JP2017192002A - Optical signal relay device and relay method - Google Patents

Abstract

An optical signal repeater and a control method capable of complementing the preamble portion of each optical burst signal without increasing the time interval between burst signals in a PON system. In an optical / electrical conversion module 71 that converts a received optical burst signal into a burst reception signal, if the end of one burst reception signal is detected, the next burst reception is performed after a predetermined reset time Trst has elapsed. A signal detection unit for starting signal detection, a delay buffer unit 73 for accumulating and delaying burst reception signals and outputting the delayed burst reception signals, and a continuous burst reception determination signal for a predetermined time. A burst signal reception determination unit 72. Control is performed so that the synchronization pattern of the delayed burst reception signal output from the buffer unit is switched to the synchronization pattern signal over a period in which the continuous burst reception determination signal exists. [Selection] Figure 3

Description

  In the PON (Passive Optical Network) system, the optical signal between the station side device (OLT) and the home side device (ONU) is optically / electrically converted by the optical / electrical module, and then again the electrical / optical module. In particular, the present invention relates to a technique for relaying an optical burst signal from a home side apparatus (ONU) to a station side apparatus (OLT).

Between an optical subscriber line station side device OLT (Optical Line Terminal; hereinafter referred to as “station side device”) and a plurality of optical subscriber line termination units ONU (Optical Network Unit; hereinafter referred to as “home side device”), There is an optical communication system that performs two-way communication via an optical fiber communication network.
In this optical communication system, a single star optical fiber communication network in which the station side device OLT and each home device ONU are radially connected by optical fibers has been constructed and put into practical use. In this network configuration, the configuration of the system and communication equipment becomes simple, but one home-side device ONU occupies one optical fiber, and this optical fiber is directly connected to the station-side device OLT by wiring. Must. Therefore, if the home-side apparatus ONU has N stations, N optical fibers that are directly connected from the station-side apparatus OLT are required, and it is difficult to reduce the price of the optical communication system.

Therefore, a PON (Passive Optical Network) system has been put to practical use as an optical communication system in which one optical fiber connected by wiring from the station side device OLT is shared by a plurality of home side devices ONU.
In this PON system, in particular, a passive optical branching device (hereinafter also simply referred to as “optical coupler”) that passively branches and multiplexes an input signal without requiring external power supply, and a station side device OLT. Are connected via an optical fiber. Furthermore, the optical fiber branched by the optical coupler is provided according to the number of the home side apparatuses ONU.

The station-side apparatus OLT and the N-station home-side apparatus ONU are based on 1-to-N transmission connected via an optical fiber and an optical coupler. Thereby, many home side apparatuses ONU can be allocated with respect to one station side apparatus OLT, and the whole installation cost can be held down.
In such a PON system, a group of signals (referred to as optical burst signals) including a large number of 0s and 1s are transmitted from one home-side device ONU to the station-side device OLT. An optical burst signal is also transmitted from another home-side apparatus ONU. The station side device OLT assigns a time slot for transmitting the optical burst signal to each home side device ONU so that these optical burst signals do not compete in time. That is, each optical burst signal is multiplexed by a time division method and transmitted to the station side apparatus OLT.

On the other hand, when the distance from the home side device ONU to the station side device OLT is long, in order to compensate for the attenuation of the optical burst signal, the optical signal is converted into a burst reception signal by the optical / electric module, and again converted by the electric / optical module. And relaying is done. This repeater is called an “optical signal repeater”.
The optical burst signal is provided with a synchronization bit portion as a preamble (payload). This synchronization bit portion is originally provided for use by the optical burst signal receiving circuit of the station side apparatus OLT.

In the optical signal repeater, it is necessary to accurately reproduce and repeat the synchronization bit portion so that the operation of the optical burst signal receiving circuit of the station side device OLT is not hindered.
The reproduction of the bit information of the preamble may be inaccurate in the optical signal repeater. If the reproduction of the bit information of the preamble becomes inaccurate in the optical signal repeater, there is a possibility that the reception of the optical burst signal of the station side apparatus OLT may be hindered.

