including data to be transmitted to the OLT 2 side, and supplies the modulation signal s 42 to the reflection modulator 17. The reflection modulator 17 modulates the downstream signal light based on the modulation signal s42 and reflects it as upstream signal light.

In this optical network system 40, the OLT 2 generates downstream signal light during service operation. The generated downstream signal light is guided by the wavelength multiplexing / demultiplexing filter 20 to a specific branching splitter 30 according to the wavelength. The downstream signal light is further time-divided into a plurality of signal lights by the branching splitter 30 and supplied to each ONU 4. In each ONU 4, the reflection modulator 17 modulates the downstream signal light based on the modulation signal s42 and reflects it as upstream signal light. The upstream signal light is guided to the OLT 2 through a path opposite to that of the downstream signal light.

Here, when upstream signal lights from a plurality of ONUs 4 are sent to the OLT 2 at the same time, the OLT 2 cannot identify the upstream signal lights of the individual ONUs 4. Therefore, the OLT 2 performs a training process. Through the training processing, the light emission period (light emission period) of the downstream signal light and the reception period of the upstream signal light are determined as time slots for each of the plurality of wavelengths. In the following description, the light emission period of the downstream signal light may be described as a time slot during transmission, and the reception period of the upstream signal light may be described as a time slot during reception. During service operation, the OLT 2 communicates with each ONU 4 based on the set time slot.

Incidentally, part of the upstream signal light generated by the OLT 2 is reflected on the transmission path 3 and may return to the OLT 2 as return light. The wavelength of the return light is the same as the wavelength of the upstream signal light transmitted from the ONU 4. Therefore, the upstream signal light received by the OLT 2 is affected (reception sensitivity deterioration due to interference or the like). The influence of the return light on the upstream signal light depends on the elapsed time from the light emission end time in the OLT 2. This point will be described in detail with reference to FIG.

FIG. 3A (a) is a timing chart showing the timing from when the downstream signal light is generated by the OLT 2 to when the OLT 2 receives the upstream signal light. In FIG. 3A (a), the horizontal axis indicates time, and the vertical axis indicates the distance of ODN 3 connecting the OLT and the ONU. As shown in FIG. 3A (a), it is assumed that the OLT 2 emits light for a predetermined period until time t0 and the downstream signal light is transmitted. Further, it is assumed that the OLT 2 receives the upstream signal light after the time t0. The downstream signal light generated by the OLT 2 transmits the ODN 3 and reaches the ONU 4 while being attenuated by the loss at the ODN 3. Downstream signal light reaching the ONU 4 is modulated and reflected toward the OLT 2 as upstream signal light. The upstream signal light passes through the reverse path to the downstream signal light and reaches the OLT 2. Here, the time from when the downstream signal light is generated until it reaches the OLT 2 as upstream signal light is defined as the round trip time (RTT). Downstream signal light generated at the end of the light emission period (time t0) reaches OLT2 at time t2 after the passage of RTT from time t0. Since the upstream signal light is reflected light of the downstream signal light, it can be seen that the OLT 2 can receive the upstream signal light only in the time zone before time t2.

When the downstream signal light is transmitted through the ODN 3, return light in the upstream direction (OLT 2) is generated due to Rayleigh scattering of the entire ODN 3 or reflection at the splice point of the optical fiber. The return light also attenuates when passing through the ODN 3. The amount of return light attenuation depends on the distance from the OLT 2 to the reflection point.

Pay attention to the upstream signal light X incident on the OLT 2 immediately after time t0 (time tx). At time tx, in addition to the upstream signal light X, the return light X also enters the OLT 2. The return light X is the return light reflected in the range from the position Lx to the ONU 4 in the ODN 3. The return light reflected on the OLT 2 side from the position Lx enters the OLT 2 before the time tx and does not enter at the time tx. If the time tx is immediately after the time t0, the position Lx is close to the OLT2. That is, the light reflected at a position where the distance from the OLT 2 is short is included in the return light X. Therefore, the return light that does not attenuate so much enters the OLT 2, and the upstream signal light X is strongly influenced by the return light X.

