JP2010041642A - Pon system, and optical communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a WDM (Wavelength Division Multiplexing)-PON (Passive Optical Network) system capable of suppressing a variation of output power per channel of an optical repeater. <P>SOLUTION: The PON system includes: a plurality of subscriber terminal devices; an optical repeater for amplifying optical signals transmitted therefrom to generate a plurality of amplified uplink optical signals; and a station-side device. The station-side device determines the number of at least one transmission enabled subscriber terminal devices capable of simultaneously transmitting optical signals among the plurality of subscriber terminal devices on the basis of the plurality of amplified uplink optical signals and sets a gain of the optical repeater in accordance with the determined number. Therefore, the variation of output power is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical transmission system. The present invention particularly relates to an optical repeater system suitable for a PON (Passive Optical Network) system.

  The PON system is an economical optical communication system in which a transmission line fiber and a station side device (Optical Line Terminal, hereinafter referred to as OLT) can be shared by a plurality of subscribers (Optical Network Unit, hereinafter referred to as ONU). .

  In optical communication, the bandwidth has been increasing with increasing traffic. A TDM (Time-Division Multiplexing) type optical communication system is known, and a communication speed suitable for this type is considered to be about 10 Gbps. In a wider band than that, WDM (Wavelength Division Multiplexing) -PON is expected to be promising, as is the case with the backbone transmission system.

The following is a list of documents that the applicant has learned.
JP 2004-072170 A JP 2004-112763 A JP 2007-195227 A Japanese Patent Laid-Open No. 10-229386

  In WDM-PON, one wavelength corresponds to each ONU. Therefore, unlike TDM-PON, it is not necessary to adjust the timing for transmitting a signal from the ONU to the OLT. Therefore, data can be transmitted basically at any timing.

  However, in a WDM-PON including an optical repeater, when each ONU transmits an optical signal freely, the power input to the optical repeater fluctuates. In general, ALC (Automatic Level Control) is applied to the optical repeater so that the total output power is constant. Therefore, when the total input power varies, the output power per channel in the optical repeater varies. In order to suppress errors and inter-wavelength interference and to protect the receiver, it is desired that fluctuations in output power be suppressed.

  By adopting an ONU having a function of always transmitting a pseudo signal when there is no upstream signal to the OLT side, fluctuations in the input power of the optical repeater can be suppressed. As a result, the output power per channel can be kept constant. However, in such a configuration, there is a problem that the power consumption of the optical repeater is remarkably increased in order to output a pseudo signal.

  A WDM-PON system that can save power and suppress fluctuations in output power per channel of an optical repeater is desired.

  A PON system according to the present invention includes a plurality of subscriber terminal devices, an optical repeater that amplifies optical signals transmitted from the plurality of subscriber terminal devices, and generates a plurality of amplified uplink optical signals, and a plurality of amplified uplink signals. The station side that determines the number of at least one transmittable subscriber terminal device that can simultaneously transmit an optical signal among a plurality of subscriber terminal devices based on the optical signal, and sets the gain of the optical repeater according to the number Device.

  An optical communication method of a PON system according to the present invention includes a step of amplifying optical signals transmitted from a plurality of subscriber terminal devices to generate a plurality of amplified upstream optical signals and transmitting the amplified signals to a station side device, A step of determining the number of at least one transmittable subscriber terminal device that can simultaneously transmit an optical signal among a plurality of subscriber terminal devices based on the amplified upstream optical signal, and setting the gain of the optical repeater according to the number With.

  According to the present invention, a WDM-PON system that can save power and suppress fluctuations in output power per channel of an optical repeater is desired.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show the configuration of an optical repeater system in a WDM-PON according to an embodiment of the present invention. FIG. 1 shows an upstream signal, and FIG. 2 shows a downstream signal. The optical repeater system includes a plurality of ONUs 1 that are subscriber terminal devices, a wavelength splitter 4 that is an optical splitter, an optical repeater 5, and an OLT 6 that is a station side device. ONU1 includes ONU1-1 to ONU1-n (n is an integer). Of these n ONUs, ONU 1-a and ONU 1-b are shown for convenience of explanation. The branch number k added to each ONU 1-k is also used as the channel number #k of the optical signal in the following description.