Therefore, a technique has been proposed in which a burst signal preamble is complemented and relayed from its head position when a burst signal is received when the optical burst signal is relayed (see Patent Document 1).
By the way, in the technique for complementing the preamble of the burst signal described above, it is necessary to accurately grasp the start time of one optical burst signal received by the optical signal repeater. It is the role of the optical / electrical module installed in the optical signal repeater that detects the beginning of the optical burst signal.

  That is, a peak hold circuit is installed in a post-amplifier (post-amplifier, comparator) installed in the subsequent stage of the photodetecting element of the optical / electric module (see Patent Document 2), and the burst received signal is received by the peak hold circuit. By detecting the rising edge of the amplitude, the head of the burst signal can be detected at high speed (at a time earlier than when the receiver in the optical signal repeater reproduces the burst signal and synchronization is established). The preamble can be complemented.

  In addition, a reset circuit that resets the peak hold circuit based on the detection of the end of the burst signal is also necessary in order to enter the reception state of the next burst signal.

Japanese Patent No. 4761135 Japanese Patent No. 4172475 Japanese Patent No. 5056909

The reset circuit monitors the pattern of the burst signal, detects the end of the burst signal, and generates a reset signal. Specifically, the end of the burst signal is detected based on the continuation of the 0 signal (in the case of GE-PON) or the burst end delimiter (in the case of 10G-EPON), and the reset signal is generated.
The time until the reset circuit detects the end of the burst signal, generates the reset signal, and cancels it, that is, the time for discharging the charge accumulated in the peak hold capacitor (reset time) is set.

The reset time needs to be set in consideration of not only the peak hold circuit but also the response to the burst signal of the preamplifier (preamplifier) and the AC coupling circuit in the preceding stage of the peak hold circuit. If only the peak hold circuit is considered, there are the following disadvantages. That is, even if the peak hold circuit is reset based on the end of the burst signal, charge remains in the preamplifier (preamplifier) and AC coupling circuit in the previous stage, so the remaining charge is erroneously detected as the next burst signal. There is a risk that.
Therefore, it is necessary to set the reset time longer than the time for discharging the charge of the preamplifier (preamplifier) or the AC coupling circuit.

  The reset time should be shorter as long as it satisfies the condition that the charge of the preamplifier and the AC coupling circuit is longer than the time of discharge (that is, the time for the charge of the preamplifier and AC coupling circuit to be discharged). Recently, the IEEE802.3av 10G-EPON has adopted 64B / 66B code as the encoding method of the PON system. This is the conventional IEEE802.3ah GE- Unlike the PON 8B / 10B code, the balance between the code 0 and code 1 (mark rate) is allowed to some extent. For this reason, it is better to set the response of the preamplifier (preamplifier) or the AC coupling circuit slower.

Note that Patent Document 3 has a description regarding deviation of 0 signal and 1 signal (baseline wander) when receiving a signal encoded by a 64B / 66B code used in 10G-EPON.
For this reason, 10G-EPON requires a longer reset time than GE-PON.
In this case, a problem arises when adjacent burst signals come in at short intervals. Since the next burst signal comes in without the previous burst signal being reset and the signal cannot be detected during the reset time, the bits near the beginning of the next burst signal are largely lost. In this case, even if the technique for complementing the preamble described in Patent Document 1 is applied, it may be possible to complement the optical burst signal from the middle of the preamble, but it is difficult to complement from the vicinity of the beginning of the preamble.

Although it is conceivable to delay the arrival of the next burst signal, the time interval (gap) between adjacent burst signals must be widened as a whole PON system, and the use efficiency of the network bandwidth is reduced. .
In view of such circumstances, the present invention increases the number of preambles of each optical burst signal as much as possible even if the optical burst signal continuously enters the repeater without increasing the time interval (gap) between the burst signals in the PON system. An object of the present invention is to provide an optical signal relay device and a relay method that can be complemented.