In consideration of the above points, it can be seen that the upstream signal light may be received in a time zone having a long elapsed time from time t0 in order to reduce the influence of the return light.

FIG. 3A (b) is a graph showing the relationship between the elapsed time from time t0 and the reception sensitivity degradation (PP) of the upstream signal light. As shown in this graph, the reception sensitivity is greatly deteriorated immediately after time t0. However, the elapsed time from time t0 becomes longer and the reception sensitivity deterioration is reduced. FIG. 3B shows the relationship between the output (Power) and the bit error rate (BER) immediately after time t0 (time tx). FIG. 3C shows the relationship between the output and the bit error rate at time t2. Comparing FIG. 3B and FIG. 3C, the bit error rate (FIG. 3C) at time t2 is smaller. That is, it can be seen that the bit error rate decreases as the elapsed time from time t0 increases. The decrease in reception sensitivity degradation and bit error rate with time indicates that the influence of return light on upstream signal light decreases with the elapsed time from time t0.

FIG. 3A (b) shows a graph when only an optical fiber is used as ODN3. If the ODN 3 is provided with a wavelength multiplexing / demultiplexing filter, a branching splitter, or the like, it is expected that the reception sensitivity deterioration is gradually reduced due to a loss due to a branch or a loss at a splice point.

As shown in FIG. 3A (b), it is assumed that an acceptable level of reception sensitivity degradation is set to ρ. The time when the reception sensitivity deterioration becomes ρ is t1. In this case, during the period from time t1 to time t2, the OLT 2 can receive the upstream signal light at an acceptable level of reception sensitivity degradation. Further, in order to receive the upstream signal light during such a period, the light emission period of the OLT 2 is set to a time zone (“t1−RTT” to t0) that is RTT before the time zone (t1 to t2). You can see that

Therefore, in this embodiment, the OLT 2 determines the time slot in consideration of the points described with reference to FIGS. 3A to 3C. That is, the OLT 2 measures a parameter based on the state of the return light as an influence degree, obtains a relationship between the parameter and an elapsed time from the end of light emission, and determines a time slot based on the obtained relationship. Below, OLT2 is explained in full detail.

FIG. 4 is a block diagram showing the configuration of the OLT 2. In FIG. 4, for convenience of explanation, only one of the plurality of ONUs 4 is illustrated.

The OLT 2 includes a band control device 1, a light source 7, a directional branching filter 8, and a receiver 9.

The light source 7 is provided to generate downstream signal light. As the light source 7, a light source capable of emitting light at a plurality of wavelengths is used. The configuration and type of such a light source 7 are not particularly limited. For example, a variable wavelength laser diode can be used as the light source 7. Further, as the light source 7, a plurality of laser diodes and a mechanism for combining light output from the plurality of laser diodes may be used. Further, as the light source 7, a light source element that emits light including a plurality of wavelengths and a mechanism that selectively extracts wavelengths from light emitted from the light source element may be used.

The directional multiplexer / demultiplexer 8 guides the downstream signal light generated by the light source 7 to the ODN 3 side. The directional multiplexer / demultiplexer 8 guides the upstream signal light transmitted from the ODN 3 side to the receiver 9. As the directional multiplexer / demultiplexer 8, for example, an optical circulator, a directional coupler (optical coupler), or the like can be used.

The receiver 9 generates a reception signal s51 based on the upstream signal light received through the directional multiplexer / demultiplexer 8.

The bandwidth control device 1 is a device that determines a time slot for communication with each ONU 4. Specifically, the bandwidth control device 1 determines a period during which the light source 7 emits light as a time slot at the time of transmission. Further, the period during which the receiver 9 receives the upstream signal light is determined as a time slot at the time of reception.

The band control device 1 includes a light emission control unit 6, a timer unit 10, an RTT (round trip time) measurement unit 11, an influence degree measurement unit 12, a first relationship calculation unit 13, a comparison unit 14, and a threshold storage. A unit 15 and a control unit 16 are provided. Among these, the light emission control unit 6, the timer unit 10, the RTT measurement unit 11, the influence degree measurement unit 12, the first relationship calculation unit 13, and the comparison unit 14 are stored in a storage device such as a ROM (Read only memory), for example. It can be realized by the bandwidth control program. In this case, the bandwidth control program can be installed in a ROM or the like from a storage medium such as a CD-ROM. On the other hand, the threshold storage unit 15 can be realized by a storage device such as a hard disk or a RAM (Random access memory).

