JP2011114667A - Pon system and station side device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably transmit an uplink optical signal even when transmission speed is accelerated. <P>SOLUTION: In the PON (Passive Optical Network) system, an OLT 12 and a plurality of ONUs are mutually connected using an optical fiber branched by an optical splitter. The OLT includes: a light-receiving element 34 which receives a burst optical signal string to which a burst optical signal outputted from each ONU is multiplexed; an amplitude level adjustment part 36 which detects a received light level for each burst optical signal; and an output light level request part 40 which requests an output light level to each ONU so that received light level difference of an adjacent burst optical signal becomes a predetermined reference value or lower based on the received light level for each burst optical signal. The ONU includes an output light level control part which controls a light level of the burst optical signal to be transmitted according to a request from the output light level request part 40. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a PON system in which a station side device and a plurality of subscriber side devices are connected to each other using an optical fiber branched by an optical splitter.

  2. Description of the Related Art Conventionally, a passive optical network (PON) system is known as a subscriber optical fiber network system for subscriber homes such as ordinary homes. In this PON system, one optical fiber connected to a station side device (OLT: Optical Line Terminal) is branched by an optical splitter and connected to a plurality of subscriber side devices (ONU: Optical Network Unit). This is an optical transmission system in which a user shares one optical fiber (see, for example, Patent Document 1).

  In the PON system, the upstream burst optical signal from each ONU is multiplexed by the TDMA (Time Division Multiple Access) method and received by the OLT as a burst optical signal sequence. In general, since the distance from each ONU to the OLT is different in the PON system, the OLT must receive burst optical signal trains having different received light levels. Therefore, the OLT optical receiver needs to have a wide dynamic range in order to appropriately receive such a burst optical signal train.

JP 2007-173908 A

  Incidentally, with the recent increase in communication traffic, the transmission speed of the PON system has been increased. For example, IEEE 802.3av standardizes a PON system having a transmission rate of 10 Gbps.

  However, it is not easy to design an optical receiver with a wide dynamic range corresponding to a high-speed optical signal such as 10 Gbps. When the dynamic range of the optical receiver is narrowed, the received signal cannot be properly identified and reproduced, and transmission characteristics such as a code error rate deteriorate.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a PON system and a station-side apparatus that can preferably transmit an upstream optical signal even when the transmission speed is increased. .

  In order to solve the above problems, a PON system according to an aspect of the present invention is a PON system in which a station-side device and a plurality of subscriber-side devices are connected to each other using an optical fiber branched by an optical splitter. The station side device includes an optical receiving unit that receives a burst optical signal sequence in which burst optical signals output from each subscriber side device are multiplexed, a detection unit that detects a received optical level for each burst optical signal, An output light level requesting unit that requests an output light level from each subscriber-side device based on a received light level for each burst light signal so that a difference between received light levels of adjacent burst light signals is a predetermined reference value or less; Is provided. The subscriber side device includes an output light level control unit that controls the light level of the burst optical signal to be transmitted in response to a request from the output light level request unit.

  According to this aspect, by performing output optical level control, the optical level difference of the burst optical signal received by the optical receiver of the station side device is reduced, so that the optical receiver is not required to have a very wide dynamic range. As a result, an upstream optical signal can be suitably transmitted even when the transmission speed is increased.

  The output light level requesting unit may request each subscriber-side device for the output light level so that the received light levels of adjacent burst optical signals are substantially equal.

  The output light level requesting unit may request the output light level from the subscriber side device every time a new subscriber side device is connected to the station side device.

  When a new subscriber-side device is connected to the station-side device, the output optical level request unit is configured so that the received optical level of the burst optical signal from the new subscriber-side device is first connected to the station-side device. The output light level may be requested from the new subscriber side device so as to approach the reception light level of the burst optical signal from the one subscriber side device.

  The output optical level request unit calculates an average received optical level of burst optical signals from all the subscriber side devices including the new subscriber side device when a new subscriber side device is connected to the station side device. The output light level may be requested from each subscriber unit so that the received light level of each burst optical signal approaches the average received light level.