  The optical signal repeater of the present invention is an optical / electrical conversion module that converts a received optical burst signal into a burst received signal, and a period during which the burst received signal converted by the optical / electrical conversion module is detected, A signal detection unit that outputs a signal detection (Signal_Detection) signal (hereinafter referred to as an SD signal), and if the end of one burst reception signal is detected, the next burst reception signal after a predetermined reset time has elapsed. The signal detection unit that starts detection of the signal, the delay buffer unit that accumulates and delays the burst reception signal output from the optical / electric module, and outputs the delayed burst reception signal, and the optical burst signal A synchronization pattern holding unit holding a synchronization pattern as a synchronization pattern signal, and a delayed burst output from the delay buffer unit A switching unit that switches between a received signal and a synchronization pattern signal held by the synchronization pattern holding unit, a timing control unit that controls switching of the switching unit, and an output signal switched by the switching unit, An electrical / optical converter for converting to an optical burst signal, monitoring the output of the signal detector, and determining that the next SD signal has been detected when the reset time has elapsed after the end of one SD signal; A continuous burst signal reception determination unit that outputs a continuous burst reception determination signal over a predetermined time is further provided, and the timing control unit is delayed from the buffer unit over a period in which the continuous burst reception determination signal exists. The switching unit is controlled to switch the synchronization pattern of the received burst signal to the synchronization pattern signal.

  According to the optical signal relay device, the following operation is obtained. If the received optical burst signal is converted into a burst received signal and the end of one burst received signal is detected, the detection of the next burst received signal starts after a predetermined reset time has elapsed, and the period during which it is detected And outputting the SD signal, accumulating and delaying the converted burst reception signal, holding the synchronization pattern of the optical burst signal as a synchronization pattern signal, and holding the delayed burst reception signal and the holding When the switched output signal is converted into an optical burst signal, the output of the signal detector is monitored, and after the completion of one SD signal, the next SD signal is When it is determined that the reset time has been detected, a continuous burst reception determination signal is output over a predetermined time, and the continuous burst reception determination signal is output. Over a period present, a synchronization pattern of the delayed burst reception signal outputted from the buffer unit, it is possible to switch on the synchronization pattern signal.

Due to this action, even after the end of one optical burst signal, even when the next optical burst signal enters before the reset time elapses (this may be referred to as continuous reception in this specification), delay buffering and continuous By using the burst reception determination signal, the synchronization pattern signal can be supplemented from the beginning of the next burst signal.
The predetermined time for the continuous burst signal reception determination unit to output the continuous burst reception determination signal is preferably after the reset time has elapsed and the time for ensuring the minimum burst interval has elapsed. The minimum burst interval can be ensured, and the processing of the station side device (OLT) of the PON system is facilitated.

  The delay buffer unit further accumulates and delays the SD signal output from the signal detection unit, outputs the delayed SD signal, and the switching unit includes a period in which the delayed SD signal exists. If the delayed burst reception signal output from the buffer unit is switched to the synchronization pattern signal over both periods in which the continuous burst reception determination signal exists, the portion before the SD signal is detected Can also be complemented.

  The continuous burst signal reception determination unit monitors the output of the signal detection unit, and outputs the continuous burst reception determination signal when the next SD signal is not detected when the reset time has elapsed after completion of one SD signal. Do not. In this case, it is possible to supplement the portion of the next received burst signal after the SD signal is detected. When the burst signal is not continuous and the portion before the SD signal is detected is complemented and relayed, the burst signal may collide on the station side device (OLT) side rather than the relay device.

The time for which the delay buffer unit delays the burst reception signal is preferably at least the reset time. After the SD signal ends, the next SD signal can supplement the part that has entered before the reset time has elapsed by the delay time.
The upper limit of the delay time is preferably a preamble time. This is because if it is longer than the preamble time, it is not necessary to perform processing based on the timing of the SD signal, and the head of the data section can be found and processing can be performed according to the timing.