  The wavelength splitter 4 combines the upstream signals transmitted from the respective ONUs 1 and transmits them to the OLT 6 via the optical repeater 5. The wavelength splitter 4 also demultiplexes the downstream signal transmitted from the OLT 6 via the optical repeater 5 and transmits the demultiplexed signal to each ONU 1. The optical repeater 5 amplifies the upstream signal and downstream signal.

[Description of operation]
Next, the operation of the optical repeater system in this embodiment will be described with reference to the flowchart of FIG. As a simple example for explanation, the following conditions are assumed.
(A) The loss budget between each ONU 1 and the optical repeater 5 and between the optical repeater 5 and the OLT 6 is the same.
(B) The transmission power of each ONU 1 and OLT 6 is the same. In other words, the power of each uplink / downlink channel input to the optical repeater is the same.
(C) The optical repeater 5 amplifies both upstream and downstream signals simultaneously.
(D) The wavelength of the upstream signal and the wavelength of the downstream signal in the same ONU 1 are not the same.

  The condition (d) can be realized by using wavelengths that are close to each other on the upstream and downstream sides and splitting both upstream and downstream wavelengths of the same channel from the wavelengths of the other channels by the wavelength splitter 4. Such processing can be realized by using a wavelength splitter having a pass region as shown in FIG. For example, the upstream signal # 1 and the downstream signal # 1 of the ONU 1-1 have different wavelengths and close wavelengths. The wavelength splitter ch # 1 provided corresponding to the ONU 1-1 has a transmission region including the wavelength band of the upstream signal # 1 and the wavelength band of the downstream signal # 1. In addition, upstream signals #k and downstream signals #k of other ONUs 1-k (k ≠ 1) do not enter this transmission region. With such a wavelength splitter, an upstream signal and a downstream signal having different wavelengths can be used in one ONU.

  Next, the operation when laying a new ONU 1 will be described. The newly laid ONU 1 is referred to as ONU 1-a. A new ONU1-a is laid (step S2). When the installed ONU 1-a operates, the OLT 6 first recognizes the ONU 1-a and measures the delay time (Discovery_Process, step S4). Details of the Discovery_Process are shown in FIG.

  Referring to FIG. 5, OLT 6 transmits a registration request signal (hereinafter “Discovery_Gate”) including current time T <b> 1 measured by the internal clock of OLT 6 to newly added ONU 1-a. On the other hand, the ONU 1-a returns a signal “Register_Request” including the transmission time T2 measured by the internal clock of the ONU 1-a. Assuming that the time when “Register_Request” arrives at the OLT 6 is T3 in the internal clock of the OLT 6, the OLT 6 can measure the delay difference ΔT between the OLT 6 and the ONU 1-a from T1, T2, T3. The OLT 6 generates a delay time table in which an identifier (LLID, Logical Link ID, etc.) for specifying the new ONU 1 -a and a corresponding delay time ΔT are associated with each other, and stores the generated delay time table in its own storage device.

  Originally, the delay time measurement is performed for timing adjustment of the upstream burst signal in the TDM PON. However, even in the WDM PON, a signal for communication with the OLT 6 such as “Report” for notifying the amount of uplink signal is sometimes saved by using a burst signal. Therefore, timing adjustment is performed by measuring a delay time. In order to save more power, avoid continuously sending the “Discovery_Gate” signal to all the non-operating ONUs 1, and when the ONU 1-a is newly registered, information on the new registration manually in advance in the OLT 6 It is good to enter.