  The output optical level request unit is adjacent to the burst optical signal from the new subscriber side device when the burst optical signal of the output optical level required by the new subscriber side device connected to the station side device cannot be transmitted. A subscriber-side apparatus that transmits a burst optical signal may be requested to reduce the output optical level.

  The output light level requesting unit may request the output light level from each subscriber apparatus periodically at a predetermined time interval.

  The output light level requesting unit may request the output light level from each subscriber-side device according to an instruction from the outside.

  The station-side apparatus further includes a code error rate measurement unit that measures the code error rate of the received burst optical signal, and the output optical level request unit includes the measured code in addition to the received optical level for each burst optical signal. The output light level required for each subscriber-side apparatus may be determined with reference to the error rate.

  The output light level control unit of the subscriber side device may transmit information on the light level range that can be output by itself to the station side device.

  The output light level control between the station side device and the subscriber side device may be performed using an Organization specific OAM frame.

  When a new subscriber-side device is connected to the station-side device, the output optical level requesting unit determines whether or not the subscriber-side device supports output optical level control, and the corresponding subscriber The output light level may be requested only from the side device.

  The output light level request unit may determine whether or not the new subscriber side apparatus supports the output light level control by referring to the OAM Version, Revision, or Vender Specific info in the Information OAM PDU frame. .

  When a new subscriber-side device is connected to the station-side device, main signal communication may be started after an output light level control sequence is performed between the station-side device and the subscriber-side device.

  It may be possible to select whether or not to perform an output light level control sequence between the station side device and the subscriber side device.

  Another aspect of the present invention is a station-side device. This device is a station-side device of a PON system that is connected to each other using a plurality of subscriber-side devices and optical fibers branched by an optical splitter, and burst optical signals output from each subscriber-side device are multiplexed. An optical receiver that receives the burst optical signal sequence, a detector that detects the received optical level for each burst optical signal, and reception of adjacent burst optical signals based on the received optical level for each burst optical signal An output light level requesting unit that requests each subscriber side device for an output light level so that the light level difference is equal to or less than a predetermined reference value.

  According to this aspect, by performing output optical level control, the optical level difference of the burst optical signal received by the optical receiver of the station side device is reduced, so that the optical receiver is not required to have a very wide dynamic range. As a result, an upstream optical signal can be suitably received even when the transmission rate is increased.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between an apparatus, method, system, program, recording medium storing the program, etc. are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where transmission speed is increased, the PON system and station side apparatus which can transmit an upstream optical signal suitably can be provided.

It is a figure which shows the PON system which concerns on embodiment of this invention. It is a figure for demonstrating the signal transmission of the up direction in a PON system. It is a figure which shows the structural example of the optical receiver in the conventional OLT. It is a figure which shows an example of the code error rate characteristic in the conventional PON system. It is a figure for demonstrating the output light level control in the PON system which concerns on embodiment of this invention. It is a figure which shows the structure of OLT which concerns on this embodiment. It is a figure which shows the structure of ONU which concerns on this embodiment. IEEE. It is a figure which shows the frame structure of Organizational specific OAM of GE-PON prescribed | regulated by 802.3. It is a figure which shows the output light level control information which OLT transmits with respect to each ONU. It is a figure which shows the output light level control information which each ONU transmits with respect to OLT. IEEE. It is a figure which shows the frame structure of the Information OAMPDU of GE-PON prescribed | regulated by 802.3. FIGS. 12A and 12B are diagrams for explaining an example of the output light level control when a new ONU is connected to the OLT. FIGS. 13A and 13B are diagrams for explaining another example of output light level control when a new ONU is connected to the OLT. FIGS. 14A to 14C are diagrams for explaining another example of output light level control when a new ONU is connected to the OLT. It is a figure for demonstrating OLT which concerns on another embodiment of this invention. It is a figure which shows the control sequence until main signal communication is started after ONU is connected to OLT. It is a figure for demonstrating an output light level control sequence in detail.