  The predetermined time for the continuous burst signal reception determination unit to output the continuous burst reception determination signal is preferably set in a range from the detection of the next SD signal to the reset time. As a result, the portion before the SD signal can be complemented by the time for outputting the continuous burst reception determination signal. If this time is set longer than the reset time, it may collide with the previous burst signal.

  The relay method according to the present invention is substantially the same as the invention according to the optical signal relay device.

  According to the present invention, there is an effect that even if optical burst signals continuously enter the repeater, the preamble portion of the optical burst signal that has entered later can be complemented as much as possible.

It is the schematic which shows the structural example of the optical communication system which connected the station side apparatus OLT and the some home side apparatus ONU with the optical fiber. It is a schematic diagram which shows the optical burst transmission of the upstream optical frame signal sent to each station side apparatus OLT via an optical fiber from each home side apparatus ONU using a time division system. It is a block diagram which shows the structure of an optical signal relay apparatus. It is a block diagram which shows the detailed internal structure of an optical / electrical module. It is a block diagram which shows the detailed internal structure of a postamplifier. It is a signal waveform diagram of each part in the optical signal repeater.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a configuration example of an optical communication system 1 in which a station side device OLT and a plurality of home side devices ONU are connected by an optical fiber.
The optical communication system 1 includes a station side device OLT2 provided in a control station side station building, and home side devices ONUs 3a, 3b,. . . (Hereinafter collectively referred to as “home-side device ONU3”), a trunk optical fiber 4a connected to the station-side device OLT2, and a branch optical fiber 4b connected to each home-side device ONU3 (hereinafter referred to collectively) An optical coupler 5 for connecting the main optical fiber 4a and the plurality of branch optical fibers 4b, and an optical signal repeater 7 inserted in the middle of the main optical fiber 4a. .

The home-side device ONU3 is a device for each subscriber to enjoy the optical network service, and is installed in the subscriber's home. The home apparatus ONU 3 is connected to a terminal device such as a personal computer (hereinafter simply referred to as a PC) 9.
The optical coupler 5 does not require any external power supply and passively branches and multiplexes the signal input from the optical fiber 4 connected to one side and outputs it to the optical fiber 4 connected to the other side. It can be made of a star coupler. Thereby, many home side apparatuses ONU3 can be allocated with respect to one station side apparatus OLT2, and the whole installation cost can be held down.

  This optical communication system 1 including the station side device OLT2 and the home side device ONU3 incorporates, for example, Gigabit Ethernet technology, and performs access section communication at a communication speed of 1.25 Gbps using an optical fiber. A GE-PON (Gigabit Ethernet-Passive Optical Network; IEEE802.3ah) system is being constructed. However, not only GE-PON but also other PON systems can be adopted. For example, a 10G-EPON (IEEE802.3av) system may be adopted.

According to this GE-PON system or 10G-EPON system, the station side device OLT2 and the home side device ONU3 communicate with each other in units of variable length frames. This frame has a synchronization bit portion including sampling data and a data portion of 64 bytes or more.
Hereinafter, a signal transmission / reception procedure in the downlink direction and the uplink direction of the signals between the home-side apparatus ONU3 and the station-side apparatus OLT2 will be described.

First, the flow of a downstream signal transmitted from a higher-level network such as the Internet network toward the home apparatus ONU 3 will be described.
In the station side apparatus OLT2 that has received the signal from the upper network, a predetermined bridge process is performed in order to specify the logical link to be relayed. At this time, the station side device OLT2 adds information such as a synchronization bit part including a logical link identifier and a PON header to the frame signal, converts it into an optical signal, and sends it to the trunk optical fiber 4a.

This downstream optical signal is composed of a combination of a transmission signal designating a specific home-side device ONU3 and an idle signal not designating the home-side device ONU3, and is a continuous signal that is not interrupted.
The optical signal sent to the trunk optical fiber 4a passes through the optical signal relay device 7, is branched by the optical coupler 5, and is sent to each home-side device ONU 3 via each branch optical fiber 4b. At this time, only the home-side apparatus ONU3 provided with the logical link can capture a predetermined optical signal. Then, the home device ONU 3 that has fetched the frame signal relays the home network interface and sends data to the terminal device such as the PC 9.