  The OLT 6 increases the gain of the optical repeater 5 in accordance with the new addition of the ONU 1-a (Step S6). Thereafter, the OLT 6 issues an upstream signal transmission permission to the newly added ONU 1-a (step S8). For details, referring to “Register (LLID notification)” and subsequent steps in FIG. 5, the OLT 6 transmits a signal “Register” indicating acceptance of registration of the new ONU 1-a to the ONU 1-a. “Register” includes an LLID (Logical Link ID) issued by the OLT 6. The OLT 6 further transmits a signal “Gate” which gives a transmission permission to the new ONU 2. This “Gate” includes a transmission start time T5 when the new ONU 1-a transmits an uplink signal and a transmission time L indicating a time during which the transmission is continued. The ONU 1-a transmits a signal “Register_ACK” indicating that “Register” has been received to the OLT 6 under the communication conditions indicated by the received “Gate”.

  After the OLT 6 increases the gain of the optical repeater 5 by a corresponding amount, the ONU 1-a outputs a pseudo signal not only when there is a real signal in the upstream direction but also when there is no real signal in the upstream direction, Continue to output upstream signals continuously. Hereinafter, the ONU state when the pseudo signal is output is referred to as a standby mode. Each time a new ONU 1 is added, such processing is performed until the number of ONUs 1 that transmit uplink signals reaches a certain standard.

  The OLT 6 determines the magnitude relationship between the number of ONUs 1 that are transmitting upstream signals (real signals or pseudo signals) and the number k stored in advance (step S9). The OLT 6 continues to add new ONUs to the ONUs 1 that permit transmission of upstream signals until the number of ONUs 1 that are communicating via the optical repeater 5 reaches k. When the number of ONUs 1 is smaller than k, transmission of uplink signals is newly permitted for ONUs 1 that are not permitted to transmit uplink signals.

  With the above settings, the number of operating ONUs 1 is kept above a certain level (step S10). As a result, the power input to the optical repeater 5 is kept above a certain level, and the fluctuation rate of the input power of the optical repeater 5 is kept low.

  The OLT 6 proceeds to the next control step when the operating ONU 1 exceeds a certain number k. That is, the OLT 6 determines the number of ONUs n (n ≧ k) that can transmit an uplink signal at a time according to the total uplink traffic amount from the ONU 1. The OLT 6 determines the number n ′ of channels to be transmitted from the OLT 6 to the ONU 1 at a time according to the amount of downstream traffic to the ONU 1. The OLT 6 sets the gain of the optical repeater 5 to a value corresponding to the total number of channels n + n ′.

  Once the ONU 1 that has received the upstream signal transmission permission receives an instruction to stop upstream signal transmission from the OLT 6, it continues to output the upstream signal by issuing a pseudo signal when there is no upstream actual signal. With this operation, the number n of upstream signals from the ONU 1 is kept constant. Similarly, the OLT 6 outputs a pseudo signal when there is no actual signal in the downlink direction until it receives an instruction to stop transmission of the downlink signal in the channel once permitted to transmit the downlink signal. With this operation, the number of downstream signals n ′ is kept constant.

  The OLT 6 determines whether the upstream signal from each ONU 1 is a normal real signal or a pseudo signal, and when it is determined to be a pseudo signal, the table shows the identifier of the ONU 1 in the standby mode and the time when the pseudo signal was switched to It has a function of storing and storing the data. The table T1 in FIG. 4 shows an example. The left column of the table T1 shows the identifier of the ONU. The middle column shows a flag indicating whether a pseudo signal is transmitted (indicated by “1”) or an actual signal is transmitted (indicated by “0”). The right column shows the transmission start time of the pseudo signal for the ONU that is transmitting the pseudo signal. Similarly, the OLT 6 has a function of transmitting a pseudo signal to a transmission channel having no downlink signal, and holding the identifier for specifying the transmission channel of the OLT 6 and the time of switching to the pseudo signal in the table T2. Table T2 in FIG. 4 shows an example.

  When an ONU that is not currently transmitting an uplink signal (referred to as ONU1-a) requests transmission of an uplink signal, the following processing is executed.