  FIG. 1 is a diagram showing a PON system 10 according to an embodiment of the present invention. As shown in FIG. 1, in the PON system 10, one backbone optical fiber 18 connected to a station side device (OLT) 12 is branched into a plurality of branched optical fibers 20-1 to 20-n by an optical splitter 14. A plurality of subscriber units (ONU) 16-1 to 16-n are connected to the ends of the branch optical fibers 20-1 to 20-n.

  In the PON system 10, the downstream optical signal from the OLT 12 to each of the ONUs 16-1 to 16-n is a continuous optical signal multiplexed by time division multiplexing (TDM: Time Division Multiplexing). On the other hand, upstream optical signals from the ONUs 16-1 to 16-n to the OLT 12 are multiplexed by the TDMA method. In TDMA, in order to prevent the optical signals from the ONUs 16-1 to 16-n from colliding, a non-signal period called a guard time is inserted between the optical signals. Therefore, unlike the downstream optical signal from the OLT to each ONU becomes a continuous optical signal, the upstream optical signal from the ONU 16-1 to 16-n to the OLT 12 is in a burst state in which signal transmission is performed intermittently. This is an optical signal.

  FIG. 2 is a diagram for explaining uplink signal transmission in the PON system 10. FIG. 2 shows a state in which burst optical signals 22-1 to 22-n transmitted from the respective ONUs 16-1 to 16-n are multiplexed by the optical splitter 14 and input to the OLT 12 as a burst optical signal train. Yes.

  In the PON system 10, since the distances of the branch optical fibers 20-1 to 20-n are different for each of the ONUs 16-1 to 16-n, a burst optical signal sequence having a different optical level for each burst optical signal is input to the OLT 12. Is done. Therefore, the OLT 12 of the PON system 10 is required to have an optical reception characteristic with a very wide dynamic range.

  FIG. 3 is a diagram illustrating a configuration example of an optical receiving unit in a conventional OLT. As shown in FIG. 3, the OLT 12 includes an O / E conversion unit 30 that performs O / E conversion on a received optical signal, and a digital signal processing unit 32 that performs predetermined digital processing on the O / E converted electrical signal. . The O / E conversion unit 30 includes a light receiving element 34, an amplitude level adjustment unit 36, and a CLK extraction unit 38.

  As shown in FIG. 3, the light receiving element 34 receives a burst optical signal sequence having a different light level for each burst signal. The light receiving element 34 converts the input burst optical signal sequence into an electric signal. This electrical signal may be a current signal or a voltage signal. This electrical signal is a burst signal sequence in which a plurality of burst signals having different amplitude levels are multiplexed.

  The amplitude level adjustment unit 36 has a function of adjusting each burst signal so as to have a constant amplitude level. The amplitude level adjusting unit 36 detects, for example, the peak value or average value of each input burst signal, and performs feedback control for switching the gain of the amplifier according to the peak value or average value.

  The CLK extraction unit 38 extracts a clock from a burst signal sequence having a constant amplitude level, and then performs identification reproduction of the burst signal sequence. The burst signal sequence identified and reproduced by the CLK extraction unit 38 is subjected to predetermined digital signal processing by the digital signal processing unit 32. As described above, the conventional OLT 12 is configured so that the CLK extraction unit 38 can appropriately perform identification reproduction by making the amplitude level of each burst signal constant by the amplitude level adjustment unit 36.

  In the amplitude level adjusting unit 36 as described above, a predetermined time is always required to detect the peak value or average value of each burst signal, and a delay time of feedback control occurs. Therefore, when the transmission speed of the PON system is increased to 10 Gbps or the like, it is not easy to develop an amplitude adjustment circuit that operates following a high-speed signal such as 10 Gbps. If the operation of the amplitude level adjustment unit 36 cannot follow the input burst optical signal string, the CLK extraction unit 38 cannot properly perform identification and reproduction, and transmission characteristics such as a code error rate deteriorate.