Next, the flow of an upstream signal sent from each home apparatus ONU 3 to a higher-level network such as the Internet network will be described.
Data from each PC 9 is converted into an optical burst signal via each home-side apparatus ONU3. The transmission rate of the bits constituting the optical burst signal is, for example, 1.25 Gbps for GE-PON and 10.3125 Gbps for 10G-EPON.

These optical burst signals are transmitted through the branch optical fibers 4, and the optical burst signals are multiplexed and transmitted through the optical coupler 5 on the trunk optical fiber 4a.
At this time, these optical burst signals are controlled to be transmitted so as not to compete with each other in time. In this control, when data is transmitted from the station-side device OLT2 to each home-side device ONU3, there is a period window (hereinafter also simply referred to as a window) in which an upstream optical signal may be transmitted to each home-side device ONU3. Assigned and notified as a control frame. Therefore, in the same optical communication system 1, the upstream optical signal transmitted from each home-side apparatus ONU 3 can avoid contention.

In this way, mutual optical communication between the home-side apparatus ONU3 and the station-side apparatus OLT2 is performed.
FIG. 2 is a schematic diagram showing optical burst transmission of an upstream optical frame signal transmitted from each home-side apparatus ONU 3 to the station-side apparatus OLT 2 via the optical fiber 4 using a time division method.
The upstream optical frame signal has a window so that the optical burst signal 6a from the home-side apparatus ONU 3a, the optical burst signal 6b from the home-side apparatus ONU 3b, the optical burst signal 6c from the home-side apparatus ONU 3c do not compete with each other in time. Sent under the control of.

The signal included in the optical burst signal from each home-side apparatus ONU3 includes a synchronization bit portion that constitutes the preamble PA and a signal such as a data portion DATA that includes a plurality of frames and cells.
The synchronization bit part is used for bit synchronization establishment of an optical burst bit synchronization circuit provided in the station side apparatus OLT2. The pattern of the synchronization bit part is an 8B10B idle signal in GE-PON. The mark ratio (ratio of 0, 1) is usually 50%, and the number of bits is fixed. In 10G-EPON, a repetitive signal of a fixed 66-bit synchronization pattern is used. The mark rate is usually 50% in the synchronous bit part, and the number of bits is fixed.

FIG. 3 is a block diagram showing the configuration of the optical signal repeater 7 of the present invention, and FIGS. 4 and 5 show details of the optical / electrical module 71 therein. FIG. 6 is a signal waveform diagram of each part in the optical signal repeater 7.
The optical signal relay device 7 is a device that converts an optical burst signal into a burst reception signal (referred to as a burst reception signal; see FIG. 6A), and relays it back to an optical signal.

In the present embodiment, the optical signal repeater 7 is a bidirectional optical signal repeater 7, one of which relays an upstream optical burst signal from the home-side device ONU to the station-side device OLT, and the other is a station. A downstream optical continuous signal from the side device OLT to the home device ONU is relayed.
As shown in FIG. 3, the optical signal repeater 7 that relays the upstream optical burst signal detects the optical / electric module 71 that converts the optical burst signal into a burst reception signal, and the start / end of reception of the optical burst signal. And a timing control unit 77 capable of performing the above.

As shown in FIG. 4, the optical / electrical module 71 includes an optical / electrical conversion element 711, a preamplifier 712 that amplifies a light detection signal (referred to as a burst reception signal) by the optical / electrical conversion element 711, and an output of the preamplifier 712. In contrast, a post-amplifier 713 that is AC-coupled via a capacitor and further amplifies the output signal of the preamplifier 712 is provided.
As shown in FIG. 5, the postamplifier 713 includes an amplifying unit 81 that amplifies the output signal of the preamplifier 712, and a binarizing unit 82 that binarizes the burst reception signal using a predetermined threshold. The post-amplifier 713 further includes a peak hold circuit 83 (intensity detection circuit) for detecting whether or not a burst reception signal is present, and a signal detection unit 84. The signal detection unit 84 compares the output of the peak hold circuit 83 with a detection threshold, and outputs an SD signal (see FIG. 6B) for a time during which the output of the peak hold circuit 83 exceeds the detection threshold.