FIG. 5 is a flowchart showing the operation of the bandwidth control device 1. The bandwidth control device 1 determines a time slot according to the procedure shown in FIG.

Step S10: Generation of RTT Measurement Downstream Signal Light When the band control process (training) is started, the light emission control unit 6 first supplies the light emission signal s1 to the light source 7 to generate the RTT measurement downstream signal light. In addition, the light emission control unit 6 generates the RTT measurement downlink signal light and simultaneously notifies the timer unit 10 to that effect. The timer unit 10 counts an elapsed time after the RTT measurement downlink signal light is generated. The downstream signal light for RTT measurement generated by the light source 7 is supplied to the ONU 4 via the ODN 3. The ONU 4 reflects the downstream signal light for RTT measurement to the OLT 2 as the upstream signal light for RTT measurement by the reflection modulation unit 17. The upstream signal light for RTT measurement that has reached the OLT 2 is received by the receiver 9. The receiver 9 notifies the RTT measurement unit 11 of the RTT measurement upstream signal light as the reception signal s51.

Step S20: Measurement of RTT The RTT measurement unit 11 refers to the timer unit 10 to generate a time from when the RTT measurement downlink signal light is generated until the receiver 9 receives the RTT measurement uplink signal light. Is calculated as the round trip time (RTT). The RTT can be measured, for example, from the time difference between the leading edge of the downstream signal light for RTT measurement and the leading edge of the upstream signal light for RTT measurement. In addition, when the RTT measurement downlink signal light is generated for a sufficiently short period in step S10, the RTT can be measured simply by measuring the reception time of the RTT measurement uplink signal light.

Step S30; Determination of Initial Time Slot Subsequently, the control unit 16 determines an initial time slot. FIG. 6A is an explanatory diagram for explaining an initial time slot. As shown in FIG. 6A, the control unit 16 sets the length of the time slot at the time of transmission (the length of the initial light emission period) to RTT. Further, the control unit 16 sets a period from the light emission end time t0 to the time after the RTT has elapsed (time t2) as a time slot at the time of reception.

Step S40: Generation of First Signal Light Subsequently, the light emission control unit 6 supplies the light emission signal s1 to the light source 7 according to the set initial time slot. The light source 7 generates the first signal light. Further, the light emission control unit 6 notifies the timer unit 10 that the light emission has ended when the light emission ends. The timer unit 10 counts the elapsed time from the light emission end time (t0). The first signal light generated by the light source 7 is supplied to the ONU 4 via the ODN 3. The signal source 18 of the ONU 4 is configured to generate a signal including a code pattern for reception error rate measurement as the modulation signal s42 during training. As the code pattern, for example, an 8B / 10B code pattern, a 64B / 66B code idle pattern, and a delimiter pattern can be used. The reflection modulation unit 17 modulates the first signal light based on the modulation signal s42 and reflects it as the second signal light. The second signal light is supplied to the OLT 2 via the ODN 3.

Step S50: Measurement of reception error rate In the OLT 2, the receiver 9 performs reception according to the initial time slot, and acquires the second optical signal. The receiver 9 supplies the acquired second optical signal to the error rate measuring unit 12 as a received signal s51. The error rate measuring unit 12 measures the reception error rate of the second optical signal. This reception error rate is a parameter based on the state of the return light as in the case of the bit error rate and reception sensitivity degradation described in FIGS. If the influence of the return light is large, the reception error rate of the second optical signal is also large. The error rate measurement unit 12 notifies the calculation result to the first relationship calculation unit 13.

Step S60: Calculation of First Relationship Subsequently, the first relationship calculation unit 13 refers to the timer unit 10 to obtain the relationship between the elapsed time from the time t0 and the reception error rate as the first relationship.