  FIG. 4 is a diagram illustrating an example of a code error rate characteristic in a conventional PON system. The vertical axis in FIG. 4 represents the code error rate, and the horizontal axis represents the level difference (dB) between adjacent burst optical signals. As shown in FIG. 4, it can be seen that the code error rate characteristics rapidly deteriorate as the level difference between burst optical signals increases.

  Also, if the idle signal provided at the head of each burst optical signal is set long, it may be possible to cope with a high transmission rate. However, in this case, the section for sending the main signal data is deleted, Bandwidth will drop.

  FIG. 5 is a diagram for explaining output light level control in the PON system 10 according to the embodiment of the present invention. In order to solve the above-described problems, in the PON system 10 according to the present embodiment, the OLT 12 controls the optical level of the burst optical signal output from each ONU 16-1 to 16-n. In this output light level control, the output light levels of the ONUs 16-1 to 16-n are controlled so that the received light levels of adjacent burst optical signals are substantially equal. An “adjacent burst optical signal” is a burst optical signal that is adjacent in time series in a burst optical signal sequence in which burst optical signals are multiplexed by TDMA. For example, in the burst optical signal sequence shown in FIG. 2, burst optical signals adjacent to the burst optical signal 22-2 are burst optical signals 22-1 and 22-3 positioned before and after the burst optical signal 22-2.

  By performing such output optical level control, the optical level of the upstream burst optical signal received by the optical receiver of the OLT 12 becomes substantially constant. Therefore, the amplitude level adjuster of the OLT 12 follows even when the transmission speed increases. Thus, the CLK extraction unit can appropriately perform identification reproduction.

  FIG. 6 is a diagram illustrating a configuration of the OLT 12 according to the present embodiment. In the OLT 12 shown in FIG. 6, the same or corresponding components as those in the OLT shown in FIG.

  The OLT 12 according to the present embodiment is connected to an O / E conversion unit 30 that converts an upstream burst optical signal sequence from the ONU into an electrical signal, a digital signal processing unit 32 that performs predetermined PON termination processing, and a subsequent stage of the OLT 12. The terminal side signal processing unit 42 that communicates with a predetermined terminal device, the E / O conversion unit 44 that transmits a downstream optical signal to the ONU, and the operations of the digital signal processing unit 32 and the terminal side signal processing unit 42 are controlled. And a control monitoring unit 46 for monitoring.

  As shown in FIG. 6, the O / E conversion unit 30 includes a light receiving element 34, an amplitude level adjustment unit 36, and a CLK extraction unit 38. The burst optical signal sequence input to the light receiving element 34 is converted into an electric signal and then input to the amplitude level adjustment unit 36. The amplitude level adjustment unit 36 detects the peak value or average value of each input burst signal, and performs feedback control to switch the gain of the amplifier according to the peak value or average value. Adjust to the amplitude level. Each burst signal adjusted to a constant amplitude level is identified and reproduced by the CLK extraction unit 38. Further, the amplitude level adjustment unit 36 outputs the detected peak value or average value for each burst signal to the digital signal processing unit 32 as optical reception level information.

  In the present embodiment, the digital signal processing unit 32 includes an output light level requesting unit 40. The output light level requesting unit 40 requests the light level to be output to each ONU based on the received light level for each burst optical signal so that the received light levels of adjacent burst optical signals are substantially equal. The output light level request from the output light level request unit 40 is set in a predetermined data frame by the digital signal processing unit 32, converted into an optical signal by the E / O conversion unit 44, and then transmitted to each ONU. The The upstream burst optical signal train and downstream optical signal are wavelength-division multiplexed by an optical coupler (not shown) and transmitted through a single backbone optical fiber.

  FIG. 7 is a diagram illustrating a configuration of the ONU 16 according to the present embodiment. As shown in FIG. 7, the ONU 16 includes an E / O conversion unit 70 that outputs an upstream burst optical signal toward the OLT, an O / E conversion unit 72 that converts a downstream optical signal from the OLT into an electrical signal, and a predetermined number. Operation of the digital signal processing unit 74 that performs the PON termination processing, the terminal-side signal processing unit 76 that communicates with a predetermined terminal device connected to the subsequent stage of the ONU 16, and the operations of the digital signal processing unit 74 and the terminal-side signal processing unit 76 And a control monitoring unit 78 for controlling and monitoring.