  The peak hold circuit 83 receives the SD reset signal (see FIG. 6C) from the timing control unit 77. The SD reset signal is determined by the timing control unit 77 to monitor the burst reception signal, for example, when the burst reception signal is completed when it is detected that “0” of the binary values of the burst reception signal continues for a predetermined time. This is a signal (SD reset signal) that is determined and sent to the peak hold circuit 83. The time of this SD reset signal is called reset time Trst. The reset time Trst is a time set by the optical signal repeater 7. If the reset time Trst is too short, the preamplifier 712 or the AC coupling circuit in the previous stage is used even if the peak hold circuit 83 is reset by the SD reset signal. Since charges remain in (AC coupling), the remaining charges may be erroneously detected as the next burst signal.

  The reset time Trst is preferably set shorter than the minimum burst signal length used in the PON system. If the burst signal is set to be equal to or greater than the minimum burst signal, the next burst signal transmitted by an ONU that does not pass through the optical signal repeater 7 (for example, ONU 3d shown in FIG. 1) may overlap within the reset time when a continuous burst reception determination is output. Because there is. By setting it shorter than the burst signal length, it is ensured that no collision occurs with such a next burst signal.

  Referring to FIG. 3, the optical / electrical module 71 supplies a signal detection signal (SD signal) indicating the presence of the optical burst signal to the timing control unit 77. The timing control unit 77 can know the reception start of the optical burst signal based on the SD signal. Further, the timing control unit 77 can monitor the output of the optical / electrical module 71 to know the end of reception. When the end of reception is detected, an SD reset signal is supplied to the optical / electrical module 71 as described above.

  In the embodiment of the present invention, a continuous burst reception determination unit 72 is provided. The continuous burst reception determination unit 72 receives the SD signal and the SD reset signal, determines that the next SD signal has been detected when one SD signal ends and the reset time Trst has elapsed. In this case, the continuous burst reception determination signal is output to the timing control unit 77 over a predetermined time. If one SD signal ends and the next SD signal is not detected after the reset time Trst has elapsed, the continuous burst reception determination signal is not output.

  If “the next SD signal is detected after the lapse of the reset time Trst”, one burst reception signal is completed, and the next burst reception signal has already entered before the reset time Trst has elapsed. ing. That is, the adjacent upstream optical burst signal enters the optical signal repeater 7 in a substantially continuous state. The continuous burst reception determination unit 72 determines such a continuous reception state of the upstream optical burst signal.

The duration of the continuous burst reception determination signal is from time T1 to time T2 when the elapsed time of the reset time Trst is 0 (see FIG. 6D). T2-T1 is set to a value satisfying 0 <(T2-T1) <Trst. T2 is set to a value equal to or greater than Trst and equal to or less than the time that the synchronization bit portion in one optical burst signal continues.
The meaning of providing T1 which is not 0 is to secure a minimum burst interval between adjacent burst signals output from the optical signal repeater 7. T2 may be set to a value equal to or longer than Trst (FIG. 6D illustrates the case of T2 = Trst).

  The burst reception signal converted by the optical / electrical module 71 is input to a clock recovery unit (not shown). The clock recovery unit extracts a clock signal synchronized with each bit of the optical burst signal based on the optical burst signal. This signal is referred to as “regenerated clock”. Then, each bit of the burst reception signal is sampled by the reproduction clock and written to the delay buffer unit 73.

The delay buffer unit 73 is composed of a FIFO memory having a depth corresponding to the delay time, and reads out with the reference clock of the optical signal relay device 7. As the reference clock, a recovered clock extracted when relaying a downstream signal from the station side terminal device OLT2 to the slave station ONU3 can be used.
Instead of using the recovered clock, a reference clock may be input from the outside and time management may be performed based on the reference clock.