Step S70: Comparison Subsequently, the comparison unit 14 compares the first relationship with a reception error rate threshold value stored in advance in the threshold value storage unit 15. Since the reception error rate indicates the influence of the return light, it should decrease with the elapsed time from time t0. Therefore, the comparison unit 14 obtains the elapsed time such that the reception error rate becomes the reception error rate threshold. The comparison unit 14 notifies the control unit 6 of the obtained elapsed time as the first elapsed time t1.

Step S80; Determination of Maximum Time Slot Length Thereafter, as shown in FIG. 6B, the control unit 6 determines the difference between the first elapsed time t1 and the RTT as the maximum time slot length. This maximum time slot length indicates the maximum length of a time slot for receiving an upstream optical signal of one wavelength.

Step S90: Time Slot Assignment As shown in FIG. 2, downlink signal light of one wavelength is time-divided and supplied to a plurality of ONUs 4. Therefore, the control unit 6 determines the length of the time zone T (ONU) used for communication with each ONU 4 so as not to exceed the maximum time slot length for each of the plurality of wavelengths. This determines the final time slot length for one wavelength. The length of the time zone T (ONU) is, for example, MPCP (multi-point control protocol) defined in IEEE 802.3ah-2004-64 Multi-point MAC Control-64.3, and ITU-TG. It can be determined using a band allocation method such as PLOAM defined in 983.1-8.3.8 MESSAGES in the PLOAM channel. As a result of the time zone T (ONU) assigned to each ONU 4, the final time slot length of one wavelength may be shorter than the maximum time slot length. In addition, the final time slot length may be different among a plurality of wavelengths.

The control unit 6 further assigns a time slot at the time of reception for each wavelength with the determined final time slot length. At this time, the time slot at the time of reception is assigned so as not to overlap between a plurality of wavelengths. Further, the control unit 6 assigns a time slot (light emission period) at the time of transmission based on the assigned time slot at the time of reception. The time slot for transmission is assigned by subtracting RTT from the time slot for reception. If the time slot allocated in this way is used, the OLT 2 can receive an upstream optical signal with a reception error rate equal to or less than a reception error rate threshold.

FIG. 7 is a timing diagram showing a state in which a time slot is assigned. As shown in FIG. 7, the control unit 6 assigns the time slots (T1 to Tn) at the time of reception so as not to overlap each other for the plurality of wavelengths (λ1 to λn). Further, the control unit 6 assigns time slots (A1 to An) at the time of transmission for each of a plurality of wavelengths (λ1 to λn). In addition, communication time zones (Tn−1 to Tn−m) for individual ONUs 4 are allocated in the time slots at the time of transmission of the respective wavelengths. The time slot (A1 to An) at the time of transmission is a time zone that is RTT before the time slot (T1 to Tn) at the time of reception. If the RTT is constant among a plurality of wavelengths, the time slots (A1 to An) at the time of transmission are assigned without overlapping.

Through the above steps S10 to S90, time slots are assigned and the training process is terminated. During service operation, downlink signal light is generated and uplink signal light is received according to the assigned time slot. At each wavelength, the upstream signal light is received in a time zone in which the reception error rate is equal to or less than the reception error rate threshold. Accordingly, it is possible to suppress deterioration in reception sensitivity of upstream signal light. In addition, since the OLT 2 can continuously emit light while switching the wavelength, the number of ONUs 2 can be expanded.

In step S70 described above, there is a case where it is already smaller than the reception error rate threshold at the stage of time t0. In this case, the elapsed time when the actual reception error rate becomes the reception error rate threshold cannot be defined. In such a case, a length equal to RTT is set as the maximum time slot length.

In addition, in order to improve the accuracy of the first elapsed time t1 obtained in step S70 described above, it is possible to use the average value of the reception error rate. That is, by repeating the process up to step S60 many times, the relationship between the average value of the reception error rate and the elapsed time can be used as the first relationship.

In step S90 described above, the control unit 6 assigns the time slot of wavelength λ1 again after assigning the time slot of wavelength λn. At this time, it is preferable to set a length of 2 × RTT or more as the interval between time slots of the same wavelength (see “T1 to T1” in FIG. 7). Thereby, it is possible to prevent the reception sensitivity from being deteriorated due to the return light from the repeated downstream signal light.