  In the present embodiment, the digital signal processing unit 74 includes an output light level request receiving unit 82. The output light level request receiving unit 82 receives the output light level request transmitted from the OLT. This output light level request is sent to the output light level control unit 80 of the E / O conversion unit 70. The output optical level controller 80 controls the optical level of the burst optical signal transmitted from the E / O converter 70 to be the optical level requested from the OLT. As a result, the optical level of each burst optical signal received by the OLT becomes substantially constant, so that the amplitude level adjustment unit of the OLT can operate following even when the transmission speed increases, and the CLK extraction unit Can properly perform identification reproduction. As a result, reception characteristics such as a code error rate can be improved.

  In the above-described embodiment, the output light level request unit of the OLT requests the output light level from each ONU so that the received light levels of adjacent burst optical signals are substantially equal. Alternatively, the output light level requesting unit may request each subscriber-side device for the output light level so that the difference between the received light levels of adjacent burst optical signals is not more than a predetermined reference value. That is, even if the optical levels of adjacent burst optical signals are not equal, the code error rate characteristics can be improved if they can be brought close to some extent. The above-mentioned “predetermined reference value” is determined by the circuit configuration of the amplitude level adjustment unit, the performance of the error correction circuit connected to the subsequent stage, and the like, and may be set as appropriate through experiments, simulations, and the like. Note that “the received light levels of adjacent burst optical signals are substantially equal” means that a predetermined reference value is set to “0”.

  FIG. 8 is a diagram illustrating a frame configuration of Organization Specific OAM of GE-PON defined by IEEE 802.3. An Organization Specific OAM frame is a frame in which a developer may freely define a PDU data field. Therefore, in the present embodiment, output light level control between the OLT and the ONU is performed using the Organization specific OAM frame.

  FIG. 9 shows output light level control information transmitted from the OLT to each ONU. This information is defined in the PDU data field of the Organization specific OAM frame shown in FIG. This control information is written by the output light level request unit of the OLT.

  In the output light level control information from the OLT to each ONU shown in FIG. 9, the data area 900 is an area in which a valid / invalid flag is written. The data area 902 is an area for writing a request method. The request method indicates how the output light level is requested for each ONU. Specifically, the request method includes a method of directly specifying an output light level value for the ONU and a method of specifying an increase / decrease value from the current output light level value. The data area 904 is an area in which an output light level request value that is directly requested to the ONU is written. Further, the data area 906 is an area in which an increase / decrease request value from the current output light level value is written.

  FIG. 10 shows output light level control information transmitted from each ONU to the OLT. This information is also defined in the PDU data field of the Organization specific OAM frame shown in FIG. This control information is written by the output light level control unit of the ONU.

  In the output light level control information from the ONU to the OLT shown in FIG. 10, the data area 1000 is an area in which a valid / invalid flag is written. The data area 1002 is an area in which the light level currently output by the ONU is written. The data area 1004 is an area in which an upper limit value of the light level that can be output by each individual ONU is written. The data area 1006 is an area in which a lower limit value of an optical level that can be output by an individual ONU is written. In addition, the data area 1008 is an area in which an individual ONU light level upper limit alarm generation threshold is written. This light level upper limit alarm generation threshold is set to a value slightly lower than the light level upper limit value that can be output by the ONU, and is used to inform the OLT that the upper limit of the light level that can be output by the ONU is almost the limit. Is done. In addition, the data area 1010 is an area in which a light level lower limit alarm generation threshold value of each individual ONU is written. This light level lower limit side alarm generation threshold is set to a value slightly higher than the light level lower limit value that can be output by the ONU, and is used to inform the OLT that the lower limit of the light level that can be output by the ONU is almost the limit. Is done.