  FIG. 6E shows a burst reception signal before being written to the delay buffer unit 73, and FIG. 6F shows a burst reception signal after being written to the delay buffer unit 73. The delay time Tdelay in the delay buffer unit 73 may be set to a value equal to or greater than Trst (FIG. 6 (f) illustrates the case of T2 = Trst). The upper limit of the setting of the delay time Tdelay is the time that the synchronization bit part continues in one optical burst signal.

The switching unit 75 switches between the synchronization pattern signal output from the synchronization pattern holding unit 74 and the burst reception signal output from the delay buffer unit 73 based on the switching signal from the timing control unit 77.
In one embodiment of the present invention, the timing control unit 77 sends a switching signal to the switching unit 75 during the period when the continuous burst reception determination signal continues (see FIG. 6D), and the delayed burst reception. The signal is switched to the synchronization pattern signal. Therefore, the delayed burst reception signal is replaced with the synchronization pattern signal. This replacement makes it possible to supplement the first portion of the burst reception signal that could not be received during the reset signal period with a minimum burst interval for the “next burst reception signal”. .

In another embodiment of the present invention, not only the burst reception signal but also the SD signal is sent to the delay buffer unit 73, and the delayed burst reception signal and the SD signal are extracted from the delay buffer unit 73. The delay time of the burst reception signal and the SD signal may be the same time.
In this case, the waveform of the delayed SD signal is shown in FIG. The timing control unit 77 performs a period during which the continuous burst reception determination signal continues (see FIG. 6D) and a period during which the delayed SD signal continues (see FIG. 6G). A logical sum (see FIG. 6H) is taken, and based on the logical sum, a switching signal is sent to the switching unit 75, and the delayed burst reception signal is switched to the synchronization pattern signal.

Note that if the timing control unit 77 continues to send the switching signal to the switching unit 75 during the period in which the logical sum continues, there is a possibility that the data portion is also replaced with the synchronization pattern, so the switching is performed within the preamble time. To cancel.
In this “other embodiment”, with respect to the “next burst reception signal”, a minimum burst interval is provided, and the previous part of the synchronization pattern in which the SD signal is not generated due to the reset time; Any part of the latter part of the synchronization pattern in which the SD signal is generated after the reset time has passed can be replaced with the synchronization pattern signal.

  In any embodiment, as described above, the delay buffer unit 73 and the synchronization pattern holding unit 74 are synchronized with the reproduction clock or the reference clock, and the switching control is also performed by synchronizing with the reproduction clock or the reference clock. No frequency fluctuations or phase fluctuations due to. Although there is a possibility that the synchronization pattern is broken at the time of switching, since it is limited to before and after one bit that has been switched, frequency fluctuation / phase fluctuation does not occur, and the mark ratio does not fluctuate greatly. It does not affect the reception of the OLT.

The electrical / optical module 76 converts the restoration signal in which the head of the synchronization bit portion is replaced with the correct synchronization pattern in this way into an optical burst signal (see FIG. 6J).
As described above, the optical burst signal can be relayed while maintaining its accurate code form.
The process when one SD signal ends and the next SD signal enters later than the time when the reset time Trst has elapsed, that is, when the optical burst signal does not continuously enter is shown in FIG. I will explain.

  In this case, the burst reception signal is delayed as described above, but the continuous burst reception determination signal is not generated (see the left part of FIG. 6D). Therefore, a switching signal is sent to the switching unit 75 based on the delayed SD signal (see FIG. 6 (h)), and the head portion of the delayed burst reception signal is switched to the synchronization pattern signal. By this processing, the beginning part of the burst reception signal which may be damaged can be replaced with the synchronization pattern signal. When the burst signal is not continuous and the portion before the SD signal is detected is complemented and relayed, the burst signal may collide on the station side device (OLT) side rather than the relay device. For example, in the case of FIG. 3, there is a possibility that the relay signal from the relay device 7 and the burst signal 6d from the slave station ONU 3d may collide, and this collision can be avoided.