Further, in the present embodiment, a case has been described in which time slots are allocated independently of the operation prior to the actual operation. However, when the reception error rate is sufficiently small, the time slot can be determined in parallel with the service operation.

In this embodiment, a reception error rate is adopted as a parameter based on the state of the return light. However, it is also possible to employ parameters other than the reception error rate as parameters based on the return light state. For example, instead of the reception error rate, the intensity of the return light may be employed. FIG. 8 is a functional block diagram showing the configuration of the band control device 1 when the intensity of the return light is adopted instead of the reception error rate. In the example shown in FIG. 8, an OTDR (Optical Time Domain Reflectometer) is provided as the first relationship measuring unit 13. One end of the OTDR is connected between the light source 7 and the directional multiplexer / demultiplexer 8, and the other end is connected between the directional multiplexer / demultiplexer 8 and the receiver 9. The OTDR detects that light is generated by the light source 7 at one end, and measures the intensity of the return light at the other end. The OTDR itself has a timer function, and measures the relationship between the elapsed time after the light is generated by the light source 7 and the intensity of the return light. That is, the first relationship can be measured.

Further, as described in FIGS. 3A to 3C, reception sensitivity deterioration (PP value) may be adopted as a parameter based on the state of the return light. However, when reception sensitivity deterioration (PP value) is adopted, it is necessary to prepare ODN3 that does not generate beat noise as a reference for measuring the PP value, which is difficult in practice.

Further, in this embodiment, each ONU 4 is configured to generate a signal including a code pattern for reception error rate measurement as the modulation signal s42. Here, it is preferable that a code pattern known on the OLT 2 side is used as a code pattern for reception error rate measurement. If the code pattern for reception error rate measurement is known on the OLT 2 side, it is not necessary to use a frame structure including a delimiter as the code pattern, and the reception error rate can be easily measured in step S50.

(Second Embodiment)
Subsequently, a second embodiment of the present invention will be described. In the first embodiment, it is assumed that the RTT is the same among a plurality of wavelengths. However, the RTT may be different between a plurality of wavelengths. For example, if the distance from the wavelength demultiplexing filter 31 to each ONU 4 is different, the RTT may be different. Further, the transmission line loss may be different between a plurality of wavelengths. As a result, the influence of error rate degradation due to beat noise may also differ for each wavelength. That is, the degree of influence of the return light on the upstream signal may differ between a plurality of wavelengths. In such a case, if time slots are assigned on the assumption that the RTT is the same, the timing at which the upstream optical signal is actually incident on the OLT 2 may overlap among a plurality of wavelengths.

FIG. 9 is a timing diagram showing an example in which upstream optical signals overlap between a plurality of wavelengths. As shown in this figure, it is assumed that the ONU 4 (λ2) to which the wavelength λ2 is assigned is longer than the ONU 4 (λ1, λ3) to which the wavelengths λ1 and λ3 are assigned. Further, as the RTT, it is assumed that the time for light to reciprocate between the OLT 2 and the ONU 4 (λ1, λ3) is used. Then, it is assumed that time slots are allocated according to the first embodiment. In this case, paying attention to the time slot of wavelength λ2, the assigned time slot T2 deviates from the time zone T2 ^* where the upstream signal light of wavelength λ2 is actually incident on OLT2. As a result, the time zone T2 ^* overlaps with the time slot T3 with the wavelength λ3, and the upstream optical signals with the wavelengths λ2 and λ3 enter the OLT 2 at the same time. If the receiver 9 does not have a wavelength separation function, it is impossible to separate and receive upstream signal lights having different wavelengths incident on the OLT at the same time. In order to avoid such collision of upstream optical signals, it is conceivable to obtain RTT with reference to ONU 4 (λ2) having the longest ODN 3 distance. However, in this case, the time slot interval between different wavelengths becomes unnecessarily long, leading to a decrease in the reception band.

Therefore, in the present embodiment, even if the RTT is different among a plurality of wavelengths, the device is devised so that the time slot is appropriately set.