  As described above, the OLT can appropriately determine the required value of the output light level for each ONU by informing the OLT of the information on the light level range and alarm generation threshold that each ONU can output. Also, the OLT issues an alarm to the PON system maintainer when the output light level of each ONU exceeds the light level upper limit alarm generation threshold or falls below the light level lower limit alarm generation threshold. Maintenance can be encouraged.

  FIG. 11 is a diagram showing a frame configuration of Information OAMPDU of GE-PON defined by IEEE802.3. This Information OAMPDU frame is a frame in which ONU information is written.

  The OLT output light level requesting unit refers to the OAM Version, Revision, or Vender Specific info in the Information OAMPDU frame, and whether the ONU newly connected to the OLT supports the output light level control of this embodiment. It can be determined whether or not. Since the ONU is a multi-vendor, an ONU corresponding to the output light level control of this embodiment is not always connected to the OLT. Therefore, by referring to the information of the Information OAMPDU frame in this way, the OLT can request the output light level only from the ONU corresponding to the output light level control.

  Next, output light level control when a new ONU is connected to the OLT will be described. In the present embodiment, the output light level request unit of the OLT requests the output light level from the ONU every time a new ONU is connected to the OLT. Some specific control examples are shown below.

  FIGS. 12A and 12B are diagrams for explaining an example of the output light level control when a new ONU is connected to the OLT. First, as shown in FIG. 12A, it is assumed that the first (first) ONU is connected to the OLT and the OLT receives a burst optical signal having an optical level of “7”. At this time, the output light level request unit of the OLT only monitors the received light level and does not perform output light level control for the first ONU.

  Next, as shown in FIG. 12B, it is assumed that the second ONU is connected to the OLT and a burst optical signal having an optical level of “3” is received. In this case, the output light level request unit of the OLT does not perform output light level control for the first ONU, and the reception light level of the burst optical signal from the second ONU is first connected to the OLT. The output light level is requested to the second ONU so as to approach the received light level of the burst optical signal from the ONU. For example, an output light level request is issued to the second ONU so that the received light level at the OLT is “7”. As a result, the received light level of the burst optical signal from the second ONU can approach that from the first ONU. For the ONUs connected to the second and subsequent units, the output light level control is performed so as to approach the received light level of the burst optical signal from the first ONU. Since the output light level is not controlled for the ONU already connected to the OLT in this way, an operation error or the like can be prevented, so that the reliability of the system can be improved.

  FIGS. 13A and 13B are diagrams for explaining another example of output light level control when a new ONU is connected to the OLT. First, as shown in FIG. 13A, it is assumed that the first (first) ONU is connected to the OLT, and the OLT receives a burst optical signal having an optical level of “7”. At this time, the output light level request unit of the OLT only monitors the received light level and does not perform output light level control for the first ONU.

  Next, as shown in FIG. 13B, it is assumed that the second ONU is connected to the OLT and a burst optical signal having an optical level of “3” is received. In this case, the output light level request unit of the OLT calculates the average received light level of burst optical signals from the first ONU and the new second ONU that are already connected. Here, the average received light level is “5”. The output light level request unit outputs the burst light signal from the first and second ONUs to the first and second ONUs so that the received light level approaches the average received light level “5”. Requires light level. Thereafter, the average received light level is calculated every time a new ONU is connected, and the output light level is controlled for all ONUs so as to approach this average received light level. Thus, by adjusting to the average received light level, the amount of change in the optical output of each ONU can be suppressed. For example, in the example of FIG. 12B, the received light level of the burst optical signal from the second ONU is increased from “3” to “7”, but in this example, it is increased from “3” to “5”. Since it only needs to increase, it is possible to avoid a situation where the output light level of the second ONU is set higher than necessary. Therefore, according to this example, the limited optical output variable range of each ONU can be used effectively.

  FIGS. 14A to 14C are diagrams for explaining another example of output light level control when a new ONU is connected to the OLT. First, as shown in FIG. 14A, it is assumed that burst optical signals from the first to fourth ONUs connected to the OLT have substantially the same received light level “7”. Thereafter, the fifth ONU is connected. As shown in FIG. 14B, this fifth ONU has an output light level at which the output light level requesting unit has a received light level “7”. Even if the request is made, it is assumed that only the light level at the received light level “3” can be output.