Although the embodiment of the present invention has been described above, the implementation of the present invention is not limited to the above, and various modifications can be made within the scope of the present invention.
The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Optical communication system 7 Optical signal relay apparatus 71 Optical / electrical module 72 Continuous burst reception determination part 73 Delay buffer part 74 Synchronization pattern holding | maintenance part 75 Switching part 76 Electric / optical module 77 Timing control part 84 Signal detection part

Claims (7)

An optical signal repeater that relays an optical burst signal,
An optical / electrical conversion module for converting a received optical burst signal into a burst received signal;
During detection of the burst reception signal converted by the optical / electrical conversion module, a signal detection unit that outputs an SD signal, and detects the end of one burst reception signal, a predetermined reset time After the elapse of time, the signal detector that starts detection of the next burst received signal,
A delay buffer unit that accumulates and delays the burst reception signal output from the optical / electrical module, and outputs the delayed burst reception signal;
A synchronization pattern holding unit holding the synchronization pattern of the optical burst signal as a synchronization pattern signal;
A switching unit for switching between the delayed burst reception signal output from the delay buffer unit and the synchronization pattern signal held by the synchronization pattern holding unit;
A timing control unit for controlling switching of the switching unit;
An electrical / optical converter that converts the output signal switched by the switching unit into an optical burst signal;
The output of the signal detector is monitored, and after the end of one SD signal, if it is determined that the next SD signal is detected when the reset time has elapsed, a continuous burst reception determination signal is output for a predetermined time. Further comprising a continuous burst signal reception determination unit,
The timing control unit controls the switching unit to switch a synchronization pattern of a delayed burst reception signal output from the buffer unit to the synchronization pattern signal over a period in which the continuous burst reception determination signal exists. An optical signal relay device.   The predetermined time for the continuous burst signal reception determination unit to output the continuous burst reception determination signal is after the reset time has elapsed and a time for ensuring a minimum burst interval has elapsed. Optical signal repeater. The delay buffer unit further accumulates and delays the SD signal output from the signal detection unit, and outputs the delayed SD signal.
The switching unit converts the delayed burst reception signal output from the buffer unit to the synchronization pattern signal over both a period in which the delayed SD signal exists and a period in which the continuous burst reception determination signal exists. The optical signal repeater according to claim 1, wherein the optical signal repeater is switched to   The continuous burst signal reception determination unit monitors the output of the signal detection unit, and outputs the continuous burst reception determination signal when the next SD signal is not detected when the reset time has elapsed after completion of one SD signal. The optical signal repeater according to any one of claims 1 to 3, wherein:   5. The optical signal relay device according to claim 1, wherein the delay buffer unit delays the burst reception signal at least the reset time. 6.   The predetermined time for the continuous burst signal reception determination unit to output the continuous burst reception determination signal is set within a range from the detection of the next SD signal to a reset time. 6. The optical signal repeater according to any one of 5 above. An optical signal relay method for relaying an optical burst signal,
Convert received optical burst signal to burst received signal,
If the converted burst reception signal is detected and the end of one burst reception signal is detected, the detection of the next burst reception signal is started after a predetermined reset time has elapsed, during the period of detection, Output SD signal,
Accumulating and delaying the converted burst received signal,
Holding the synchronization pattern of the optical burst signal as a synchronization pattern signal;
Switching between the delayed burst reception signal and the held synchronization pattern signal,
A relay method for converting the switched output signal into an optical burst signal,
When monitoring the output of the signal detector and determining that the next SD signal has been detected when the reset time has elapsed after the end of one SD signal, a continuous burst reception determination signal is output for a predetermined time;
A relay method, wherein a synchronization pattern of a delayed burst reception signal output from the buffer unit is switched to the synchronization pattern signal over a period in which the continuous burst reception determination signal exists.

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