FIG. 10 is a configuration diagram showing the configuration of the OLT 2 according to the present embodiment. In the present embodiment, the light source 7 includes a plurality of light source elements (7-1 to 7-n) so that each of the plurality of wavelengths (λ1 to λn) can emit light independently. Further, the light source 7 is provided with a wavelength multiplexing filter 19 (WDM) so that light generated by the plurality of light source elements (7-1 to 7-n) is superimposed and guided to the directional demultiplexer. Yes. The light emission control unit 6 (6-1 to 6-n) is configured to control each of the plurality of light source elements (7-1 to 7-n) independently. Further, the RTT measurement unit 62 is configured to measure the RTT for each of a plurality of wavelengths. The first relationship calculation unit 13 is also configured to measure the first relationship for each of a plurality of wavelengths. The threshold storage unit 15 is set with a reception error rate threshold for each of a plurality of wavelengths. Since other configurations can be the same as those of the first embodiment, detailed description thereof is omitted.

FIG. 11 is a flowchart showing the operation of the bandwidth control device 1 according to the present embodiment. As shown in FIG. 11, in the present embodiment, the processing from step S10 to step S80 in the first embodiment is executed for each of a plurality of wavelengths (λ1 to λn). Accordingly, the RTT and the maximum time slot length are obtained for each of the plurality of wavelengths (λ1 to λn).

In step S90, the control unit 6 assigns the time slots at the time of reception so as not to overlap for each of the plurality of wavelengths (λ1 to λn). Then, based on the assigned reception time slot, the transmission time slot is assigned.

FIG. 12 is a timing chart showing how time slots are assigned in the present embodiment. As shown in FIG. 11, the time slot T1 at the time of receiving the wavelength λ1 is assigned to the period from time t1s to time t1e. A time slot T2 at the time of receiving the wavelength λ2 is assigned to a period from time t2s to time t2e. A time slot T3 at the time of receiving the wavelength λ3 is assigned to a period from time t3s to time t3e. A time slot Tn at the time of reception of the wavelength λn is assigned to a period from time tns to time tne. The time slots T1 to Tn at the time of reception are assigned so as not to overlap in time. On the other hand, each RTT of a plurality of wavelengths (λ1 to λn) is obtained separately as RTT1 to RTTn. The time slot A (λ1) at the time of transmission of the wavelength λ1 is assigned to a period from “t1s-RTT1 to t1e-RTT1”. The time slot A (λ2) at the time of transmission of the wavelength λ2 is assigned to a period from “t2s-RTT2 to t2e-RTT2”. The time slot A (λ3) at the time of transmission of the wavelength λ3 is assigned to a period from “t3s-RTT3 to t3e-RTT3”. The time slot A (λn) at the time of transmission of the wavelength λn is assigned to a period from “tns-RTTn to tne-RTTn”. In order to set the time slot length of each wavelength, information on the required bandwidth of the wavelength group in which the bandwidth required by each ONU is bundled is required. This process is given as requested bandwidth information. However, the means for collecting requested bandwidth information and the bandwidth distribution method are not related to the gist of the present embodiment, and thus description thereof is omitted.

The time slot at the time of transmission may overlap at different wavelengths. However, in this embodiment, since the light source 7 emits light of a plurality of wavelengths independently, there is no problem. In addition, the time slot at the time of reception coincides with the time zone in which the upstream optical signal actually reaches the OLT 2. Therefore, even if the RTT is different among a plurality of wavelengths, uplink signals having different wavelengths do not reach the OLT 2 at the same time. Further, since the light emission periods may overlap between a plurality of wavelengths, time slots can be assigned so that the bandwidth can be utilized to the maximum.

This application is based on Japanese Patent Application No. 2008-308014 filed on Dec. 2, 2008, claiming the benefit of priority from that application, the disclosure of that application should be cited Is incorporated here as it is.