(1) The OLT 6 searches the table T1 for an ONU (referred to as ONU1-b) that is transmitting a pseudo signal instead of a real signal among the ONUs that are currently transmitting an uplink signal. The OLT 6 instructs the ONU 1-b to disconnect the upstream signal transmission, and then gives a signal transmission permission to the ONU 1-a.

(2) When there is no ONU 1 that is transmitting a pseudo signal, the OLT 6 that has received the upstream signal transmission request increases the number of channels that can be transmitted at a time to n + 1, and the gain of the optical repeater 5 corresponds to the increase. Increase Thereafter, the OLT 6 issues a signal transmission permission to the ONU 1-a.

  Each ONU 1 transmits a signal “Report” that notifies the OLT 6 of the uplink signal amount periodically and sequentially. The OLT 6 can recognize from the signal “Report” that the ONU 1-a requests signal transmission. The ONU that is transmitting the actual signal transmits the actual signal including the signal “Report” to the OLT 6. The ONU in the standby mode transmits a signal “Report” at the time assigned from the OLT 6. Since each ONU 1 transmits an optical signal in order, the increase in the uplink signal is a maximum of one channel. For this reason, there is no large variation in the number of channels.

  However, in such a process, there is no merit of power saving by setting the ONU 1 that has not transmitted the uplink signal to a state in which the output of the optical signal is stopped (hereinafter referred to as hibernation mode). As a method for improving this problem, the following processing can be employed. In the Discovery_Process, a transmission possible time of “Report” is set in advance in each ONU 1. When there is no real signal, the ONU 1 shifts to a standby mode in which a pseudo signal is transmitted (step S28). The OLT 6 monitors the elapsed time after the ONU shifts to the standby mode. When the predetermined time has elapsed (step S30), the OLT 6 decreases the gain of the optical repeater 5 by one channel (step S32). The ONU 1 then shifts to the hibernation mode after obtaining permission from the OLT 6 when there is no upstream signal for a certain time or longer (step S34).

  When the ONU 1 needs to transmit an uplink signal in the hibernation mode (step S12), the ONU 1 recovers from the hibernation mode to the normal operation mode (step S14). The ONU 1 does not transmit “Report” immediately at that time, but transmits “Report” at the time assigned in advance (step S16). In this way, periodic “Report” is not required, which saves power. In addition, “Report” does not collide with other ONUs, and the maximum fluctuation of the uplink signal falls within one channel. FIG. 7 shows the operation of each ONU. “Report” is transmitted in different time zones for ch # 1, ch # b, and ch # n.

  In order to keep the output power fluctuation rate per channel in the optical repeater due to this fluctuation low, it is desirable to increase n + n 'to some extent even when there is no traffic. For example, if n + n ′ is set to about 10, the output power fluctuation per channel of the optical repeater may be about 10%, that is, about 0.4 dB.

Similarly, when it is desired to transmit a downlink signal on a channel other than the channel currently transmitting the downlink signal (hereinafter referred to as ch # a), the following processing is performed.
(1) The OLT 6 searches the table T2 for a channel (hereinafter referred to as ch # b) that is transmitting a pseudo signal instead of a real signal among channels that are currently transmitting a downlink signal. If there is a channel transmitting a pseudo signal (there is step S18), a signal instructing to stop the optical output of the ONU of the channel is transmitted to set the ONU to the hibernation mode (step S20). ), Ch # a signal transmission permission is issued (step S22).
(2) When there is no channel transmitting a pseudo signal (without step S18), the number of channels that can be transmitted at one time is set to n ′ + 1, and the gain of the optical repeater is increased correspondingly (step S24). , Ch # a signal transmission permission is issued (step S26).

  In addition, when the time during which a certain ONU 1 or OLT 5 is transmitting a pseudo signal exceeds a certain time, the OLT 5 reduces the gain of the optical repeater 5 by a corresponding amount, and then the corresponding ONU or the corresponding channel. Stop the light output.

  The above control makes the total number of channels input to the optical repeater, that is, the optical power constant, and sets the optical repeater to a gain corresponding to the number of channels, thereby reducing the output of the optical repeater per channel. It can be controlled constantly. As a result, it is possible to save power for the unused ONU, OLT channel, and optical repeater 5.