  In such a case, the output light level requesting unit outputs to the first and fourth ONUs that transmit burst optical signals adjacent to the burst optical signal from the newly connected fifth ONU. Request to reduce the light level. The output light level request unit has received light levels of burst optical signals from the first and fourth ONUs, the received light level “7” of the first and fourth ONUs, and the fifth ONU. The output light level is preferably controlled so as to approach the received light level “5”, which is an intermediate value of the received light level “3”.

  Thus, when there is an ONU whose output light level is at the adjustment limit, the amount of change in the received light level is small with respect to the ONU that transmits adjacent burst optical signals before and after the burst optical signal from the ONU. By controlling so that the amplitude level adjusting unit of the OLT can operate following even when the transmission speed increases, the CLK extracting unit can appropriately perform identification reproduction. As a result, reception characteristics such as a code error rate can be improved.

  As described above, instead of or in addition to performing output light level control on the ONU every time a new ONU is connected to the OLT, the output light level requesting unit of the OLT is periodically updated at predetermined time intervals. Alternatively, the output light level control may be performed on the ONU. By periodically performing the output light level control in this manner, high quality communication can be provided.

  Further, the output light level request unit of the OLT may perform output light level control on each ONU according to an instruction from a maintenance person of the PON system. In this case, if any abnormality occurs in the PON system, it can be dealt with immediately, and the PON system network can be operated stably.

  FIG. 15 is a diagram for explaining an OLT according to another embodiment of the present invention. In the OLT 12 shown in FIG. 15, the same or corresponding components as those in the OLT shown in FIG.

  In the OLT 12 according to this embodiment, the terminal-side signal processing unit 42 includes a code error rate measuring unit 1502 that measures the code error rate of the received upstream burst optical signal, and a test frame for code error measurement on the downstream optical signal. The difference is that a test frame insertion portion 1504 to be inserted is provided. In the present embodiment, the output light level requesting unit 40 requests each ONU by referring to the code error rate measured by the code error rate measuring unit 1502 in addition to the received light level for each burst optical signal. Determine the output light level. Specifically, the output light level requesting unit 40 first sets each ONU so that the received light level difference between adjacent burst optical signals is equal to or less than a predetermined reference value based on the received light level information for each burst optical signal. The output light level is required. Thereafter, the output light level requesting unit 40 refers to the code error rate measured by the code error rate measuring unit 1502 and requests each ONU for the output light level again so that the code error rate is minimized. By referring to the code error rate in this way, the output light level can be requested to each ONU more optimally, and the code error rate characteristic can be improved.

  FIG. 16 is a diagram showing a control sequence from when the ONU is connected to the OLT until the main signal communication is started. In the PON system according to the above-described embodiment, when an ONU is connected to the OLT, after the PON Discovery and OAM Discovery sequences are executed, an ONU authentication sequence is executed, and whether or not the connected ONU is permitted. It is confirmed. Thereafter, the above-described output light level control sequence is performed between the OLT and the ONU.

  FIG. 17 is a diagram for explaining the output light level control sequence in detail. As shown in FIG. 17, when an output light level is requested from the OLT to the ONU, the output light level is changed in the ONU. The OLT verifies whether or not the input light level has reached the requested target value. If the target value is not reached, the output light level is requested again from the ONU. When the target value is reached, the output light level control sequence is terminated.

  Returning to FIG. 16, after the output light level control sequence is completed, main signal communication is started. As described above, by executing the output light level control as one sequence until connection establishment before main signal communication, communication can be performed under optimum transmission conditions immediately after connection establishment.

  It may be possible to select whether or not to perform the above-described output light level control sequence for each PON system. By doing so, it is possible to improve the flexibility of the communication service and realize a hierarchical support quality for access / core.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  10 PON system, 12 OLT, 14 optical splitter, 16 ONU, 34 light receiving element, 36 amplitude level adjustment unit, 38 CLK extraction unit, 40 output optical level request unit, 80 output optical level control unit, 1502 coding error rate measurement unit.