Claims

A light emission control unit for causing a light source provided in the first node to emit light in a predetermined period until time t0 and supplying a first optical signal generated by the light source to the second node via a transmission line;
An influence measuring unit that measures, as an influence, a parameter based on a state of the return light when a part of the first optical signal is reflected as return light to the first node side in the transmission path;
A first relationship calculation unit for obtaining a relationship between an elapsed time from the time t0 and the influence level as a first relationship;
A control unit for determining a time slot used for communication between the first node and the second node based on the first relationship;
An optical network bandwidth control apparatus comprising:
An optical network bandwidth control device according to claim 1,
The influence measuring unit reflects and modulates the first optical signal by the second node, and receives the second optical signal as the second optical signal as the influence by the second optical signal. An optical network bandwidth controller that measures the reception error rate.
An optical network bandwidth control device according to claim 2, comprising:
The influence level measuring unit measures the reception error rate by using any one of 8B / 10B code, 64B / 66B code code violation frequency, and error correction code correction frequency.
An optical network bandwidth control device according to claim 1,
The influence degree measurement unit is a bandwidth control device for an optical network that measures the intensity of the return light as the influence degree.
An optical network bandwidth control device according to any one of claims 1 to 4,
Furthermore,
An RTT measurement unit that measures a time from when light is generated by the light source to when the light is reflected by the second node and received by the first node as a round trip time;
A comparison unit that calculates the elapsed time at which the error rate becomes the influence threshold by comparing the first relationship with a predetermined influence threshold, as a first elapsed time t1;
Comprising
The control unit is an optical network bandwidth control apparatus that determines the time slot based on a difference between the round trip time and the first elapsed time t1.
An optical network bandwidth control device according to claim 5, comprising:
The light source can emit light of a plurality of wavelengths,
The transmission path includes a wavelength multiplexing / demultiplexing filter that receives light generated at the first node and outputs each of a plurality of wavelengths in different directions,
The second node is a band control device for an optical network in which a plurality of the second nodes are connected so that light of different wavelengths is supplied to the wavelength multiplexing / demultiplexing filter.
An optical network bandwidth control device according to claim 6, comprising:
The transmission line further includes an optical branching element provided between a wavelength multiplexing / demultiplexing filter and each of the second nodes,
An optical network bandwidth control device in which a plurality of the second nodes are connected to the optical branching element.
An optical network bandwidth control device according to claim 7, comprising:
The control unit is an optical network that determines a time zone used for communication with each of the second nodes by one of MPCP (multi-point control protocol) and PLOAM (physical layer operations administration and maintenance). Bandwidth control device.
An optical network bandwidth control device according to any one of claims 6 to 8,
The first relationship calculation unit calculates the first relationship for each of the plurality of wavelengths,
The said control part is a zone | band control apparatus of the optical network which determines the said time slot separately about each of these wavelengths based on the said 1st relationship about each of these wavelengths.
An optical network bandwidth control device according to claim 9,
The said control part is the zone | band control apparatus of the optical network which sets the space | interval of the said time slot in each said wavelength more than twice the said round trip time.
A bandwidth control device for an optical network according to claim 9 or 10, comprising:
The RTT measurement unit measures the round trip time for each of the plurality of wavelengths,
The said control part is a zone | band control apparatus of the optical network which determines the said time slot so that the reception time zone may not overlap between these wavelengths based on each of the round trip time of these wavelengths.
An optical network bandwidth control device according to claim 11, comprising:
The light source includes a plurality of laser diodes that emit light having different wavelengths,
The said control part is a zone | band control apparatus of the optical network which determines the said time slot irrespective of whether the light emission period in the said light source overlaps temporally between these wavelengths.
A bandwidth control device for an optical network according to any one of claims 1 to 12,
A light source that transmits an optical signal toward the second node based on the time slot;
A receiver for receiving an optical signal returned from the second node based on the time slot;
An optical network center device.
An optical network center device according to claim 13,
A user device connected as a second node to a center device of the optical network;
An optical network system comprising:
Causing the light source provided at the first node to emit light during a predetermined period until time t0, and supplying the first optical signal generated by the light source to the second node via a transmission line;
Measuring a parameter based on a state of the return light as an influence when a part of the first optical signal is reflected as return light to the first node side in the transmission path;
Obtaining a relationship between an elapsed time from the time t0 and the degree of influence as a first relationship;
Determining a time slot to be used for communication between the first node and the second node based on the first relationship;
An optical network bandwidth control method comprising:
An optical network bandwidth control program for realizing the optical network bandwidth control method described in claim 15 by a computer.