FIG. 1 shows the configuration of an optical repeater system. FIG. 2 shows the configuration of the optical repeater system. FIG. 3 shows the pass region of the wavelength splitter. FIG. 4 shows a table for storing information on ONU pseudo signals. FIG. 5 shows the Discovery_Process of the new ONU. FIG. 6 shows the operation of the optical repeater system. FIG. 7 shows a time period in which the ONU can transmit the Report signal.

Explanation of symbols

1 ONU
4 Wavelength splitter 5 Optical repeater 6 OLT

Claims (10)

A plurality of subscriber terminal devices;
An optical repeater that amplifies optical signals transmitted from the plurality of subscriber terminal devices to generate a plurality of amplified upstream optical signals;
Based on the plurality of amplified upstream optical signals, the number of at least one transmittable subscriber terminal device capable of transmitting an optical signal simultaneously among the plurality of subscriber terminal devices is determined, and the optical repeater is determined according to the number A PON system comprising: A PON system according to claim 1,
The PON system in which each of the at least one transmittable subscriber terminal device transmits a pseudo signal to the station side device when not transmitting a real signal to the station side device. A PON system according to claim 2,
When the station-side device detects the pseudo signal, the storage device stores a detection time and a pseudo-signal transmitting terminal device identifier that identifies the at least one transmittable subscriber terminal device that has transmitted the pseudo signal. PON system to store. A PON system according to claim 3, wherein
When the station side device recognizes that the pseudo signal is transmitted for a predetermined time or more from the first terminal device among the at least one transmittable subscriber terminal device by referring to the detection time, A PON system configured to lower the gain of the optical repeater and to remove the first terminal device from the list of the at least one transmittable subscriber terminal device. A PON system according to claim 3 or 4,
When the second terminal device joins the plurality of subscriber terminal devices and starts transmission of signals to the station side device, the station-side device stores the pseudo signal transmitting terminal device stored in the storage device The at least one transmittable subscriber terminal device specified by the identifier is removed from the list of the at least one transmittable subscriber terminal device, and the second terminal device is removed from the at least one transmittable subscriber terminal device. PON system to add to the list. A PON system according to any one of claims 2 to 5,
The station side device searches for the terminal device identifier during pseudo signal transmission when the third terminal device joins the plurality of subscriber terminal devices and starts transmitting signals to the station side device. When it is determined that the at least one transmittable subscriber terminal device transmitting the pseudo signal does not exist, the gain of the optical repeater is set to be increased and then the station of the third terminal device is set. A PON system that allows signal transmission to the building side equipment. A PON system according to any one of claims 1 to 6,
The station side device transmits a notification transmission enabling time to the fourth terminal device when the fourth terminal device performs a new registration procedure for joining the plurality of subscriber terminal devices,
When the fourth terminal apparatus starts signal transmission after recovering from the suspension mode in which optical communication with the station side apparatus is suspended, the signal transmission enabling time of the signal amount of optical communication with respect to the station side apparatus is transmitted. A PON system that notifies the station side device at the timing shown in FIG. A PON system according to any one of claims 2 to 6,
The station building side device keeps the input power to the optical repeater above a certain level by keeping the number of the at least one transmittable subscriber terminal device above a predetermined number. Amplifying optical signals transmitted from a plurality of subscriber terminal devices to generate a plurality of amplified upstream optical signals and transmitting them to the station side device;
Based on the plurality of amplified upstream optical signals, the number of at least one transmittable subscriber terminal device capable of transmitting an optical signal simultaneously among the plurality of subscriber terminal devices is determined, and the optical repeater is determined according to the number A method for setting the gain of the PON system. An optical communication method for a PON system according to claim 9,
The PON system optical communication method, wherein each of the at least one transmittable subscriber terminal device transmits a pseudo signal to the station side device when a real signal is not transmitted to the station side device.

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