Claims (16)

A PON system in which a station side device and a plurality of subscriber side devices are connected to each other using an optical fiber branched by an optical splitter,
The station side device
An optical receiver for receiving a burst optical signal sequence in which burst optical signals output from each subscriber side device are multiplexed;
A detector for detecting the received light level for each burst optical signal;
An output light level requesting unit that requests an output light level from each subscriber-side device based on a received light level for each burst light signal so that a difference between received light levels of adjacent burst light signals is a predetermined reference value or less; With
The PON system, wherein the subscriber side device includes an output optical level control unit that controls an optical level of a burst optical signal to be transmitted in response to a request from the output optical level request unit.   2. The PON system according to claim 1, wherein the output optical level request unit requests each subscriber-side device for an output optical level so that the received optical levels of adjacent burst optical signals are substantially equal.   3. The output light level request unit requests an output light level from the subscriber side device every time a new subscriber side device is connected to the station side device. The PON system described.   The output optical level requesting unit is configured such that when a new subscriber-side device is connected to the station-side device, the received optical level of a burst optical signal from the new subscriber-side device is first set to the station-side device. 4. The output optical level is requested to the new subscriber side device so as to approach the reception optical level of the burst optical signal from the first subscriber side device connected to the first subscriber side device. The PON system described in 1.   The output optical level request unit is configured to receive an average burst optical signal from all the subscriber side devices including the new subscriber side device when the new subscriber side device is connected to the station side device. 4. An optical level is calculated, and an output optical level is requested from each subscriber side device so that the received optical level of each burst optical signal approaches the average received optical level. The PON system described.   When the output optical level request unit cannot transmit a burst optical signal of the output optical level required by the new subscriber side device connected to the station side device, the burst optical signal from the new subscriber side device is transmitted. The PON system according to any one of claims 1 to 5, wherein the subscriber-side apparatus that transmits a burst optical signal adjacent to a signal is requested to reduce an output optical level.   The PON system according to any one of claims 1 to 6, wherein the output light level requesting unit periodically requests the output light level from each subscriber side device at a predetermined time interval.   8. The PON system according to claim 1, wherein the output light level request unit requests an output light level from each subscriber-side device according to an instruction from the outside. The station side device further includes a code error rate measuring unit that measures a code error rate of the received burst optical signal,
The output light level requesting unit determines an output light level required for each subscriber apparatus by referring to a measured code error rate in addition to a received light level for each burst optical signal. The PON system according to any one of claims 1 to 8.   10. The PON system according to claim 1, wherein the output light level control unit of the subscriber side device transmits information on an optical level range that can be output by the subscriber side device to the station side device.   The PON system according to any one of claims 1 to 10, wherein output optical level control between the station side device and the subscriber side device is performed using an Organization specific OAM frame.   The output light level request unit determines whether or not the subscriber-side device supports output light level control when a new subscriber-side device is connected to the station-side device. 12. The PON system according to claim 1, wherein an output light level is requested only from the subscriber side device.   The output light level request unit refers to an OAM Version, Revision, or Vender Specific info in an Information OAM PDU frame to determine whether the new subscriber-side device supports output light level control. The PON system according to claim 12.   When a new subscriber-side device is connected to the station-side device, main signal communication is started after an output optical level control sequence is performed between the station-side device and the subscriber-side device. The PON system according to claim 1, wherein:   15. The PON system according to claim 14, wherein whether or not to perform an output light level control sequence between the station side device and the subscriber side device can be selected. A station-side device of a PON system connected to each other using a plurality of subscriber-side devices and an optical fiber branched by an optical splitter,
An optical receiver for receiving a burst optical signal sequence in which burst optical signals output from each subscriber side device are multiplexed;
A detector for detecting the received light level for each burst optical signal;
An output light level requesting unit that requests an output light level from each subscriber-side device based on a received light level for each burst light signal so that a difference between received light levels of adjacent burst light signals is a predetermined reference value or less; ,
A station-side device comprising:

Images